Everything About Transparent Solar Panels: Working, Cost, Pros, And Cons
With many evolutionary technologies hitting the market, solar technology has progressed with the invention of a transparent solar panel.
These are the new generation of energy panels that use window surfaces to generate electricity. The prime motive is to save farmlands since the installation of large-scale solar panels requires a lot of space.
This is a new technique for gathering solar energy through Windows or glass surfaces, often termed photovoltaic glass. It can transform any glass or window panel into an electricity-generating PV cell.
How Does A Transparent Solar Panel Work?
An invisible solar panel selectively traps sun rays that are not visible to the naked eye. It does so by using a Transparent Luminescent Solar Contractor (TLSC).
- The TLSC comprises organic salts that can absorb selected invisible UV rays and visible infrared light.
- The new ray formed is then directed towards the borders of the window lanes.
- The PV-coated window converts the new rays into usable energy.
The glasses are coated with a thin layer of photovoltaic ink or film. The TLSC has an efficiency of 10%. However, this can be increased by using them in every household and commercial place.
The efficiency of a Transparent Solar Panel
The efficiency of these panels is somewhat low compared to traditional solar panels, which is around 10 percent.
Poly solar panels have an efficiency of somewhere between 13 to 15 percent. Mono perc panels have an efficiency of about 16 to 21 percent. Bifacial modules have the highest efficiency rate (about 27 percent).
In comparison to all its peers, a partially transparent panel has an average efficiency of 7.2 percent. The amount of energy created depends on several factors like the window’s location and the amount of sunlight received. A large window solar panel is more efficient.
Introduction and Background
In recent years, there has been a significant progress demonstrated in both the RD and industrialisation of novel BIPV products, materials, and also the window-integrated PV (WIPV) solar window systems. In particular, research progress has been made throughout the last decade in fields such as the development of large-area semi-transparent luminescent solar concentrators (LSC) and functional materials for use in solar Windows (Li et al. 2016; Vasiliev et al. 2016; Alghamedi et al. 2014; Reinders et al. 2018; and others). Due to the globally recognised need to effectively decarbonise the built environments, novel types of BIPV and high-transparency solar Windows are currently receiving increasing attention. Of special importance is the emergence of newly-commercialised glass-basedhigh-transparency and completely visually-clear BIPV technologies and systems, which have been demonstrated in practical architectural deployment applications.
Even with surging commodity increasing manufacturing costs for solar PV, its capacity additions were forecast to grow by 17% in 2021. This will set a new annual record of almost 160 GW in added generation capacity. Solar PV alone accounts for 60% of all renewable capacity additions (IEA Renewables-2021 (2021)). The addition of solar generation capacity in built environments is limited by the available unshaded roof and wall areas, therefore enabling Windows to generate electricity simultaneously with providing HVAC and lighting energy savings represents an attractive way forward to achieve substantial and long-term decarbonisation. In buildings with high window-to-wall ratios, installing glazing systems with electricity generation provides perhaps the only viable way to decarbonise, even if window-generated electric power per unit area is (invariably) a fraction of that available from conventional PV.
Recent Developments in BIPV and Transparent Window-Integrated PV
Modern BIPV module suppliers have continued to offer an increasing range of products, trending towards systems of continually increasing power conversion efficiency (PCE), the choice of reflected colours, and with a brodening range of semi-transparency options. Multiple new technologies have appeared on the market in recent years, utilising new functional materials and system design types.
2.1. Current Trends and Technologies in Conventional BIPV
Multiple comprehensive reviews of recently-developed BIPV technologies and their performance characteristics are available, eg Biyik et al. (2017) and Vasiliev et al. (2019), with newer sources also continuing to appear in the literature. Fig. 1 provides an outlook on the BIPV technology types which have been commercialised widely at present, including the most commonly known semi-transparent patterned-semiconductor-based glazing systems. The naturally occurring (and fundamental) trade-off between glass transparency and power generation per unit area is approached differently in systems utilising different energy-conversion materials, resulting in a range of power-vs-transparency options, most of which do not result in colour-free visually-clear appearance.
Additionally, no pathways towards increasing the PV Yield (measured in kWh/kWp/year) compared to the roof- or wall-mounted monocrystalline silicon PV systems have been demonstrated in conventional BIPV so far, since these systems rely intrinsically on single-plane-oriented patterned active materials, usually deployed without sun-tracking or light concentration options. At the module level, the manufacturing scalability of large-area ( approx. 2m²) BIPV panels is only possible when tiled mono-Si wafers are laminated in-between glass plates, covering a substantial fraction of visual aperture (eg Fig.1 (c)).
