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Fresnel solar steam generator. Fresnel solar steam generator

Fresnel solar steam generator. Fresnel solar steam generator

    US5632147A. Solar powered steam turbine generator. Google Patents

    Publication number US5632147A US5632147A US08/629,835 US62983596A US5632147A US 5632147 A US5632147 A US 5632147A US 62983596 A US62983596 A US 62983596A US 5632147 A US5632147 A US 5632147A Authority US United States Prior art keywords rotor combination according working fluid steam inlet Prior art date 1996-04-10 Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.) Expired. Fee Related Application number US08/629,835 Inventor William Greer Original Assignee Greer; William Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.) 1996-04-10 Filing date 1996-04-10 Publication date 1997-05-27 1996-04-10 Application filed by Greer; William filed Critical Greer; William 1996-04-10 Priority to US08/629,835 priority Critical patent/US5632147A/en 1997-05-27 Application granted granted Critical 1997-05-27 Publication of US5632147A publication Critical patent/US5632147A/en 2016-04-10 Anticipated expiration legal-status Critical Status Expired. Fee Related legal-status Critical Current



    • F03G6/00 — Devices for producing mechanical power from solar energy
    • F03G6/06 — Devices for producing mechanical power from solar energy with solar energy concentrating means
    • F03G6/065 — Devices for producing mechanical power from solar energy with solar energy concentrating means having a Rankine cycle
    • Y02E10/00 — Energy generation through renewable energy sources
    • Y02E10/40 — Solar thermal energy, e.g. solar towers
    • Y02E10/46 — Conversion of thermal power into mechanical power, e.g. Rankine, Stirling or solar thermal engines


    A solar steam generator has a hollow steam rotor mounted for rotation in a closed compartment located within a larger housing. The rotor is made of heat conductive material and is supplied with water or other working fluid through an inlet at its central hub. A plurality of steam jet outlets are located around the periphery of the rotor; and they are oriented to cause the rotor to spin as the water or working fluid inside is heated to a boiling temperature. To cause the fluid in the rotor to boil, Fresnel lenses, located in an open end of the housing, FOCUS heat from the sun onto the rotor and the chamber in which it is located. Steam and fluid which exit from the nozzles is recovered in the sealed chamber and is returned through a condenser-reservoir, from which it is supplied back to the water inlet of the rotor.


    The availability of unlimited solar energy, in the form of solar radiation and heat, is an attractive source of energy for many purposes. Many applications for harnessing or using solar radiation to generate electricity or a useful mechanical output exist. For example, silicon solar cells which respond to light from the sun are used to generate electricity, which then may be used directly or stored by charging a battery. Typically, solar cells generate only small amounts of electricity; so that solar cell systems generally are used to operate electronic devices requiring relatively low power levels.

    Solar cell arrays many square feet in size have been used to power direct current motors to operate pool pumps and the like. Typically, however, solar cell arrays need to be extremely large in order to produce any substantial quantity of electricity. As a result, such solar cell arrays have not been found to be a practical source for utilizing energy from the sun, in all but a few specialized cases.

    Another approach to harnessing the energy of the sun is to FOCUS the solar radiation through a lens system onto a contained boiler to generate steam. The steam then may be utilized to turn a rotor, which operates an electric generator.

    Systems have been developed for utilizing solar energy in a closed loop sealed system to generate electric power. One such system is disclosed in the Parker U.S. Pat. No. 4,945,731. The Parker patent discloses a heat cycle engine in the form of a hollow cylindrical container enclosing a working fluid in the form of a radiant energy absorber. A window is disposed in the first end of the container to receive solar energy, which is concentrated on the window from a parabolic reflector. The working fluid is heated in the area behind the window, and then travels toward the opposite end of the container to operate a turbine. The cooled fluid then returns back to the end adjacent the window on a continuous basis. The turbine located within the container is coupled through a magnetic coupling to an external shaft, which may be used to drive an electric generator. The system of this patent uses specialized working fluid selected from halogens and interhalogens; and the system is relatively complex and expensive to manufacture.

    Another type of closed loop, hermetically sealed solar power generator is disclosed in the patent to Smith U.S. Pat. No. 4,391,100. The Smith patent discloses a closed loop, sealed, recirculatory water solar powered generator which has a hollow globular water boiler with a focusing lens in it. Solar energy is reflected onto the lens from a parabolic mirror; and the heat then is focused on the water inside the boiler. Steam is generated and is obtained from the top of the boiler to drive a steam turbine. The water then passes through a condenser to a reservoir, from which it returns back to the boiler. The boiler and the steam turbine are separate parts in this system; but the system of Smith is of more simple construction than the system of the Parker patent and uses a readily available, inexpensive working fluid in the form of water.

    Another system of the same general type as the one disclosed in the Smith patent is disclosed in the patent to Lane U.S. Pat. No. 4,213,303. This patent is directed to a sun tracking, solar energy boiler using a lens system to heat a small tube of water to create steam. The steam then is used to drive a turbine, the shaft of which is coupled to an electric generator to produce useful output energy. The condensed steam then is supplied back to a condenser and reservoir, from which it is supplied again to the boiler tube.

    A different system for converting solar energy to low cost mechanical or electrical power is disclosed in the Abbot U.S. Pat. No. 3,654,759. The Abbot patent divides a reflected solar input beam into a plurality of concentrated cones of solar radiation through the use of a Fresnel lens array. Each of these cones of concentrated radiation then is focused on a relatively thin black box to heat air contained within the box. When a suitable pressure is built up within a box, the heated air is passed outwardly through a valve and to a nozzle directed to a turbine to rotate the turbine. The different boxes are opened and closed at different times to admit air into the boxes, and then to release the pressurized heated air from the boxes in a timed sequence to continuously apply jets of heated air to different portions of the rotor to rotate it. The mechanical motion of the rotor then is used to produce electrical energy.

    The foregoing systems of the prior art all include various disadvantages. The Abbot system is not a closed system, and therefore is subject to variations in the supply of ambient air used in the system. Clearly, the greater the temperature differential between the air entering into the boxes and that to which the air is heated by the lens system, the greater the power output from the Abbot system. Therefore, it is desirable to separate, to as great a degree as possible, the output nozzles used to drive the turbine from the location of the input air to the boxes. The other patents, which have been discussed above, all are relatively complex in the number of components and in the array of lenses and specialized boilers which must be incorporated.

