Water-Soluble Photoinitiators in Biomedical Applications
Faculty of Chemical Engineering and Technology, Krakow University of Technology, Warszawska 24, 31-155 Krakow, Poland
Abstract
Light-initiated polymerization processes are currently an important tool in various industrial fields. The advancement of technology has resulted in the use of photopolymerization in various biomedical applications, such as the production of 3D hydrogel structures, the encapsulation of cells, and in drug delivery systems. The use of photopolymerization processes requires an appropriate initiating system that, in biomedical applications, must meet additional criteria such as high water solubility, non-toxicity to cells, and compatibility with visible low-power light sources. This article is a literature review on those compounds that act as photoinitiators of photopolymerization processes in biomedical applications. The division of initiators according to the method of photoinitiation was described and the related mechanisms were discussed. Examples from each group of photoinitiators are presented, and their benefits, limitations, and applications are outlined.
Introduction
Currently, polymerization processes are one of the most widely used chemical processes in various fields of industry [1,2]. One of the most modern and rapidly developing methods of obtaining polymers is light-induced polymerization, i.e., photopolymerization [3,4,5,6]. The technique of converting liquid monomers to solid polymers under the influence of applied light is widely developed in the polymer materials sector in the industry of solvent-free paints [7], varnishes [8], and adhesives [9], in optoelectronics [10], in the printing industry for 3D printing materials [11,12,13,14,15,16,17], and many others. Numerous advantages of photopolymerization, such as performing reactions at ambient temperature, lack of solvents, and extremely short processing times, made light-initiated polymerization perfectly suited for biomedical applications (Figure 1) [18,19].
The global market for photopolymerization in biomedical applications can be divided into various groups based on the area of application in the medical sector. The main segments are: dentistry [20,21,22,23], tissue engineering [24,25,26,27,28,29], bioimaging [30,31], drug delivery systems [32,33,34,35], and medical devices. In dentistry, photochemical-initiated processes are used for the filling of hard dental tissue cavities with photocured polymer composites [36,37,38,39]. An interesting application of photopolymerization processes is the production of photo-crosslinked polymeric biomaterials especially those based on totally or partially degradable materials [40,41,42,43,44], scaffolds for tissue culture [45,46,47,48,49], and diagnostic genetic or cellular matrixes [50,51,52,53,54,55,56,57,58].
The unquestionable advantages of the photopolymerization technique in the context of applications in tissue engineering and biomedical science are primarily its ability to form structures of any geometry as well as the deposition of such materials on various carriers. Lack of these possibilities is often a limitation of the functionality of biomaterials obtained through conventional polymerization processes.
Due to the mechanisms of polymerization as well as the type of used monomers and initiating systems, there is a distinction between radical photopolymerization and cationic photopolymerization, which are the basic processes used in light-initiated polymerization technologies. Radical photopolymerization is a chain reaction consisting of three main stages: initiation, propagation, chain growth, and termination (which may be accompanied by side reactions) [59]. Free-radical photopolymerization is mainly used for acrylate and methacrylate monomers. The factor that limits the usefulness of radical photopolymerization is the occurrence of oxygen inhibition caused by the presence of atmospheric oxygen during the polymerization process. The negative influence of oxygen on polymerization is reflected, for example, by extinguishing the excited states of the initiator, which, in turn, affects the efficiency of the whole process. It is the free-radical polymerization, however, that is mostly used in biomedical applications, as proven by numerous literature reports [60,61,62,63,64].
The second type of polymerization is cationic photopolymerization, which is particularly interesting and relatively widespread in industrial applications, since it has a number of major advantages that make this process practical [65]. The living nature of cationic photopolymerization guarantees that the reaction continues to be effective even after shutting down the radiation source [66]. This enables a high degree of conversion to be achieved, which plays an extremely important role in the industrial practice. For this reason, photoinitiated cationic polymerization is becoming increasingly prevalent in global markets as an easy and energy-saving method for obtaining cross-linked polymers [67,68]. Despite its numerous advantages, cationic polymerization is very unlikely to be used in biomedical applications. One of the reasons is that cationic initiators generate strong protonic acids during initiation, whose acidic character negatively affects cell cultures [69]. The second reason is the sensitivity of cationic photopolymerization to moisture and water. Numerous scientific articles prove that the presence of water slows down or inhibits the polymerization reaction [70]. In addition, water can act as a chain transfer agent and promote the growth of new chains, which reduces the average molecular weight of the obtained polymer [71].
One of the basic requirements of photocuring systems used in biomedical sciences is their total or partial solubility in water. Water-based photocuring systems have already garnered interest since the late 1970s. Even then, it was well known that the use of water as a non-toxic, green, and cheap solvent was the solution to many problems related to the classical, organic compositions [72]. In addition, aqueous formulations can, in many cases, provide a reaction efficiency that cannot be achieved with conventional organic systems. Interestingly, the oxygen concentration in aqueous systems is an inch lower than in organic preparations, which significantly reduces oxygen inhibition for radical photopolymerization processes. Therefore, the use of water-soluble photoinitiators in aqueous systems for light-initiated polymerization is of great importance in the rapidly growing medical industry, and this article provides an overview of the literature related to the development of water-soluble initiators and their use in biomedical applications.
The Dynamics of the Development of Water-Soluble Photoinitiators
The key role in light-initiated polymerization processes is played by the initiating system, which influence, among others, the speed of polymerization and the degree of monomer conversion. This has led scientists to concentrate on the development of photoinitiators, which poses major challenges. The dynamics of developing water-soluble photoinitiators have been visualised in Figure 2 as the number of articles published in the analysed subject matter between 1970 and 2019.
As can be seen, photoinitiators have their origins in the 1970s, when waterborne compositions gained popularity in the painting and coating industries, but the increase in water solubility did not always follow the required lack of toxicity of these initiators. A genuine breakthrough was made at the beginning of the 21st century when popular initiators, such as 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone (Irgacure 2595) and water-soluble derivatives of acylphosphine oxides, e.g., monoacylphosphine oxide (MAPO) and bisacylphosphine oxide (BAPO), were used in new biomedical applications and started to play an important market role. The development of these initiators resulted in an increasing interest in the use of photoinitiated polymerization processes in biomedical applications, which reflects the high level of published scientific articles. Since then, scientists have worked on improving water solubility, initiation efficiency, and cytotoxicity reduction of the initiators discovered in the year 2000. Innovative photoinitiators designed depending on their application, e.g., initiators for two-photon laser polymerization, have also been proposed. An overview of the articles relevant to this topic can be found in the following chapters.
Types of Photoinitiators for Photopolymerization Processes
The initiating systems based on one-component, two-component, or multi-component photoinitiators undoubtedly play a key role in photopolymerization processes [73,74,75,76,77]. Photoinitiating systems not only determine the mechanism of the reaction, but also affect its performance, curing speed, and final properties of the polymer, such as hardness and viscosity. The selection of a photoinitiator is essential to achieve the right photopolymerization reaction rate and the desired polymer properties. The basic parameters determining the selection of the photoinitiator are maximum absorption wavelength λmax and a molar extinction coefficient ε. The efficiency of the photoinitiator is directly related to its structure, which influences the range of absorption and quantum efficiency of the photochemical and photophysical processes taking place in excited states [78]. Regardless of the type and mechanism of initiation, the photoinitiator should exhibit the following features (Figure 3):
compatibility between the absorption characteristics of photoinitiators and the emission characteristics of the light source,
good solubility in the polymerized composition – for biomedical applications – and good water solubility,
Other factors to be taken into account when performing the photopolymerization reaction are the structure and physicochemical properties of the monomers, the phenomenon of oxygen inhibition (in the case of free-radical polymerization), the influence of stabilisers or other additives present in the monomers, the thickness of the polymerizing layer, the type and intensity of the light source, and the viscosity of the composition.
In the case of an in vivo photopolymerization reaction, it is particularly important to reduce the toxicity of the initiator, especially when exposed to light. Free radicals produced during initiation may react with the main components of living cells, such as proteins and nucleic acids, which may affect the condition and viability of cells. Based on the mechanism of initiation of photoinitiators, a distinction is made between radical and cationic photoinitiators. In biomedical applications, radical photopolymerization processes are dominant.
Free-radical photopolymerization is an example of a classic photochemical chain reaction in three main stages: initiation, propagation, and termination, which leads to the formation of oligomers or polymers [79,80]. Depending on the structure of a radical photoinitiator, free radicals may be formed in the process of homolytic photodissociation of the photoinitiator molecule – type I photoinitiators. This group of photoinitiators includes peroxides, peresters, iminosulphones, or ketones, where photofragmentation is performed by binding, for example, O-O, S-S, S-N or C-C at α or β – carbon atom to the carbonyl group [69]. In the case of Type II photoinitiators, the excited initiator molecule reacts with the appropriate co-initiator such as an electron donor or acceptor or a hydrogen donor in order to produce the appropriate radicals or radical-ions [81]. The photo initiation process using type I or type II initiators is presented in Figure 4. Types I and II photo initiations are single- and two-molecular processes, respectively. The second type is usually slower and less efficient due to the presence of competitive processes during the excitation of the photoinitiator by the monomer, co-initiator, and atmospheric oxygen. Conversely, the photon energy in the visible range is generally lower than the dissociation energy of individual organic compound bonds. Therefore, it is particularly difficult to obtain a highly efficient initiator operating in the visible range. Because of that, it is often in this range that the bimolecular systems are used.
Currently, multi-component photoinitiation systems, based on electron transfer, and systems based on hydrogen abstraction, are interesting options. The reaction of electron transfer is based on the interaction of an excited electron donor or acceptor with a second component (electron acceptor or donor respectively) in the ground state, which is responsible for the photoinduced electron transfer process. An excited photosensitiser molecule, as the primary light absorber in multiradical systems, can perform a dual role (Figure 5) [82]:
where the photosensitiser acts as an electron donor, the transfer of the electron to the co-initiator creates a cationic radical of the sensitizer particle and an anionic radical of the co-initiator;
where the photosensitiser is an electron acceptor, it undergoes photoreduction, and the electron transfer products are the anionic radical formed on the sensitizer molecule and the cationic radical formed on the co-initiator.
