WO2009144700A1

WO2009144700A1 - Solar energy system

Info

Publication number: WO2009144700A1
Application number: PCT/IL2009/000166
Authority: WO
Inventors: Gavriel J. Iddan
Original assignee: Rdc - Rafael Development Corporation Ltd.
Priority date: 2008-04-16
Filing date: 2009-02-11
Publication date: 2009-12-03

Abstract

Disclosed are apparatuses, systems and methods for dual purpose solar energy harvesting combining electricity and heat generation and uses of the harvested energy. The solar energy system comprises a sun tracking light concentrator concentrating the solar radiation to a substantially parallel concentrated beam; a spectral filter directing photons of the concentrated beam substantially having energies readily convertible to electricity towards a photovoltaic cell and photons of the concentrated beam substantially having energies not readily convertible to electricity towards a light absorber. The system further comprises a cell cooler for maintaining low photocell temperature and solar heat remover for removing heat from the light absorber.

Description

SOLAR ENERGY SYSTEM

FIELD OF THE INVENTION

The present invention primarily relates to an apparatuses, systems and methods for dual purpose solar energy harvesting combining electricity and heat generation and uses of the harvested energy.

BACKGROUND OF THE INVENTION

Solar energy is in use world-wide. Both heat energy harvesting and direct conversion of solar to electrical power are known in the art.

Solar light concentration for efficient solar energy harvesting is also known. Light concentrator are generally of the imaging or non-imaging type. Imaging Solar Concentrators (ISC) are generally having a narrow collecting field most suitable at the Sun Belt countries. Non-imaging Solar Concentrators (NSC) are generally having a wide collecting field and are more suitable for the cloud belt countries

Methods of desalination are well known in the art. General information and specific designs are readily available.

EP0019016 to Simon filed on Dec. 20, 1979 describes a reflecting solar concentrator incorporating spectral filters, separating the solar spectrum into three portions: First portion fits a Si solar cell; the remaining spectrum is then separated to the UV section and IR section. The UV is converted by a suitable cell and the IR is converted to heat. The invention teaches the incorporation of two filters operating in conjunction with a convergent solar beam. No description of the design of the filters is mentioned.

US 4,713, 493 to Ovshinsky filed on Dec. 6, 1985 describes in a filter used to separate solar spectrum, specifically to remove the UV portion known to damage covalent bonds (polymers etc.) and the IR portion that generates heat. Also, transparent conductors are described for the purpose of extracting electrical energy from the Photo Voltaic (PV) layers.

The invention is not related to light concentrators nor is heat harvesting described.

USP 5,959,239 to Baldasaro filed on June 2, 1997 describes a thermovoltaic semiconductor device incorporating an interference plasma filter attached to said semiconductor for reflecting the long wave length radiation. The device is not related to splitting the solar spectrum and no reference is made to concentration and collimation.

US 6,015,950 to Converse filed on may 13, 1997 describes spectrum splitting by refractive elements.

US 4,021,267 to Dettling Describes a re-collimating device incorporating diffractive components.

US 6,407,328 to Kleinwachter filed on Feb. 2, 2001 teaches front surface as well as back surface cooling of a PV cell.

US 6,689,949 to Ortabasi filed on may 17, 2002 teaches a cavity having its inside surface covered with a mosaic of PV elements, each selective to a narrow spectral range and reflecting the other portion. It is believed that the configuration will be more efficient then Multi Junction setup. The device a described uses a plurality of PV cells. The cells are the main cost contributors to the system cost and should be avoided in our application.

A paper titled "A new strategy for improved spectral performance in solar power plants" A.G. Imenes et. al. Solar Energy 80 (2006) pp. 1263 - 1269; analyses the design of an optimal spectrum splitting filter base on the following assumptions: In a converging beam of solar illumination resulting in this paper from a heliostat - fits a different circular filter to each angle of incidences thus eliminating the degradation of interference filters when operating outside of the designated angle. The result is a complex filter which may be to expensive.

US 7,166,797 to Dziendziel filed on Aug. 14, 2002 teaches the design of a tandem filter transmitting energies above gap energy Eg and reflecting energies below Eg. Since the filter is intended for thermal source significant portion of the energy is in the far IR. A single interference filter cannot handle the task hence an additional plasma filter is incorporated in tandem.

The proposed filter is not capable of reflecting the energies much higher then Eg that contribute significant.

US application 2005/0091979 to Bareis filled on Oct. 22,2004 teaches the use of a parabolic concentrator and a secondary, generating a parallel beam (Mersenne - Cassegrain configuration). The cell is located at the center of the primary mirror and the filter near the cell or near the secondary mirror.

SUMMARY OF THE INVENTION

The present invention primarily relates to an apparatuses, systems and methods for dual purpose solar energy harvesting combining electricity and heat generation and uses of the harvested energy. The present application teaches an efficient way of combining solar energy utilization for simultaneous Photo-Voltaic (PV) generation as well as heat harvesting. The proposed systematic approach may yield an efficient, low cost system applicable for miscellaneous applications and can be scaled efficiently to a desired size.

PV conversion:

Responsivity of a typical Si PV cell is within the region of 400 nm and 1000 nm. Almost all solar photon arriving to the cell within this energy wavelength will yield electrons, yet large portion of the photon energy in solar spectral band turns into heat.

Photons of lower energy having longer wavelength (IR) are not converted into electricity and contribute only heat if not deflected or allowed to pass through the cell.

Even in the case of multi-junction PV cells the non-convertible solar portion of the spectrum preferably should not be allowed to turn into heat in the cell. Preferably, solar cell should be kept at the lowest possible temperature to improve the efficiency. Reducing the size of the PV cell by light concentration allows using higher cost-per-area cells with improved conversion efficiency.