    It is desirable to provide a solar powered steam turbine generator which is efficient in operation, which overcomes the disadvantages of the prior art, and which is simple and inexpensive to manufacture.

    It is an additional object of this invention to provide an improved solar powered steam turbine where the steam is generated directly within the turbine itself.

    It is a further object of this invention to provide a solar powered, self-contained, closed loop steam turbine generator.

    In accordance with a preferred embodiment of this invention, a system for converting solar radiation to useful energy comprises a thin, hollow rotor made of heat conductive material, mounted for rotation about its axis in a housing. The rotor has a plurality of outlet jets located about the periphery, oriented to cause rotation of the rotor when steam issues from the outlet jets. Working fluid is supplied to an inlet in the rotor; and a lens is mounted in the housing to FOCUS solar radiation on the rotor to heat the working fluid therein. This produces steam or expanded working fluid within the rotor, which issues from the outlet jets to cause rotation of the rotor.

    FIG. 6 is a detail of a portion of one of the features of the embodiment specifically shown in FIGS. 1 and 2.

    Reference now should be made to the drawing, in which the same reference numbers are used throughout the different figures to designate the same components. FIG. 1 is a top front perspective view of a preferred embodiment of the invention, in the form of a system for converting solar radiation to useful energy. As shown in FIG. 1, a housing has a semi-cylindrical curved top and a flat bottom 12, with an open end in which is a mounting plate 14. The mounting plate 14, in turn, has four Fresnel lenses 46 uniformly located about a central axis of the cylinder from which the top 10 forms a section. This is seen most clearly in FIG. 2.

    As indicated most clearly in FIG. 3, the housing 10, 12 also includes a short semi-cylindrical section having a bottom 15, which comprises a continuation of the curve of the top 10 (as shown most clearly in FIG. 4). This section 15 is enclosed by two end plates 16 and 18. The plate 16 preferably is made of metal, whereas the plate 18 may be made either of heat conductive material, such as metal, or it may comprise a glass plate having a circular opening at its center, through which a hub 34 mounted in a bearing 36 is located. If a glass plate 18 is used, a metal support brace configuration 20, as shown in FIG. 5, may be used to support the hub 34 and bearing 36 relieving stress from the glass of the plate 18. A seal is made between the bearing 36 and the plate 18; and a similar seal is made on the opposite side in the plate 16 to support a bearing 32 for an output shaft 30. Thus, the plates 16 and 18 and section 15 form a closed, hermetically sealed chamber within the housing 10.

    The shaft 30 is attached to a rear circular plate 22 of a hollow rotor, the opposite face of which comprises a circular plate 24. The plate 24 is parallel to and faces the support plate 18 in the housing 10, 12. In the partially cut-away view of the rotor shown in FIG. 3, it may be seen that the rotor is relatively thin in a transverse direction compared to the diameter of the end plates 22 and 24. The periphery or circumference of the rotor is covered by a rim 26, through which a plurality of steam jet nozzles 28 are formed. The nozzles 28 all are oriented to direct steam exiting from the interior of the rotor 22, 24, 26, in a generally tangential direction to cause rotation of the rotor when steam under pressure issues from the nozzles formed in the ends of the outlet jets 28.

    An inlet for working fluids, typically water, is provided through the center of the hub 34 through an inlet pipe 44, which communicates directly with the rotor interior to supply working fluid to the rotor 22, 24, 26 located within the housing 10 and inside the compartment or chamber formed by the end plates 16 and 18.

    The system is completed by providing a drain 50 through the bottom 12 and the semi-cylindrical section 15 to remove spent steam and water accumulating within the interior of the chamber formed by the plates 16 and 18. This spent steam and water passes through an outlet pipe 52 into a condenser/reservoir 54, which in turn is connected through a pipe 56 and a check valve 58 to the inlet pipe 44. This forms a closed loop, sealed system. At such time as initial working fluid or make up fluid (such as water) is required, the fluid is supplied through a pipe 60, as shown in FIGS. 1 and 3.

    In operation, the open end of the housing 10, which is closed with the panel 14 having the Fresnel lenses 46 in it, is oriented to receive direct solar radiation from the sun. To do this, solar tracking devices (not shown) may be employed to optimize the operation of the system which is shown in FIG. 3. Any standard tracking system may be employed for this purpose.

    The sun radiation passes through the Fresnel lenses 46, as shown in FIG. 3, which then FOCUS the radiation onto or through the plate 18 and onto the front flat circular panel 24 of the rotor. This focused solar radiation causes a substantial heating of the working fluid within the rotor, causing its expansion, and, in the case of water, causing the water to boil, producing steam. The expanded fluid and/or steam then is expelled under pressure through the nozzles 28 to spin the rotor in the direction of the arrow shown in FIG. 4. The output shaft 30 of the rotor is connected through a gear box 38 (FIG. 3) to drive an electrical generator 40, thereby producing useful electrical output from the system.

    As the steam and expanded heated working fluid exits under pressure from the nozzles 28, it is collected at the drain 50 and is supplied back to the reservoir 54, as described above. A check valve 58 in the system prevents the pressurized working fluid/steam buildup within the rotor interior from flowing back in the opposite direction through the inlet pipe 44. If the working fluid is water, the orifices in the steam jet nozzles 28 ideally have an internal diameter of from approximately 0.001 inches to 0.003 inches to prevent leakage of unheated or unpressurized working fluid or water from the nozzles 28 when the system is first started up, or when it is not in use. A small of amount of leakage can be tolerated; but by choosing the nozzle diameters to be within this range, optimum operation of the system is attained. Variations of the nozzle size and the number of nozzles 28 relative to the internal volume of the rotor 22, 24, 26 may be effected to optimize the operating conditions of the system for any particular application.

    Ideally, the rotor is made of heat-conductive materials, such as copper, and the end plates 22 and 24 are made to be as thin as possible. In addition, the chamber formed between the support plates 16 and 18 is hermetically sealed and, preferably, is made to impede outward heat transfer through these plates into the other interior portions of the housing 10, 12. The plate 16 may be made of insulating material, since no heat rays or concentrated light rays from the solar energy need to pass through this plate. The plate 18, as described above, may be made of heat-conductive metal or transparent glass, as desired.

