GB2572383A

GB2572383A - Hybrid photovoltaic-thermal collector

Info

Publication number: GB2572383A
Application number: GB1805009.6A
Authority: GB
Inventors: Markides Christos; Mellor Alex; Ramos Alba
Original assignee: Ip2ipo Innovations Ltd
Current assignee: Ip2ipo Innovations Ltd
Priority date: 2018-03-28
Filing date: 2018-03-28
Publication date: 2019-10-02
Also published as: WO2019186161A1; GB201805009D0

Abstract

A hybrid photovoltaic-thermal collector 2 comprises: a photovoltaic cell 10 for generating electricity using solar radiation in a Region I of the electromagnetic spectrum, where Region I is defined by wavelengths between 300 nm and the band gap of the semiconductor material of the photovoltaic cells 10; a solar-thermal generator 8 for heating a working fluid using solar radiation in at least a Region II of the electromagnetic spectrum, where Region II is defined by wavelengths between the band gap of the semiconductor material and 4 µm; where the photovoltaic cells 10 are thermally decoupled from the solar thermal collector 8; and, where the outlet temperature of the solar thermal generator 8 is higher than the temperature of the photovoltaic cells 10. Also disclosed is a system comprising: the hybrid collector 2; a tank and a plurality of pipes. Further disclosed is a method of harvesting energy using the hybrid collector comprising supplying a cold fluid at a specific temperature and pressure to the collector and receiving hot fluid having a specific temperature from the collector.

Description

Hybrid photovoltaic-thermal collector

Field of the Invention

The present invention relates to a hybrid photovoltaic-thermal collector and to a system 5 including a hybrid photovoltaic-thermal collector.

Background

Energy from the Sun can be harvested using different approaches.

One approach is to use photovoltaic cells to convert solar energy directly into electricity. Another approach is to employ solar-thermal collectors to use the solar energy to generate a stream of hot fluid which, in turn, can be used to generate electricity by a thermodynamic power cycle. Yet another option is to use solar-thermal collectors to generate hot water for space heating in buildings, for the provision of domestic hot water, and for other uses.

Different approaches can be combined in a single, integrated (or “hybrid”) collector.

For example, a hybrid photovoltaic-thermal collector combines photovoltaic cells and a thermal absorber which can be used to heat a fluid, typically water. This allows electricity and a stream of hot fluid to be generated using one collector.

Two types of photovoltaic-thermal collector are known.

In a first type of collector, a photovoltaic cell and a thermal absorber are combined in a stack. A fluid flow is passed under or over the thermal absorber to extract heat. An example of such a device is disclosed in US 2013/42902 Al. A drawback of this arrangement is, however, that the photovoltaic cell operates at an elevated temperature (he. above ambient temperature) as it is in thermal contact, with the heated fluid which is desired at elevated temperatures (relative to the ambient). The performance of photovoltaic cells deteriorates as temperature of the cells increases.

In a second type of‘spectrally split’ collector, incident solar radiation is split into two or more components. One component is directed to an absorber for heating a fluid, while other component is directed to photovoltaic cells for directly converting the energy into electricity. An example of such a device is described in Z. Holman and Z. Yu: “High- 2 efficiency solar power with integrated storage”, SPIE Newsroom, DOI:

10.1117/2.1201508.006071 (2015).

S. Hassani et al.·. “A cascade nanofluid-based PV/T system with optimized optical and thermal properties”, Energy, volume 112, pages 963 to 975 (2016) describes nanofluidbased photovoltaic-thermal collectors which employ spectral splitting. The collectors include gallium arsenide or silicon photovoltaic cells sandwiched between two flow channels, one running over the top of the photovoltaic cells and the other under the cells. In one design, two separate channels are used and in another design, a single, 10 double-pass channel is used. A nanofluid running in the lower flow channel is used to remove heat from the photovoltaic cells and a nanofluid passing through the upper flow channel is used as an optical bandpass filer. Both designs employ a high-temperature heat-transfer fluid in the form of Therminol (RTM) VP-1 and silver nanoparticles.

Collectors employing spectral splitting tend to operate at highly-elevated temperatures,

i.e. well above too °C, typically above 300 °C. To achieve this, the collectors use dedicated mirrors or lenses to concentrate sunlight which usually require complex and costly sun-tracking arrangements which have a large footprint, and which are typically deployed in arrays over areas typically exceeding several square kilometres. Hassani et 20 al. (2016) recommend solar concentrations above too for their collector.

The solar spectrum encompasses a wavelength range between roughly 300 nm and 4 pm. PV solar cells only convert a region of this spectrum to electrical power. The region that can be converted to electrical power, denoted Region I, encompasses the range 25 between 300 nm and a wavelength Ath, where A_th corresponds to the bandgap of the semiconductor material(s) that comprises the PV cell. The remaining part of the solar spectrum that cannot be converted to electrical power, denoted Region II, encompasses the range between the wavelength Ath and 4 pm. Region II can still be used to generate useful thermal energy if absorbed by a solar thermal generator.

Summary

According to a first aspect of the present invention there is provided a hybrid photovoltaic-thermal collector, for example in the form of a flat panel, comprising a solar-thermal generator for heating a working fluid using solar radiation in at least

Region II a of the electromagnetic spectrum, wherein the solar thermal generator comprises at least one channel for the working fluid comprises at least one and one or more photovoltaic cell(s) for generating electricity using solar radiation in Region I of the electromagnetic spectrum, which is thermally decoupled from the solar-thermal generator wherein an outlet temperature of the solar thermal generator is higher than a 10 maximum temperature of the photovoltaic cell(s).

Most of the solar radiation in Region II ofthe electromagnetic spectrum is not absorbed by the PV cells, such that the outlet temperature of the solar thermal generator is higher than the average temperature ofthe PV cells. The collector does not include a solar concentrator or has a solar concentrator which provides a concentration no more than 2*

Thus, a non-/low-concentration hybrid photovoltaic-thermal collector can be used to heat a working fluid (such as water or a water-based emulsion, suspension or solution, 20 or other fluid) to a temperature (for example, up to the boiling-point temperature of the fluid, which for water is about 100 °C at atmospheric pressure, but optionally to higher temperatures) and at a pressure (for example, at low pressures dose to 1 atmosphere, but optionally to higher pressures) which is structurally easy to handle and yet is still sufficiently hot for the chosen application and end-user needs.

Without a solar concentrator, the hybrid photovoltaic-thermal collector can be simpler to manufacture and to install, more compact and with fewer moving parts, and also less sensitive to its installed positioning and orientation, i.e. less reliant on tracking in order to achieve optimal performance. A stationary (i.e. non-tracking) solar collector in the 30 form of a flat panel, can be installed on a roof or a wall and so can be used by domestic, commercial and industrial users. In addition, the hybrid photovoltaic-thermal collector can be less sensitive to the breakdown of the incident sunlight into its direct and diffuse components. In this case, the collector can also be used in geographical areas having lower direct normal irradiance (such in the middle latitudes) and in cloudy conditions.

-4The hybrid photovoltaic-thermal collector may comprise a plurality of photovoltaic cells, for example, in the form of a photovoltaic module (or “unit”) or photovoltaic layer consisting of a number of cells interconnected electrically.