Light concentration and spectral filtering: To reduce the amount of heat dissipated in the cell, the non-convertible portion of the spectrum should preferably be deflected away and harvested separately. In the case of non-concentrated conversion such as simple solar panels the spectral splitting and separate harvesting may be expensive due to the large size filter that is required. When using concentrators, the splitting can be done on a narrow beam hence, a small splitter is enough, thus reducing its cost.

Several light concentration configurations are presented. A Cassegrain configuration is advantageous as the concentrated beam is substantially parallel, thus easing filter design and manufacturing. Fresnel concentrator and other concentrators and sun tracking methods are also presented. As an alternative to beam splitting filtering, the unconvertible radiation may be allowed to pass through the PV cell such as IR transparent Si and absorbed afterwards as heat.

Cell cooling:

As is well known keeping the cell at low temperature say less then 60 degrees Centigrade improves the efficiency of conversion, hence cooling may preferably be applied.

Harvesting the non-convertible portion of the spectrum:

The non-convertible portion of beam which is directed the energy away from the PV cell, directed at a heat absorbing device used for converting the light into heat which is removed from the absorber and used. The heat is removed from the heat absorber by fluid flowing in. Optionally, a secondary concentrator stage assists in reducing the focal area thus enabling a higher temperature even in the case of imperfect sun tracking.

Higher fluid temperature enables water desalination without high vacuum requirement. Conceptually the system just described is capable of operating autonomously providing desalinated water directly by solar energy while the electricity required by the process is generated on site by the PV section. Preferably, the desalination method is Multi-Effect Desalination, (MED) or the more conventional multistage flash desalination. Higher temperature also enables the use of a heat engine and generator to produce additional electricity as well as operating a absorption cooler

Material processing:

Melting Aluminum requires about 0.1 kWh per kg at temperature exciding 670 deg. C. Such a temperature can easily obtainable by focusing the solar radiation on a specially designed furnace properly insolated yet enabling the penetration of the focused radiation into the said furnace via an IR transparent window that could be made of quartz, sapphire, Spinel or any material known to be suitable. One embodiment shows a single concentrator incorporating a secondary mirror capable of steering the energy beam to a stationary ground furnace.

Mounting and sun tracking of the solar concentrator: High concentration ratio requires the precise pointing of the concentrator towards the sun with two degrees of freedom. Gimbaled mechanisms that can achieve it are well known yet; they are quite expensive and have to be robust to withstand the elements. If however the concentrator is housed inside a protective dome, cheaper parts may be used for the concentrator, aiming and tracking and energy harvesting sub-systems.

Dom may be made of a plastic material such as PMMA, glass or other transparent material may eliminate the wind disturbances and the effect of rain thus enabling the design of a low cost two degrees of freedom mechanism hence significantly reducing the over all cost of the concentrator unit. The domed concentrators may be arranged in a large field for larger energy production scale and higher fluid temperature by allowing the fluid to pass through few stages in tandem.

According to an exemplary embodiment of the invention, an energy harvesting apparatus is provided comprising: a photovoltaic cell; a light absorber; an energy concentrator receiving solar energy and concentrating said solar energy to a concentrated beam; and a spectral filter receiving said concentrated beam and directing photons of said concentrated beam substantially having energies readily convertible to electricity towards said photovoltaic cell and photons of said concentrated beam substantially having energies not efficiently convertible to electricity towards said light absorber.

In some embodiments the apparatus further comprises a fluid cell cooling system maintaining temperature of said photovoltaic cell.

In some embodiments the apparatus further comprises a fluid heat harvesting system for removing heat from said light absorber. In some embodiments the apparatus further comprises a fluid heat harvesting system for removing heat from said light absorber, wherein said fluid cell cooling is used to preheat cooling fluid prior to removing heat from said light absorber.

In some embodiments the energy concentrator is a Cassegrain concentrator. In some embodiments the concentrated beam is substantially a parallel beam when it traverses said spectral filter.

In some embodiments the spectral filter is interference filter.

In some embodiments the harvested solar energy is used for water desalinization. hi some embodiments the apparatus further comprising sun tracking system aiming said concentrator towards the sun.

In some embodiments the apparatus further comprising a protective transparent cover, protecting said system.

In some embodiments a substantial part of said system is produced using production methods used in auto making industry. hi some embodiments part of said protective transparent cover is cylindrical.

According to another aspect of the invention, a system for harvesting solar energy is provided comprising an array of solar energy harvesting apparatuses, wherein each apparatus comprising: a photovoltaic cell; a light absorber; an energy concentrator receiving solar energy and concentrating said solar energy to a concentrated beam; a spectral filter receiving said concentrated beam and directing photons of said concentrated beam substantially having energies readily convertible to electricity towards said photovoltaic cell and photons of said concentrated beam substantially having energies not efficiently convertible to electricity towards said light absorber; and a sun tracking system aiming said concentrator towards the sun.

In some embodiments each of said apparatuses in said array is housed in a protective transparent cover, protecting said system.

In some embodiments said array is a linear array and said linear array is housed in an enclosure having a protective transparent cover, protecting said array. In some embodiments said array is positioned such that long axis of sais array is substantially normal to the apparent sun daily motion.

According to another aspect of the current invention, a method of solar energy harvesting is provided, the method comprising: concentrating solar radiation to a concentrated beam; directing photons of said concentrated beam substantially having energies efficiently convertible to electricity towards a photovoltaic cell; directing photons of said concentrated beam substantially having energies not efficiently convertible to electricity towards a light absorber; converting to electricity light directed to said photovoltaic cell; and converting to heat light directed towards said light absorber.