    Typically, the focal length of the Fresnel lenses 46 for a relatively small generator is approximately 10 inches, with the diameter of the lenses 46 for such an arrangement being on the order of 4 inches. Obviously, larger lenses, and an increased number of lenses 46, may be employed for larger installations capable of generating more power.

    Although the output of the rotor 22, 24, 26 has been indicated as applied to drive an electric generator 40, this rotational output may be utilized in any other manner desired, since rotation of a shaft to obtain useful output is well known for a variety of different applications.

    The foregoing description of the preferred embodiment of the invention is to be considered as illustrative and not as limiting. Various changes and modifications will occur to those skilled in the art for performing substantially the same function, in substantially the same way, to achieve substantially the same result without departing from the true scope of the invention as defined in the appended claims.

    Claims ( 20 )

    a hollow rotor having a central axis and made of heat conductive material, said rotor mounted for rotation about its axis in said housing, said rotor further having a plurality of outlet jets located about the periphery of said rotor and oriented to cause rotation of said rotor when steam issues from said outlet jets, and said rotor further having an inlet for supplying working fluid to the interior thereof;

    at least one lens mounted in said first end of said housing to FOCUS solar radiation on said rotor to heat the working fluid therein, producing steam within said rotor whereby said steam issues from said outlet jets.

    The combination according to claim 1 wherein said rotor is mounted in a hollow sealed compartment for containing steam and working fluid exiting from said nozzles; and

    fresnel, solar, steam, generator

    The combination according to claim 1 wherein said at least one lens comprises a plurality of Fresnel lenses mounted in the same plane in said first end of said housing.

    The combination according to claim 1 wherein said plurality of said outlet jets are located at equal distance intervals about the periphery of said rotor.

    The combination according to claim 1 wherein said inlet of said rotor is located on the central axis of said rotor.

    The combination according to claim 1 wherein said inlet of said rotor is located on the central axis of said rotor.

    The combination according to claim 7 wherein said plurality of said outlet jets are located at equal distance intervals about the periphery of said rotor.

    The combination according to claim 1 further including an output shaft coupled with the central axis of said rotor; and an electric generator coupled with and powered by said output shaft.

    The combination according to claim 9 wherein said at least one lens comprises a plurality of Fresnel lenses mounted in the same plane in said first end of said housing.

    The combination according to claim 1 wherein said rotor is a circular rotor comprised of front and back circular plates the diameter of which is substantially greater than the axial thickness of said rotor.

    The combination according to claim 12 wherein said rotor is mounted in a hollow sealed compartment for containing steam and working fluid exiting from said nozzles; and

    The combination according to claim 13 further including a condenser reservoir coupled with said water outlet and further coupled with said inlet of said rotor for supplying working fluid to said inlet of said rotor.

    The combination according to claim 14 further including an output shaft coupled with the central axis of said rotor; and an electric generator coupled with and powered by said output shaft.

    The combination according to claim 15 further including source of make up water for said condenser-reservoir.

    The combination according to claim 15 wherein said at least one lens comprises a plurality of Fresnel lenses mounted in the same plane in said first end of said housing.

    The combination according to claim 18 wherein said inlet of said rotor is located on the central axis of said rotor.

    The combination according to claim 19 wherein said plurality of said outlet jets are located at equal distance intervals about the periphery of said rotor.

    US08/629,835 1996-04-10 1996-04-10 Solar powered steam turbine generator Expired. Fee Related US5632147A ( en )

    Priority Applications (1)

    Application Number Priority Date Filing Date Title
    US08/629,835 US5632147A ( en ) 1996-04-10 1996-04-10 Solar powered steam turbine generator

    Applications Claiming Priority (1)

    Application Number Priority Date Filing Date Title
    US08/629,835 US5632147A ( en ) 1996-04-10 1996-04-10 Solar powered steam turbine generator

    Family Applications (1)

    Application Number Title Priority Date Filing Date
    US08/629,835 Expired. Fee Related US5632147A ( en ) 1996-04-10 1996-04-10 Solar powered steam turbine generator

    Cited By (11)

    Cited by examiner, † Cited by third party

    Publication number Priority date Publication date Assignee Title
    US6000211A ( en ) 1997-06-18 1999-12-14 York Research Corporation Solar power enhanced combustion turbine power plant and methods
    US6550248B1 ( en ) 2002-06-21 2003-04-22 Bruce Sangster Electrical generating system using solar energy
    US20050011513A1 ( en ) 2003-07-17 2005-01-20 Johnson Neldon P. Solar energy collector
    US20070221210A1 ( en ) 2006-03-20 2007-09-27 Steven Polk Solar power plant
    US20130118167A1 ( en ) 2008-06-01 2013-05-16 John Pesce Thermo-Electric Engine
    US8650877B1 ( en ) 2013-03-11 2014-02-18 Gary R. Gustafson Solar panels that generate electricity and extract heat: system and method
    US8656717B1 ( en ) 2011-09-22 2014-02-25 Robert M. Parker Solar powered generator assembly
    US20150102602A1 ( en ) 2012-03-02 2015-04-16 Yanmar Co., Ltd. Power generating device
    WO2015067966A3 ( en ) 2013-11-08 2015-07-16 Solar Steam Limited System for steam power generation from solar radiation
    RU2704380C1 ( en ) 2018-12-11 2019-10-28 Федеральное государственное бюджетное научное учреждение Федеральный научный агроинженерный центр ВИМ (ФГБНУ ФНАЦ ВИМ) Solar power plant
    WO2020142012A3 ( en ) 2018-12-03 2021-01-21 Kulac Erkan Solar energy power generation system comprising a concentrated lens

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    US6000211A ( en ) 1997-06-18 1999-12-14 York Research Corporation Solar power enhanced combustion turbine power plant and methods
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    WO2015067966A3 ( en ) 2013-11-08 2015-07-16 Solar Steam Limited System for steam power generation from solar radiation
    WO2020142012A3 ( en ) 2018-12-03 2021-01-21 Kulac Erkan Solar energy power generation system comprising a concentrated lens
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    Legal Events


    Effective date: 20010527


    Fresnel solar steam generator

    Large-scale solar power generation got its start in the Mojave Desert of California more than 20 years ago. The Solar Electric Generating System (SEGS) was built by Luz Industries, delivering a total of 354 megawatts (MW) of power, which it still generates to this day. SEGS is a parabolic trough solar installation that uses concave mirrors to FOCUS the sun’s rays on oil-filled pipes. The fluid in these pipes is then pumped to make high-pressure steam, driving turbine generators and creating electricity. Since then, solar power at a utility-scale level has evolved in a number of exciting and revolutionary technologies. The promise of this market pressure and innovation holds great things to come in competitive renewable energy.