In addition to the classic single, binary, and multi-component photoinitiators, there are also two-photon initiators (2PP) that undergo two-photon polymerization. This type of process is a powerful tool to build a variety of 3D matrices with micro-accuracy and nano-accuracy. A two-photon polymerization process is characterised by high penetration depth and high spatial selectivity. In this case, it is possible to use live cells to create 3D structures, thanks to the use of low-energy photons, which are safe for cells [83,84]. Two-photon photoinitiators should be sensitive to absorption because, during the initiation, they absorb two photons from the near infrared (NIR) area. In addition, they are characterised by highly conjugated π-systems and strong donor–acceptor groups [85]. The initiation process is not fully clarified, but it is suspected that, after absorbing the photons, the electron is transferred from the initiator’s donor–acceptor group to the π-electron core [86]. The transfer of the electron between the initiator and the monomer generates an exciplex and results in the formation of radicals that initiate the polymerization reaction (Figure 6) [87].
Type I Initiating System for Free-Radical Photopolymerization
4.1. α-hydroxyketones and Their Derivatives
One of the basic methods for increasing the solubility of traditional radical photoinitiators is their chemical modification, which consists of adding appropriate groups to the structure of the photoinitiator [88] [89,90,91]. The groups designated for this purpose are: non-ionic ethers, polyethers, hydroxyethers [92], ionic substitutes such as quaternary ammonium salts, sulphonates, carboxylic acids, and thiosulphates [93,94,95]. The most common solubilising group is the hydroxyl group, which can be found in the most popular water-soluble initiator: Irgacure 2959 – 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone. This initiator contains ketone groups as functional groups and it is one of the first commercially available water-soluble photoinitiators to be used in a variety of areas. Despite its drawbacks, such as low water solubility below 2% and a narrow absorption range reaching only the UV-A − 365 nm range, this initiator has become widespread and a range of water-soluble initiators has been created on its core. One of the most important advantages of this group of initiators is the possibility of inexpensively modifying the primary carboxylic group [96,97,98]. One of the disadvantages of Irgacure 2959, as well as its derivatives, is the need to use UV light. Its maximum absorption is at 276 nm and, due to its poor absorption, Irgacure 2959 requires extended exposure time. As well known, the use of such a light source for cross-linking processes in biomedical applications has a significant negative impact on the functioning of cells, which causes their mutation or death [99,100,101]. Other derivatives from the Irgacure family have also been tested for biological purposes, including Irgacure 184 (1-hydroxy-cyclohexyl-phenylketone), Irgacure 369 (2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone) [102], and Irgacure 907 (2-Methyl-4′-(methylthio)-2-morpholinopropiophenone) [103,104,105]. Williams et al. compared the cytotoxicity of Irgacure 2959, Irgacure 651 (2,2-dimethoxy-2-phenylacetophenone), and Irgacure 184 [106]. The following relationship has been noted for all initiators. Initiator toxicity grows with increasing concentration of the initiator as well as with increasing exposure time to UV light. Irgacure 2959 turned out to be the best of this group, as the remaining two proved to be toxic to cells at a minimum concentration. The structures of α-hydroxyketones and their derivatives are shown in Figure 7.
Irgacure 2959 is a type I photoinitiator that, when irradiated, cleaves into two radicals, benzoyl and alkyl, which can both initiate a polymerization reaction [107,108]. Irgacure 2959 is a widely used photoinitiator for preparing hydrogel materials using poly(ethylene glycol) diacrylate – PEGDA [109,110,111,112,113], gelatin-methacryloyl – GelMA [114,115], and methacrylated hyaluronic acid – MeHA [115,116] (Figure 8). This initiator is also used for cell encapsulation [117,118,119,120,121], for the targeted delivery of drugs and cells [122,123], and for the production of scaffolds for cell cultures [124,125,126,127,128].
Liska et al. have developed new water-soluble initiators containing carbohydrate residues and co-polymerising derivatives of these residues. The noted water-soluble initiators consisted of alkylphenones, benzophenones, and thioxanthones, and were accompanied by carbohydrates such as glucose and cellulose [129]. The proposed initiators proved to be highly effective in the initiation process, and those based on known structures, e.g., Irgacure 2959, have great potential in biomedical applications.
Another group of initiators, proposed in 1998 by Kojim et al., are based on 2-benzyl-2-(dimethylamino)-1-(4-morpholinophenyl)-1-butanone (BDMB), and more specifically on its water-soluble derivative: sodium 4-[2-(4-morpholino)benzoyl-2-dimethylamino] butylbenzenesulphone (MBS) [130]. Over time, the popularity of the MBS initiator and its modifications led it to find its way into biomedical applications, e.g., the microfabrication of scaffolds [131,132] and the printing of protein microstructures [133].
4.2. Phosphine Derivatives
Currently, scientists are working on modifying the already known initiators in order to either increase their water solubility or increase their absorption range and, consequently, obtain a fast and efficient initiating system [134]. Mono-acylphosphine oxides (MAPO) and bi-sacylphosphine oxides (BAPO) are mainly water-insoluble initiators that absorb in the 380–450 nm range. One of the first commercially available mono-acylphosphine initiators is TPO – diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (Figure 9). This initiator absorbs in the range of 350–380 nm. During initiation, it decays into reactive radicals, which provide high efficiency in the polymerization process. Its advantages also include good thermal stability and lack of colour and odour. This initiator, however, is poorly soluble in an aqueous medium [135].
Therefore, TPO derivatives with increased water solubility were created. The first reports of water-soluble initiators being TPO derivatives date back to 1991, when Majima et al. synthesised lithium phenyl-2,4,6-trimethylbenzoylphosphinate LAP, which proved to have good spectroscopic properties and high water solubility [136]. Their work was continued by Fairbanks et al. who, in 2009, improved the synthesis of the LAP initiator [137]. LAP is a widely used initiator for obtaining hydrogel materials using: PEGDA [138], GelMA [139], and other monomers [140,141].
Benedikt et al. analysed various modifications of bisacylphosphine oxides and compared the spectroscopic characteristics, polymerization kinetics, and cytotoxicity of the following derivatives: BAPO-OLi and BAPO-ONa (Figure 9) [142,143]. Both modifications were suitable as highly effective initiators for obtaining hydrogel materials. Additionally, BAPO-OLi ensured high cell viability [144]. The basic spectroscopic properties of MAPO-based and BAPO-based initiators, as well as the comparison of their solubility and toxicity, are presented in Table 1. Wang et al. performed a modification of BAPO by grafting its structure into a polyethylene glycol (PEG) chain, which improved its water solubility and allowed it to print a hydrogel with high optical resolution and good mechanical parameters [145].
In addition, scientists Pawar et al. have developed TPO water-dispersible nanoparticles, characterised by an absorption range of 380–420 nm, while maintaining a high molar excitation coefficient and good solubility in water [146]. TPO nanoparticles were prepared by Rapid conversion of volatile microemulsions into water dispersible powder. This is a process that can be applied to various photoinitiators. Neither chemical modification of TPO nor the addition of organic solvents were required to obtain an efficient initiator, which maintains the outstanding spectroscopic properties of the TPO nano initiator and provides efficient 3D printing of hydrogel materials such as the production of highly stretchable hydrogels using digital light processing (DLP) [147].
4.3. Azo-Initiators
The water-soluble azo-initiator – 2,2’-azobis[2-methyl-N-(2-hydroxyethyl) promionamide] (VA-086) – becomes increasingly popular because of its low cytotoxicity in both precursor and radical forms, while its absorbance range offers the possibility of using different sources in the far UV range [148]. Occhetta et al., in their research on the production of hydrogel microstructures, have proven that the use of the VA-086 initiator allows for a very high optical resolution printout and also provides a high cell viability rate even after long exposure to light. Occhetta’s 3D micro-pellets were not only biocompatible, but also created an environment favourable to proliferation [149].
In turn, Wang et al. proved that the VA-086 initiator has great potential in tissue engineering, where the light source is a laser diode. By appropriately selecting the diameter of the beam and its burning time at one point, the final degree of conversion of the obtained polymeric materials can be controlled [150]. They also proved that the problem of obtaining hydrogel porous materials, caused by nitrogen release during the initiation reaction with the VA-086 initiator (Table 2), can be solved by appropriate exposure time selection. Han et al. proposed a two-component initiating system combining the initiator Irgacure 2959 and VA-086, which resulted in improved mechanical properties of the obtained polymer network, with a minimised radiation dose and reduced exposure time [151].
Type II Initiating System for Free-Radical Photopolymerization
5.1. Eosin-Y
Eosin-Y is used as a photoinitiator due to its excellent spectroscopic properties, which makes it suitable for use with light sources in the visible range and safe for living organisms. Eosin-Y is an example of the type II initiator, which needs a second molecule, such as an electron donor, to initiate a polymerization reaction [152] (Figure 10). An example of such a co-initiator, which will be reduced during the reaction, is amine, e.g., triethanolamine. After the absorption of light, eosin is excited to a triplet state and then becomes an acceptor of the electron given by the amine. As a result of this process, eosin’s radical anion and radical cation of the amine are formed. Then, as a result of proton transfer from the amine radical cation, two neutral radicals are formed: the amino radical and the eosin radical (Table 2) [153,154]. Work on the Type II initiating system, Eosin-Y with amine, started in 1991 by Fouassier, Sawhney, et al., during which hydrogels were produced based on polyethylene glycol (PEG) [155]. As an initiating system, Eosin-Y/ethylamine was used in ratios of 0.4% w/v and 3.5% w/v, respectively [156]. Eosin has become very popular in the process of surface polymerization for the encapsulation of living cells, including islets of Langerhans [157,158,159]. Another important application of Eosine-Y is targeted drug delivery [160]. Eosin-Y is a widely used initiator for obtaining hydrogel materials, using mainly poly(ethylene glycol) diacrylate [161,162] and gelatin-methacryloyl [163]. In addition, Shih et al. have proven that Eosin can successfully act as a single-component photo initiating system in a thiol-ene photo-click polymerization reaction [164].
5.2. Riboflavin (B2)
Riboflavin is a naturally occurring yellow pigment, which is widely used in biomedical applications due to its high water solubility and biocompatibility [165] (Figure 10). Thus, the use of riboflavin as an initiator for hydrogel production would not only be harmless to cells but even beneficial. Riboflavin’s spectroscopic characteristics are favourable. It has a wide absorption range with four maximums: 223 nm, 267 nm, 373 nm, and 444 nm [166], and absorbs strongly between 330 and 470 nm, which makes it particularly attractive as an alternative to other synthetic initiators [167].