In some embodiments the method further comprising using at least part of said converted electricity and at least part of said converted heat for desalination of water. In some embodiments the steps of: concentrating solar radiation to a concentrated beam; directing photons of said concentrated beam substantially having energies efficiently convertible to electricity towards a photovoltaic cell; directing photons of said concentrated beam substantially having energies not efficiently convertible to electricity towards a light absorber; converting to electricity light directed to said photovoltaic cell; and converting to heat light directed towards said light absorber, are performed in an array of solar harvesting apparatuses.

In some embodiments at least one of the steps of: directing photons of said concentrated beam substantially having energies efficiently convertible to electricity towards a photovoltaic cell; and directing photons of said concentrated beam substantially having energies not efficiently convertible to electricity towards a light absorber, further comprises additional light concentration by an additional nonimaging light concentrator.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings:

Figure Ia schematically depicts a system 100 for dual purpose solar energy harvesting according to an exemplary embodiment of the current invention.

Figure Ib schematically depicts a system 180 for dual purpose solar energy harvesting having split thermal system according to another exemplary embodiment of the current invention.

Figure lc(i) and figure Ic(H) schematically depict cross section and top views of non-imaging light concentrator according to an exemplary embodiment of the current invention. Figure 2a schematically depicts the solar spectrum; while figure 2b schematically depicts transmission and reflection characterizations according to an exemplary embodiment of the current invention.

Figure 3 schematically shows rough estimation of energies in a dual purpose energy harvesting apparatus 150 cording to an exemplary embodiment of the current invention.

Figure 4a schematically depicts a dual purpose system 400 for solar energy harvesting incorporating a reflective concentrator according to an exemplary embodiment of the current invention.

Figure 4b schematically depicts a dual purpose system 450 for solar energy harvesting incorporating a reflective concentrator according to an exemplary embodiment of the current invention.

Figure 5a schematically depicts a system 500 for dual purpose solar energy harvesting having a Cassegrain tracking concentrator housed in a transparent protective dome according to an exemplary embodiment of the current invention.

Figure 5b and 5c schematically depict front and side vies respectively of a system 550 for dual purpose solar energy harvesting having a Cassegrain tracking concentrator housed in a transparent protective dome according to another exemplary embodiment of the current invention.

Figure 5d and 5e schematically depict some details of front and side vies respectively of a system for dual purpose solar energy harvesting having a Cassegrain tracking concentrator housed in a transparent protective dome according to another exemplary embodiment of the current invention. Figure 6a schematically depict an array 600 of systems for dual purpose solar energy harvesting such as systems 400, 450, 500 or 550 or combinations of these system types according to an exemplary embodiment of the current invention.

Figure 6b schematically depicts a solar desalination system 650 according to an exemplary embodiment of the current invention.

Figure 7 schematically depicts a rooftop energy harvesting system 701 comprising a linear array of energy harvesting apparatuses for sloped roof mounting 700 according to an exemplary embodiment of the current invention.

Figure 8 schematically depicts a linear array of energy harvesting apparatuses with two dimensional sun tracking 800 according to an exemplary embodiment of the current invention.

Figure 9a schematically depicts a dual purpose system 900 for solar energy harvesting incorporating a reflective concentrator and a IR transmitting PV cell 130' according to an exemplary embodiment of the current invention.

Figure 9b schematically depicts some details of exemplary embodiment of planar combined embodiment of combined energy harvesting absorber 910 according to an exemplary embodiment of the current invention.

Figure 10 schematically depicts a solar operated furnace system 1000 having a stationary furnace 1010 and a curved-flat concentrating/steering mirrors according to an exemplary embodiment of the current invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention primarily relates to an apparatuses, systems and methods for multi-purpose solar energy harvesting combining electricity and heat generation and uses of the harvested energy.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

For clarity, non-essential elements were omitted from some of the drawings.

System 100 may be functionally divided to two sub-systems: light concentrator 150 and light utilization unit 151.

In the exemplary depicted embodiment of figure Ia, light concentrator 150 is a Mersenne-Cassegram concentrator of a special configuration that puts out a substantially homogeneous and parallel beam. However, other types of light concentrators, as known in the art may be used as concentrator 150. For example, concentrator 150 may be any optical system that produces a substantially parallel concentrated solar beam. In other embodiments detailed below, other types of light concentrators 150 will be depicted.

Parallel solar radiation 110 enters the system and is concentrated by a two mirror Cassegrain concentrator into a parallel or nearly parallel concentrated beam 112. The Cassegrain concentrator comprises at least two curved reflectors: primary reflector 114 and secondary reflector 116. Concentrated beam 112 is split by band transmitting spectral beam splitter 120 to two beams:

A central band beam 122 comprising essentially of photons having energies suitable to be absorbed by photovoltaic cell 130; and

A heat carrying beam 124 comprising essentially of photons having energies not suitable to be absorbed by photovoltaic cell 130, which is absorbed by heat harvesting absorber 140. Heat generated by light absorption in absorber 140 is harvested and removed by fluid heat remover 141 which may be integrated into or in thermal contact with absorber 140. Preferably, absorber 140 has a highly light absorbing surface as known in the art, for example black coating and/or structured surface.

Photovoltaic cell 130 may be any photovoltaic cell known in the art generating electrical energy output 135. Type of photocell is selected according to cost and efficiency optimization. Since the beam impinging on cell 130 is concentrated, it is advantageous to use high efficiency photovoltaic cell in spite of its high cost per square centimeter. Heat generation in cell 130 is reduced by removing a substantial amount of light having wavelength outside the effective conversion band of cell 130.For example Si, GaAs cells, or their compounds, or other solid state cells or combination of cells may be used. In some embodiments, combined cell having wide spectral conversion may be used, Transmission band of beam splitter 120 is selected to match the transmitted photon energy to the type. Optionally, additional concentration optics (not seen in this figure) may be used to further concentrate beam 122 onto cell 130. Optionally the additional concentration optics is a lens or a curved mirror or a plurality of optical elements. It should be noted that the additional concentration optics may not maintain parallelism of the beam and may in fact be a non-imaging optics.