    Solar Thermal

    Solar thermal energy is designed to harness solar energy for heat, which is then used to generate electricity. Solar thermal, also referred to as Concentrated Solar Power (CSP) differs significantly from photovoltaics. Photovoltaic technology generates electricity directly from sunlight, whereas solar thermal energy uses lenses and reflectors to concentrate solar heat to generate power. This heat is then used to generate electricity which can be stored or released directly onto the grid. In recent years the solar thermal market has experienced renewed growth and a number of technologies have emerged that include solar dishes, solar troughs, solar towers and linear fresnel reflectors.

    Parabolic Trough

    Trough technology is mature and clean, with a long track record demonstrating viability in large-scale application. The technology has been in use since the 1980s. Today, more than 300MW of solar troughs are in operation, with more than 6GW currently in development.

    A parabolic trough is a solar concentrator that tracks the sun around a single, rotational axis. Sunlight is reflected from parabolic-shaped mirrors and is concentrated onto the receiver tube at the focal point of the parabola. For CSP applications, synthetic heat transfer oil pumped through the receiver tube and is heated to approximately 752 F (400 C). The oil transports the heat from the solar field to the power block where the energy is converted to high-pressure steam in a series of heat exchangers. This steam is converted into electrical energy using a conventional steam turbine.

    The main components of parabolic trough technology include the trough reflector, a receiver tube or heat collection element, and the sun tracking system and support structure.

    The cylindrical parabolic reflector reflects incident sunlight from its surface onto the receiver at the focal point. Typically, the reflector is made of thick glass silver mirrors formed into the shape of a parabola. Mirrors can be made from thin glass, plastic films or polished metals. The receiver tube or heat collection element consists of a metal absorber surrounded by a glass envelope. The absorber is coated with a selective coating to maximize energy collection and to minimize heat loss. This glass envelope is used to insulate the absorber from heat loss, and is typically coated with an anti-reflective surface to increase the transmittance of light through the glass to the absorber. For high temperature CSP applications, the space between the absorber and glass tube is evacuated to form a vacuum. The sun tracking system is an electronic control system and associated mechanical drive system used to FOCUS the reflector onto the sun. Usually made of metal, the collector support structure holds the mirrors in accurate alignment while resisting the effects of the wind.

    Compact Linear Fresnel Reflector

    The Compact Linear Fresnel Reflector (CLFR) is a solar collector and steam generation system conceived in the early 1990s in Australia. Solar concentrators boil water with focused sunlight, creating high-pressure steam that drives a conventional turbine to generate electricity on a utility-scale. This high-pressure steam can also be used to augment power at existing fossil-fired plants, increasing a facilitys energy output and reducing its emissions. A third use of CLFR is for industrial applications that require large amounts of high-temperature steam, such as enhanced oil recovery and food processing.

    A CLFR system, which consists of multiple solar collector lines, gathers energy by reflecting and concentrating sunlight to roughly 30 times the intensity of sunshine at the Earths surface. Mirrors FOCUS the sunlight on an elevated absorber to heat and boil water, resulting in high-temperature steam that then drives a conventional turbine housed in a power block. Computer systems typically manage the mirror positions, tracking the motion of the sun throughout the day to maintain the FOCUS point on the absorber.

    CLFR systems are both environmentally sound and durable. CLFR does not burn any fuels nor produce any pollution. The steam generated by CLFR collectors is recondensed to water and reused, minimizing the overall water consumption. At night and during stormy weather, the reflector units invert, exposing steel to the sky for reduced exposure to weather events such as ice, hail and high winds.

    Parabolic Dish-Stirling Engine

    Originally developed by Robert Stirling in 1816, the Stirling cycle uses a working fluid (typically Helium, Nitrogen or Hydrogen gas) in a closed cylinder containing a piston. A Dish-Stirling system is composed of a solar concentrator with high reflectivity, a cavity solar receiver, and a Stirling engine, or microturbine that is attached to an alternator. The operation consists of heating a fluid located in the receiver until reaching a temperature approximate to 1382F (750C). This energy is used to generate power by the engine or microturbine. Typically, the system uses solar tracking to maximize the exposure to the suns rays.

    A dish/engine system uses a mirrored dish (similar to a very large satellite dish). The dish-shaped surface collects and concentrates the sun’s heat onto a receiver, which absorbs the heat and transfers it to fluid within the engine. The heat causes the fluid to expand against a piston or turbine to produce mechanical power. The mechanical power is then used to run a generator or alternator to produce electricity.


    Tower systems are made up of a heliostat field comprised of movable mirrors, which are oriented according to the solar position, in order to reflect the solar radiation concentrating it up to 600 times on a receptor located on the upper part of a tall tower. This heat is transferred to a fluid, generating steam that in turn expands on a turbine that is coupled to a generator to produce electricity.

    The main components of tower technology include a heliostat, the receiver and the tower. The heliostats capture solar radiation and direct it to the receiver. They are composed of a reflective surface, a supporting structure and mechanisms used to orientate them, following the suns movement. The most commonly-used reflective surfaces are glass mirrors. The receiver sits atop the tower, and transfers received heat to an operating fluid (e.g., water, molten salts). This fluid is then transported to other parts of the plant to generate high temperature steam which then produces electricity through a turbine. Rounding out these main components is the tower, which holds a boiler on the top of the structure, and is built to a height above the heliostat field to receive the solar radiation from the heliostats.


    Photovoltaics (PV) allow for direct conversion of light into electricity, hence its name: photo=light, and voltaic=electricity. Photovoltaic technology uses a conducting material which performs this process, such as silicon. Advances in technology continue to bring to the market different material applications which have both provided thinner modules of silicon, and also the usage of other semiconducting materials to achieve thinner applications and improved efficiency in converting light to electricity. Since the development of the first solar cell in 1954, its usage has continued to grow steadily along with its efficiency.