Riboflavin is a type II photoinitiator, which requires the presence of a co-initiator as an electron donor during the initiation of the polymerization reaction. Therefore, various initiating systems were studied. Bertolotti et al. examined a riboflavin/triethylamine initiation system for the photopolymerization of methacrylate hydrogels, which proved to be very efficient [168,169,170,171]. In order to produce a hydrogel free of unnecessary chemicals, however, the scientists proposed to use L-arginine as a co-initiator in the initiation process with riboflavin, since it contains amino groups as amino acids, which are electron donors [172]. Furthermore, in addition to initiating polymerization processes effectively, this co-initiator is biocompatible and well soluble in water. Additionally, it has been proven that the small concentration of riboflavin (0.01–0.5 wt.%) provides the fastest cross-linking as well as good physicochemical properties for the obtained hydrogel, while using 10% amine as a co-initiator [165]. The generation of riboflavin radicals and, thus, the reaction rate is also strongly influenced by the applied pH. In addition, it has been proven that following irradiation with visible light and UV light in the presence of oxygen, riboflavin produces reactive oxygen species such as: singlet oxygen, peroxide anion radicals, and others [173,174]. As a photoinitiator, riboflavin has already been used in in vivo studies for the treatment of corneal-related diseases, and the resulting hydrogels have proven to have promising physicochemical properties [175].
5.3. Camphorquinone and Its Modifications
One of the most popular initiators is camphorquinone (CQ), which belongs to the aliphatic α-ketones (Figure 10). The efficiency of this initiator in a one-component system is insufficient, while adding a second component, e.g., in the form of a tertiary amine as an electron donor, increases the efficiency of initiation. The mechanism is based on the process of electron–proton transfer [176]. Such combinations are widely used for the cross-linking of tooth fillings based on methacrylate resins [177]. Unfortunately, as an initiator in the visible range, camphorquinone has its drawbacks. First of all, it gives a strongly yellow product after the polymerization reaction, which makes the end product aesthetically unappealing. Additionally, camphorquinone has poor solubility in water, which limits the possibility of using this initiator to create hydrogel polymer networks [178].
In order to increase the water solubility of camphorquinone, it was modified to obtain carboxylated camphorquinone, while maintaining good spectroscopic properties [179,180]. The most commonly used co-initiators with CQ are amines: triethylenamine and ethyl-4- N,N.dimethylaminobenzoate (Table 2) [181,182,183]. Ternary initiation systems were also studied, which proved to be very effective and harmless to cells: the initiator, camphorquinone, the co-initiator, amine, and the accelerator, thioxantone or iodine salt [104,184]. The main direction of application of this initiator is the production of hydrogels for targeted drug delivery and in situ polymerization [185,186,187,188,189] as well as the production of biodegradable hydrogels for tissue engineering or biocompatible materials for application, e.g., in temporomandibular joints [190,191].
Two-Photon Photoinitiators (2PP) for Free-Radical Photopolymerizations in Biomedical Applications
As mentioned earlier, two-photon polymerization is a powerful tool for building 3D matrices with accuracy even on a nanometric scale, and, at the same time, enables spatial control and high depth of light beam penetration [192]. The light source is used in a near-infrared (NIR) region, which makes it possible to conduct the process in the presence of living cells [193]. The use of two-photon technology has, therefore, attracted significant interest in recent years [194,195,196,197,198,199]. For this technique, it is essential to select a suitable two-photon initiator which, when used in biomedical applications, must be water soluble, thermally stable, optically stable in the dark, non-toxic, and should generate free radicals easily [200,201]. The comparison of one-photon and two-photon polymerization is shown in Figure 11.
The challenge for two-photon initiators is to increase their water solubility. One of the methods for increasing hydrophilicity is the addition of non-ionic surfactants. Jkaverii et al. carried out two-photon polymerization using a commercially available initiator from the Irgacure family, Irgacure 651, with the addition of a surfactant, AF240 [202]. The disadvantage of this solution is the unfavourable influence of surface agents on the biocompatibility of obtained materials [203]. Initiators that undergo homolytic decay during irradiation, such as LAP [204] or VA-098 presented earlier, are characterised by relatively low π-system conjugation, poor two-photon absorption, and are, thus, less efficient in processes using laser as an irradiation source [205]. The popular Irgacure 2959 initiator can also be used in this case [206], but it is only suitable for 2PP at 515 nm [207,208]. Chichkov et al. used Irgacure 369 as a 2PP initiator in order to obtain biocompatible scaffolds. This compound, however, has a small cross-section in the NIR range [209] and its absorption maximum is at 369 nm, which makes it inconvenient when using a laser light source in the 750–800 nm range [210,211,212]. Some well-known type II initiators, such as Eosin-Y [213], erythrosine [214], and rose Bengal [215,216,217,218,219], in combination with amines, can be used as two-photon initiators of polymerization (Figure 12). The long exposure time and high intensity of radiation, however, makes it necessary to create initiators that ensure fast cross-linking using a small amount of light. Tromayer et al. proposed the preparation of a two-photon macromolecular initiator, which is based on cyclic dibenzylidene ketones and hyaluronic acid as the initiator core [220]. A biocompatible 2PP type initiator was obtained, which ensured the efficient initiation of the two-photon polymerization reaction and high cell viability, while hyaluronic acid, as the initiator’s core, provided it with adequate solubility in an aqueous medium.
The most effective way to increase water solubility is to introduce functional groups, such as quaternary ammonium salts or carboxylic salts, into the chromophore core, which is known for its high two-photon activity. Woo et al. have introduced quaternary ammonium cations for this purpose and the resulting WSPI initiator (1,4-bis(4-( N,N.bis(6-( N,N,N.trimethylammonium)hexyl)amino)-styryl)-2,5-dimethoxybenzene tetraiodide) has led to the creation of hydrogel materials containing living cells [221,222]. WSPI was also used to obtain protein hydrogels based on thiol and vinyl copolymers [223]. Another group of two-photon initiators includes compounds for which water solubility is guaranteed by the incorporation of carboxylic groups into the structure. This group includes BSEA (2,5-bis-[4-(diethylamino)-benzylidene]-cyclopentanone [224]), P2CK (3,3’-((((1E,1’E)-(2-oxocyclopentane-1,3-diylidene)bis(methanylylidene))bis(4,1-phenylene))bis(methylazanediyl))dipropanoate) [225,226], and G2CK (sodium 2,2’-((((1E,1’E)-(5-methyl-2-oxocyclohexane-1,3-diylidene)bis(methanylylidene))bis(4,1-phenylene))bis(methylazanediyl))diacetate) (Figure 13).
Currently, a promising application of two-photon absorption is two-photon excited photodynamic therapy (TPE-PDT), which, due to its deep penetration, lack of cytotoxicity, and high selectivity, is widely studied and developed. The selection of appropriate photosensitisers is key to effective TPE-PDT. Such a compound must meet the following criteria: hydrophilicity, biocompatibility, and non-toxicity to cells. In order to increase water solubility, the structure of two-photon initiators should be modified, such as by introducing carboxylic groups or attaching polyethylene glycol particles to the chain. Yang et al. proposed a series of carboxylate modified benzylidene cyclopentanone (Y1–Y4) as potential sensitizers for use in two-photon therapy [227]. The structures and full names of the initiators are shown in Figure 14. All obtained derivatives were characterised by a broad range of absorption in the visible range, and studies, including EPR, proved that the proposed water-soluble compound can effectively generate radicals. It was shown that the introduction of a larger number of hydrophilic groups into the initiator’s structure increases the biological safety of this initiator due to the lower probability of such a molecule being captured by cells [228]. Huang et al. proposed a new series of initiators (T1–T3), which not only initiated the two-photon photopolymerization process effectively but also ensured high cell viability [229]. The structures and full names of the initiators are shown in Figure 14.
Inclusion Complexes of the Host-Guest Type: Photoinitiator—Cyclodextrin
An interesting way to increase the solubility of hydrophobic initiators in water is through the host-guest chemical interaction. Cyclodextrins are cyclic oligosaccharides built from different amounts of optical active groups, called glucopyranose units (Figure 15 A) [230]. Due to their unique molecular structure, these compounds have the ability to cluster into small molecules with a hydrophobic cavity and hydrophilic outer surface and are, thus, able to form host-guest-type systems [231,232,233]. Many scientists have, therefore, proposed to increase the solubility of initiators by creating inclusion complexes with different types of cyclodextrin [234]. Balta et al. created thioxanthone photoinitiators using host-guest interactions with β-cyclodextrin (Figure 15 B) [235]. In turn, Temel et al. developed inclusion complexes using benzophenone and methylated β-cyclodextrin (Figure 15 C) [236]. Similar initiating systems for hydrogel formation were obtained by Ayub through complexation of 2,2-dimethoxy-2-phenyl acetophenone and methylated-β-cyclodextrin (Figure 15 D) [237]. Such a procedure ensured that a transparent hydrogel with a high degree of cross-linking was obtained. Xing et al. developed a 7-bis(2-(4-pentaneoxyphenyl)-vinyl)anthraquinone and a 2-hydroxypropyl-β-cyclodextrins (2-HP-β-CDs) initiating system, which allowed the production of hydrogel materials with the use of two-photon polymerization [238].
Multi-Component Water-Soluble Photo Initiating Systems
Multi-component initiating systems are very popular in the processes of photo induced polymerization reactions, mainly due to the fact that their absorption characteristics can be compatible with the emission characteristics of the light sources, such as UV-A-LEDs and Vis-LEDs. Such systems are also used in biomedical applications. Zuo et al. proposed to use of commercial fluorescent brighteners (styrene-based, coumarin-based, and 2,5-bis(benzoxazolyl)thiophene-based derivatives) together with commercially available iodine salt–diphenyliodonium hexafluorophosphate–to create hydrogel materials [239]. Coumarin derivatives together with water-soluble N-methyldiethanolamine acted as a multi-component initiating system to create a hydrogel with (hydroxyethyl)methacrylate [240]. The same amine co-initiator was used to obtain hydrogel through an amine–diketopyrrolopyrrole (DKPP) derivative system [241,242]. The structures of widely used additives in multi-component initiating systems for biomedical applications are shown in Figure 16.
