WO2012093327A1

WO2012093327A1 - A photovoltaic device

Info

Publication number: WO2012093327A1
Application number: PCT/IB2011/056024
Authority: WO
Inventors: Siu Chung Tam; Shiu Ming TAM; Wing Kit LAM; Moh Kim WONG
Original assignee: Siu Chung Tam; Tam Shiu Ming; Lam Wing Kit; Wong Moh Kim
Priority date: 2011-01-04
Filing date: 2011-12-30
Publication date: 2012-07-12

Abstract

The present invention provides a photovoltaic device comprising a body; a receiving means for receiving solar radiation from the body; a reflecting means for reflecting solar radiation to the receiving means mounted on a first surface of the body; and a first photovoltaic member adapted for converting the solar radiation to electricity mounted on a second surface of the body.

Description

A PHOTOVOLTAIC DEVICE

FIELD OF INVENTION

The present invention relates broadly to a device for producing a voltage when exposed to radiant energy (especially light). More specifically, the present invention relates to a device adapted for converting solar radiation including direct sunlight and scattered sunlight into electricity.

BACKGROUND OF INVENTION Concentration/concentrator photovoltaics (CPV) system has gained traction in recent years, owing to the commercial availability of affordable terrestrial CPV solar cells and modules, and the recognition that the long-term cost per installed peak watt ($/Wp) or cost per generated kilowatt-hour ($/kWh) will be lower than prevailing solar photovoltaics (PV) system, which are mainly based on monocrystalline silicon. However, while CPV system has potential economic benefits, they can only operate efficiently under direct sunlight. CPV system cannot operate effectively in cloudy or aerosol-infected environments, where scattered sunlight cannot be focused onto the CPV receiver.

The problem to be solved is to improve the efficiency of existing photovoltaic device in order to maximize the electrical output by capturing the maximum solar radiation by the device. SUMMARY OF INVENTION

Typically, the reflecting means further comprises an optical filter adapted for allowing a portion of the solar spectrum with wavelength between 300 nm and 800 nm to pass though. Typically, the reflecting means is adapted to reflect a remaining portion of the solar spectrum which is not filtered by the optical filter to the receiving means.

Typically, the reflecting means is mounted on a surface of a transparent portion of the body, the at least one first photovoltaic member is mounted on an opposite surface of the transparent portion of the body. Typically, the transparent portion of the body forms a passage for allowing the portion of the solar spectrum to reach the first photovoltaic member.

Typically, the transparent portion of the body is made of glass.

Typically, the optical filter is formed by a material comprising zirconium oxide.

Typically, the optical filter is formed by a material comprising silicon dioxide. Typically, the optical filter is formed by a material comprising magnesium fluoride. Typically, the optical filter is formed by a material comprising aluminum.

Typically, the reflecting means is formed by a material comprising aluminum.

Typically, the reflecting means further comprises a second photovoltaic member adapted for converting the solar radiation to electricity being mounted below the optical filter.

Typically, the reflecting means is mounted on a surface of a non-transparent portion of the body, the first photovoltaic member is mounted on an opposite surface of the non-transparent portion of the body.

Typically, the non-transparent portion of the body is made of a photovoltaic material.

Typically, the first photovoltaic member comprises a substance of copper indium gallium selenide (CIGS).

Typically, the first photovoltaic member comprises a substance of cadmium telluride (CdTe).

Typically, the body further comprises a photovoltaic portion comprising the first photovoltaic member.

Typically, the second photovoltaic member comprises a substance of copper indium gallium selenide (CIGS).

Typically, the second photovoltaic member comprises a substance of cadmium telluride (CdTe). Typically, the second photovoltaic member comprises a substance of GalnP.

Typically, the receiving means comprises a concentrator photovoltaic array receiver adapted for providing electricity and heat from the solar radiation which is reflected by the reflecting means;

Typically, the concentrator photovoltaic array receiver is a CPV material with a triple junction structure comprising GalnP, GalnAs and Ge.

Typically, the concentrator photovoltaic array receiver is a CPV material with a double junction structure comprising GalnAs and Ge.

Typically, the receiving means further comprises a thermal conductive element for dissipating the heat from the concentrator photovoltaic array receiver.

Typically, a rigid layer adapted for protecting the body is mounted to the first and second surfaces of the body.

Typically, the second surface of the body comprises a textured surface.

Typically, the second surface of the body comprises an anti-reflection coating adapted for maximizing the efficiency of the first photovoltaic member.