The photovoltaic cell(s) may be interposed between a face for receiving solar radiation and the solar-thermal generator or working-fluid flow channel, and the photovoltaic cell(s) maybe configured to transmit the solar radiation in at least Region II and potentially a portion of Region I of the electromagnetic spectrum.

The solar thermal generator may absorb the transmitted solar radiation in at least Region II of the electromagnetic spectrum.

The hybrid photovoltaic-thermal collector may further comprise one or more fluid and/or solid thermal-absorber layer(s) for absorbing solar radiation in Region II and 15 potentially a portion of Region I of the electromagnetic spectrum, wherein the thermalabsorber layer(s) may be placed below the photovoltaic cell(s) and above or below the working-fluid channel(s), and either act as or are in thermal contact with the working fluid or the channel(s). A thermal-absorber may comprise a fluid, which can be a gas or liquid, or a mixture, and/or a solid material, which can be a channel wall, an additional 20 layer, coating or particulate additive to, or suspension in the fluid phase.

The hybrid photovoltaic-thermal collector may further comprise one or more optical coating(s) on the various layers between the receiving face and the back face of the collector, for example on a face for receiving solar radiation, or on a thermal insulator, or between the face for receiving solar radiation and the thermal insulator.

The hybrid photovoltaic-thermal collector may further comprise at least one layer of thermally insulating fluid and/or solid material interposed between the photovoltaic cell(s) and the solar-thermal generator, or elsewhere.

The hybrid photovoltaic-thermal collector may further comprise one or more cavities interposed between the solar-thermal generator and the photovoltaic cell(s) or between the channel(s) and the photovoltaic cell(s). One or more cavities may be at least partially evacuated. One or more cavities maybe filled with a gas. The collector may further comprise a working fluid or other fluid(s) in the channel(s).

-5“

The working-fluid flow channel may be a first channel and the solar collector may further comprise a second channel for the working fluid or a different fluid interposed between the face for receiving solar radiation and the solar-thermal generator. The second channel maybe above or below and in thermal contact with the photovoltaic cell(s). The second channel may be interposed between the photovoltaic cell(s) and the solar thermal generator, or the between the photovoltaic cell(s) and the fluid and/or solid thermal-absorber layer(s), or the photovoltaic cell(s) maybe interposed between the second channel and the solar thermal generator, or he photovoltaic cell(s) may be interposed between the second channel and the fluid and/or solid thermal-absorber 10 layer(s). The second channel maybe in fluid communication with first channel, and fluid from the second channel may flow into the first channel or vice versa.

The solar-thermal generator or working-fluid flow channel may be interposed between the face for receiving solar radiation and the photovoltaic cell(s). The channel may be a 15 first channel and the collector may further comprise a second channel for the working fluid or a different fluid. The second channel may be above or below and in thermal contact with the photovoltaic cell(s). The second channel may be interposed between the photovoltaic cell(s) and the fluid and/or solid thermal-absorber layer(s), or the photovoltaic cell(s) may be interposed between the second channel and the fluid and/or 20 solid thermal-absorber layer(s). The first and second channels may be in fluid communication, and fluid from the one channel may flow into the other. The collector may further comprise one or more fluid and/or solid thermal-absorber layer(s) for absorbing solar radiation in at least Region II and potentially a portion of Region I of the electromagnetic spectrum and the photovoltaic cell(s) may be interposed between 25 the channel(s) and fluid and/or solid thermal-absorber layer(s). The collector may further comprise at least one layer of thermally i nsulating fluid and/or solid material interposed between the solar-thermal generator and the photovoltaic cell(s), or between the channel and the photovoltaic cell, or elsewhere. The collector may further comprise one or more cavities interposed between the solar-thermal generator and the 30 photovoltaic cell(s) or between the channel(s) and the photovoltaic cell(s). One or more cavities maybe at least partially evacuated or filled with a gas. The collector mayfurther comprise a working fluid or other fluid(s) in the channel(s). The collector may further comprise one or more fluid and/or solid thermal-absorber layer(s) for absorbing solar radiation in at least Region II and potentially a portion of Region I of 35 the electromagnetic spectrum interposed between a face for receiving solar radiation and the photovoltaic cell(s) and which is thermally decoupled from the photovoltaic

- 6 cell(s). The channel(s) may be interposed between the fluid and/or solid thermalabsorber layer(s) and the photovoltaic cell(s). Alternatively, the fluid and/or solid thermal-absorber layer(s) maybe interposed between the channel(s) and the photovoltaic cell(s). The collector may further comprise a thermal absorber in thermal 5 communication with the channel.

The photovoltaic cell(s) may comprise a semiconductor material having a bandgap corresponding to a first wavelength and the solar-thermal generator can absorb sufficient radiation at a second wavelength to raise the temperature of the solar10 thermal generator, wherein the first wavelength lies at the second wavelength or below the second wavelength, for example, within 300 nm, preferably 200, or more preferably 150 nm of the second wavelength.

The photovoltaic cell(s) may comprise a semiconductor material having a bandgap corresponding to a first wavelength no more than 1,200 nm.

The photovoltaic cell(s) may comprise a semiconductor material having a bandgap corresponding to a first wavelength no more than 1,170 nm.

The photovoltaic cell(s) may comprise a semiconductor material having a bandgap corresponding to a first wavelength no more than 1,000 nm.

The photovoltaic cell(s) may comprise a semiconductor material having a bandgap corresponding to a first wavelength no more than 900 nm.

The photovoltaic cell(s) may comprise a semiconductor material having a bandgap corresponding to a first wavelength no more than 850 nm.

The photovoltaic cell(s) may comprise a semiconductor material having a bandgap 30 corresponding to a first wavelength no more than 750 nm.

The photovoltaic cell(s) may comprise a semiconductor material haring a bandgap corresponding to a first wavelength no more than 600 nm.

The photovoltaic cell(s) may comprise a semiconductor material having a bandgap corresponding to a first wavelength no more than 500 nm.

The photovoltaic cell(s) may comprise silicon, cadmium sulphide, cadmium telluride, silicon, silicon heterojunction, copper indium gallium (di)selenide, aluminium gallium arsenide, gallium arsenide, gallium phosphide, indium phosphide cadmium sulphide, a perovskite, dye sensitised or other organic material.

The hybrid photovoltaic-thermal collector may be configured to be a flat panel.

The hybrid photovoltaic-thermal collector may comprise reflectors. The collector may 10 not include a solar concentrator.

The hybrid photovoltaic-thermal collector may comprise a solar concentrator, wherein the concentration is no more than 2.

According to a second aspect of the present invention there is provided a system comprising the hybrid photovoltaic-thermal collector according to the first aspect having first and second ports in fluid communication with the at least one channel, a heat storage tank, the heat, storage tank having first and second and third and fourth ports and configured to cause the fluid in the tank to be stratified into relatively hot fluid at the fourth port at a top of the storage tank and relatively cold fluid at a bottom of the storage tank and pipes configured to fluidly communicate the working fluid to the first, and second ports of the tank.

The heat storage tank may further comprise a heat, exchanger comprising a loop or coil 25 having first and second ends in fluid communication with the first and second ports of the tank.

The system may further comprise a pump arranged to pump the working fluid through the hybrid photovoltaic-thermal collector at a pressure no more than 30 atmospheres.

The system may further comprise a pump arranged to pump the working fluid through the hybrid photovoltaic-thermal collector at a pressure no more than 10 atmospheres.