Fields of Application for Water-Soluble Photoinitiators
In recent years, polymeric hydrogels have garnered plenty of interest in terms of their potential application due to the fact that their structural and biochemical properties are similar to those of the extracellular matrix (ECM) of most tissues [229]. over, they show high porosity, which ensures high permeability to nutrients, oxygen, and metabolic products. The properties of these materials can also be adapted to the mechanical properties of soft tissues. Hydrogels for tissue engineering should be hydrophilic in order to promote cell adhesion, while the three-dimensional structure of these scaffolds should be porous to facilitate cell and nutrient diffusion [184,243]. Hydrogels are produced by cross-linking hydrophilic monomers or oligomers. Although hydrogels can be formed by conventional polymerization methods, e.g., thermally, using thermal initiators or initiators acting on the principle of redox reaction, polymerization under the influence of light is of the greatest interest. Compared to other methods, photopolymerization has many advantages: it is a very fast reaction (lasting from a few seconds to a few minutes) and allows spatial control over the resulting hydrogel, which permits the creation of various shapes that fit into the tissue structure. Currently, photo induced systems for the production of hydrogels include: radical polymerization under the influence of ultraviolet (UV) and visible (Vis) lights in water, or two-photon photopolymerization and thiol-en photopolymerization [245,246,247]. Hydrogels with an interpenetrating polymer network structure are also becoming increasingly more popular [248]. Photocured hydrogel materials are used in numerous applications, e.g., biosensing [249,250], encapsulation [18,251,252], drug delivery systems [253,254], scaffolding for the cell culture [255,256], in situ polymerization [257,258], and even direct polymerization in living cells [259,260]. All techniques of 3D printing are highly developed [261,262], including laser writing [263,264], inkjet bioprinting [265], and stereolithography [202,266,267]. Other applications include the production of various materials, including scaffolds [268] and layered hydrogels using surface photopolymerization [269].
Conclusions
In conclusion, interest in water-soluble photoinitiators has been ongoing for almost half a century. Significant developments in medicine, including nanomedicine [270], promote the advancement of photopolymerization processes, as well as the necessary initiating systems in the near future. The currently available modern technologies of nanomedicine, such as targeted drug therapy, modern analysis, and diagnostics of diseases, and the production of materials for cell or tissue culture, will require new and increasingly improved initiators that will meet all the criteria for the introduction of materials into the medical market.
The development of water-soluble initiating systems is likely to take two directions. First, it will be based on the synthesis of completely new Type I or Type II photoinitiators with a wide absorption range reaching the visible range and, additionally, fulfilling a number of other requirements, such as lack of cytotoxicity, biocompatibility, and high initiation efficiency. Such photoinitiators can be applied, among others, in the processes of in situ polymerization, in targeted drug delivery, and in cell encapsulation, which may positively affect the treatment of some diseases, such as type I diabetes by the encapsulation of islets of Langerhans.
The second direction of development is the study of two-photon photoinitiators (2PP), which will allow the effective production of hydrogel materials containing living cells with the use of 3D laser printing with extremely high resolution. The constant challenge is to obtain initiators with a simple and inexpensive synthesis path in which the scale can be easily transferred to the industry.
This literature review has presented previous achievements in the field of water-soluble initiators in biomedical applications and has pointed at likely development paths and potential applications of photopolymerization processes.
Author Contributions
Conceptualization, formal analysis, data curation, writing—original draft preparation, visualization, W.T.; Conceptualization, writing—review and editing, J.O. Both authors have read and agreed to the published version of the manuscript.
Funding
The project: “WAY TO EXCELLENCE. a comprehensive university support program” implemented under the Operational Program Knowledge Education Development 2014-2020 co-financed by the European Social Fund WND-POWR.03.05.00-00-Z214 /18 funded this publication.
Expert insights on Malaysia’s residential solar-energy policies: shortcomings and recommendations
Lin-Sea Lau and others. Expert insights on Malaysia’s residential solar-energy policies: shortcomings and recommendations, Clean Energy, Volume 6, Issue 4, August 2022, Pages 619–631, https://doi.org/10.1093/ce/zkac043
Abstract
Malaysia has a long way before achieving the 20% renewable-energy penetration by 2025. Currently, merely 2% of the country’s electricity is generated by renewable energy sources including solar power. Unlike the abundant literature about solar energy, qualitative studies that FOCUS on experts’ opinions on the weaknesses of residential solar-energy policies have received less attention, particularly in the context of Malaysia. Understanding the flaws in the existing policies would lead to creating a better policy framework for solar-energy development. Thus, this study aims to identify the shortcomings of the current government initiatives and policies that deter solar photovoltaic adoption among households from experts’ perspectives. Experts also provide recommendations for better future policy design and implementation. This study employs a qualitative research approach (via semi-structured interviews) in collecting experts’ viewpoints. Key concerns emerging from the interviews include insufficient financial support, lack of awareness programmes and subsidized electricity tariffs. Also, interviewed experts suggest sufficient financial incentives, increased public awareness programmes and comprehensive legislation aimed at safeguarding consumer interests as a means to raising solar-energy adoption in the country. This underlines the need for policymakers to create public awareness, provide financial support and develop regulatory measures aimed at managing solar companies for the sake of solar development in Malaysia.
Introduction
The negative impacts on the environment and other issues associated with fossil fuels have forced many countries to change their environmental policies towards achieving sustainability in the renewable-energy industry [ 1, 2]. Solar energy has become one of the best sustainable energy sources that will gradually replace the use of fossil fuels for the production of electricity [ 1, 3]. Globally, renewable-energy policies were designed to address the problems of energy development along with the development of the renewable-energy industry to sustain its growth, including energy production, distribution and consumption [ 3, 4]. According to RED21’s global status report, renewable-energy policies were present in nearly all countries worldwide by the end of 2018 and relatively found at all levels of government projects [ 5]. Such initiations have supported the generation and use of renewable energy in 168 countries worldwide. Among others, solar energy has been the leading renewable energy source.
Over the past two decades, the price of solar energy has decreased substantially, leading to greater potential for its adoption. It is expected that the global residential solar capacity will grow from 58 GW in 2018 to 143 GW in 2024. Among others, China is the largest growth market, followed by the USA, Australia and Japan as a result of solar photovoltaic (PV) remuneration packages such as net metering and buy all, sell all in these countries. However, many developing and emerging economies in Asia such as Malaysia, Indonesia and India are lagging behind due to inadequate policy incentives, lack of rules and regulations, and low or subsidized household electricity tariffs [ 6]. According to Burke (2019), the uptake of solar energy faces many challenges including policy deficiencies and heavy subsidies for fossil fuels in Asian countries [ 7]. Governments’ energy and climate-change policies have been seen as important factors influencing solar installation in Asia [ 8]. In other words, even though of solar technologies are diminishing, the degree to which a country is successful in expanding its solar industry depends very much on the country’s solar-related policies and strategies [ 9]. According to the International Energy Agency, decisions by the policymakers such as the setting of ambitious targets and implementation of appropriate policies could play a paramount role in enhancing solar usage in a particular nation [ 10].
Malaysia appears to be an appropriate case study in the sense that it is of paramount importance for the country to increase renewable-energy usage due to two reasons. First, the renewable-energy initiatives allow the country to reduce its reliance on imported fossil fuels. As Malaysia’s domestic oil and gas reserves are expected to run out by 2029, the country will be forced to import fossil fuels for electricity generation [ 11]. However, the of imported fossil fuels are heavily dependent on exchange-rate fluctuations, which will potentially expose Malaysia to economic risk [ 12]. Second, the widespread use of renewable energy is essential for Malaysia to address its climate-change challenges. Between 1971 and 2020, for example, the country’s carbon dioxide emissions increased at an annual rate from 14.7 to 262.2 million tonnes [ 13]. Among the available renewable energy sources, solar energy is of the greatest potential in Malaysia as the country is located within the Sunbelt with at least 10 sun hours daily. This enables the generation of electricity using solar power throughout the country all year round [ 14].
Solar PV industry in Malaysia
Historically, solar PV installation was first introduced in Malaysia via the pioneering solar PV rural electrification programme in 1982. Under the scheme, ~100 homes at several selected remote villages throughout the country had solar PV installed. In 2000, the first grid-connected PV system was launched by the country’s largest electricity utility company. This was then followed by a 5-year programme called SURIA 1000 for the period between 2006 and 2010. The programme provided subsidies to successful bidders for the installation of solar PV systems in their homes. Most importantly, SURIA 1000 has also opened up opportunities for the public and industry to be directly involved in solar-related initiatives [ 15]. Since then, many multinational companies have started to set up PV cells and modules manufacturing plants in Malaysia. 1 In 2011, the renewable-energy feed-in tariff (FiT) mechanism was established under the Renewable Energy Act 2011. The FiT allows the sale of electricity generated from solar PV systems to the utility company at a fixed premium price for a specific time period [ 16]. The FiT programme came to an end in 2017. It was replaced by net energy metering (NEM), which enables solar users to produce electricity with solar net metering and sell the excess electricity to power grids [ 17]. Since January 2019, NEM has been improved by introducing the true NEM concept that enables excess solar energy produced to be exported back to the grid on a ‘one-on-one’ offset basis [ 18].
To ensure the successful implementation of solar projects, financial supports are essential to solar adopters [ 19, 20]. In Malaysia, securing financing for the purpose of solar PV installation has been challenging as most bankers are not familiar with the industry, particularly when it comes to risks and liabilities. To encourage renewable-energy usage, the government has established the Green Technology Fund Scheme (GTFS) to finance green projects with an allocation of RM1.5 billion in 2010. Companies who succeed in securing loans from participating banks are entitled to a 2% interest subsidy and the government’s guarantee of 60% of the approved loan. In the meantime, the government has provided two forms of green technology incentives, i.e. Green Investment Tax Allowance (GITA) and Green Income Tax Exemption (GITE), for companies that engage in green projects [ 21]. However, individuals or household investors are not eligible to apply for these incentives. In short, finances and fiscal incentives have been granted to only companies, not individuals, in Malaysia.
The existing public green policies in Malaysia are with the aim of achieving the national renewable-energy mix target of 20% by 2025 [ 22]. However, despite various incentives and strategies to encourage the growth of the renewable-energy sector, clean energy sources (including solar PV) constitute merely 2% of the total electricity-generation capacity in Malaysia. Specifically, the residential sector contributes merely 9.14 megawatts to the installed capacity of solar PV in Malaysia. Most of the installed PV capacity comes from the commercial (i.e. 25.60 megawatts) and industrial (i.e. 355.76 megawatts) sectors [ 23]. Thus, increased efforts are required to enhance the adoption of solar PV technologies, particularly among households in Malaysia.