Typically, the device further comprises a supporting structure adapted for receiving a plurality of the bodies, the supporting structure comprises a pair of concave and convex surfaces, the reflecting means of the plurality of the bodies are mounted on the concave surface of the supporting structure. Typically, a heat engine adapted for generating electricity from the heat conducted by the thermal conductive element is mounted to the receiving means.

Typically, a homogenizer for homogenizing the solar spectrum is mounted to the concentrator photovoltaic array receiver. Typically, the photovoltaic device further comprises a moving device adapted for rotating the supporting structure to a direction substantially in a direction of the sun.

Typically, the supporting structure may be oriented in any direction based on data received by a neighboring global positioning system (GPS) device.

DESCRIPTION OF THE DRAWINGS

This and other objects, features and advantages of the present invention will become apparent upon reading of the following detailed descriptions and drawings, in which:

Figure 1 shows a perspective view of an embodiment of the present invention;

Figure 2 shows a top view of the embodiment of the present invention; Figure 3 shows a sectional "A- A" view of Figure 2;

Figure 4 shows a sectional "B-B" view of Figure 2;

Figure 5 shows a schematic diagram of a first embodiment of the present invention;

Figure 6 shows a schematic diagram of an existing CPV system which does not include any PV elements in its design; Figure 7 shows a schematic diagram of an existing CPV CHP system which does not include any PV elements in its design;

Figure 8 shows a schematic diagram of a second embodiment of the present invention; Figure 9 shows a schematic diagram of a third embodiment of the present invention;

Figure 10 shows a graph which illustrates second PV material or a first photovoltaic member converts solar radiation shorter than cutoff wavelength into electricity while the reflected solar radiation will be converted by CPV array receiver (sourced from: R. R. King and F. Eddy, Ultra-High Efficiency Multijunction Cell and Receiver Module, Phase IB: High Performance PV Exploring and Accelerating Ultimate Pathways, Report No. NREL/SR-520-47602, rev. March 2010);

Figure 11 shows a graph which illustrates special response of CIS family and GaAs family of solar cells (sourced from: P. Ho, "Solar energy is hot (in Chinese) ", Feb 2010); Figure 12 shows a schematic diagram of a fourth embodiment of the present invention;

Figure 13 shows a schematic diagram of a third embodiment of the present invention when there is no direct sunlight;

Figure 14 shows a body which is made of transparent material of the third embodiment of the present invention; and Figure 15 shows a body which is merged with the first photovoltaic member of the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION In the present invention, it is viable and advantageous to have an integrated CPV and

PV system to drive down unit cost in terms of $/Wp and $/kWh, and simultaneously unit land use in terms of hectares per peak megawatt (ha/MWp) and hectares per generated megawatt-hour (ha/MWh). Furthermore, waste heat from cooling the CPV receiver or the receiving means may be utilized to provide warm water for utility use, generate electricity through heat engines, or otherwise in order to maximize the use of the incident solar energy. Typically, if a CPV or PV system simultaneously generates warm water for utility or process applications, the system is referred to as a combined heat and power (CHP) system.

In the present invention, the design of a CPV-PV system is described. The CPV-PV system may also be configured to produce more electricity output from a heat engine, or generate utility-grade hot water as in a CPV-PV CHP system.

The present invention makes use of CPV system and PV system. For the CPV system, a CPV system typically comprises the following key subsystems: CPV receiver or the receiving means, concentration optics, 2-axis tracker, and balance of system. The CPV receiver or the receiving means consists of a packaged module or an extended array, which is typically made of high-temperature high-efficiency PV solar cell material such as metamorphic or lattice-matched triple-junction GaInP/Ga(In)As/Ge. As sunlight is concentrated onto the surface of the CPV material, surface temperatures may reach up to 1,000°C and efficient cooling must be maintained to reduce junction temperatures. CPV materials are required to operate at low junction temperatures to yield high quantum efficiencies and prolong working lives. While silicon or other solar cell photovoltaic materials may be used, multi-junction CPV material systems are usually chosen for their optimized high efficiencies over the entire useful spectrum of the solar radiation. The disadvantages of choosing multi-junction GaAs-based material systems are the relatively higher cost and higher indirect carbon emission per unit area compared to silicon or other solar cell photovoltaic materials.

The concentration optics should have as high a concentration ratio as possible, to reduce the cost of CPV solar cell material per unit area of sunlight footprint. This is important as the cost of the CPV solar cell receiver accounts for a significant percentage of the system cost. Today, concentration ratio between 500X - 1200X is commercially attainable. Optical configurations may be based on refractive, reflective, or diffractive design, frequently coupled with beam homogenizers prior to incidence onto the CPV receiver or the receiving means.