Preferably, cell 130 is cooled to maintain its high light to electricity conversion efficiency. Preferably, liquid cooling is used. In the depicted embodiment, liquid such as water or purified water or other coolant enters the cell cooler 134, in thermal contact with cell 130 via coolant input 136.

In the depicted embodiment, cooling liquid from cell cooler 134 enters heat harvesting absorber 140, where it is further heated by energy absorbed from heat carrying beam 124 and exits via coolant output 146.

Optionally PV cell 130 is not actively cooled; or is cooled by a cooling system independent of heat absorber 140; or cooled by a closed circle liquid cooling, for example with a liquid to air heat exchanger; or actively cooled thus optionally is cooled below room temperature.

Optionally, additional concentration optics (not seen in this figure) may be used to further concentrate beam 124 onto absorber 140. Optionally the additional concentration optics is a lens or a curved mirror or a plurality of optical elements. It should be noted that the additional concentration optics may not maintain parallelism of the beam and may in fact be a non-imaging optics. Heat carrying beam 124 comprises of Infra-Red (IR) light having photon energy not efficiently converted to electrical energy by cell 130. Optionally, Heat carrying beam 124 further comprises of short wavelength light such as blue and/or Ultra- Violet (UV) light having photon energy not efficiently converted to electrical energy by cell 130. Optionally, the band transmitting beam splitter is replaced with a band reflecting filter, so that the roles of beams 124 and beam 122 are reversed.

PV cell 130 is preferably maintained at low temperature to improve light to electricity conversion efficiency. In contrast, some thermal utilization processes may benefit from operating at high temperature.

Accordingly, in the depicted embodiment, low temperature cooling liquid enters the cell cooler 134, in thermal contact with cell 130 via coolant input 136. Medium temperature liquid exiting cell cooler 134 is split 166 to first and second branches.

First branch enters heat harvesting absorber 140, where it is further heated by energy absorbed from heat carrying beam 124 and exits via high temperature output 176, and than directed to high temperature heat utilization subsystem 171.

Second branch is directed to medium temperature heat utilization subsystem 172.

Preferably, medium temperature liquid exiting the high temperature heat utilization subsystem 171 is combined with medium temperature liquid exiting cell cooler 134 before it enters the medium temperature heat utilization subsystem 172.

Low temperature liquid exiting medium temperature heat utilization subsystem 172 is returned to coolant input 136.

Branching ratio between first and second branches may be adjusted according to solar energy availability and/or energy utilization. Alternatively, high temperature and medium temperature subsystems are separated.

Figure lc(i) and figure lc(ii) schematically depict cross section and top views of non-imaging light concentrator according to an exemplary embodiment of the current invention.

In contrast to Cassegrain telescopes that use mirrors of high optical quality, concentrator 150 used in the current embodiment preferably uses low cost optics. For example, one or both mirrors 114 and 116 may be made of molded plastic with reflective coating or pressed metal sheet. Optionally spherical optical elements are used. Preferably, optical surfaces of concentrator 150 are highly light reflecting.

However, since concentrator 150 is not used for optical image forming, optical figure of optical surfaces of concentrator 150 need not be as accurate as is used in imaging devices.

Due to the lower optical quality of mirrors 114 and 116, concentrated beam 122 may have optical aberrations and generally be wider that the theoretical image of the sun when it arrives at the plane of cell 130. Additionally, sun tracking system (depicted for example in figures 5) may not be perfect, causing beam 122 to wonder about cell 130. Additionally, it may be advantageous to further reduce the size of cell 130 and/or absorber 140 to decrease its cost or increase its efficiency.

Accordingly, optional non-imaging concentrator 191 may be installed in proximity to cell 130 and/or absorber 140. Reflective surface of non-imaging concentrator 191 reflects stray rays 192 and off limit rays 193 towards cell 130.

Figure lc(ii) depicts a top view of non-imaging concentrator 190' according to an exemplary embodiment of the invention wherein the reflector is made of a plurality (six are depicted in this exemplary embodiment, but number may vary) of reflective elements 191(a) to 191(1).

Reflectors 191, and 191 (a) to 191(f) may be made of molded plastic with reflective coating or pressed metal sheet.

Figure 2a schematically depicts the solar spectrum; while figure 2b schematically depicts transmission and reflection characterizations according to an exemplary embodiment of the current invention.

Figure 2a schematically shows the solar intensity at ground level. The spectra is influenced by atmospheric absorption and scattering and thus may vary according to location, time of day and weather conditions. Generally, solar intensity peaks at the visible part of the spectrum.

Depending on the type of PV cell used, only photons with wavelength between λι and λ₂ may be efficiently converted to electricity, while photons with wavelength shorter than X₁ or longer than λ₂ may be absorbed and converted to heat. Heat generated in the VP cell may need to be removed to keep the cell at low temperature. It is thus advantageous to direct substantially only the PV convertible photons having wavelength between λ_\ and λ₂ to the PV cell and direct photons with wavelength shorter than λl or longer than λ₂ to a heat harvesting absorber.

Accordingly, figure 2b schematically depicts a desired transmission and reflection characteristics of a spectrum separator filter. Preferably, the filter reflects as close to 100% of photons with wavelength shorter than X₁ or longer than λ₂ and transmitters as close to 100% of photons with wavelength between X₁ and λ2. In realistic filter, reflection and transmission coefficients only approach 100%, and the transition from reflection and transmission is not sharp.