This is due to the current range-to-resolution ratio limitations in industrial laser-patterning machines used to remove semiconductor material layers from parts of substrate area; also the lithography processes used to deposit a fine grid of conductors have similar limitations (eg Fig.1 (d, e, f)). With increasing thickness of the front coverglass used to laminate conventional mono-Si, which may be necessary for environmental safety reasons (eg wind load resistance, or if requiring walkable-roof safety assurance), the module PCE drops rapidly beyond ~3mm of the front glass thickness, for reasons such as geometric shading, light scattering and absorption by glass, refraction and reflectance.
While there is continued materials-related progress being made in terms of increasing PCE and novel PV materials (eg perovskites, kesterites, etc.) are being proposed for window-integrated PV systems, new approaches are required to broaden the range of available PV glass products. This is particularly true for the manufacturers targeting the development of high-transparency, area-scalable, and high-efficiency clear solar Windows, which could then even resemble ordinary window types while providing energy savings and generation.
2.2. Trends and Challenges in Semi-Transparent Window-Integrated PV
In order to find innovative ways of designing semi-transparent solar Windows of higher PCE and improved PV Yield characteristics (though only the PV Yield can be meaningfully compared to standard PV modules), not only novel functional materials but also modifications in the structure of PV-integrated glazing systems are required. Reinders et al. (2018), Vasiliev et al. (2016), Alghamedi et al. (2014), and others described several novel and recently-developed approaches to the WIPV glazing design utilising some results from the well-established field of luminescent solar concentrators (LSC), in combination with recent developments in the materials science of thin films, luminescent materials, and photonics. The task of designing highly transparent LSC-type devices of relatively high PCE involves considering fundamental trade-offs and theory limits described by Yang et al. (2017).
It is important to note that the main performance characteristics of any LSC-type device are governed by Eq. (1), where G is geometric gain, P is photon collection probability (often also called “optical efficiency”), and Copt is optical power concentration factor; detailed definitions for these parametersare available from Desmet et al. (2012).
In Eq.(1), the geometric gain is adjustable by the window system designer, and is largely governed by the window dimensions and the design of PV modules placed near window perimeter/edge areas to collect light. Typical values of G for ~1m2 Windows are between ~5-10, dependent on whether solar PV strips are also placed around backside perimeter near glass edges. The photon collection probability, on the other hand, is a function of core technology used within the LSC-type glazing system, especially the luminescent and/or scattering materials and components used, eg glass panes chemistry, heat-mirror-type optical coating(s), any diffractive elements, and the overall optical arrangement of these components.
Examples and Discussion
3.1. High-Transparency Window-Integrated PV: Installation Examples
The first commercial property-based installation of Clearvue solar Windows (Fig. 2) has been made at Warwick Grove Shopping Centre in Perth, in early 2019. A comprehensive analysis of its observed energy harvesting performance is available from Vasiliev et al. (2019).
Solar Windows of dimensions 1.2m x 1.2m were installed onto NE roof area (4 Windows), NW roof area (4 Windows), Nth wall (8 Windows just below entry sign), and strongly-shade east wall (2 Windows). The maximum instantaneous electric power output so far observed, measured at the AC battery by Enphase Envoy data-logging interface was just below 300 W; the yearly generation was ~0.5 MWh, in line with the predicted performance considering the relevant capture loss and system loss factors.
A more recent (2021) installation example of Clearvue solar Windows is Murdoch University Solar Greenhouse (Fig. 3), in which 3 out of 4 grow-rooms (~50m2 floor area each) were built using solar Windows on the north wall, on the 20-degree tilted north-facing roof, and also on the west-facing wall. 153 solar Windows in total represented an installed capacity near 6.2 kWp, which has led to strongly offsetting the running costs of greenhouse during 2021 in terms of HVAC system operation. In summary, the winter-time daily electric energy consumption in Clearvue grow-rooms was at about a third of that needed to maintain microclimate in the reference grow-room glazed with conventional glass. The PV installation contained 13 Enphase 7 microinverters each connected to a parallel bundle of ~12 Windows; the system is also exporting energy to the grid, with the self-consumed energy fraction being near 70%.
The microclimate in each grow-room was finely controlled using a custom-designed HVAC system, keeping the temperature setpoints within /-2 °C to optimise the plant growth. Even with this fine control of microclimate applied continually, the PV installation has offset min. ~40% of the total energy costs in Clearvue grow-rooms.
Fig. 5 shows the results of the summer-time PV Yield comparison made with a conventional PV or BIPV system installation of identical installed capacity placed onto a north-facing vertical wall in Perth. The energy production data for December 2021 from Enphase Envoy interface shows a 53.4% energy production increase, compared to that expected from a conventional PV installation of same capacity.