The electro-mechanical 2-axis tracker working in conjunction with a sun sensor is used to align the aperture of the solar concentrator normal to incident solar radiation at all times. The two axes are the elevation axis and the azimuth axis, respectively. Common designs involve the use of gears and drive motors, to provide tracking movements of approximately 90° in elevation and 180° in azimuth. For refractive and diffractive designs, the tracker frame has to bear the weight of the CPV modules. For reflective designs, the tracker frame has to support the reflecting elements (e.g. curved mirrors, plane mirrors) against a conic surface (e.g. paraboloidal, spherical, ellipsoidal), so that the incident solar radiation will be reflected towards the CPV receiver or the receiving means. The CPV receiver or the receiving means may be located at the primary focus (e.g. Newton design) or secondary focus of the reflective layout (e.g. Cassegrain design), and has to be supported by a spider structure fixed onto the tracker frame. Sturdiness and durability of the 2-axis tracker are important as the entire tracker and its load have to be designed to last for at least 20 years and withstand wind speeds typically in excess of 140 km/h. Depending on the system design, balance of system (BOS) consists of DC combiners, inverters, AC combiners, grid-tied connectors and control, sun sensor, sun tracking electronics, sun irradiance monitor, anemometer, global positioning system (GPS), wireless transceiver for remote monitoring and control, lightning conductors, de-icing device, heat sink / cooler, water tank, etc. For the PV system, it typically comprises the following key subsystems: PV panel and balance of system.

The PV receiver is usually made into the shape of flat panels mounted on to structures facing the general direction of the mid-day sun. Technically, a PV panel operates at one sun (IX) solar conditions, though there are designs to use reflectors for low concentration ratios for higher efficiency, or trackers to increase its total energy output. Common PV materials include monocrystalline silicon (m-Si), polycrystalline silicon (p-Si), amorphous silicon (a-Si), cadmium telluride (CdTe), copper indium diselenide (CIS), copper indium gallium diselenide (CIGS), dye-sensitized polymers, and others. Among these PV materials, varying degree of response to scattered solar radiation has been studied. Good candidates to operate efficiently under scattered radiation include a-Si, CIS, and CIGS. The components for balance of system (BOS) are the same as those required by CPV systems.

Referring to the above CPV system and PV system, the present invention focuses on combined CPV-PV systems with reflective concentrators.

Proposed CPV-PV system design

Figure 1 shows an embodiment of the present invention and it relates to the maximization of electrical output from a reflective CPV-PV system. The obvious solution of fixing PV panels behind the concentration dish is an obvious solution and is not considered here.

Direct sunlight

In a first embodiment, when there is direct sunlight, the CPV receiver or a concentrator array receiver of a receiving means will generate electricity from the focused solar radiation, complemented by those generated by a PV material or a second photovoltaic member affixed on to the frame of the concentration dish. The PV material or the second photovoltaic member, such as CIGS, CIS, a-Si or some other PV material, may be deposited onto a separate substrate and stacked against the reflectors or a reflecting means, as shown in Figure 5. The PV material or the first photovoltaic member essentially captures the scattered solar radiation at the back of the concentration dish and converts it into electricity. When there is direct sunlight, the intensity of the scattered radiation is usually very high, depending on the terrain and vegetation around the CPV-PV system. The total amount of electricity that can be generated by the PV panels is therefore substantial. The energy efficiency of the CPV-PV system may further be enhanced using heat engine and/or the CHP concept as outlined in Figure 6 and Figure 7.

In a second embodiment, the PV material or the first photovoltaic member may be deposited on to the back surface of the same reflector substrate or a body, as shown in Figure 8. Hard protective coatings or a rigid layer may be deposited on both surfaces for higher durability. Textured surface or anti-reflection (AR) coating may also be applied on to the rear PV coating or the first photovoltaic member for higher coupling efficiency.