The system may further comprise a pump arranged to pump the working fluid through 35 the hybrid photovoltaic-thermal collector at a pressure no more than 1.5 atmospheres.

Alternatively, the system may be arranged for thermosiphoning.

The system maybe configured such that the working fluid is arranged to enter the hybrid photovoltaic-thermal collector through the first port and to leave the hybrid photovoltaic-thermal collector through the second port.

The photovoltaic cell(s) is/are preferably thermally anchored to the temperature of the working fluid entering the hybrid photovoltaic-thermal collector.

According to a third aspect of the present invention there is provided a method of harvesting energy using the hybrid photovoltaic-thermal collector of the first aspect. The method comprises supplying cold working fluid at. a first, temperature and pressure to the hybrid photovoltaic-thermal collector, and receiving hot working fluid at a second temperature from the hybrid photovoltaic-thermal collector, wherein the first temperature is no more than the ambient or mains-water temperature and the second temperature is no more than 300 °C, and the pressure is no more than 30 atmospheres.

The second temperature is preferably no more than 150 °C and the pressure is preferably no more than 10 atmospheres. The second temperature is more preferably no more than 80 °C and the pressure is more preferably no more than 1.5 atmospheres.

-9Brief Description of the Drawings

Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure i is a schematic block diagram of a hybrid solar-energy harvesting system;

Figures 2a and 2b illustrate two arrangements for spectrally splitting solar radiation;

Figure 3a schematically shows a first set of plots of absorptivity and external quantum efficiency against wavelength in a region relevant to solar irradiance;

Figure 3b schematically shows a second set of plots of absorptivity and external quantum efficiency against wavelength in a region relevant to solar irradiance;

Figure 4a is a schematic diagram of a first transmissive spectral splitting hybrid photovoltaic-thermal solar collector;

Figure 4b is a schematic diagram of a second transmissive spectral splitting hybrid photovoltaic-thermal solar collector;

Figure 4c is a schematic diagram of a third transmissive spectral splitting hybrid photovoltaic-thermal solar collector;

Figure 4d is a schematic diagram of a first absorptive spectral splitting hybrid photovoltaic-thermal solar collector;

Figure 4e is a schematic diagram of a second absorptive spectral splitting hybrid photovoltaic-thermal solar collector;

Figure 4f is a schematic diagram of a third absorptive spectral splitting hybrid photovoltaic-thermal solar collector;

Figure 5a illustrates an indirect-type hot-water storage tank employing stratification; and

Figure 5b illustrates a direct type hot-water storage tank employing stratification.

Detailed Description of Certain Embodiments

Referring to Figure 1, a hybrid solar-energy harvesting system 1 is shown.

The hybrid solar-energy harvesting system 1 includes a stationary' (i.e. non-tracking) 30 hybrid photovoltaic-thermal collector 2 (herein simply referred to as a “collector”) which can be mounted on a roof (not shown) or wall (not shown) of a domestic, commercial or industrial building (not shown) or to the ground (not shown).

The collector 2 preferably takes the form of a flat panel and has an area of between, for 35 example, 0.2 m² and 10 m². Thus, the collector 2 or a few collectors 2 (for example, up

- 10 to ten) can be used in a small-scale installation, for example, on the roof of house. An array of collectors 2 (for example, more than ten) can be used in larger installations.

As will be explained in more detail later, the collector 2 gathers radiation 3 (herein also referred to as “sunlight” or simply “light”) from the Sun 4 and generates electricity 5 and heats a working fluid 6 (which may simply be referred to as a “fluid”), such as water or air, or a different pure fluid or fluid mixture or suspension, from an input temperature Tin to an output temperature Tout thereby resulting in a heated working fluid 6.

The collector 2 can operate using direct sunlight and using indirect (i.e. diffuse) sunlight 3, for example, in overcast conditions. The collector 2 does not employ a dedicated concentrator, which can include lenses and/or mirrors to achieve medium or high levels of concentration, but may employ potentially but not necessarily simple 15 reflectors to achieve very low concentration levels (< 2). Not using a concentrator simplifies the collector 2 thereby making it easier to manufacture and to install, and also reduces the reliance for tracking in order to deliver optimal performance.

The collector 2 includes a solar-thermal generator 8 (which may also be referred to as a 20 “solar-thermal absorber”) for heating the working fluid 6 using solar radiation 3 in an infrared region of the electromagnetic spectrum. Infrared radiation maybe absorbed by the working fluid 6 and/or by solid layers(s). The solar-thermal generator 8 includes a fluid channel 9 for the working fluid 6. The fluid channel 9 may comprise a single wide channel. The fluid channel 9 may comprise a set of two or more pipes, arranged in 25 parallel, connected at their ends to first and second manifolds (not shown). The collector 2 also includes a set of one or more photovoltaic cells 10 for generating electricity using solar radiation 3 in a visible region of the electromagnetic spectrum. The photovoltaic cells 10 are thermally decoupled from the solar-thermal generator 8. This can help to discourage or prevent heating of the photovoltaic cells 10.

The visible region of the electromagnetic spectrum lies in a range from about 300 nm up to about 800 nm. The photovoltaic cells 10 have an absorption threshold Ath, which maybe, for example about 500 nm for cadmium sulphide (CdS), 900 nm for cadmium telluride (CdTe) or 1,200 nm for silicon (Si). The infrared part of the electromagnetic 35 spectrum (herein also referred to as a “first infrared part” or “near-infrared part” of the electromagnetic spectrum) lies in a range from about 800 nm to about 3 pm, or 3,000

- 11 nm. A further infrared part of the electromagnetic spectrum (herein also referred to as a “second infrared part” or “mid-infrared part of the spectrum) lies in a range from about 3 nm to about 50 pm. Both ranges are as defined in the ISO 20473 scheme.

The collector 2 has first and second opposite faces u, 12 (herein referred to as “front and back faces” or simply “front and back”). The front face 11 is configured to receive solar radiation 3, i.e. to allow radiation 3 to reach the solar-thermal generator 8 and the photovoltaic cells 10. Figure 1 is schematic and, as will be explained for example with reference to Figures 2a and 4a, the photovoltaic cells 10 maybe disposed between the front face 11 and the solar-thermal generator 8. The collector 2 is installed in such a way to be orientated such that radiation 3 falls on the front face 11. The collector 2 is preferably installed ha ving a fixed inclination and so it. does not track movement of the Sun 4 across the sky.

Between the front and back faces 11,12, the collector 2 generally has a layered construction and includes a stack 13 of layersi4i, 142. The stack 13 includes a first layer i4i containing the solar-thermal absorber 8 and fluid channel. The stack 13 also includes a second layer 14- containing the photovoltaic cells 10.

Depending on how spectral splitting is achieved, the photovoltaic cells 10 may lie between the front face 11 of the collector 2 and the solar-thermal generator 8 and channel 13, or the solar-thermal generator 8 and channel 9 may lie between the front face 11 and the photovoltaic cells 10. The primary function of the channel in the solarthermal generator is to heat the fluid through the collector 6.

In either case, the collector 2 may include another fluid channel 15 (herein referred to as “a second fluid channel 15”) above or below and in thermal contact with the photovoltaic cells 10. The same working fluid 6 may flow in the fluid channel 9 (which in this arrangement is referred to as the “first fluid channel”) and in the second fluid channel 15. In this arrangement, the working fluid 6 may be introduced into the second fluid channel 15 and then flow into the first fluid channel 9. In other arrangements, different sets of fluids and even different types of fluids may be used in different fluid channels. The primary function of the flow through the second fluid channel 15 is to remove heat from and cool the photovoltaic cells 10.