Contributions of the study
Indeed, the successful design and implementation of solar policies require inputs from various stakeholders in the solar PV industry [ 24–27]. In other words, to enhance the effectiveness of energy policies, insights from the experts (e.g. officials from the relevant government agencies and academicians from the energy field) are also essential, besides consumers. Considering merely the viewpoints of potential customers may not allow the policymakers to produce comprehensive energy policies that are beneficial to the residential solar PV market. However, research remains scarce that has looked into the feedback of industrial experts, government officials and academicians in shaping future solar policies. Much of the research on solar PV has focused on consumer behaviour and experiences in solar PV adoption [ 14, 28–30]. Additionally, even though some studies have sought experts’ opinions pertaining to solar PV adoption, they have emphasized the general factors affecting the usage of the technology [ 31, 32]. Some other past studies [ 33–35] have investigated the impact of public policy on the solar-energy industry. However, none has explored specifically the role of public policy in influencing solar PV installation among residential consumers particularly in the context of Malaysia. Numerous past studies on Malaysia have performed a review on the current situation of solar-energy adoption in the country. Amongst others, some studies have been focusing on the potential or outlook of solar power [ 36–38] while the remaining studies discuss the effectiveness of the existing solar policies [ 39–42]. In particular, our study builds upon a recent study [ 40] that analysed the new solar policies and frameworks in Malaysia that focused on solar PV business models. The authors conducted interviews with business representatives and customers. Differently from [ 40], we extend the research by employing a qualitative research approach that involves interviews with industrial players, academicians and government officials that remains absent in the literature. Another uniqueness of our study, if compared with [ 40], is that we explore solar experts’ opinions on the overall effectiveness of Malaysian solar policies and their suggestions for further policy improvements. Thus, the aim of our study is to determine the shortcomings of the current government initiatives and policies that hinder solar PV adoption among households in Malaysia from the perspectives of energy experts. Policy recommendations are also sought from the experts. Thus, this analysis could provide a better understanding of the weaknesses of the existing solar programmes and most importantly furnish information for better future policy design and implementation. The research findings could contribute significantly for policymakers in creating effective strategies aiming at enhancing the usage of residential solar PV systems. The study also provides valuable inputs that could help in the development and growth of the solar PV industry in Malaysia. Lessons learnt from Malaysia’s experience are highly relevant, particularly for other developing countries in Asia.
Literature review
Carley et al. [ 43] posited that solar energy is one of the cleanest renewable energy sources with almost zero negative impact on the environment. However, several studies instigated that the production and consumption of more solar energy to replace fossil fuels in a country require the introduction of effective energy policies [ 44, 45].
Countries such as Germany, the UK, Sweden, Spain, Italy and others are among the top 10 countries with the biggest proportion of renewable energy [ 3, 42, 43]. Meanwhile, countries such as China, the USA, Germany, Japan and India are the top solar-energy producers globally [ 1, 3, 44, 46]. Assoa et al. [ 47] posited that Japan, India, China, South Korea and Singapore are leading in terms of solar-energy usage in the Asian region. However, Assoa et al. [ 47] and Mamat et al. [ 48] have shown that slow adaptation to the use of solar energy in some developing countries in Asia is mainly due to inadequate energy policies. Southeast Asian countries stand at a crossroads regarding their contribution to climate change and rely heavily on fossil fuels for transport and electricity. According to Assoa et al. [ 47], the Southeast Asian region requires a more sustainable energy policy to reduce the use of fossil fuel as an energy source. To reach the aspirational target of 25% renewable energy source in the region by 2025, the Southeast Asian countries will have to substantially scale up their deployment of renewables in the power sector through adequate and sustainable solar-energy policies.
The initiatives taken by the Association of Southeast Asian Nations (ASEAN) to enhance energy production, consumption and distribution policy are vital to ensure the achievement of energy efficiency and efficiency standards in the region [ 49]. Solangi et al. [ 50] and Mamat et al. [ 48] pointed out that energy policies that are significant to support the development of renewable energy such as the use of solar energy have been explicitly made to determine the national commitment by all the 10 ASEAN member countries including Indonesia, Brunei, the Philippines, Malaysia, Vietnam, Singapore, Cambodia, Laos, Myanmar and Thailand. Findings from Solangi et al. [ 49], Blazquez et al. [ 51] and Assoa, et al. [ 47] have revealed that as part of the energy policy implications, the use of solar energy for electricity generation has significantly risen over the years. For instance, Singapore’s contribution to the use of renewable energy such as solar energy has increased with their continuous efforts to eradicate the use of fossil fuels. However, the Philippines has targeted to reduce its energy intensity by 40% by 2030 as part of its contribution to sustainable energy consumption.
Most Southeast Asian countries share the common goal of expanding renewable-energy production because they have a large capacity for natural energy resources and face environmental problems that include carbon emissions. However, with the energy policies already implemented, most are moving in the right direction to promote sustainable energy production and consumption [ 48]. In Malaysia, the renewable-energy policy ensures an increase in capacity from renewable energy to 4000 MW by 2030, while Brunei has set a target of 10% renewable electricity generation by 2035. Singapore’s primary renewable-energy policy aims to increase PV capacity to 400 MW by 2030. Thailand has ambitious targets to increase renewable-energy consumption to 30% by 2036. This includes increasing the share of renewable electricity-generation capacity to 20.11% and the share of renewable energy in transport fuel consumption to 25.04% by 2036. The renewable-energy policy in the Philippines focuses on tripling renewable electricity installation capacity by 2030. Cambodia aims to increase hydropower capacity to 3453 MW by 2030 to realize the potential of new energy capacity. Vietnamese policy on renewable energy ensures that the share of non-hydro renewable power generation capacity increases to 12.5% by 2025 and 21% by 2030 [ 48, 52, 53].
In the Asian region, advocacy for renewable-energy programmes is steadily increasing due to the implementation of new or revised energy policies in the region [ 54]. Indonesia’s renewable-energy targets of 23% by 2025 and 31% by 2050, for example, are supported by clear policies and regulations. Such policies ensured the establishment of the ‘Badan Koordinasi Energi Nasional’, also known as ‘BAKOREN’. The policy gives more consideration to conservation, diversification and clean and renewable energy [ 55]. In their study, Liu et al. [ 56] highlighted the Renewable Energy Law of the People’s Republic of China, which was introduced in 2006 and outlines the general conditions for renewable energy (RE) and the importance of this energy source for the People’s Republic of China. In addition, there are other energy policies, including the Renewable Energy Law Amendment, which aims to efficiently reduce the cost of renewable energy and ensure that electricity grid operators in China purchase all electricity generated from renewable sources [ 54, 56]. In the Far East Asia region, Japan’s renewable-energy policy, also known as the ‘Strategic Energy Plan’, ensures the promotion of the diffusion of renewable energy resources (solar energy, biomass, renewable heat and small/medium hydropower) [ 57].
According to Kardooni et al. [ 58], Malaysia has targeted to achieve 20% renewable energy in the electricity-generation mix by 2025 even though the country’s current energy source is largely natural gas and coal. The policy to promote the use of solar-energy sources is gradually contributing to the energy conservation strategy [ 48, 49]. Malaysia’s framework for energy development was first formulated in the early 1970s. Since then, prominent energy policies have been introduced to enhance the development of sustainable energy. The most significant step towards sustainable energy development was the introduction of the Fifth Fuel Policy in 2000 in which solar, biomass, biogas and hydro energy were recognized as potential renewable energy sources for electricity generation [ 49]. Thereafter, new policies have been initiated towards the utilization of renewable energy and the promotion of energy efficiency to replace fossil fuels with renewables [ 59]. Solangi et al. [ 49] indicate that the renewable-energy policy and action plan that were outlined in the 10th Malaysia Plan (2006–2010) not only provided an alternative to energy sources but also encouraged the use of renewable energy such as solar energy. However, the new policies that will be implemented in the 12th Malaysia Plan (2021–2025) concerning renewable energy are expected to create more jobs, promote sustainable development and create new opportunities for businesses and industries to positively impact the country’s economic growth [ 59].
Policymakers in Malaysia have initiated numerous policies and laws to increase the capacity of renewable energy in the national electricity-generation mix [ 40]. Among the various policy initiatives to increase energy consumption capacity, the Malaysian government has introduced a solar PV project, also known as ‘MySuria’, to increase the income of the bottom 40% of households, also known as ‘B40’, by not only increasing the knowledge and awareness of solar energy but also promoting the adoption of solar PV energy technology to reduce the cost-of-consumption rate and generate additional income [ 41]. As part of these initiatives to generate additional income through the adoption of PV, the government has committed to enforcing the FiT law introduced in 2011 to promote energy-generation capacity, especially in rural areas, while generating additional monthly income for low-income earners [ 60]. In this regard, Alam et al. [ 61] argued that households are more likely to embrace PV solar technology if they have the opportunity to test it out before it is put into widespread use and find that it meets their needs. However, if people could see the advantages of PV solar technology in action, it would change their minds about using it. However, people could be hesitant to fully invest in PV if there is a lack of marketing, adoption readiness, motivation and competence, as well as the absence of legislation mandating PV’s usage [ 62]. To increase the usage of PV in Malaysia, Solangi et al. [ 63] argued that obstacles such as high solar-panel costs and a lack of accurate information about harnessing solar energy should be eliminated. Their findings revealed that 80% of respondents think that government subsidies would be the greatest way to increase solar-energy consumption throughout the country. These were confirmed by Solangi et al. [ 64] who found that 80% of Malaysians are interested in switching to PV solar but they lack the expertise and resources to do so. Households argued that the Malaysian government should raise subsidies for solar-energy products to make them more affordable. For this reason, it is crucial now to educate the public about solar PV technology and its advantages. Public opinion has a significant effect on the diffusion of solar PV. The public’s embrace of solar PV depends on emphasizing both its utility and its simplicity of operation [ 65]. Al-Fatlawi et al. [ 66] found that although there is interest in solar PV system adoption among households in Malaysia, many individuals still do not realize the benefits of using PV solar such as financial benefits. The study showed that ~36% of Malaysians are close to being ready to invest in solar PV projects but they need financial support to lower the initial capital cost of these projects.
According to Koerner et al. [ 40], the Malaysian PV industry has experienced accelerated growth and Rapid development since the introduction of the FiT and other renewable-energy policies. In 2008, a new energy policy was introduced with five strategic FOCUS areas that specifically address recurring problems, including poor governance, lack of a regulatory framework, limited market oversight and lack of institutional policies. These five FOCUS areas consist of (i) Renewable Energy Foundation Law (RE); (ii) Guiding RE Business Environment; (iii) Human Capital Development; (iv) Renewable Energy Research and Development Action Plan and (v) advocacy programmes. The aim of this renewable-energy policy was to accelerate the adoption of solar PV, reduce the long-term cost of building-integrated PV technology and avoid greenhouse gas emissions from fossil-fuel power plants [ 61]. However, to increase the usage of solar PV and boost its competitiveness, Malaysia should establish a robust financial support structure such as financing options and taxes. Although Malaysia is among the top 10 nations producing solar panels, the PV industry in Malaysia is still tiny, leading to a lower rate of adoption. To compete with other nations in solar energy, Malaysia must expand the quota size and give some enticing incentives [ 67]. To achieve this, the Malaysian government should be committed to maximizing the country’s potential in promoting solar energy by providing effective incentive schemes [ 68]. In this regard, Koerner et al. [ 40] argued that to increase the use of solar PV in the residential sector, regulators and policymakers should work together with the industry to raise public awareness about the technology beyond the purely economic benefits, with an emphasis on climate-change mitigation and the reduction of carbon emissions. The study suggested that communication channels between businesses and educational and research institutions need to be strengthened to develop efficient solar-energy applications that could compete internationally.