Multilayer dielectric coating may be used to manufacture a spectral separator filter.

The aim is maximizing the electric power produced:

P_Elec.

- R(λ,η_q)dλ

Wherein: E₁ (λ) is the solar spectrum;

^ _Heat i-^{s me} generated heat;

V_q ⁼ f(λ,T) is the quantum efficiency; and

_ q - λ

R(λ, η.) = ~ η_a is the responsively of PV cell; h ' C

Under the constrain of:

P_H,_at - dλ - P_mec,

Wherein

T ' = g{P_Heat) is Temperature in degrees Kelvin.

Maximizing P_Elec requires solving the following two equations: δ^_{= O and} a^_{= o}

Resulting in optimal wavelengths: λ_\ and λ₂ leading to a filter shape as shown in fig. 2b.

A simple high quality spectrum splitting interference filter can be optimized to deliver a sharp band that reflects the waves corresponding to energies smaller then X₁ and reflecting in addition energies much higher then λ₂ that contribute a lot of heat degrading the overall efficiency of the PV cell.

Assuming a light concentrator collecting 4000 Watt of incoming solar radiation 110 from an approximate area of for example 2x2 meter (4 m2).

Approximately 200W may be lost 110' due to optical losses in concentrator 150.

Concentrated beam 112 is split to central band beam 122 and heat carrying beam 124 of approximately 1800W by beam splitter 120 which may cause optical loss 120' of approximately 200W.

Central band beam 122 impinges PV cell 130. Approximately 200W of the impinging energy may be lost 130' to incomplete absorption and thermal losses, and of the rest, approximately 1200W is converted to electricity 135 and approximately 400W is converted to heat to be removed by cell cooler 134.

Heat carrying beam 124 of approximately 1800W impinging on heat absorber 140. Approximately 200W of the impinging energy may be lost 140' to incomplete absorption and thermal losses, and of the rest, approximately 1600W is converted to heat 141 ' to be removed by heat remover 141.

In all, the system yields approximately 2000W of heat at coolant output 146. It should be noted that the numerical example is given for demonstration only. Actual performances of real system will depend on selection of components and actual design.

Based on this numerical example, assuming: Water as coolant with flow of approximately 28 liter per hour; heat absorber and PV cell having approximately 100 cm2 areas; heat removers comprising copper plates of 0.5 cm thickness; and taking into account the material properties of water and copper; it is estimated that: cell temperature will rise by approximately 12 degrees C; heat absorber temperature will rise by approximately 50 degrees C; and only 2 degrees C temperature difference will be developed across the copper plate in the heat remover of the heat absorber (lees across the copper plate in the heat remover of the PV cell).

Parallel solar radiation 110 enters the system 400 and is concentrated by a primary curved mirror 410 concentrator into a converging beam 412.

Concentrated beam 412 is split by band transmitting spectral beam splitter 420 acting as secondary reflector to two beams: A transmitted central band beam 422 comprising essentially of photons having energies suitable to be absorbed by photovoltaic cell 130; and

A heat carrying beam 424 comprising essentially of photons having energies not suitable to be absorbed by photovoltaic cell 130, which is absorbed by heat harvesting absorber 440. Optionally band transmitting spectral beam splitter 420 is flat or concave instead of convex.

Optionally a secondary concentrating mirror 425 is used to further concentrate beam 412 onto absorber 440.

Photovoltaic cell 130 may be any photovoltaic cell known in the art generating electrical energy output. Type of photocell is selected according to cost and efficiency optimization. Since the beam impinging on cell 130 is concentrated, it is advantageous to use high efficiency photovoltaic cell in spite of its high cost per square centimeter. Heat generation in cell 130 is reduced by removing a substantial amount of light having wavelength outside the effective conversion band of cell 130.For example Si or GaAs cells or other light to electricity converting cell may be used. In some embodiments, combined cell having wide spectral conversion may be used, Transmission band of beam splitter 420 is selected to match the transmitted photon energy to the type. In contrast to transmission band beam splitter 120 of figure 1, beam splitter 420 is operated at near normal incidence angle, which may ease its design and manufacturing. However, incidence angle vary across the surface of splitter 420. Varying incidence angle may cause variation in the transmitted wavelength spectra, causing departure from optimal design and necessitates finding a compromise between band transmission near the center of the splitter and its outer area. Alternatively, spatially varying splitter may be design and manufactured, for example by spatially varying the layer thickness of an interference filter, to overcome this disadvantage.

Optionally, additional concentration optics (not seen in this figure) may be used to further concentrate beam 422 onto cell 130. Optionally the additional concentration optics is a lens or a curved mirror or a plurality of optical elements. It should be noted that the additional concentration optics may not maintain parallelism of the beam and may in fact be a non-imaging optics.

Preferably, cell 130 is cooled to maintain its high light to electricity conversion efficiency. Preferably, liquid cooling is used. In the depicted embodiment, liquid such as water or purified water is used in cell cooler 434.

Heat carrying beam 424 comprises of Infra-Red (IR) light having photon energy not efficiently converted to electrical energy by cell 130. Optionally, Heat carrying beam 424 may further comprises of blue and/or Ultra- Violet (UV) light having high photon energy which causes undesired heating of the cell 130.

Optionally, the band transmitting beam splitter is replaced with a band reflecting filter, so that the roles of beams 424 and beam 422 are reversed.