Similar PV Yield comparison results for the wall-based Windows were also observed in other months (eg Nov 2021 and Jan 2022, when the weather was at its most stable for Perth). The PV Yields exceeding these available from conventional BIPV systems were expected, due to the design of Clearvue Windows featuring the reduced angle-of-incidence sensitivity of electric power output. This makes these solar Windows attractive for the (intrinsically multi-oriented) BIPV installations.
3.2. High-Transparency WIPV: Future Directions
With BIPV field installations continuing to grow worldwide, using an increasing range of products and different features, there is an increasing research attention to the contributions these systems will be making in terms of decarbonisation and sustainability.
During the second half of 2021, ClearVue commissioned energy efficiency and sustainability specialists, Footprint (Canada) to develop an energy-efficient archetype model office building named “ClearZero” to demonstrate how ClearVue’s world-leading window integrated photovoltaics can be used to assist in the design of highly energy efficient, energy neutral buildings. We completed the design of an Archetype model building of 15,000 m2 internal area (an artist’s rendering based on architectural design software is shown in Fig.6 (Peacock, 2022)), to demonstrate how ClearVue Windows can achieve a Net Zero or Near Zero energy-use building operation.
A transparent solar panel breakthrough at the Swiss Federal Institute of Technology Lausanne
Transparent solar panels are part of the second generation of solar cell technology. While electricity is still generated through the movement of electrons, it’s done using different materials. It’s also done through solar cells that capture only part of the solar spectrum, allowing visible light to pass through.
Officially known as dye sensitized solar cells (DSCs), these transparent cells were invented back in 1991 at Switzerland’s École Polytechnique Fédérale de Lausanne (EPFL). Professor Michael Gratzel and Dr. Brian o’Regan get credit for the invention, which is why DSCs are also known as the Gratzel cell (GCell).
Early versions of DSCs needed direct sunlight to work properly, and they also produced far less electricity than traditional solar cells. Traditional solar cells have an average efficiency of 20%, which means it converts 20% of the solar energy it absorbs into usable energy. DSCs hit a record high of 12% by 2011.
The latest breakthrough from the team at EPFL changes all that. Updated DSCs have an efficiency rate of 30% in ambient light conditions and 15% in direct sunlight. They can also work with any type of visible light, be it natural, artificial, indoors or outdoors.
In addition to their transparency, DSCs are beneficial for their flexibility, relatively low-cost, and wide range of color options.
How these solar panels can work as Windows
The magic ingredient in dye-synthesized solar cells is the dye, which creates electricity once it’s exposed to light.
- Dye is applied to the solar panels.
- When light hits the dye, the dye captures photons from the light.
- Energy from the photons is then used to excite electrons, which is what chlorophyll does in photosynthesis. When an electron is excited, that means it carries a higher energy level than its usual base state.
- The excited electron is injected into a white pigment called titanium dioxide, a common pigment found in white paint.
- The electron is then pulled away from the titanium dioxide by a crystallized form of titanium dioxide called nanocrystalline titanium dioxide.
- An electrolyte in the cells closes the circuit, causing the electrons to go back to the dye.
Movement of the electrons is what produces the energy, which we can then harvest into rechargeable batteries or other electronic devices of our choice.
As the first public building to use DSCs, the SwissTech Convention Center has had transparent yellow and orange solar panels in place since 2012.
The Copenhagen International School hopped on the DSC bandwagon in 2017, introducing a new building covered in blue-colored transparent solar panels. The building is outfitted with 12,000 panels, which are able to provide about 300 megawatt hours of electricity every year – which is more than half the amount of energy the school uses.
Lightweight versions of DSCs are also already being sold on a large scale for commercial use to power portable devices. They work for smaller items, such as headphones, and can also use ambient light to power components in the Internet of Things (IoT).
When will these solar panels be available for public use?
With the latest advances making DSCs more efficient, it may not be all that long before these solar panels are available for public use. But no one can say exactly when.
A number of companies are making strides in that direction:
EnergyGlass produces a glass system that generates energy from any light source. They appear to work on largescale building projects, integrating the system into building window designs to generate electricity.
SolarWindow creates ultra-lightweight liquid coatings that can be applied to glass and plastics to generate electricity. They offer partnership opportunities, but no products yet available to the general public.
Ubiquitous Energy produces an energy-generating film coating designed to absorb infrared and ultraviolet light while allowing visible light to get through. They are not yet available to the public, with the company noting it will be selling through window manufacturers.
How this solar panel innovation can help the transition to net-zero emissions
Transparent solar panels have phenomenal potential. While they could be great for personal use in your home or car, they could be absolutely mind-blowing if used in skyscrapers across the world.
Every tall building with Windows could be turned into a veritable solar farm. A solar energy team at Michigan State University predicted transparent solar technology may be able to generate about 40% of the energy needed throughout the entire United States.