    Flat Panel Photovoltaic

    Flat panel photovoltaic (PV) cells are usually made of silicon, which is a semiconductor that can absorb and insulate the photons present in sunlight, freeing the electrons to be used as electric current. In flat panel PV, silicon is placed under non-reflective glass where it collects the electromagnetic energy of the sun, and conducts it as electric current. Each flat panel is made up of a number of solar cells, and through metal connections, the panel is able to conduct all the electricity generated in direct current to a converter which turns it into alternating current. That alternating current is then transmitted to the grid where it is carried to its end use.

    Thin Film

    Many commercial solar cells use what is called a thin film of material to convert sunlight into electricity. Thin film solar cells use layers of semiconductor materials only a few micrometers thick. Among the materials used in thin film are amorphous silicon and cadmium telluride. Amorphous silicon is a special form of crystalline silicon which is deposited as an extremely thin film (far thinner than the thickness of a human hair) and requires only about 1% of the silicon used in crystalline systems. Cadmium telluride uses both cadmium and telluride to produce a thin film of electricity-generating panels at a cost-effective rate, and with a capability of maintaining substantial generation at higher temperatures.

    Concentrated PV

    Concentrating sunlight onto PV offers the ability to improve the efficiency of the cell itself, and to increase the supply of photons to the cells. Some of the technologies being developed and used include Fresnel point FOCUS, Fresnel line FOCUS and low concentration. Fresentl point FOCUS (high concentration-GaAs) lenses concentrate direct solar radiation onto a focal point, providing concentration ratios of 500 and reducing the needed surface area of the PV cell. With this capability, higher quality and more expensive materials like Gallium Arsenide are used for the semiconductors. By comparison, Fresnel line FOCUS (medium concentration-Si) lenses are flat cylindrical lenses that condense or diffuse light in a linear direction. This technology has lower concentration ratios than Fresnel point lenses, so high efficiency silicon semiconductors are used instead of expensive GaAs semiconductors. Also used is low concentration technology which uses mirrors instead of lenses to concentrate solar radiation. Since the solar radiation is much less condensed, conventional silicon semiconductors are often used because of their affordability.

    Institute for Future Intelligence (IFI)

    Linear Fresnel reflectors are a type of concentrated solar power that uses long, thin segments of mirrors to FOCUS sunlight onto a fixed absorber located at a common focal line of the reflectors, similar to a Fresnel lens. The concentrated light energy is converted through the absorber into the thermal energy of a fluid, which then goes through a heat exchanger to power a steam generator or be used as process heat in industrial processes. It doesn’t make sense to burn oil or coal to generate high temperature if we can get it from the sun. The simplicity, scalability, and flexibility of linear Fresnel reflectors make it an appropriate technology to consider.

    There are many design options for a linear Fresnel reflector array. The key factors include the dimension and spacing of the reflectors, the height of the absorber tube, and the orientation of the reflectors (azimuth). There can also be multiple absorbers, as shown in the following model. In this design, the mirrors are laid out in the same way but they reflect the sunlight alternately to the two absorbers (e.g., 1, 3, 5. reflect to the absorber on the east side and 2, 4, 6. to the absorber on the west side).

    Analyzing output of linear Fresnel reflectors with two receivers based on daily simulation

    The effect of the receiver height

    The higher we mount the receiver tube, the more energy the reflectors can collect. This can be easily studied using an Aladdin simulation shown below.

    Comparison between two Fresnel reflector arrays aiming at receiver tubes mounted at different heights

    The effect of the array azimuth

    Linear Fresnel reflectors are usually aligned in the north-south direction. The following simulation compares the outputs of two arrays, one with zero azimuth and the other with 90° azimuth (meaning that the reflectors are essentially aligned in the east-west direction).

    Comparison between two Fresnel reflector arrays aligned in different azimuths

    Linear Fresnel reflector arrays around the world

    Tucson Electric Power (TEP) and AREVA Solar constructed a 5 MW linear Fresnel reflector solar steam generator at TEP’s H. Wilson Sundt Generating Station — not far from the famous Pima Air and Space Museum. The following is an Aladdin model of the TEP station.

    If you are interested, please click here to read about the analysis of the TEP station and explore more Aladdin models of existing Fresnel reflector arrays around the world.

    Solar Desalination Using Fresnel Lens as Concentrated Solar Power Device: An Experimental Study in Tropical Climate

    Solar desalination is a renewable energy-driven method that produces freshwater from saline/brackish water. Conventional solar desalination units are equipped with an inclined transparent condensing plate placed over a feedwater basin containing saline water. The process is limited to a small quantity of production because of scattered solar irradiation and the unavailability of solar heat due to intermittent cloudy weather. In this study, a Fresnel lens has been used to concentrate solar energy onto a spot to increase the local temperature of feedwater and the evaporation rate. Flat Fresnel lenses on a double sloped passive solar still were used, where the focal points were adjusted to fall directly on the feedwater. The experiments were conducted for two different geometries and alongside the comparison between the conventional and the modified solar still; the number of Fresnel lenses was also varied. Saline solution with a concentration of 20,000 ppm was used as the feedwater. The research is aimed to be implemented for producing freshwater in the natural weather conditions of Malaysia. It was found that using two Fresnel lenses instead of a single large one gives a boost to the production of freshwater per unit solar irradiation by 39%. The produced water has a total dissolved solids (TDS) value of 37 ppm, which is well within the drinking water standard range according to the World Health Organization.


    Solar desalination is the process that involves evaporation of a saline solution utilizing solar power, either directly or indirectly, followed by condensation of the generated vapor. In other words, solar distillation is a combination of humidification and dehumidification within a solar energy-driven setup (Belessiotis et al., 2016). This process is described as similar to a naturally occurring hydrological cycle, where the formation of the vapors from surface of liquids gets transported by wind to buildup and precipitate, and in the case of solar stills, vapors condensate on the colder surfaces inside the still (Lal et al., 2017). Conventional solar stills are basic devices that use the concept of a greenhouse by trapping heat during solar exposure and in turn, heats the stored feedwater within the device and increases its evaporation rate. Solar irradiation enters the still through a transparent cover underneath which the feedwater is stored. Upon striking the basin, the radiation is mostly absorbed by the basin. From the heated surface, infra-red electromagnetic waves are emitted and get trapped by the transparent cover, giving rise to the temperature within the system (Kumar and Tiwari, 2011). Solar stills can be a viable solution to produce drinking water in rural areas that lack fossil fuel/electric energy sources. However, the water quantity obtained from solar stills is not as high as its quality (Sharon and Reddy, 2015). The most affecting parameters on the still productivity and efficiency include the location, available solar intensity, ambient temperature, material and thickness of the glass cover, water depth in the basin, and the wind velocity (Al-harahsheh et al., 2018).