During operation, the temperature 7p_V of the photovoltaic cells 10 preferably lies close to the temperature Ί\_α of the fluid 6 supplied to the collector 2, which is usually at ambient or mains (cold water) temperature, which is typically between 10 and 40 °C, and below the temperature T_01rt of the heated fluid 6, which is generally at or below 100 °C and is typically around 80 °C but can be higher if this is desirable in a given application. Operating the photovoltaic cells 10 at this temperature can help maintain a high photovoltaic conversion efficiency or, expressed differently, avoid a decrease in photovoltaic conversion efficiency, which can occur if photovoltaic cells 10 operate at higher temperatures. Operating the photovoltaic cells 10 at low temperatures can also help to reduce convective heat losses, which tend to increase at higher temperatures.

Convective heat losses maybe reduced to such a degree that the use of evacuated spaces maybe avoided. Furthermore, operating the photovoltaic cells 10 at low temperatures can also help to reduce the thermal degradation of the photovoltaic cells 10 and to increase their lifetime, along with the lifetime of the whole collector.

Referring still to Figure 1, the collector 2 is electrically coupled to an electrical load 16 which may take the form of a dc-to-ac converter and/or electrical storage. The collector 2 may be fluidly coupled to a storage tank 17. The collector 2 may include first and second ports 18,19. The ports 18,19 maybe fluidly coupled via respective sets of pipes 20 19, 20 to first and second ports 22, 23 of a heat storage tank 17. The collector 2, storage tank 17, pipes 20, 21 define a fluid circuit 24 through which the working fluid 6 may flow. The fluid circuit 24 may include other components, such as a pump 25, valves (not shown), inlets and outlets (not shown) for charging the circuit 24. The fluid circuit need not include a pump, but may employ thermosiphoning. The storage tank 17 may include third and fourth ports 29,30 which may be coupled to a heat load 31 via pipes 32,33 carrying a fluid 34, preferably but not necessarily, water.

As will be explained in more detail later, if a heat storage tank 17 is included in the hybrid solar-energy harvesting system 1, it is arranged for stratified operation.

Generating hot fluid 6 and storing this in the tank 17 helps in extending the operational hours of the hybrid solar-energy harvesting system 1 and offers a buffer between the incident sunlight and the user’s demand for hot water.

The collector 2 spectrally splits radiation 3 into different parts while relying on preferential transmission or absorption, and not reflection. Some reflection can be performed internally by the arrangement of layers or coatings of selected materials, but

-13 the collector 2 design does not rely on this taking place. In particular, solar radiation 3 in the visible and near-infrared regions of the electromagnetic spectrum passes through the collector 2 in a single pass and is selectively transmitted or absorbed as it passes through the collector 2 so as to achieve spectral splitting. This can be achieved in different ways, as will now be explained with reference to Figures 2a, 2b and 3.

Referring in particular to Figure 2a, a first type of collector 2_X uses a first spectral splitting arrangement (“transmissive spectral splitting”) in which radiation 3 in a first part of risible and infrared regions of the electromagnetic spectrum reaches the photovoltaic cells 10 which absorb radiation 31 in the risible region of the spectrum up to a wavelength Ath corresponding to the bandgap E_s of an active material, i.e. (for example, a semiconductor material) forming the junction of the photovoltaic cells 10. The remaining radiation 3, in this case radiation from above the wavelength Ath, i.e. a second part of the visible region of the spectrum, and into the infrared regions of the spectrum is then absorbed by the solar-thermal generator 8 and is captured by the working fluid 6 in the fluid channel 9.

Referring in particular to Figure 2b, a second type of collector 2₂ uses a second spectral splitting arrangement (“absorptive spectral splitting”) in which radiation 3 in the visible 20 and near-infrared regions of the electromagnetic spectrum reaches the solar-thermal generator 8 which extracts heat to the working fluid 6 in the fluid channel 9 by absorbing radiation from above the wavelength A_th and into the near-infrared regions of the spectrum. The remaining radiation 3, in this case radiation 3 in the visible region of the spectrum up to a wavelength Am, is transmitted through the solar-thermal generator 25 8 to be absorbed and converted into electricity by the photovoltaic cells 10. The remaining radiation 3 can pass through optional dichroic, bandpass or heat-absorbing layers (which may be glass, plastic or other material) on its way to the photovoltaic cells

10.

In both types of collector 2_b 22, a second fluid channel 15 in thermal contact with the photovoltaic cells 10 can be provided so as to cool the photovoltaic cells 10.

Referring again to Figure 1, the photovoltaic cells 10 directly convert incident solar irradiance into electricity, while the working fluid 6 flowing through the collector 2 collects incident solar irradiance that is not converted into electricity by the

-14photovoltaic cells 10 and instead generates a thermal output., in other words, a stream of a hot fluid 6 to be stored or used directly by an end user.

Solar energy outside the sensitive range of photovoltaic cells 10 which is not converted into electricity can cause heating of the photovoltaic cells io if suitable measures are not taken. In particular, if solar energy outside the sensitive range of the photovoltaic cells io is absorbed by the photovoltaic cells io, it will heat up the photovoltaic cells io, thereby increasing the temperature of the photovoltaic cells io and so lead to a deterioration in performance. Therefore, by discouraging, avoiding and/or preventing io solar energy outside the range of a photovoltaic cells io from being absorbed, performance of the cells io can be maintained. On the other hand, it may be desirable to capture this faction of the incident, solar energy as thermal energy by heating a fluid.

In both spectral splitting arrangements, the choice of photovoltaic cell design (aspects of which include choice of semiconductor material, material morphology, and cell arrangement) can affect not. only the electrical efficiency of the collector 2, but also the relative fraction of energy captured by the photovoltaic cells io and the working fluid 6. If a suitable semiconductor material is used, then the photovoltaic cells io can be operated efficiently at lower temperatures compared to thermal contact systems which 20 deliver heated water at the same temperature. This can lead to higher efficiencies overall at the same temperature and/or the ability to deliver heated fluid at a higher temperature heat, at the same or similar efficiencies. As mentioned earlier, it can mean that arrangements for reducing losses from convective heat losses (such as, for example evacuating parts of the collector) can be avoided, and also it can lead to lower rates of 25 thermal degradation of the photovoltaic cells io and to an increase their lifetime, along with the lifetime of the whole collector.

Certain cell designs can operate at a higher temperature with smaller penalties to electrical efficiency when operated. For example, heterojunction with intrinsic thin30 layer cells consisting of amorphous- and crystalline-silicon, cadmium telluride- and -copper indium gallium (di)selenide-based cells can experience a decrease in efficiency of about 2-3 % per io °C (which almost half that for bulk silicon).