Parallel solar radiation 110 enters the system 450 and is concentrated by a Fresnel concentrator 460 concentrator into a converging beam 462. Concentrated beam 462 is split by band transmitting spectral beam splitter 470 to two beams:

A transmitted central band beam 472 comprising essentially of photons having energies suitable to be absorbed by photovoltaic cell 130; and A heat carrying beam 474 comprising essentially of photons having energies not suitable to be absorbed by photovoltaic cell 130, which is absorbed by heat harvesting absorber 480.

Optionally band transmitting spectral beam splitter 470 is concave or convex..

Photovoltaic cell 130 may be any photovoltaic cell known in the art generating electrical energy output. Type of photocell is selected according to cost and efficiency optimization. Since the beam impinging on cell 130 is concentrated, it is advantageous to use high efficiency photovoltaic cell in spite of its high cost per square centimeter. Heat generation in cell 130 is reduced by removing a substantial amount of light having wavelength outside the effective conversion band of cell 130. For example Si or GaAs cells may be used, hi some embodiments, combined cell having wide spectral conversion may be used,

Transmission band of beam splitter 470 is selected to match the transmitted photon energy to the type. Incidence angle vary across the surface of splitter 470. Varying incidence angle may cause variation in the transmitted wavelength spectra, causing departure from optimal design and necessitates finding a compromise between band transmissions at different locations of the splitter. Alternatively, spatially varying splitter may be design and manufactured, for example by spatially varying the layer thickness of an interference filter, to overcome this disadvantage.

Optionally, additional concentration optics (not seen in this figure) may be used to further concentrate beam 472 onto cell 130. Optionally the additional concentration optics is a lens or a curved mirror or a plurality of optical elements. It should be noted that the additional concentration optics may not maintain parallelism of the beam and may in fact be a non-imaging optics.

Preferably, cell 130 is cooled to maintain its high light to electricity conversion efficiency. Preferably, liquid cooling is used. In the depicted embodiment, liquid such as water or purified water is used in cell cooler 434. Heat carrying beam 474 comprises of Infra-Red (IR) light having photon energy not efficiently converted to electrical energy by cell 130. Optionally, Heat carrying beam 474 further comprises of blue and/or Ultra- Violet (UV) light having high photon energy not efficiently converted to electrical energy by cell 130 and cause undesired heating cell 130. Additionally, high energy photons may cause degradation of cell 130 and/or its supports.

Parallel solar radiation enters the system trough transparent protective dome 520. Optionally, dome 520 is sphere like structure. Similarly to the system depicted in figure 1, solar radiation is concentrated by a two mirror Cassegrain concentrator into a substantially parallel or nearly parallel concentrated beam. The Cassegrain concentrator comprises at least two curved reflectors: primary reflector 114 and secondary reflector 116 supported by support beams 516. The concentrated beam enters the dual purpose energy harvesting apparatus 150.

Flexible cord 545 comprising electrical cables and fluid hoses is connected to the dual purpose energy harvesting apparatus 150 for conducting generated electrical power and for carrying cooling fluid used for harvesting solar heat and optionally cooling the PV cell.

Cassegrain concentrator and energy harvesting apparatus 150 are supported by, and pivot about elevation axis 545 which allows the entire system 100 to track the elevation motion 540 of the sun using controlled motors (not seen in this figure).

Supports 542, carrying pivot 545 are attached to pedestal 535 which rotates in respect to foundation 537, thus allowing the entire structure to track the rotation motion 530 of the sun using controlled motors (not seen in this figure). Optionally, dome 520 rotated with pedestal 535, however, in some embodiments dome 520 and optionally pedestal 535 are stationary and only support 542 rotates.

In some embodiments the entire dome is transparent. In some embodiments only parts of the dome is transparent. In some embodiments the dome is made of inflatable plastic membrane. In some embodiments the dome is made of few parts and may be disassembled for easy maintenance.

Electrical cords and fluid pips (not seen in this figure) carry the harvested energy from system 500 to an energy utilization subsystem (not seen in this figure).

Figure 5b and 5c schematically depict front and side vies respectively of a system 550 for dual purpose solar energy harvesting having a Cassegrain tracking concentrator housed in a transparent protective dome according to another exemplary embodiment of the current invention. Parallel solar radiation enters the system trough transparent protective dome

520'. hi the depicted embodiment of this figure, dome 520' is preferably substantially a section of a cylinder and may be cheaply manufactured by banding a sheet of glass or transparent plastic.

Similarly to the system depicted in figure 1, solar radiation is concentrated by a two mirror Cassegrain concentrator into a parallel or nearly parallel concentrated beam. The Cassegrain concentrator comprises at least two curved reflectors: primary reflector 114' and secondary reflector 116' supported by support beams 516'. The concentrated beam enters the dual purpose energy harvesting apparatus 150' trough a hole 555 in primary mirror 114'. Preferably, mirrors 114 and optionally 116' are rectangular to better utilize the available light collecting space within the cylindrical dome.

Part 512 of back side of the dome may be made of opaque material. Sun tracking is performed using tracking motors. For example elevation tracking motor 563 controls the elevation aiming of the system using the optional chain or belt 564. Azimuthal motor 566 rotates trie turret comprising the pedestal 567 carrying the dome and system about a vertical axis in respect to foundation 568.

In the depicted exemplary embodiment, energy harvesting 150' comprises of closed loop PV cell cooling sub-system comprising a coolant circulating pump 571, radiator 572 and fan 573.

Electrical cable 575 carries the harvested electrical energy.

Figure 5d and 5e schematically depict some details of front and side vies respectively of a system for dual purpose solar energy harvesting having a Cassegrain tracking concentrator housed in a transparent protective dome according to another exemplary embodiment of the current invention.

Figures 5d and 5e show how cheap, mass production methods may be used for reducing production cost of the energy harvesting system.

For example, figure 5d shows wheels 588 used for enabling rotation of the turret around the vertical axis.