Methodology
A qualitative research method was adopted to achieve the research objectives of this study. The qualitative approach is a commonly used research method in social sciences that enables researchers to gain in-depth insights and knowledge on an issue [ 69, 70]. Among others, interviews are frequently adopted in qualitative research in which researchers are able to converse with the participants. Thus, on most occasions, a better understanding of interviewees’ opinions and experience on a particular topic can be obtained [ 71]. In energy studies, researchers apply qualitative research methods to collect detailed personal viewpoints on a particular technology or technological-related policies [ 72]. This study has two primary purposes. The first is to discuss the shortcomings of current solar-related initiatives/policies/programmes from experts’ perspectives. The second is to discuss experts’ proposals on the future actions that can be taken by the government in increasing the adoption of solar PV in Malaysia. Hence, there will be no defined hypothesis tested in this study.
2.1 Data collection
Data collection was divided into three waves as three groups of experts were targeted: academicians, government officials and industrial players. The selection of experts from the academic arena, industry and government bodies serves the purpose of obtaining deeper insights into the development of the solar industry and its policies in Malaysia. Each group of experts could provide different views based on different perspectives, thereby providing a more comprehensive set of findings and insights. Semi-structured interviews were deployed to collect essential information from these experts. Individual in-depth interviews could provide an opportunity to explore an unclear issue or situation in a more detailed manner [ 29, 73]. All interviews were conducted from October 2019 to December 2019. Specifically, interviews with the industrial players were conducted at the premise of the Malaysian Photovoltaic Industry Association. Inputs from academicians were collected via interviews held at various universities. Interviews with government officials were conducted at the premises of related government agencies such as the Sustainable Energy Development Authority and Energy Commission and the 10th International Greentech Eco Products Exhibition Conference held in Kuala Lumpur in October 2019. All interviews were audio-recorded upon approval from the interviewees and transcribed at the later stage.
To achieve the research objectives, 25 individuals were interviewed by the principal investigator together with her research team members. Specifically, a total of 5 solar-related government agencies, 10 academicians in the field of renewable energy and 10 representatives from solar companies were involved. For government agencies, the representatives were either a chairperson, director or vice president of the agencies. All the academicians were professors who have vast experience in renewable-energy research. Meanwhile, the representatives of solar companies were either managers, key decision makers or chief executive officers. Potential participants were contacted in person via e-mail and given standard information about the research project. Upon their agreement, the participants were then contacted to discuss further at the date and venue of the interview. Before the commencement of the interviews, interviewees were shown documents about the research project. Written consent for the interview was then obtained from the participants. Each interview session took ~30 minutes. A token of appreciation was given to all the participants at the end of each interview session.
The survey consisted of two main areas covering (i) the shortfall of current government solar-energy initiatives and policies and (ii) necessary actions to be taken by the government to increase the number of residential solar users. The interview questionnaire (available at Clean Energy online as Supplementary Data ) contained two pre-determined open-ended questions that included: (i) What are the shortcomings of current government initiatives and policies that deter households from installing solar PV? (ii) What future actions need to be taken by the government to increase residential solar PV adoption? Each of the scheduled questions was then followed by sub-questions or ‘probes’ that could encourage participants to share more in-depth information [ 74]. Based on two general questions, there were 24 questions probed during the interview sessions.
2.2 Data analysis
The collected qualitative data were then transcribed. In this process of transcription, the entire conversation content was transcribed in word form manually. All interview responses were coded and transcribed based on several themes. Subsequently, these transcribed data were compared and analysed in terms of similarities and differences of views across experts within each of the respondent groups and across the three expert groups of academicians, government officials and industrial players [ 9].
Major findings
3.1 Shortcomings of current policies and initiatives
This section demonstrates results obtained from expert interviews that were conducted to find out experts’ viewpoints on the shortcomings of current policies and initiatives in relation to residential solar adoption in Malaysia. Data obtained from the interviews have been transcribed and reported in four main themes, namely financial support, awareness programmes, subsidized electricity tariffs and NEM. These main themes explain the extent to which each of the various types of current solar initiatives and policies is deficient in promoting residential demand towards solar energy. All interviewees were asked to identify the weaknesses of current government policies that discourage residential solar adoption from their personal perspectives. The four most important shortfalls in the existing policies or themes that emerged from the experts’ interviews are discussed below. The summary of the responses is portrayed in Table 1.
Summary responses on shortcomings of current government policies
| Financial support | X X X X X |
| Awareness programmes | X X X X X X |
| Subsidized electricity tariffs | X X X X X X |
| Net energy metering | X X X X |
| Academicians | A01 A02 A03 A04 A05 A06 A07 A08 A09 A10 |
| Financial support | X X X X X X X |
| Awareness programmes | X X X X X X |
| Subsidized electricity tariffs | X X X X X |
| Net energy metering | X X |
| Government agencies | G01 G02 G03 G04 G05 |
| Financial support | X X X |
| Awareness programmes | X X |
| Subsidized electricity tariffs | X X X |
| Net energy metering | X X |
| Financial support | X X X X X |
| Awareness programmes | X X X X X X |
| Subsidized electricity tariffs | X X X X X X |
| Net energy metering | X X X X |
| Academicians | A01 A02 A03 A04 A05 A06 A07 A08 A09 A10 |
| Financial support | X X X X X X X |
| Awareness programmes | X X X X X X |
| Subsidized electricity tariffs | X X X X X |
| Net energy metering | X X |
| Government agencies | G01 G02 G03 G04 G05 |
| Financial support | X X X |
| Awareness programmes | X X |
| Subsidized electricity tariffs | X X X |
| Net energy metering | X X |
The interview participants consisted of five solar-related government agencies (represented by numbers G01–G05), 10 academicians in the field of renewable energy (represented by numbers A01–A10) and 10 representatives from solar companies (represented by numbers I01–I10).
Summary responses on shortcomings of current government policies
| Financial support | X X X X X |
| Awareness programmes | X X X X X X |
| Subsidized electricity tariffs | X X X X X X |
| Net energy metering | X X X X |
| Academicians | A01 A02 A03 A04 A05 A06 A07 A08 A09 A10 |
| Financial support | X X X X X X X |
| Awareness programmes | X X X X X X |
| Subsidized electricity tariffs | X X X X X |
| Net energy metering | X X |
| Government agencies | G01 G02 G03 G04 G05 |
| Financial support | X X X |
| Awareness programmes | X X |
| Subsidized electricity tariffs | X X X |
| Net energy metering | X X |
| Financial support | X X X X X |
| Awareness programmes | X X X X X X |
| Subsidized electricity tariffs | X X X X X X |
| Net energy metering | X X X X |
| Academicians | A01 A02 A03 A04 A05 A06 A07 A08 A09 A10 |
| Financial support | X X X X X X X |
| Awareness programmes | X X X X X X |
| Subsidized electricity tariffs | X X X X X |
| Net energy metering | X X |
| Government agencies | G01 G02 G03 G04 G05 |
| Financial support | X X X |
| Awareness programmes | X X |
| Subsidized electricity tariffs | X X X |
| Net energy metering | X X |
The interview participants consisted of five solar-related government agencies (represented by numbers G01–G05), 10 academicians in the field of renewable energy (represented by numbers A01–A10) and 10 representatives from solar companies (represented by numbers I01–I10).
3.1.1 Financial supports
A financial incentive is the most-mentioned theme identified from the interviews. Basically, it is true for all three groups of interviewees. Most of the participants (15 out of 25 interviewed) believe that there is lack of financial support from the government to encourage solar PV installation in homes. This response was given by some of the interviewees from the industry as well as scholars from universities. Five and seven out of 10 interviewees from solar companies and universities, respectively, talked about financial support. A few representatives from solar companies pointed out that:
‘It is difficult to get individuals to install solar PV because they don’t get any financial assistance to do so. To many, upfront cost is too high.’ (I03)
‘Without incentives, the breakeven for households will take around 10 years, whereas for commercial will be only 3.5 years due to tax incentives.’ (I06)
‘Middle-income and low-income groups can’t afford the high installation cost unless there is financial incentive. They would rather spend their money on other essentials, but not solar PV.’ (I08)
Some responses from the academicians are as follows:
‘It seems not worth to invest in solar PV without financial supports as the payback period is too long.’ (A05)
‘Too little financial help is given to the households at this moment.’ (A08)
‘The installation cost for solar PV remains high as long as there is no financial support from the government.’ (A10)
Three of the five experts from government agencies share similar views to industrial players and academicians that financial incentives are absent to stimulate solar-energy adoption among households in Malaysia. Unlike companies, the government provided financial incentives to the companies such as tax incentives. As stated by the representatives from one of the government agencies:
‘Unfortunately, the current financial incentives are only meant for companies, not for households.’ (G01)
‘Basically, I have to admit that the residential sector has been neglected when it comes to solar energy adoption. I don’t see much financial help from the government so far.’ (G05)
3.1.2 Awareness programmes
Weak public awareness of solar technology is perceived as one of the most important factors leading to low solar PV adoption among households. When asked about their opinions on households’ awareness, most of the participants (14 out of 25 interviewed), particularly academicians and industry players, agree with the point that the existing government policies are inadequate in creating public awareness and acceptance of solar energy. At present, there are awareness programmes such as the Annual Malaysian Photovoltaic Industry Association National Solar Roadshow aimed at educating and encouraging the installation of solar PV on commercial and industrial rooftops, but not at homes. Specifically, 6 of 10 academicians interviewed have highlighted the deficiencies of the existing public awareness programmes; as a few of the representatives put it:
‘The government has not done enough to create awareness among the people towards solar energy.’ (A01)
‘Many Malaysians are not aware of the benefits of using solar as they are not exposed to this kind of information.’ (A06)
‘I have not seen proper solar awareness programs to encourage residential usage.’ (A09)
On the other hand, 6 of 10 industrial representatives did indicate the incompleteness of the current awareness programmes, as some interviewees from the industry said:
‘There are some limited awareness campaigns but failed to draw crowds.’ (I02)
‘In Malaysia, people get information about solar energy via mostly family members and friends, or from solar companies, but not from government organized awareness programs.’ (I05)
‘I can hardly see any awareness campaigns by the government to promote the usage of solar PV.’ (I08)
Only two representatives (out of five interviewed) from the government agencies provided insights concerning awareness programmes. For instance, one of the governmental representatives described public awareness of solar energy as follows:
‘Many people don’t know much about solar energy out there. I can say the existing awareness programs are insufficient and not that effective.’ (G05)
3.1.3 Subsidized electricity tariffs
Numerous interviewed experts mentioned that a low electricity price due to heavy subsidies serves as a deterrent to the development of the residential solar sector in Malaysia. Electricity consumers in the country are eligible to receive fuel subsidies from the government. According to Tenaga Nasional, 2 fuel subsidy refers to the amount of fuel cost subsidized by the government for each unit of electricity consumed [ 75]. In terms of subsidized electricity, of our 10 interviewees from solar PV companies, 6 stated that cheap electricity demotivate households from adopting solar energy. As mentioned by three of the interviewees:
‘People are not encouraged to go for solar energy as the existing electricity price is relatively much cheaper.’ (I04)
‘Heavily subsidized electricity is making solar PV investment less attractive.’ (I05)
‘Consumers have no reason to use solar energy since the current electricity bill is low due to government subsidy.’ (I09)
Meanwhile, over half (three out of five) of representatives from government agencies indicated a concern over low electricity as a hindrance to achieving high demand for solar energy among households in the country. One of the representatives stated:
‘It will be very difficult for the residential solar sector to expand if the government chooses to subsidize electricity continuously.’ (G04)
Of participants from the higher learning institutions, half of them opined (i.e. 5 out of 10) that subsidized electricity is a critical factor in deterring people from using solar PV technology to generate electricity. Some of the responses are shown below:
‘From economic point of view, people will not use solar because electricity is cheap.’ (A07)
‘The policy of subsidizing electricity is bad for the development of solar energy.’ (A10)
3.1.4 NEM
NEM was introduced by the government in 2017 to encourage the uptake of solar PV technology. This scheme was implemented to replace the FiT programme, which was first introduced in 2011 and then scrapped in 2016 [ 76]. The solar industry proposed to the government to modify the concept of NEM from the existing net billing to true net energy metering in 2018. Under the improved NEM scheme, excess energy generated from solar PV could be exported back to the grid based on a ‘one-on-one’ offset basis starting in January 2019, replacing the Displaced Cost earlier. A quota allocation of 500 MW was provided for new NEM up to the end of 2020 [ 18].