A suitable form of photovoltaic cell preferably has a narrow spectral sensitivity range (e.g. Ath less than 1,000 nm), while retaining a high electrical conversion efficiency (e.g.

greater than 20 %). This can help capture a smaller fraction of the total energy in the

-15solar spectrum to the photovoltaic cells for generating electricity at high efficiency, leaving a larger fraction of the spectrum for absorption by the thermal absorber and generate a thermal output at high efficiency. Examples of suitable forms of photovoltaic cell includes cells in which the semiconductor material is silicon (Si), cadmium telluride (CdTe), silicon heterojunction, copper indium gallium (di)selenide (CIGS), aluminium gallium arsenide gallium arsenide (GaAs), cadmium sulphide (CdS), gallium phosphide, indium phosphide cadmium sulphide or a perovskite, dye sensitised or other organic material amongst others. The photovoltaic cells 10 may include multiple junctions formed by layers of different semiconductor materials, to achieve the desired spectral splitting and resulting balance (ratio) between the electrical 5 and thermal 6 outputs ofthe collector 2 in a simple, low-cost way.

Figure 3a schematically shows plots of absorptivity of the fluid and/or solid thermal absorber layer(s) and semiconductor external quantum efficiency (EQE) against.

wavelength, and also spectral irradiance in a case where thermal absorption takes place in the fluid 6, particularly in the second type of collector s₂ (Figure 2b).

Figure 3b schematically shows plots of absorptivity ofthe fluid and/or solid thermal absorber layer(s) and semiconductor external quantum efficiency (EQE) against wavelength, and also spectral irradiance in a case where thermal absorption need not take place in the fluid 6, particularly in the first type of collector 2_X (Figure 2a).

As explained earlier, the photovoltaic cells convert light into electrical energy up to a certain wavelength Au, corresponding to the band gap energy 1¾ of the semiconductor 25 material (herein this range of wavelengths is referred to as the “solar photovoltaic range”). Sunlight with wavelengths below this threshold can be converted into electrical energy in the cell. Sunlight with wavelengths above this threshold is not converted into electrical energy, but can cause the cell to heat up (herein this range of wavelengths is referred to as the “solar thermal range”).

In the first and second spectral splitting arrangements, the aim is for the photovoltaic cells 10 only to absorb radiation in the solar photovoltaic range, and for radiation in the solar thermal range to be absorbed elsewhere in the collector 2. In doing so, the photovoltaic cells 10 absorb less sunlight and therefore operate at a lower temperature, 35 which can help improve their voltage output and overall efficiency. If radiation across the entire solar photovoltaic range is absorbed by the photovoltaic cells 10, the output

-16 current should not be reduced as a result of spectral splitting. Furthermore, if radiation in the solar thermal range is absorbed elsewhere in the collector 2, it will contribute to the thermal output 6 of the collector 2, without affecting its electrical output 5.

In the first spectral splitting arrangement, the photovoltaic cells 10 can be arranged to be transmissive in the solar thermal range, possibly by making them bifacial. Sunlight is first incident on the photovoltaic cells 10, which absorb radiation in the solar photovoltaic range, and the solar thermal range is transmitted to the underlying solarthermal generator 8 further inside the collector 2.

In the second spectral splitting arrangement, sunlight is first incident on the solarthermal generator 8, such as the working fluid or an absorptive fluid and/or solid filter which absorbs radiation in the solar thermal range but which transmits radiation in the solar photovoltaic range. Water or water containing additives can be used in some 15 cases, since they absorb wavelengths above a threshold of around 1,000 nm, as well as other fluids, solid layers such as the channel walls, additional coating layers or other.

In either configuration, to maximise the amount, of light that can be transmitted through the photovoltaic cells 10 without compromising output current, photovoltaic 20 cells 10 having a low conversion threshold wavelength (e.g. below 1,000 nm if water is used) can be employed, such as, for example, CdTe-based photovoltaic cells 10. Furthermore, if the second spectral splitting arrangement is used, if the absorptive spectral filter is a water channel, a photovoltaic cell 10 can be used whose conversion threshold coincides with the absorption threshold of water. For example, this can be 25 achieved using CdTe-based photovoltaic cells 10 and water. Additives to the water phase, such as fluid substances (e.g. glycol) to form mixtures and/or solid particulate additives, can be added to water to increase its absorptivity in the range between 900 and 1,400 nm. This can be used to decrease the thickness of the water channel, for example, to as little as 1 cm. Alternative fluid and/or solid additives can be selected for 30 different photovoltaic cell materials.

Moreover, in either configuration, the photovoltaic cells 10 can be thermally coupled to the incoming fluid so as to be held at a low temperature, for example at 40 °C, and not to the outgoing fluid which is at a higher temperature, for example at 60 °C. In this 35 way, the photovoltaic cells 10 can be actively cooled, rather than heated.

Transmissive, spectral splitting collectors 2,

Referring to Figure 4a, a first transmissive spectral splitting collector 2i, 2_1;i is shown in more detail.

The collector 21,1 includes a stack of layers which includes, in order from the back face 12 to the front face 11, a base comprising optional thermal insulation 41, the fluid channel 9, an optional thermal absorber 43, an optional set of one or more optical coatings 44, a thermal insulator 45, the photovoltaic cells 10, an optional thermal absorber 47 and one or more optional windows 48 with optional optical coatings (not shown) proriding a top. The layers may be enclosed between the base and cover by side walls comprising thermal insulation 49. The optical coating may be on one or more windows, and/or the photovoltaic cell(s), and/or any of the thermal absorber layer(s), channel walls or other solid layers.

The thermal insulation 41, 49 may take the form of foil-faced mineral wool, foil-faced polyisocyanurate, high-temperature rubber, insulating foam or other suitable material. Typically, the thermal insulation may have a thickness of, for example, between 10 and 100 mm.

The fluid channel 9 may take the form of a network of metal pipes (not shown), for example copper pipes, haring an outer diameter between, for example, 5 to 20 mm. If a thermal absorber 43 is provided, the pipes (not. shown) are arranged to be in thermal contact with the thermal absorber 43. For example, the pipes (not shown) may be soldered to the thermal absorber 43. Instead of a network of pipes, the fluid channel 9 may comprise a single wide channel. The fluid channel 9 is arranged to be able to withstand a pressure up to 30 bar (3 MPa) and flow rates in a range from the order of 1 to 10 (or, from a few to a few 10s) litres per hour per unit area of collector.

As explained earlier, the fluid 6 may take the form of water which may further include glycol and/or light-absorbing nanoparticles, or another working fluid phase with added fluid substance(s) and/or solid particulate additives.

The thermal absorber 43 may comprise a sheet of metal, such as a copper or steel sheet, for example having a thickness of, for example, up to 5 mm. The thermal absorber 43 may be absorptive in full solar range of wavelengths or just in the solar thermal range.

-18The set of one or more optical coatings 44 can be used to promote absorption. For example, an absorptive low-emissivity coating can be used in the form of cupric oxide, black chromium or nickel-plated copper.

The thermal insulator 45 is used to thermally decouple the photovoltaic cells 10 from the solar-thermal generator 8. This may take the form of cavity which is filled with suitable gas, such as air or argon, or be at least partially evacuated.

The photovoltaic cells io may take the form an array of interconnected photovoltaic cells, which may be encapsulated in a glass. The photovoltaic cells 10 may take the form of a self-contained, off-the-shelf photovoltaic module. As explained earlier, the photovoltaic cells 10 comprise a suitable semiconductor material such as silicon (Si), cadmium telluride (CdTe), silicon heterojunction, copper indium gallium (di)seienide (CIGS), aluminium gallium arsenide, gallium arsenide (GaAs), cadmium sulphide (CdS) gallium phosphide, indium phosphide cadmium sulphide or a perovskite, dye sensitised or other organic material, amongst, others.