    The geometrical dimension of a solar still plays an important role in the efficiency of the system. A direct correlation between still height, length, width, and distillate production was tested on conventional single slope solar still (Feilizadeh et al., 2017). The height of the basin wall was found to have a negative relationship with production, however, wider still produced higher yield due to the general increase in solar irradiance (SI) area, up to an optimum ratio of width over the length of 0.15 (W/L = 0.15). The effect of the tilt angle of the inclined cover plate was also studied. The tilt angle of the cover plate should be approximated to the latitude of location and the basin water depth was suggested to have a negative relationship with production (Selvaraj and Natarajan, 2018). In other words, lower water depth would give a higher yield of distillate. A linear decrement in productivity was found with increasing water depth (Akash et al., 2000). In the case of distillate production, glass cover gave the highest yield among other materials, compared to plastic sheet and Polyethylene terephthalate. An 18% reduction in yield was reported when plastic is used instead of glass (Bhardwaj et al., 2013). Although having a superior yield compared to other materials, it was emphasized by Bhardwaj et al. (2013) that the negative characteristics of glass, such as brittleness, heavyweight, and higher maintenance cost make plastic a more suitable candidate for low cost, portable builds. Also in another study (Pollet and Pieters, 2000), the cover thickness showed a negative relationship to the transmittance of the cover, hence affecting the yield of the still.

    Besides these factors, a lower intensity of solar irradiation is also a major cause for limited production. To increase the local temperature by focusing solar irradiation has been practiced through solar concentrators. These devices have been categorized as concentrated solar power (CSP) devices. Major solar concentrator types in the form of parabolic dishes and their trough variant were tested in Yadav and Yadav (2004), Chaouchi et al. (2007), Gorjian et al. (2014)’s study and reviewed by Dsilva Winfred Rufuss et al. (2016). Yet, less FOCUS was given to Fresnel lens solar concentrator especially for solar desalination, even lesser for the radial variant, which is described in Gorjian et al. (2014).

    This research aims to study the effectiveness of Fresnel lens in solar still applications and its viability as an additional equipment for the small-scale usage. Fresnel lens generally has a smaller footprint as compared to the more popular parabolic reflectors or convex lenses. A thin sheet of Fresnel lens can perform similarly as whole convex lenses or parabolic dishes; with little to no penalty to thickness when a smaller focal length is required. In this sense, Fresnel lens is also a better option when comparing the mobility and weight with that of other concentrators. The lenses are made from acrylic, therefore, it is lightweight and fabrication of the still is quite simple when the Fresnel lens is directly attached to the inclined lid.

    In a study by Soni et al. (2019), it was concluded that a Fresnel lens is more suitable to be applied for solar power concentration in water heating application in the region between 15°N and 40°S with Minimum Direct Normal Irradiation (DNI) of 1.9kW h/m 2 /yr and occasionally at higher latitudes.

    The work presented here has been conducted in Malaysia that is located at 3.14°N, with an average DNI value of around 800°kW h/m 2 /yr (Solargis, 2019). With this data, there is a need to investigate the overall effect of associating Fresnel lens and observe if there is any improvement compared to a conventional solar still. There is a research gap of applying CSP in solar desalination in Malaysia, although the nation is making Rapid progress with photovoltaic (TENAGA, 2019). With climate change, freshwater scarcity is slowly seeping into the region with longer dry spells across peninsular Malaysia. Installation of a Reverse Osmosis water desalination plant is Sarawak (News Report) reflects the necessity of seawater desalination for the population in the bay areas. Recently there has been a research shift toward freshwater production by harnessing Malaysia’s solar energy potentials (Abujazar et al., 2018; Hakim et al., 2018; Rafiei et al., 2019) pertaining to the need for drinking water produced sustainably; especially for the underprivileged population in the bay areas.

    This study targets an initial investigation of the performance of Fresnel lenses as a solar concentrators for solar desalination in the persistent tropical weather of Malaysia. In this study, a solar still is equipped with flat radial Fresnel lenses to concentrate solar irradiation onto a single point in the saline water basin in the natural environment. As the data were taken in natural environment, the effect of changing weather patterns was minimized by the practice of normalizing the produced water to solar irradiation.

    The flat radial Fresnel lens used in this study were chosen instead of the linear Fresnel lens due to its higher achievable temperature at its focal point. Comparisons between the performance of conventional solar stills and a Fresnel-lens-equipped solar still were done by evaluating the hourly saline water temperature differences, internal and external solar still temperature differences, SI and distillate yield. The tests were conducted for two different design solar stills, to investigate the effect of a single Fresnel lens and multiple Fresnel lenses. The target for this research is to find the optimum conditions for Fresnel-lens-coupled solar still operation, together with investigating the viability and effectiveness of Fresnel lens application in solar still application.

    Materials and Methods

    Working Principle of the Solar Still

    Solar still is among the simplest form of solar desalination processes which consists of a basin containing saline/brackish water. The basin is covered with an inclined glass/transparent lid through which the solar heat enters and generates vapor from the contaminated water due to the partial pressure difference between the basin and the glass lid. The generated vapor is condensed on the inner side of the inclined glass/transparent lid and collected as the distillate. The transparent lid acts as the greenhouse to trap the heat inside the still. Figure 1 below shows the process for a simple solar still with a double slope. The double slope has been selected in the design to optimize the availability of solar irradiation throughout the day; without much necessity to rotate according to the Sun’s travel path in the sky.

    FIGURE 1. Working Principle of a double-sloped solar still.