In a third embodiment, it will involve the use of a suitable second PV material or the second photovoltaic member and a short-pass optical filter or an optical filter (also more precisely being known as short-pass dichroic mirror or short-pass dichroic interference filter), as shown in Figure 9. In the third embodiment, the rear PV material or the first photovoltaic member will work on scattered solar radiation from the background terrain and vegetation, while the second PV material or the second photovoltaic member will work on direct incident sunlight. By judiciously optimizing the cutoff wavelength of the short-pass optical filter or the optical filter with respect to the second PV material or the second photovoltaic member, the transmitted portion of the solar radiation will be captured efficiently by the second PV material or the second photovoltaic member, while the reflected solar radiation will fall on to the receiving means. Therefore, the total electrical energy generated by the CPV array receiver or the concentrator array receiver and the second PV material or the second photovoltaic member will be higher than that produced by the CPV array receiver or the concentrator array receiver alone when working with a mirror coating on the reflector substrate or the body. For example, a triple junction GalnP/GalnAs/Ge CPV detector or the concentrator array receiver may have a spectral electrical current density response curve as shown in Figure 10. Using a short-pass optical filter or the optical filter, radiation at the short end of the solar spectrum will fall onto the second PV material or the second photovoltaic member, such as CIS or CIGS, while the reflected solar radiation will fall on to the 3 J CPV array receiver or the concentrator array receiver. This is possible because the spectral response of the CIS family of PV solar cells have efficiencies higher than or similar to that of the GaAs family at the shorter wavelength region of the AMI.5 low-altitude solar spectrum. This is illustrated in Figure 11. Alternatively, as shown in Figure 14, the reflector substrate or the body would be made of a transparent material which is allowed the sunlight to pass through and arrive at the rear PV material or the first photovoltaic member.

Alternatively, as shown in Figure 15, the body of the present invention can be a PV material or it can be merged with the first photovoltaic member. In the extreme case, the 3J structure may also be entirely replaced by a 2J structure

(e.g. GalnAs/Ge), with the second PV material or the second photovoltaic member taking on substantially the composition of the top 3J material or its equivalent (e.g. GalnP or CIGS). Higher total efficiency is expected. Shorter energy payback time (EPBT) may be achieved. Total cost of production may also be reduced due to lower requirement on J-ratio balancing and higher manufacturing yield for the CPV structures.

In a fourth embodiment, it is a further modification of the third embodiment of the present invention and it may be effected by stacking the second PV material or the second photovoltaic member with the rear PV material or the first photovoltaic member, as shown in Figure 12, or even eliminating the second PV material or the second photovoltaic member altogether by using the rear PV material the first photovoltaic member to convert both filtered front-transmitting and rearward scattered sunlight, as is known to people skilled in the trade.

Scattered sunlight

When there is no direct sunlight, such as the case when it is overcast or when the atmosphere is suspended with aerosol, the reflective concentration optics or the reflecting means will be ineffective in focusing scattered sunlight on to the CPV array receiver or the concentrator array receiver. Under such conditions, different PV materials will respond to scattered sunlight with different efficiencies, among which CIS/CIGS and a-Si are high performers.

When there is no direct sunlight, the CPV-PV system may be parked at the default stowing position, or may be set to point to the direction of the zenith. In this way, for example, by using the third embodiment of the present invention, the rear PV material or the first photovoltaic member will continue to consume solar radiation scattered from the terrain and vegetation nearby, while the second PV material or the second photovoltaic member deposited on the other side of the reflector substrate or the body will utilize short-pass filtered incident solar radiation scattered through the clouds or off aerosols suspended in air. Figure 11 illustrates this scenario.

The total PV output should further be optimized through close-loop control to track the best pointing direction for the concentration dish. This may be achieved by monitoring the outputs from the rear PV material or the second photovoltaic member and the second PV material or the first photovoltaic member for the whole system while moving the whole concentration dish or a plurality of the bodies about the existing pointing direction. Intelligent software monitoring and control could assure the PV subsystem of low-power smooth tracking while attaining maximum total PV electrical output.

Alternatively, the PV outputs from a single or cluster of receiver substrates monitored using miniature actuators may be compared to determine to determine if the pointing direction needs to be adjusted. Yet alternatively, the outputs from quadrants or a larger number of segments of the concentration dish may be analyzed to determine the optimum pointing direction, by employing a working principle similar to that of a quadrant photodiode.

Claims

CLAIMS I claim:

1. A photovoltaic device comprising:

a body; a receiving means for receiving solar radiation from the body; a reflecting means for reflecting solar radiation to the receiving means mounted on a first surface of the body; and a first photovoltaic member adapted for converting the solar radiation to electricity mounted on a second surface of the body.

2. The photovoltaic device according to Claim 1 , wherein the reflecting means further comprises an optical filter adapted for allowing a portion of the solar spectrum with wavelength between 300 nm and 800 nm to pass though.