An upper surface 50 of the photovoltaic cells 10 may have an anti-reflection coating and/or a transmissive low-emissivity coating. The anti-reflection coating is used to reduce reflection of light in the solar range at an interface. It can take the form of a thin 20 layer of dielectric material such as magnesium fluoride, silicon nitride, silicon oxide, or titanium oxide, or a dispersion of nanoparticles of the same material, such as silicon oxide, for example, having a thickness of between 10 and 200 nm. Moth-eye texturing of the surface 50 can also be used. A lower surface 51 of the photovoltaic ceils 10 may also have an anti-reflection coating and/or a transmissive low-emissivity coating.

The thermal insulator 47 may take the form of cavity which is filled with suitable gas, such as air or argon, or be at least partially evacuated. The window(s) 48 is (are) transmissive in the solar range of wavelengths, i.e. in risible and near infrared portions of the spectrum.

The window(s) 48 may comprise a glass, for example, a low-iron soda lime glass and has a thickness, for example, of between 2 and 10 mm. The window(s) 48 is (are) transmissive in the solar range of wavelength.

Upper and lower surfaces 52, 53 of the window 48 or windows may include an antireflective coating. The upper surface 52 may include a coating, for example a

-19transmissive low-emissivity coating, which is reflective in the mid infrared range of wavelengths.

In the first transmissive spectral splitting collector 2-,, 2_1;2, the photovoltaic cells 10 are not actively cooled by the fluid 6. However, in the following examples, the spectral splitting collectors include additional fluid channels which can be used to actively cool the photovoltaic cells io.

The order of the fluid channel 9, optional thermal absorber 43 and optional coating 44 10 may be changed. For example, the optional thermal absorber 43 may be disposed on the thermal absorber 44 if present and the fluid channel 9 may be disposed on the optional coating 44 if present or the thermal absorber 44 if present.

Referring to Figure 4b, a second transmissive spectral splitting collector 2_t, 2j,₂ is shown. The second transmissive spectral splitting collector 2i, 2_1;2 is the same as the first, transmissive spectral splitting collector 2_υ 2_1>2 (Figure 4a) except that it has an additional fluid channel 54 disposed between the photovoltaic cells 10 and the thermal insulator 45 and/or cavity. Fluid 6 is arranged to flow from the additional fluid channel 54 into the fluid channel 9.

Referring to Figure 4c, a third transmissive spectral splitting collector 2., 2i,₃ is shown.

The third transmissive spectral splitting collector 2_b 2,,3 is the same as the first transmissive spectral splitting collector 2i, 2_i;2 (Figure 4a) except that it has an additional fluid channel 54 disposed above (or “in front of’) the photovoltaic cells 10.

Fluid 6 is arranged to flow from the additional fluid channel 54 into the fluid channel 9.

Absorptive spectral splitting collectors 2?

Referring to Figure 4d, a first absorptive spectral splitting collector 2₂, 2_2>i is shown in more detail.

The collector 2_2;i includes a stack of layers which includes, in order from the back face to the front face 11, a base comprising optional thermal insulation 61, an optional fluid channel 15, an optional thermal absorber 63, the photovoltaic cells 10, optional thermal insulator and/or optional coating layer 64, thermal insulator and/or cavity 65, the fluid channel 9, an optional thermal absorber 66 and an one or more optional window(s) 67 with optional optical coatings (not shown) providing a top. The layers

- 20 may be enclosed between the base and cover by side walls comprising thermal insulation 68.

The thermal insulation 61, 68 may take the form of foil-faced mineral wool, foil-faced polyisocyanurate, high-temperature rubber, insulating foam or other suitable material. Typically, the thermal insulation may have a thickness of, for example, between io and loo mm.

The additional fluid channel 15 may take the form of a network of metal pipes (not shown), for example copper pipes, having an outer diameter between, for example, 5 to mm. If a thermal absorber 63 is provided, the pipes (not shown) are arranged to be in thermal contact with the thermal absorber 43. For example, the pipes (not shown) may be soldered to the thermal absorber 63. Instead of a network of pipes, the fluid channel 9 may comprise a single wide channel.

The lower fluid channel 15 may communicate the same fluid 6 that flows through the upper fluid channel 9 which is used to absorb radiation in the near infrared range of the spectrum. As explained earlier, the fluid 6 make take the form of water which may further include glycol and/or light-absorbing nanoparticles, or another working fluid 20 phase with added fluid substance(s) to form mixtures and/or solid particulate additives. A different fluid 69, however, for example, water or air, may flow through the lower fluid channel 15. The fluids 6, 69 may be different, for example, one fluid maybe water and the other may be water comprising light-absorbing nanoparticles.

The thermal absorber 63 may comprise a sheet of metal, such as a copper or steel sheet, for example having a thickness of, for example, up to 5 mm.

The photovoltaic cells 10 may take the form an array of interconnected photovoltaic cells, which maybe encapsulated in a glass. The photovoltaic cells 10 may take the 30 form of a self-contained, off-the-shelf photovoltaic module. As explained earlier, the photovoltaic cells 10 comprise a suitable semiconductor material such as silicon (Si), cadmium telluride (CdTe), silicon heterojunction, copper indium gallium (di)selenide (CIGS), aluminium gallium arsenide, gallium arsenide (GaAs), cadmium sulphide (CdS) gallium phosphide, indium phosphide cadmium sulphide or a perovskite, 35 amongst, others.

- 21 An upper surface 70 of the photovoltaic cells 10 may have an anti-reflection coating and/or a transmissive low-emissivity coating. The anti-reflection coating is used to reduce reflection of Light in the solar range at an interface. It can take the form of a thin layer of dielectric material such as magnesium fluoride silicon nitride, silicon oxide, or titanium oxide, or a dispersion of nanoparticles of the same material , such as silicon oxide, for example, having a thickness of between 10 and 200 nm. Moth-eye texturing of the surface 50 can also be used. A lower surface 71 of the photovoltaic cells 10 may also have an anti-reflection coating and/or a transmissive low-emissivity coating.

The thermal insulator 64 may take the form of cavity which is filled with suitable gas, such as air or argon, or be at least partially evacuated. The thermal insulator 64 transmits radiation in the visible region of the electromagnetic spectrum.

The thermal insulator 65 is used to thermally decouple the photovoltaic cells 10 from the solar-thermal generator 8. This may take the form of glass or other insulating material. The thermal insulator 65 transmits radiation in the visible region of the electromagnetic spectrum.

The fluid channel 9 may take the form of a network of glass pipes (not shown), for example low-iron soda lime glass, having an outer diameter between, for example, 2 to 10 mm. Instead of a network of pipes, the fluid channel 9 may comprise a single wide channel. The thermal insulator 9 transmits radiation in the visible region of the electromagnetic spectrum. The channel can b be separated into multiple channels vertically and/or laterally by including additional horizontal or vertical sidewalls between water channels. The fluid channel 9 is arranged to be able to withstand a pressure up to 30 bars (3 MPa) and flow rates in a range from the order of 1 to 10 (or, from a few to a few 10s) of litres per hour per unit area of collector.

As explained earlier, the fluid 6 make take the form of water which may further include glycol and/or light-absorbing nanoparticles, or other fluid and/or solid additives.