For example, figure 5e shows side walls 589 made of bent sheet metal produced by methods used in the car manufacturing industry.

Similarly, bottom of turret 587 may be manufactured. Optionally, side walls 589 and bottom of turret 587 may be manufactured as one piece. Similarly, secondary mirror supporting beams 586 may be manufactured.

Preferably, as many parts as possible in the entire system is manufactured using manufacturing practices adopted from auto making industry where production cost has been minimized. For example transparent dome may be made by glass bending methods used for windshield making.

Figure 6a schematically depict an array 600 of systems for dual purpose solar energy harvesting such as systems 400, 450, 500 or 550 or combinations of these system types according to an exemplary embodiment of the current invention.

Large array 600 of energy harvesting system may power a large heat utilizing subsystem in addition to supply electric power to electric utilizing subsystem or to be connected to main electrical grid. Optionally, some or all the energy harvesting in the array produce thermal energy, electrical energy or both.

For example heat utilizing subsystem may be a desalinization plant. Optionally, electrical power generated by the array 600 us used for powering pumps and other equipment in the array and the heat utilizing subsystem. Optionally, desalinization plant is a distillation desalinization plant, optionally

Solar desalination system 650 comprises at least one energy harvesting system such as systems 400, 450, 500, 550 etc. Preferably, sy7stem 650 comprises an array 600 of energy harvesting systems.

Preferably, a multi effect desalination setup 660 uses solar heating is used for desalination. Alternatively flash multistage desalination is used. Optionally, other desalinization methods are used.

Salt water is pumped by salt water pump 662 and enters the desalinization setup 660 through salt water inlet 664.

Salt water within desalination setup 660 is heated by heating fluid circulation 672 which is heated by absorbing solar radiation in energy harvesting system or the array 600 of solar energy harvesting systems. Desalinization products exit the desalination setup 660 via brine outlet 669 and desalinated water outlet 668 respectively.

Preferably, energy harvesting systems in array 600 are connected in parallel, however other piping configurations are possible.

Optionally, electrical power generated by array 600 is conducted via cable 682 to a control unit 684. Preferably some of the generated electric power is used for powering elements of system 650, such as salt water pump 662, heating fluid circulation pump 674, tracking motors of the solar energy harvesting systems, etc. Optionally, excess electrical energy (if any) is sold to power utility companies through power grid connection 686. Power grid connection 686 may optionally be used for powering the desalinization setup during nights and bad weather conditions.

Optionally, excess electrical energy (if any) is locally used for example for reverse osmosis desalinization. Optionally, system 650 further comprising energy storage unit for storing excess electrical energy.

Preferably, linear array of energy harvesting apparatuses for sloped roof mounting 700 is mounted on a sloped roof 710 having a slop angle and orientation such that array 700 is substantially directed towards the sun during daytime. Alternatively, array 700 is installed on hillside or on a support such that angle and orientation such that array 700 is substantially directed towards the sun during daytime.

Some angular deviation may be compensated by skewing the optical system and/or tilting the energy harvesting apparatuses 720 which may be any or combination of few of the types 400; 450; 500; 550; or similar types. Daily sun motion tracking is performed by rotating array 700 about its long axis 730. Seasonal adjustment mechanism 732 is used to compensate the yearly variations of sun inclination. While daily sun motion tracking is preferably automatic and motorized, seasonal adjustment mechanism 732 may be manual or motorized.

Optionally, rooftop energy harvesting system 701 is under a transparent cover, for example a transparent section or sloped roof 710 (not seen in this figure).

Alternatively, linear array of energy harvesting apparatuses for sloped roof mounting 700 is housed in a protective transparent sheath. Alternatively each of energy harvesting apparatuses 720 is housed in a protective transparent sheath. Figure 8 schematically depicts a linear array of energy harvesting apparatuses with two dimensional sun tracking 800 according to an exemplary embodiment of the current invention.

Preferably a plurality of energy harvesting apparatuses 720 are installed under a transparent protection 810.

Energy harvesting apparatuses 720 are pivotally attached to a rotation drive shaft 812 and rotate with said shaft to track the daily sun motion.

Additionally, energy harvesting apparatuses 720 are pivotally attached to elevation drive shaft 814 which by its sliding motion 816 controls the elevation angle of apparatuses 720.

The combined two dimensional aiming control of rotation drive shaft 812 and elevation drive shaft 814, sun tracking is achieved.

Rotation drive shaft 812 is actuated by rotation motor 822. Elevation drive shaft 814 is actuated by elevation motor and gears 824, preferably attached to rotation drive shaft 812.

Flexible cords 830 comprising thermal energy harvesting hoses, and/or electric energy harvesting cables. Optionally, cords 830 are combined into main conduit 833 leading to energy utilization unit external to array 800.

Parallel solar radiation 110 enters the system 900 and is concentrated by a primary curved mirror 410' concentrator into a converging beam 412'. Concentrated beam 412' enters a combined energy harvesting absorber 910 comprising an IR transmitting PV cell 930 which absorbs the short wavelength radiation and convert it to electricity, and transmits long wavelength radiation which absorbed by thermal absorber 940 which converts it to thermal energy.

Fluid cooling 943 preferably removes heat from PV cell 930, preferably maintaining temperature of cell 930 low enough to increase light to electricity conversion efficiency. Preferably, cell 930 is positioned at or near the focal spot 922 of converging beam 412' such that size of cell 930 may be kept small to decrease the cost of said cell.

Optionally, front surface (facing the incoming radiation) of cell 930 is coated with UV reflecting coating to decrease heat generated by absorbing UV radiation for which the conversion efficiency of cell 930 is low. Optionally and alternatively, UV reflective or absorptive filter (not seen in this figure) is placed in front of cell 930.