3. The photovoltaic device according to Claim 2, wherein the reflecting means is adapted to reflect a remaining portion of the solar spectrum which is not filtered by the optical filter to the receiving means.

4. The photovoltaic device according to Claim 2, wherein the reflecting means is mounted on a surface of a transparent portion of the body, the at least one first photovoltaic member is mounted on an opposite surface of the transparent portion of the body.

5. The photovoltaic device according to Claim 4, wherein the transparent portion of the body forms a passage for allowing the portion of the solar spectrum to reach the first photovoltaic member.

6. The photovoltaic device according to any one of Claims 2 to 5, wherein the transparent portion of the body is made of glass.

7. The photovoltaic device according to any one of Claims 2 to 5, wherein the optical filter is formed by a material comprising zirconium oxide.

8. The photovoltaic device according to any one of Claims 2 to 5, wherein the optical filter is formed by a material comprising silicon dioxide.

9. The photovoltaic device according to any one of Claims 2 to 5, wherein the optical filter is formed by a material comprising magnesium fluoride.

10. The photovoltaic device according to any one of Claims 2 to 5, wherein the optical filter is formed by a material comprising aluminum.

11. The photovoltaic device according to Claim 1 , wherein the reflecting means is formed by a material comprising aluminum.

12. The photovoltaic device according to Claim 2, wherein the reflecting means further comprises a second photovoltaic member adapted for converting the solar radiation to electricity being mounted below the optical filter.

13. The photovoltaic device according to Claim 1, wherein the reflecting means is mounted on a surface of a non-transparent portion of the body, the first photovoltaic member is mounted on an opposite surface of the non-transparent portion of the body.

14. The photovoltaic device according to Claim 13, wherein the non-transparent portion of the body is made of a photovoltaic material.

15. The photovoltaic device according to Claim 1, wherein the first photovoltaic member comprises a substance of copper indium gallium selenide (CIGS).

16. The photovoltaic device according to Claim 1, wherein the first photovoltaic member comprises a substance of cadmium telluride (CdTe).

17. The photovoltaic device according to Claim 1, wherein the body further comprises a photovoltaic portion comprising the first photovoltaic member.

18. The photovoltaic device according to Claim 12, wherein the second photovoltaic member comprises a substance of copper indium gallium selenide (CIGS).

19. The photovoltaic device according to Claim 12, wherein the second photovoltaic member comprises a substance of cadmium telluride (CdTe).

20. The photovoltaic device according to Claim 12, wherein the second photovoltaic member comprises a substance of GalnP.

21. The photovoltaic device according to Claim 1, wherein the receiving means comprises a concentrator photovoltaic array receiver adapted for providing electricity and heat from the solar radiation which is reflected by the reflecting means;

22. The photovoltaic device according to Claim 21, wherein the concentrator photovoltaic array receiver is a CPV material with a triple junction structure comprising GalnP, GalnAs and Ge.

23. The photovoltaic device according to Claim 21, wherein the concentrator photovoltaic array receiver is a CPV material with a double junction structure comprising GalnAs and Ge.

24. The photovoltaic device according to Claim 21, wherein the receiving means further comprises a thermal conductive element for dissipating the heat from the concentrator photovoltaic array receiver.

25. The photovoltaic device according to Claim 1, wherein a rigid layer adapted for protecting the body is mounted to the first and second surfaces of the body.

26. The photovoltaic device according to Claim 1, wherein the second surface of the body comprises a textured surface.

27. The photovoltaic device according to Claim 1, wherein the second surface of the body comprises an anti-reflection coating adapted for maximizing the efficiency of the first photovoltaic member.

28. The photovoltaic device according to Claim 1, wherein the device further comprises a supporting structure adapted for receiving a plurality of the bodies, the supporting structure comprises a pair of concave and convex surfaces, the reflecting means of the plurality of the bodies are mounted on the concave surface of the supporting structure.

29. The photovoltaic device according to Claim 24, wherein a heat engine adapted for generating electricity from the heat conducted by the thermal conductive element is mounted to the receiving means.

30. The photovoltaic device according to Claim 21, wherein a homogenizer for homogenizing the solar spectrum is mounted to the concentrator photovoltaic array receiver.

31. The photovoltaic device according to Claim 28, wherein the photovoltaic device further comprises a moving device adapted for rotating the supporting structure to a direction substantially in a direction of the sun.

32. The photovoltaic device according to Claim 28, wherein the supporting structure may be oriented in any direction based on data received by a neighboring global positioning system (GPS) device.