    Materials Selection

    This study aims to benefit people with resource scarcity in rural or coastal regions where access to clean water is limited. Therefore, the selection of cheaper material and easy design have been given priority during fabrication of the setup. Wood has been used as the outer still body material for its high workability and high thermal insulation property. Proper sealing has been provided using silicone sealant to prevent vapor from escaping the system. The basin has been made out of stainless steel. Material for the transparent cover was also decided to be of clear polycarbonate sheets instead of the conventional glass cover. While glass cover provides higher condensation performance, it was not considered in this case for brittleness and lower workability.

    As mentioned by (Selvaraj and Natarajan (2018), insulation contributes largely to retaining heat within the solar still and increased productivity. Polystyrene was used to insulate the gap between the bottom of the metal basin and the wooden solar still frame to reduce thermal dissipation through the bottom of the solar still.

    In the selection between linear and radial Fresnel lens, the different focusing profile of both types of lenses is the key point. For the linear Fresnel lens, the flat surfaces within the lens are aligned parallel to each other, with one more slanted than the other from inward to outward, creating a series of focusing surfaces to a central axis, at a distance to the lens. For the radial Fresnel lens, the ring-shaped focusing surfaces slant to face a center point, with each ring placed concentric to each other. It has been found from a recent study (Huang et al., 2017) that the radial Fresnel lens can achieve a sunlight concentration ratio 3.9 times higher than that of the linear lens with a much smaller receiving area. Comparing the construction and focusing profile of both types of Fresnel lenses, the selected radial Fresnel lens which provides a point-FOCUS profile enables solar irradiation to be focused onto one spot instead of a line, significantly heating up elements on the focal point (Xie et al., 2011). The Fresnel lenses used in this experiment were made of polymethyl methacrylate (PMMA) (Acrylic).

    Experimental Setup and Variables

    Two different design setups with different aspect ratios were used with and without Fresnel lenses. They are categorized as:

    i) Solar still without Fresnel lens (Model A-0 and Model B-0).

    ii) Solar still with Fresnel lens (Model A-F and Model B-F).

    A double sloped passive solar still (Model-A) with a basin size of 500 × 500 × 100 mm was constructed. Figure 2A is Model A without any Fresnel lens (termed as Model A-0). Model A equipped with a single Fresnel lens (Model A-F) is seen in Figure 2B. Model A has a Length/Width (L/W) ratio of 1.0 and Model B has an L/W ratio of 2.0. By estimating from the data of (Feilizadeh et al. 2017)’s study, around 10% increase in productivity can be recorded when increasing from L/W = 1 to L/W = 2.

    FIGURE 2. (A)Solar still setup with no Fresnel lens (Model A-0). (B) Solar still with single Fresnel lens (Model A-F). (C) Wider Solar still with no Fresnel lens (Model B-0). (D) Wider solar still with multiple Fresnel lenses (Model B-F).

    Another solar still (Model-B) with a wider aperture to solar irradiation was built to accommodate multiple Fresnel lenses. The basin size for this model is 700 × 350 × 100 mm. This model has been tested with no Fresnel lens (Model B-0) and with the addition of two Fresnel lenses on the slope (Model B-F). The two arrangements of Model B are seen in Figures 2C,D respectively. A frame was constructed to hold the Fresnel lenses parallel to the inclination angle of the top covers, as seen in Figures 2B,D, whereby the focal points of the lenses fall onto the feedwater stored in the stainless-steel basin during solar irradiation period. Table 1 summarizes the structure and materials for these four models.

    TABLE 1. Design and materials specification of the four models.

    To conduct the experiments, the setup was installed at a location where solar irradiation was not blocked within the duration of the experiment. Saline water solution with 20,000 ppm concentration was fed to each model. The solar still was lifted from the ground using bricks to accommodate for the height of the measuring bottle. As shown in Figure 2A, three separate thermocouple channels wires (in blue) were inserted into the still. One of the thermocouple wires was immersed into the saline water and was made sure not to be in contact with the basin. The second wire was allowed to hang within the solar still above the basin, but not in contact with any other components. This is to record the internal temperature of the solar still. These thermocouple wires were made sure to be sealed along with the whole solar still as to not cause leakage at the inserts to the still. The third was attached to the basin surface and along the path where the focal point of the Fresnel lens passed through. This is to measure the temperature of the focusing spot. While the total energy entering the system is said to be equal with and without the solar concentrator due to the area receiving solar energy is equal for both cases, theoretically, the use of solar concentrator could raise the local temperature of the focal point significantly to induce more evaporation, thus increased vapor pressure within the still and resulting in higher condensation rate and more distillate yield.

    The SI was experimentally measured using SM206 High Precision Solar Power Meter by aligning the solar power meter perpendicular to the incoming SI on the transparent cover. Temperatures were recorded hourly along with the solar irradiation. The distillate levels were also measured using a weighing scale on an hourly basis. Experiments were conducted in Sungai Long, Selangor, Malaysia in March 2019. The average TDS value of the distillate was measured with a TDS EC Tester. The value was averaged at 37 ppm, which is well below the WHO drinking water standard of 500 ppm.

    Results and Discussions

    Solar Irradiation (SI) and its Effect on Temperature for Different Setups

    In this section, the performance of the solar still under variable operating parameters like solar irradiation and temperature has been discussed.

    The graphs and calculations have been prepared based on SI or the insolation. Although the sensitivity study conducted by Chhatbar (2011) showed that DNI is the parameter with the highest influence on the energy yield of CSP plants, however, the solar power meter provided the data for SI only and it was the base for calculations of total productivity.

    Furthermore, the major objective to conduct this study is to analyze the performance of a passive solar still equipped with Fresnel lens experimentally in the tropical climate of Malaysia, therefore calculations of DNI has not been considered in this study.

    Figures 3A,B represent the solar irradiation and feedwater temperature for the four models considered in this study. The experiments were conducted on different days and it can be seen that the patterns of received solar irradiation varied on these days. Figure 3A shows the hourly solar irradiation between 8.00 am and 6.00 pm. For Models A-0 and A-F, the solar irradiation exposure time and intensity were and almost similar. While for Models B-0 and B-F, the exposure times are comparable, however, model B-0 faced a drop in solar irradiation intensity around 2.00 pm, due to the appearance of Cloud at that time. This uncertainty is commonly associated with all renewable energy resources. And therefore, necessary normalization of data to observe the productivity from different setups was practiced which is described in “Overall Performance Using Fresnel Lens”section.