Our interviewees from government agencies have mixed views on the introduction of NEM. Some agree with its implementation while the remaining (two out of five interviewees) would prefer the FiT scheme. One of the interviewees who opposed the launch of NEM said:
‘FiT is a better scheme. It should be re-proposed.’ (G03)
Among the industry participants, 4 of 10 had Комментарии и мнения владельцев on the introduction of NEM as a way to allow more public at large to generate clean energy at home:
‘If your electricity bill is less than RM300, it is not worth for you to install solar PV.’ (I01)
‘NEM will only help those consumers who fall under the high electricity tariff block.’ (I06)
Overall, the interviewees from the universities are less sensitive to NEM as a policy that can discourage the adoption of solar technology among households. Only 2 of 10 have mentioned the disadvantages of NEM. For instance, one of the interviewees has stated:
‘NEM is not a subsidy because consumers still need to install the solar PV themselves. That’s why it can’t encourage solar usage.’ (A09)
3.2 Recommendations on future actions to enhance residential solar adoption
On top of discussing current government initiatives and policies, the interviews were conducted to gather suggestions and feedback from academicians, government agencies and industry players on necessary future actions to enhance Malaysians’ intention to use solar PV. Three main themes emerged from the data collected. These main themes explain what should be done by the government to improve residential solar PV uptake. The discrepancies and similarities in opinions of different interviewees are presented below. Table 2 shows the summary of responses on necessary future actions to enhance residential solar adoption.
Summary of responses on necessary future actions to enhance residential solar adoption
| Provide financial incentives | X X X X X X X |
| Enhance public awareness | X X X X X |
| Legislation to protect solar consumers | X X |
| Academicians | A01 A02 A03 A04 A05 A06 A07 A08 A09 A10 |
| Provide financial incentives | X X X X X X |
| Enhance public awareness | X X X X X X |
| Legislation to protect solar consumers | X X X X X |
| Government agencies | G01 G02 G03 G04 G05 |
| Provide financial incentives | X X X |
| Enhance public awareness | X X X |
| Legislation to protect solar consumers | X X |
| Provide financial incentives | X X X X X X X |
| Enhance public awareness | X X X X X |
| Legislation to protect solar consumers | X X |
| Academicians | A01 A02 A03 A04 A05 A06 A07 A08 A09 A10 |
| Provide financial incentives | X X X X X X |
| Enhance public awareness | X X X X X X |
| Legislation to protect solar consumers | X X X X X |
| Government agencies | G01 G02 G03 G04 G05 |
| Provide financial incentives | X X X |
| Enhance public awareness | X X X |
| Legislation to protect solar consumers | X X |
The interview participants consisted of five solar-related government agencies (represented by numbers G01–G05), 10 academicians in the field of renewable energy (represented by numbers A01–A10) and 10 representatives from solar companies (represented by numbers I01–I10).
Summary of responses on necessary future actions to enhance residential solar adoption
| Provide financial incentives | X X X X X X X |
| Enhance public awareness | X X X X X |
| Legislation to protect solar consumers | X X |
| Academicians | A01 A02 A03 A04 A05 A06 A07 A08 A09 A10 |
| Provide financial incentives | X X X X X X |
| Enhance public awareness | X X X X X X |
| Legislation to protect solar consumers | X X X X X |
| Government agencies | G01 G02 G03 G04 G05 |
| Provide financial incentives | X X X |
| Enhance public awareness | X X X |
| Legislation to protect solar consumers | X X |
| Provide financial incentives | X X X X X X X |
| Enhance public awareness | X X X X X |
| Legislation to protect solar consumers | X X |
| Academicians | A01 A02 A03 A04 A05 A06 A07 A08 A09 A10 |
| Provide financial incentives | X X X X X X |
| Enhance public awareness | X X X X X X |
| Legislation to protect solar consumers | X X X X X |
| Government agencies | G01 G02 G03 G04 G05 |
| Provide financial incentives | X X X |
| Enhance public awareness | X X X |
| Legislation to protect solar consumers | X X |
The interview participants consisted of five solar-related government agencies (represented by numbers G01–G05), 10 academicians in the field of renewable energy (represented by numbers A01–A10) and 10 representatives from solar companies (represented by numbers I01–I10).
3.2.1 Provide financial incentives
Not surprisingly, for all three groups of interviewees, the provision of financial assistance is one of the most suggested strategies to enhance solar PV adoption among individuals. Many interviewees opined that measures such as tax incentives and subsidies are able to encourage solar-energy usage. Six of 10 academicians who participated in the interviews stressed the importance of granting financial incentives in stimulating residential solar PV installation. Academicians’ example quotes are as follows:
‘It would be better that Malaysian government could offer tax incentive or subsidy on the installation of solar PV which currently only applied to commercial users.’ (A02)
‘To help the households financially should be the government priority now.’ (A05)
‘The government should give tax rebate or something like that to the individuals so that cost of installation can be reduced.’ (A09)
Most industry players agree with the recommendation that financial support should be provided to the residential sector to increase the adoption of solar PV. Seven of 10 representatives interviewed proposed financial incentives as a remedy to the problem of low solar-energy usage among individuals in Malaysia. Several interviewees from the industry expressed their views as follows:
‘Households need financial supports to shorten the payback period of solar investment.’ (I03)
‘The commercial sector is currently taking advantage of tax saving, the residential sector needs the same too.’ (I08)
‘If Malaysia wants to achieve the renewable energy goal of 20% by 2025, to give financial incentives to individual PV installers is a must.’ (I10)
On top of that, the majority of government officers (three of five) also agreed with the point that financial incentives are essential in stimulating solar PV installation in homes. Example recommendations are shown below:
‘Probably, government can subsidize, give tax incentive. That is how solar energy can be encouraged.’ (G01)
‘Financial incentives should be given to make return on investment more attractive.’ (G05)
3.2.2 Enhance public awareness
Over the years, Malaysia’s dependency on fossil fuels in electricity generation has led to excessive carbon dioxide emissions. However, people have shown little concern about the adverse effects of air pollution. In the meantime, public awareness of the importance of switching from fossil fuels to renewable energy sources such as solar energy remains low [ 20, 69]. According to most of the participants in our study, raising public awareness is paramount to encouraging the utilization of solar energy among households.
Among the academicians, 6 of 10 highlighted the significant role of public awareness in reaching renewable-energy goals in Malaysia. In particular, some academicians suggested that the government should promote the concept of renewable energy such as solar PV and create public awareness by working more closely with both traditional and social media. As two of the interviewees put it:
‘The government should make use of the social media and promote it in television as well.’ (A07)
‘advertise in the media to create awareness.’ (A10)
Another academician opined that government could incorporate the concept of renewable energy into the school curriculum:
‘Government can do more like promoting the idea of solar energy at schools. I don’t see the school curriculum has been designed to include the renewable energy.’ (A03)
Half of the representatives (5 out of 10) from solar companies had a similar view that educating the public is one of the best strategies to increase the solar PV adoption rate among Malaysian households, as shown by the following responses:
‘Government can work with the industry to organize more awareness campaigns such as roadshows and so forth.’ (I02)
‘Awareness creation must start from young.’ (I05)
‘Of course, people don’t install solar PV because they don’t know about it. Thus, awareness programs should be enhanced in Malaysia.’ (I06)
Among the government officers, three out of five recommended increasing the number and effectiveness of awareness programmes for solar PV. As stated by one of the interviewees:
‘To make sure that more people know about solar PV and its benefits, we have to design more awareness programs.’ (G05)
3.2.3 Develop legislations to protect solar consumers
At present, there are several main statutory laws that govern the renewable-energy sector such as the Electricity Supply Act 1990, Energy Commission Act 2001 and Renewable Energy Act 2011 in Malaysia [ 77]. However, none of these laws aims to prevent consumer exploitation from solar companies. Thus, a comprehensive legal and regulatory framework is required to protect the rights of solar consumers in Malaysia, as suggested by some of the interviewees.