IR radiation, not absorbed by cell 930 propagates towards, and absorbed by thermal absorber 940. Fluid cooling 943 preferably removes heat from thermal absorber 940 to be used by thermal energy utilization unit external to system 900.

Figure 9b schematically depicts some details of exemplary embodiment of planar combined embodiment of combined energy harvesting absorber 910 according to an exemplary embodiment of the current invention. In the depicted embodiment, UV photons 971 are reflected from the optional

UV reflective filter 972. Additionally or alternatively, transparent filter 972 uses as protective cover only. Additionally or alternatively, filter 972 absorbs UV radiation. Alternatively, filter 972 is absent.

Medium energy range photons 973 are absorbed by PV cell 930 (here depicted as N-P solid state junction, however PIN solid state device may be used) which generates electric energy schematically depicts as "V".

Long wavelength photons 977 propagate to and absorbed by thermal absorber 940.

Preferably, the structure is thermally insulated by thermal insulation 980 which may extent to the sides of the structure.

Low temperature cooling fluid enters the structure via cooling fluid input port 981 and flows trough channels 982 in cell cooler 983.

Medium temperature cooling fluid exits 984 the cell cooler 983 and enters thermal absorber cooler 985 where it flows through similar channels to exit at high temperature fluid output port 986. Preferably, cell cooler 983 and optionally also thermal absorber cooler 985 are transparent. For example, cooler 983 and optionally also thermal absorber cooler 985 are made of glass or quartz.

Optionally, cooling fluid in the channels is in direct contact with PV cell 930 and thermal absorber 940.

Preferably a gap 987 separate cell cooler 983 and thermal absorber cooler 985 and acts as thermal isolation.

Figure 10 schematically depicts a solar operated furnace system 1000 having a stationary furnace 1010 and a curved-flat concentrating/steering mirrors according to an exemplary embodiment of the current invention.

One disadvantage of using a Cassegrain light concentration in conjunction with a high temperature furnace is the necessity to locate the furnace in the moving focal spot. The embodiment of figure 10 overcome this limitation by directing a converging beam 1012, focused by the two-dimensional steered concaved mirror 1014 onto a small, flat mirror 1020 which directs the focused beam 1021 into stationary furnace 1010. Optionally mirror 1020 is curved instead of flat. Optionally mirror 1020 is mounted on a steerable mount and is used for aiming beam 1021 into furnace 1010. Alternatively, mirror 1020 is stationary.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub combination.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

Claims

1. An energy harvesting apparatus comprising: a photovoltaic cell; a light absorber; an energy concentrator receiving solar energy and concentrating said solar energy to a concentrated beam; and a spectral filter receiving said concentrated beam and directing photons of said concentrated beam substantially having energies readily convertible to electricity towards said photovoltaic cell and photons of said concentrated beam substantially having energies not efficiently convertible to electricity towards said light absorber.

2. The apparatus of claim 1 and further comprises a fluid cell cooling system maintaining temperature of said photovoltaic cell.

3. The apparatus of claim 1 and further comprises a fluid heat harvesting system for removing heat from said light absorber.

4. The apparatus of claim 2 and further comprises a fluid heat harvesting system for removing heat from said light absorber, wherein said fluid cell cooling is used to preheat cooling fluid prior to removing heat from said light absorber.

5. The apparatus of claim 1 wherein said energy concentrator is a Cassegrain concentrator.

6. The apparatus of claim 1 wherein said concentrated beam is substantially a parallel beam when it traverses said spectral filter.

7. The apparatus of claim 1 wherein said spectral filter is interference filter.

8. The apparatus of claim 1 wherein harvested solar energy is used for water desalinization.

9. The apparatus of claim 1 and further comprising sun tracking system aiming said concentrator towards the sun.

10. The apparatus of claim 9 and further comprising a protective transparent cover, protecting said system.

11. The apparatus of claim 10 wherein substantial part of said system is produced using production methods used in auto making industry.

12. The apparatus of claim 10 wherein said part of said protective transparent cover is cylindrical.

13. A system comprising an array of apparatuses of claim 9.

14. The system of claim 13 wherein each of said apparatuses in said array is housed in a protective transparent cover, protecting said system.

15. The system of claim 13 wherein: said array is a linear array and said linear array is housed in an enclosure having a protective transparent cover, protecting said array.

16. The system of claim 15 wherein said array is positioned such that long axis of sais array is substantially normal to the apparent sun daily motion.

17. A method of solar energy harvesting comprising: concentrating solar radiation to a concentrated beam; directing photons of said concentrated beam substantially having energies efficiently convertible to electricity towards a photovoltaic cell; directing photons of said concentrated beam substantially having energies not efficiently convertible to electricity towards a light absorber; converting to electricity light directed to said photovoltaic cell; and converting to heat light directed towards said light absorber.

18. The method of claim 17 and further comprising using at least part of said converted electricity and at least part of said converted heat for desalination of water.

19. The method of claim 17 wherein the steps of: concentrating solar radiation to a concentrated beam; directing photons of said concentrated beam substantially having energies efficiently convertible to electricity towards a photovoltaic cell; directing photons of said concentrated beam substantially having energies not efficiently convertible to electricity towards a light absorber; converting to electricity light directed to said photovoltaic cell; and converting to heat light directed towards said light absorber, are performed in an array of solar harvesting apparatuses.

20. The method of claim 17 wherein at least one of the steps of: directing photons of said concentrated beam substantially having energies efficiently convertible to electricity towards a photovoltaic cell; and directing photons of said concentrated beam substantially having energies not efficiently convertible to electricity towards a light absorber, further comprises additional light concentration by an additional non-imaging light concentrator.