The thermal insulator 66 may take the form of cavity which is filled with suitable gas, such as air or argon, or be at least partially evacuated. The thermal insulator 66 is transmissive in the solar range of wavelengths, i.e. in visible and near infrared portions 35 of the spectrum.

“ 22 The window(s) 67 may comprise a glass, for example a low-iron soda lime glass, and has a thickness, for example, of between 2 and 10 mm. The window(s) 67 is (are) transmissive in the solar range of wavelength.

Upper and lower surfaces 72, 73 of the window may include an anti-reflective coating. The upper surface 72 may include a coating, for example a transmissive low-emissivity coating, which is refl ective in the mid infrared range of wavelengths.

Referring to Figure 4e, a second absorptive spectral splitting collector 2₂, 2_2;2 is shown.

The second absorptive spectral splitting collector 2₂, 2_2;2 is the same as the first absorptive spectral splitting collector z₂, 2₂-₂ (Figure 4d) except that it has an additional absorber layer 74 disposed above (or “in front, of’) the fluid channel 9.

This additional absorber layer 74 is transparent, in the visible region of the electromagnetic spectrum, but absorptive in the near infrared part. This layer 74 can be used to perform absorptive spectral splitting additionally or alternatively to the fluid in channel 9. The fluid channel 9 is still used, but it no longer needs to provide absorptive spectral splitting.

Referring to Figure 4f, a third absorptive spectral splitting collector 2₂, 2₂,₃ is shown. The third absorptive spectral splitting collector 2₂, 2₂₎₃ is the same as the second absorptive spectral splitting collector 2₂, 2_2>2 (Figure 4e) except that the fluid channel 9 is disposed above (or “in front of’) the thermal absorber 74.

Heat storage tank 17

Referring to Figure 1 and to Figures 5a & 5b, the heat storage tank 17 can be arranged for stratified operation.

The collector 2, the storage tank 17 and the fluid circuit 24 (in particular the flow rate in the fluid circuit 24) are arranged so that the working fluid 6 enters the collector 2 cold,

i.e. at a relatively low temperature Tin, for example where T_m is about 10 to 40 °C, and leaves the collector 2 hot, i.e. at a relatively high temperature T_oai, for example where Tout is about 50 to 80 °C, or higher depending on the application and end-user needs. This is in contrast to conventional hybrid photovoltaic-thermal collectors, in which T_ia and Tout are similar, e.g. having a temperature difference ΔΤ = T_out - T_r, up to about 5 to °C. As explained earlier, having a larger temperature difference Δ7¹ (i.e. 30 °C or more) allows the collector 2 to operate more efficiently while promoting stratification, which helps to improve overall system performance.

The collector 2, the storage tank 17 and the fluid circuit 24 can be arranged to help achieve this. For example, low flow rates (e.g., of about 10 litres per hour per unit area of collector) can help to achieve large temperature differences, ΔΤ > 30 °C, through the collector 2, which correspond to equivalent large temperature differences between the top 84 and bottom 85 sections of the tank. Flow rates in conventional hybrid photovoltaic-thermal collectors are typically around 60 to 100 litres per hour per unit 10 area of collector.

The heat storage tank 17 can be an indirect-type heat storage tank or a direct heat storage tank.

Referring in particular to Figure 5a, an indirect-type heat storage tank 17,171 is shown.

The working fluid 6 is passed through a heat exchange loop or coil 81 which is connected to the first and second ports 22, 23 and which is disposed within the lower portion 85 of the tank 17 close to the bottom 82 of the tank 17. The heat exchange loop 20 or coil 81 may be disposed in the upper portion 84 of the tank 17 close to the top 83 of the tank 17.

Cold water 34 is fed via the third port 29 at or close to the bottom 82 of the tank 17 and hot water 34 is extracted via the fourth port 30 at or close to the top 83 of the tank 17.

However, a second heat exchange loop or coil (not shown) for water may be used.

As the water 34 in the tank 17 is heated, it rises towards the top 83 of the tank 17 by natural convection and so the water 34 in the tank 17 separates into an upper, hot region 84 and a lower, cold region 85 that are separated by a thermocline 86.

The indirect-type heat storage tank may take the form of a monovalent-type or bivalent-type.

Referring in particular to Figure 5b, a direct-type heat storage tank 17,172 is shown.

The heat storage tank 17,172 is similar to the indirect-type heat storage tank 17,17. except that the heat exchange loop or coil 81 is omitted and fluid 6 is fed directly into

-24the tank. As with the indirect-type storage tank, the flow inlet port 23 maybe disposed within the upper portion 84 of the tank 172 close to the top 83 of the tank 172.

For both types of tank, the collector 2, the storage tank 17 and the fluid circuit 24 are arranged so there is gradual charging of the tank with hot water from the top downwards as thermal energy is delivered, using natural buoyancy of hot water, which is lighter than cold water, which coll ects at the top 83 of the tank.

In contrast, in a “non-stratified” (or “thermally well-mixed”) arrangement, all or substantially all of the water inside the tank has a uniform temperature which gradually increases due to charging with thermal energy during the day, and only becomes available when it reaches 60 °C temperature at full charge, which occurs at the same time throughout the entire volume of water in the tank.

In conventional hybrid photovoltaic-thermal collectors, the temperature rise through the collector is small, typically a few degrees centigrade, e.g. around 5 °C. This is achieved by using high fluid flow rates through the collector, which are advantageous in these collectors as they promote the removal of heat from the photovoltaic cells. In contrast, the system 1 described herein is arranged to provide a greater temperature rise through the collector, e.g. > 30 °C and so deliver hot water at 60 °C. In other applications, the flow rates and fluids will differ, as will the temperature rise through the collector 2 and the temperature change along the height of the storage tank 17.

In conventional hybrid photovoltaic-thermal collectors, the small temperature rise through the collector is reflected by a small temperature change along the height of the storage, i.e. drop through the tank (in the case of a direct-type heat storage tank) or through the heat exchanger (in the indirect-type heat storage tank.

The system 1 can provide a compact system whereby electricity and useful thermal energy can be generated using a single aperture area. It can be configured in different ways to serve different climates and/or users. The system 1 can be efficient whereby a collector can achieve an overall efficiency of up to about 65%, or higher.

Modifications

It will be appreciated that, various modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known in the design, manufacture and use of photovoltaic cells, solar thermal collectors and hot water systems, and component parts thereof and which may be used instead of or in addition to features already described herein. Features of one embodiment may be replaced or supplemented by features of another embodiment.

Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or 10 not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

1. A hybrid photovoltaic-thermal collector (2) comprising:

a solar thermal generator (8) for heating a working fluid (6) using solar radiation

5 in at least Region II of the electromagnetic spectrum, wherein the solar thermal generator (8) comprises at least one channel (9) for the working fluid (6); and one or more photovoltaic cell(s) (10) for generating electricity using solar radiation in a Region I of the electromagnetic spectrum, which is thermally decoupled from the solar thermal generator,

10 wherein an outlet temperature of the solar thermal generator (8) is higher than a maximum temperature ofthe photovoltaic cell(s) (10).

2. The hybrid photovoltaic-thermal collector of claim 1, wherein the one or more photovoltaic cell(s) (10) is (are) interposed between a face (11) for receiving solar

15 radiation and the at least one channel (9), and the photovoltaic cell(s) (10) is (are) configured to transmit the solar radiation in at least Region II ofthe electromagnetic spectrum.