    FIGURE 3. (A) Hourly solar irradiation pattern. (B) Hourly feedwater temperature. (C) Hourly temperature difference between feedwater and ambient. (D) Hourly water production.

    In Figure 3B, the effect of the solar irradiation on the feedwater temperature for each model is shown. It can be seen for Model A-0 and Model A-F that although they received an equivalent amount of solar irradiation, the feedwater temperature in the afternoon for Model A-F had a drastic increase in feedwater temperature. For the feedwater temperature of Model B-0 and Model B-F, Model B-F maintained a steady and slightly higher value compared to that of Model B-0. However, a sudden drop in temperature is seen as expected around 2.00 pm, which is caused by the sudden drop in solar irradiation for Model B-0 due to rain occurring at that instance.

    Temperature Difference Between Feedwater and Ambient and its Effect on Hourly Water Production

    Figures 3C,D are the hourly temperature differences and the water yield from each of the four models. The temperature difference (ΔT) is calculated between the feedwater and ambient temperature as that is the major potential difference for evaporation to occur. The more this difference, the more should be the partial pressure difference between the feedwater and the ambient, which would cause more evaporation. From Figure 3C, it is clear that Model B-0 and Model B-F which inherently had a wider aperture to solar irradiation attained the higher ΔT, compared to Model A-0 and Model A-F. It is seen from Figure 3D that both the Models equipped with Fresnel lens (A-F and B-F) tend to produce the highest water yield on an hourly basis compared to those without a Fresnel lens.

    Overall Performance Using Fresnel Lens

    In the previous sections “Solar Irradiation (SI) and its Effect on Temperature for Different Setups,” and “Temperature Difference Between Feedwater and Ambient and its Effect on Hourly Water Production,” the temperature and water yield have been discussed with respect to hourly solar irradiation. It has also been observed that the solar irradiation was not constant during the experiments conducted with four different arrangements. Therefore, it is needed to normalize the experimentally obtained data to reach a decision about the performance of Fresnel lenses as a solar concentrator.

    Along with the addition of Fresnel lenses, the overall performance per square meter of the area has been investigated in this section.

    First, the average water yield per solar irradiation (SI) was calculated for the four models for solar exposure hours. The average solar irradiation for Models A-0 and A-F were 1,053 and 1,165 W/m 2 respectively, while for Models B-0 and B-F were 718 and 737 W/m 2. respectively. Based on these data, Figure 4 shows the comparison of water yield flux per day per average solar irradiation. It is seen that in terms of the daily water yield flux against SI, a 9.7% improvement was obtained with the application of the Fresnel lens between Model A-0 and Model A-F. A significant improvement of 26.4% was observed between the averages Water Yield against SI for Model B-F, compared to Model B-0, as seen in the figure.

    FIGURE 4. Daily water yield per average solar irradiation (SI).

    A further comparison was conducted between Model A-F and Model B-F to observe the total water production per unit total solar irradiation and how the number of Fresnel lens influences the water production. Figure 5A shows the summarized result of total water yield over total SI for the four models. The Model B-F produced the highest amount of distillate per total solar irradiation. Compared to model A-F, with a single Fresnel lens, the Model B-F with two Fresnel lenses produced about 39% more water per total SI for the day.

    FIGURE 5. (A) The total water yield over total SI. (B) The total water yield per unit area over total SI.

    The effect of total solar exposure area of the feedwater basin for these models was also compared; as seen in Figure 5B, the total water yield per total SI was again calculated per unit area of the feedwater basin. It has been found that the total water yield per unit area was highest for Model B-F, which had a solar exposure area of 700 × 350 mm 2. with an L/W ratio of 2.0 compared to Model A (0 and F) which had an area of 500 × 500 mm 2. with an L/W ratio of 1.0. When compared between Models A and B, it was seen that Model B had an increase in production by 22%, while with added Fresnel lens, the performance of Model B was 41.8% higher.


    This study was conducted as an initial investigation to observe the applicability of the Flat Fresnel lens as a cheap CSP device, which is conducted through experiments on different geometry solar stills varying the number of lenses. The study revealed that incorporating the Fresnel lens in tropical weather can enhance the overall production of distillate from a solar still, although the location does not receive strong DNI. This study has opened up the possibility of further exploration in this field through more vigorous experiments. The findings can be summarized as:

    Fresnel lens increases the total production from a solar still. The addition of Fresnel lenses increased the average and total production rate for different geometry solar stills.

    Using multiple Fresnel lenses instead of a single one provides multiple hotspots and causes more evaporation of feedwater, thus leading to higher total production per total solar irradiation by 39%.

    The increased length/width ratio caused significant improvement in production for all models, with the highest performance improvement of 41.8% for the Fresnel lens associated model.

    Data Availability Statement

    The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

    Author Contributions

    WSC: (Methodology, Investigation, Validation, Formal analysis, Data Curation, Writing. Original Draft). ZYH: Conceptualization, Formal analysis, Project administration. RB: Formal analysis, Validation, Data Curation, Resources, Writing Review and Editing, Supervision, Project administration, Funding acquisition.


    The work has been conducted in Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman and the study has been supported by Universiti Tunku Abdul Rahman (UTAR) internal Grant IPSR/RMC/UTARRF/2018-C1/R01.

    Conflict of Interest

    The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


    This work has been funded by Universiti Tunku Abdul Rahman (UTAR)’s internal grant: “UTAR Research grant IPSR/RMC/UTARRF/2018-C1/R01.” Authors are grateful to Centre for Photonics and Advanced Materials Research for providing facilities and support.


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    Keywords: solar energy, solar desalination, solar still, concentrated solar power, Fresnel lens

    Citation: Choong WS, Ho ZY and Bahar R (2020) Solar Desalination Using Fresnel Lens as Concentrated Solar Power Device: An Experimental Study in Tropical Climate. Front. Energy Res. 8:565542. doi: 10.3389/fenrg.2020.565542

    Received: 25 May 2020; Accepted: 10 September 2020; Published: 22 October 2020.

    Copyright © 2020 Choong, Ho and Bahar. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    fresnel, solar, steam, generator

    Correspondence: Rubina Bahar,

    This article is part of the Research Topic

    Emerging Technologies for Sustainable Development: From Smart Cities to Circular Economy

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