If transparent solar panels were then combined with rooftop panels, it’s possible solar technologies could generate enough energy to meet 100% of the demand.
Why our future depends on innovations like these for long-term, sustainable energy use
The demand for energy continues to increase, but non-renewable resources do not. Oil, coal and other traditional fuel sources are eventually going to become depleted. Traditional fuel sources are also known for generating emissions that cause pollution, further eroding the overall health of the earth.
Unlike fossil fuels, solar energy is renewable as well as sustainable. It’s going to last as long as the sun does. It’s also a clean way to produce energy, lacking the emissions and pollution associated with traditional resources.
Like the latest breakthrough in DSCs, solar technologies continue to advance and improve. The global solar output in 2004 was 2.6 gigawatts (GW), enough to meet a scant 0.01% of the energy demand across the world. By 2015, global solar output was at 302 (GW), able to meet 1.8% of the worldwide demand.
A 2014 prediction from the International Energy Association says 27% of the world’s energy could be generated by solar power by 2050.
If the second generation of solar cell technology has already brought us transparent panels that can be used as Windows, it’s exciting to think what advancements may come next. (Like the Stanford scientists who recently made progress on solar panels that work at night).
The third generation of solar is what’s in store for the future and, if the innovations continue with the same level of creativity and success, it promises to be more brilliant than ever.
Recent developments in the field of transparent solar cell technology
Apart from the research work conducted by Professor Richard Lunt and his team at MSU, there are some other research groups and companies working on developing advanced solar-powered glass Windows. Earlier this year, a team from ITMO University in Russia developed a cheaper method of producing transparent solar cells. The researchers found a way to produce transparent solar panels much cheaper than ever before.
Regular thin-film solar cells have a non-transparent metal back contact that allows them to trap more light. Transparent solar cells use a light-permeating back electrode. In that case, some of the photons are inevitably lost when passing through, thus reducing the devices’ performance. Besides, producing a back electrode with the right properties can be quite expensive, says Pavel Voroshilov, a researcher at ITMO University’s Faculty of Physics and Engineering.
For our experiments, we took a solar cell based on small molecules and attached nanotubes to it. Next, we doped nanotubes using an ion gate. We also processed the transport layer, which is responsible for allowing a charge from the active layer to successfully reach the electrode. We were able to do this without vacuum chambers and working in ambient conditions. All we had to do was dribble some ionic liquid and apply a slight voltage in order to create the necessary properties, adds co-author Pavel Voroshilov.
PHYSEE, a technology company from the Netherlands has successfully installed their solar energy-based “PowerWindow” in a 300 square feet area of a bank building in The Netherlands. Though at present, the transparent PowerWindows are not efficient enough to meet the energy demands of the whole building, PHYSEE claims that with some more effort, soon they will be able to increase the feasibility and power generation capacity of their solar Windows.
California-based Ubiquitous Energy is also working on a “ClearView Power” system that aims to create a solar coating that can turn the glass used in Windows into transparent solar panels. This solar coating will allow transparent glass Windows to absorb high-energy infrared radiations, the company claims to have achieved an efficiency of 9.8% with ClearView solar cells during their initial tests.
In September 2021, the Nippon Sheet Glass (NSG) Corporation facility located in Chiba City became Japan’s first solar window-equipped building. The transparent solar panels installed by NSG in their facility are developed by Ubiquitous Energy. Recently, as a part of their association with Morgan Creek Ventures, Ubiquitous Energy has also installed transparent solar Windows on Boulder Commons II, an under-construction commercial building in Colorado.
All these exciting developments indicate that sooner or later, we also might be able to install transparent power-generating solar Windows in our homes. Such a small change in the way we produce energy, on a global scale could turn out to be a great step towards living in a more energy-efficient world.
Not there just yet
If this almost sounds too good to be true, well sort of is. The efficiency of these fully transparent solar panels is around 1%, though the technology has the potential to reach around 10% efficiency.- this is compared to the 15% we already have for conventional solar panels (some efficient ones can reach 22% or even a bit higher).
So the efficiency isn’t quite there yet to make transparent solar cells efficient yet, but it may get there in the not-too-distant future. Furthermore, the appeal of this system is that it can be deployed on a small scale, in areas where regular solar panels are not possible. They don’t have to replace regular solar panels, they just have to complement them.
When you think about it, solar energy wasn’t regarded as competitive up to about a decade ago.- and a recent report found that now, it’s the cheapest form of electricity available so far in human history. Although transparent solar cells haven’t been truly used yet, we’ve seen how fast this type of technology can develop, and the prospects are there for great results.
The mere idea that we may soon be able to power our buildings through our Windows shows how far we’ve come. An energy revolution is in sight, and we’d be wise to take it seriously.