Half of the academicians (5 out of 10) have expressed their concern about the need to have stricter laws to protect consumer interests. According to them, consumers would feel unsecured with solar investment without such legislation. The participants have given Комментарии и мнения владельцев such as:
‘Some of the solar companies are not reliable. Thus, better regulations are needed to be imposed on them.’ (A04)
‘To gain households’ confidence, the government has to control what solar companies are doing.’ (A08)
The two representatives from government agencies who responded have given statements as follows:
‘You will never know whether you will be cheated at the end of the day. To protect the consumers, stricter law is the only way out.’ (G01)
‘I know many cases where solar PV companies can’t give satisfactory technical supports and after sales services to customers. That’s why we need to have more stringent rules and regulations to govern them.’ (G03)
Only a minority of representatives from the solar industry (2 out of 10) acknowledged the need to strengthen the rules and regulations imposed on solar companies. One of the interviewees said:
‘It is difficult to get a good installer. Smaller solar companies are in particular not stable. I think it’s time to do something to protect the consumers.’ (I01)
Discussion
Interview sessions have been carried out with participants from government agencies, industries and academia. The participants’ feedback has been analysed thematically under four themes of financial support, awareness programmes, subsidized electricity tariffs and NEM. This section will discuss the findings in a detailed manner.
The findings show both discrepancies and similarities in opinions within the same cohort of respondents and among different groups of interviewees. The majority of industrial representatives from solar companies opine that there are obvious weaknesses in the current policies. Similarly, from academicians’ points of view, most of the current solar strategies are ineffective in encouraging residential solar PV adoption due to certain shortfalls. However, governmental representatives have mixed views on the adequacy of current solar policies. Some agree with the existing efforts while others argue that deficiencies do exist in the current policies. The study suggests the possibility of policymakers introducing extra rebates for solar PV homeowners. Mamat et al. [ 48] also pointed to the similar view that the government should play its role by improving the effectiveness of the energy policies towards sustainable energy. For instance, the introduction of solar PV projects, also known as ‘MySuria’, will enable lower-income households to generate additional income through the adoption of solar PV [ 41].
Representatives from the solar companies have pointed out high installation cost as the main barrier to solar-energy adoption among households. over, a lack of financial support from the government will increase the breakeven cost and hinder households to install solar PV relative to the commercial sector.
Under the 10th Malaysia Plan (2006–2010), green technology incentives such as GITA and GITE aimed to promote the use of renewable energy [ 49] and are designed with the purpose of increasing companies’ involvements in environmentally friendly activities. Under these schemes, companies that carry out green technology activities or provide green technology services can apply for tax incentives. Yet, households have not benefited from these incentives. The government representatives admitted that the residential sector has been neglected in terms of financial support when comes to solar PV adoption.
However, Solangi et al. [ 63] disagreed that limited solar-energy adoption was due to high solar-panel costs and limited information. Their findings revealed that 80% of respondents thought that government subsidies would be the greatest way to increase solar-energy adoption. Hence, more comprehensive financial schemes that cater to respective stakeholders such as industries and individuals should be made available. This would enable homeowners to get a loan to improve their home’s energy efficiency. Zainuddin et al. [ 68] and Husain et al. [ 67] also agreed that government should be committed to promoting solar energy via the provision of various incentive schemes.
Although Malaysian policymakers have initiated numerous policies and laws to increase the capacity of renewable energy in the national electricity-generation mix [ 40], still there is a lack of public awareness of the importance of solar PV adoption among Malaysians. This scenario contributed to the slow adoption of solar PV. Academicians claimed that the government have not done enough to create public awareness and that there are no proper awareness programmes in place. However, the industry players admitted that there are awareness programmes such as the Annual Malaysian Photovoltaic Industry Association National Solar Roadshow aimed at educating and encouraging the installation of solar PV on commercial and industrial rooftops, but not focusing on the residential sector.
Malaysian households mostly obtain information about solar PV from their family members, relatives and friends, but not from the government’s organized campaigns. This shows that the efforts taken by the government to promote solar PV have been unable to grasp public attention thus far. over, limited information made available to households on the benefits of solar PV systems hinders installation. Similarly, Al-Fatlawi et al. [ 66] have pointed out that many individuals are still not aware of the benefits of using solar PV.
Government representatives have admitted the truth that the existing awareness programmes are insufficient and ineffective to create public awareness towards solar PV adoption. It is recommended to raise awareness and widen access to homeowners through a rent-to-own scheme, for example, that would make solar PV affordable. With such publicity campaigns, it is expected to graduate a surge in interest and foresee a rise in residential solar adoption in the near future.
On the other hand, subsidized electricity tariffs provided by Malaysia National Energy have led to low electricity costs for Malaysian households. Electricity consumers in the country are eligible to receive fuel subsidies from the government. According to Malaysia National Energy, fuel subsidy refers to the amount of fuel cost subsidized by the government for each unit of electricity consumed. Hence, participants from government agencies, industry and academician agreed that this subsidy serves as a deterrent for the development of the residential solar sector in Malaysia.
Last but not least, the shortcomings of NEM—a new mechanism introduced by the government in 2017 to replace the FiT—were highlighted in the interviews. The main objective of the NEM scheme is to encourage the uptake of solar PV technology. The solar industry has proposed to the government to modify the concept of NEM from the existing net billing to true net energy metering in 2018. Under the improved NEM scheme, excess energy generated from solar PV could be exported back to the grid based on a ‘one-on-one’ offset basis starting in January 2019, replacing the Displaced Cost earlier [ 18]. However, some government agencies’ representatives mentioned that the FiT scheme is better as compared with the NEM scheme and the FiT scheme should be re-proposed. The industry players further commented that solar PV installation is only suitable for households with a monthly electricity bill of 300 Malaysian Ringgit.
Based on the discussion above, it is revealed that our findings are consistent with Assoa et al. [ 47] and Mamat et al. [ 48] who claimed that the slow adoption of solar energy was mainly due to inadequate energy policies. Thus, the authorities could promote solar energy to the public by introducing more effective programmes. Koerner et al. [ 40] also suggested that communication channels between stakeholders in the solar-energy discipline should be strengthened to increase the use of solar PV towards a reduction in carbon emissions.
In the long run, increased usage of solar energy among Malaysian households will tend to cut greenhouse gas emissions from fossil-fuel power plants [ 78]. This study has deeply discussed the shortcomings of the existing energy policies and future strategies to enhance residential solar PV adoption via a qualitative approach that has not been found in previous studies.
Conclusion and policy implications
By using a qualitative approach (via individual in-depth interviews), this study enables the compilation of solar experts’ viewpoints on policy shortfalls and recommendations for better solar-energy policies in Malaysia. The responses from most of the participants portray the existing initiatives undertaken by the government as inadequate and ineffective in promoting solar PV usage among Malaysian households. Indeed, several policy flaws have been identified. In addition, the respondents have recommended solar policies and programmes that should be in place to enhance demand for solar PV systems.
Previous research acknowledged the importance of solar policies in determining the demand for solar systems among Malaysian households [ 40–42]. However, none of these previous studies has scrutinized the role of solar policies by using a qualitative approach. Scientifically, our study contributes to the existing literature by collecting experts’ opinions and feedback on the shortcomings of current solar initiatives taken by the Malaysian government. Furthermore, this study also attempts to gather experts’ suggestions on what could be done by the government to improve solar-related policies in the country. To our knowledge, this strand of research is absent in the literature. Our findings, therefore, could contribute to this theme by shedding light on the experts’ policy viewpoints when it comes to solar PV adoption. The findings of this study also provide a better understanding of residential solar PV usage in Malaysia.
Based on our findings, several important policy implications are produced as follows. First, our results show that there is a lack of public awareness of the solar-related schemes introduced by the government and the benefits of solar power on the environment. Therefore, public awareness and education campaigns should be launched to ensure that households are informed of the government’s solar initiatives and the importance of using solar PV to reduce pollution. In such a case, the policymakers could engage electronic or traditional media as well as community leaders to share information with the public on solar PV programmes and their benefits. Furthermore, the public should also be exposed to an energy curriculum and activities in schools from a young age. The curriculum could introduce school children to different types of energy sources and their environmental impacts. In a nutshell, educating the public is one of the most important strategies that can be taken by the government to enhance the installation of solar PV systems.
Second, the current renewable-energy policies such as GITA, GITE and GTFS have been focusing on providing financial incentives to companies that engage in green projects and activities. However, tax incentives and financial support are not granted to households who wish to install solar PV systems at home. In line with the government’s goal of achieving 20% renewable energy generation by 2025, it is thus important to ensure that not only the industrial and commercial sectors receive financial assistance for solar PV utilization, but also the residential sector. Currently, households are unwilling to install solar PV systems as the payback period for investment is up to 10 years with limited financial incentives from the government. Thus, the policymakers should formulate appropriate subsidy or incentive programmes that are able to reduce the payback period and upfront costs of solar PV investment so that homeowners could be encouraged to adopt the technology. The Malaysian government can draw on the practical experience of other governments to construct relevant support schemes for solar PV usage. In Australia, for example, the provision of solar incentive schemes from both the state and the federal government has encouraged the uptake of solar PV systems among households. At the federal level, the government grants solar subsidies to homeowners for solar-panel installation. With this subsidy scheme, the upfront costs of solar PV have been reduced by ~30%. Additionally, certain state governments in Australia also provide solar-panel rebates and interest-free loans for residential solar installation [ 79].
Third, our findings also suggest that there is a shortage of reliable solar companies in the market that can provide satisfactory technical support and service to solar PV adopters. A responsible solar PV provider should be able to provide customers with complete operation and maintenance services to maximize the performance of solar PV systems throughout their period of usage. In relation to this, appropriate regulatory measures aimed to govern the actions of solar suppliers should be developed and implemented by policymakers for the sake of solar users. Once households are convinced and confident with the capability and reliability of solar companies, they will be encouraged to install solar PV at home.
This study has two main limitations. First, the results are indicative instead of conclusive due to the small sample size. Second, the exploratory nature of this qualitative study has the drawback that the data have been subjectively analysed and interpreted. Our study, being exploratory in nature, is able to create a few opportunities for future research. In short, more future studies are required to refine our findings. First, future researchers may consider using a larger sample size and/or a mixed research method, i.e. combining qualitative and quantitative research approaches. The results generated from different methods can enhance our understanding of the advantages and drawbacks of solar policies in Malaysia. Second, an identical study could be extended to other developing countries (such as the Philippines and Thailand) to investigate the effectiveness of their existing solar-related policies. The similarity between Malaysia and other developing countries is that renewable energy constitutes an insignificant proportion of the total energy mix. Finally, comparative studies between developed countries (particularly those with solid solar policies) and the developing world can also be carried out in the future. Such research could probably provide important lessons for the developing countries in refining their solar policies and hence enhancing the use of solar energy.
Footnotes
Malaysia is the world’s third largest producer of solar PV cells and modules (Malaysian Investment Development Authority, 2017).
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