3. The hybrid photovoltaic-thermal collector of claim 2 wherein the solar thermal

20 generator (8) is configured to absorb the transmitted solar radiation in at least Region II of the electromagnetic spectrum.

4. The hybrid photovoltaic-thermal collector of any of claims 1 to 3, further comprising:

25 a thermal absorber (43) for absorbing solar radiation in at least Region II of the electromagnetic spectrum, wherein the thermal absorber (43) is interposed between the photovoltaic cell(s) (10) and the at least one channel (9) and is in thermal communication with the channel (9).

30 5. The hybrid photovoltaic-thermal collector of claim 1 to 3, further comprising:

a thermal absorber (43) for absorbing solar radiation in at least Region II ofthe electromagnetic spectrum, wherein the at least one channel (9) is interposed between the photovoltaic cell(s) (10) and the thermal absorber (43), and the thermal absorber (43) is in thermal communication with the channel (9).

6. The hybrid photovoltaic-thermal collector of any one of claims i to 3, wherein the channel (9) is a first channel and wherein the solar collector further comprises:

a second channel (54) for the working fluid (6) or a different working fluid (69), wherein the second channel (54) is interposed between the photovoltaic cell(s) (10) and

5 the first channel (9), wherein the second channel (54) is in thermal communication with the photovoltaic cell(s) (10).

7. The hybrid photovoltaic-thermal collector of any one of claims 1 to 3, wherein the channel (9) is a first channel and wherein the solar collector further comprises:

10 a second channel (54) for the working fluid (6) or a different working fluid (69), wherein the photovoltaic cell(s) (10) is (are) interposed between the first (9) and second (54) channels, wherein the second channel (54) is in thermal communication with the photovoltaic cell(s) (10).

15

8. The hybrid photovoltaic-thermal collector of any of claims 1 to 7, further comprising:

one or more optical coatings (44) on a face (11) for receiving solar radiation, or on a thermal insulator (41), or between the face (11) for receiving solar radiation and the thermal insulator (41).

9. The hybrid photovoltaic-thermal collector of any one of claims 1 to 8, further comprising:

at least one cavity (45) interposed between the photovoltaic cell(s) (10) and the solar thermal generator (8).

10. The hybrid photovoltaic-thermal collector of claim 8, wherein one of the at least one cavity (45) is at least partially evacuated.

11. The hybrid photovoltaic-thermal collector of claim 9 or 10, wherein a one of the at 30 least one cavity (45) is filled with a gas.

12. The hybrid photovoltaic-thermal collector of any one of claims 1 to 8, further comprising:

at least one layer (45) of thermally insulating material interposed between the

35 photovoltaic cell(s) (10) and the solar thermal generator (8).

-2813- The hybrid photovoltaic-thermal collector of any preceding claim, further comprising:

a working fluid (6) in the at least one channel (9).

5 14. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the at least one channel (9) is a first channel and wherein the solar collector further comprises:

a second channel (54,) for the working fluid (6) or a different working fluid (69) interposed between a face (11) for receiving solar radiation and the solar thermal

10 generator (8).

15. The hybrid photovoltaic-thermal collector of claim 14, wherein the second channel (54) is interposed between the photovoltaic cell(s) (10) and the solar thermal generator (8).

16. The hybrid photovoltaic-thermal collector of claim 14, wherein the photovoltaic cell(s) (10) is (are) interposed between the second channel (54) and the solar thermal generator (8).

20

17. The hybrid photovoltaic-thermal collector of any one of claims 14 to 16, wherein the second channel (54) is in fluid communication with first channel (9).

18. The hybrid photovoltaic-thermal collector of claim 1, wherein the at least one channel (9) is interposed between a face (11) for receiving solar radiation and the

25 photovoltaic cell(s) (10)), the one or more photovoltaic cell(s) (10) is (are) configured to absorb the transmitted solar radiation in at least Region II of the electromagnetic spectrum.

19. The hybrid photovoltaic-thermal collector of claim 18, wherein the solar thermal

30 generator (8) is configured to absorb the solar radiation in at least Region II of the electromagnetic spectrum.

20. The hybrid photovoltaic-thermal collector of claim 18 or 19, further comprising: a thermal absorber (74) for absorbing solar radiation in at least Region II of the

35 electromagnetic spectrum, wherein the thermal absorber (74) is interposed between th

-29photovoltaic cell(s) (10) and the at least one channel (9), and the thermal absorber (74) is in thermal communication with the channel (9).

21. The hybrid photovoltaic-thermal collector of claim 18 or 19, further comprising:

5 a thermal absorber (74) for absorbing solar radiation in at least Region II of the electromagnetic spectrum, wherein the at least one channel (9) is interposed between the photovoltaic cell(s) (10) and the thermal absorber (74), and the thermal absorber (74) is in thermal communication with the channel (9).

10

22. The hybrid photovoltaic-thermal collector of claim 18 or 19, wherein the channel (9) is a first channel and wherein the solar collector further comprises:

a second channel (15) for the working fluid (6) or a different working fluid (69), wherein the photovoltaic cells (10) is (are) interposed between the first and second channels (9,15), wherein the second channel (15) is in thermal communication with the 15 photovoltaic cell(s) (10).

23. The hybrid photovoltaic-thermal collector of claim 22, wherein the first and second channels (9,15) are in fluid communication.

20

24. The hybrid photovoltaic-thermal collector of any of claims 18 to 23, further comprising:

25. The hybrid photovoltaic-thermal collector of any one of claims 18 to 24, further comprising:

a thermal absorber (63) for absorbing solar radiation in at least Region II of the electromagnetic spectrum, wherein the photovoltaic cell(s) (10) is (are) interposed 30 between the channel (9) and the thermal absorber (63).

26. The hybrid photovoltaic-thermal collector of any one of claims 18 to 25, further comprising:

at least one layer of thermally insulating material (65) interposed between the

35 channel and the photovoltaic cell(s) (10).

-3027- The hybrid photovoltaic-thermal collector of any one of claims 18 to 24, further comprising:

at least one cavity (65) interposed between the channel (9) and the photovoltaic cell(s) (10).

28. The hybrid photovoltaic-thermal collector of claim 27, wherein the at least one cavity (65) is at least partially evacuated.

29. The hybrid photovoltaic-thermal collector of claim 27 or 28, wherein at least one 10 cavity (65) is filled with a gas.

30. The hybrid photovoltaic-thermal collector of any one of claims 18 to 29, further comprising:

a working fluid (6) in the at least one channel (9).

31. The hybrid photovoltaic-thermal collector of any one of claims 18 to 25, further comprising:

at least one layer of thermally insulating material (65) interposed between the photovoltaic cell(s) (10) and the solar thermal generator (8).

32. The hybrid photovoltaic-thermal collector of any one of claims 18 to 31, further comprising:

one or more thermal absorber (74) for absorbing solar radiation in at least Region

II of the electromagnetic spectrum interposed between the face (11) for receiving solar 25 radiation and the photovoltaic cell(s) (10), and which is thermally decoupled from the photovoltaic cell(s).

33. The hybrid photovoltaic-thermal collector of claim 32, wherein the at least one channel (9) is interposed between the thermal absorber (74) and the photovoltaic

30 cell(s) (10).

34. The hybrid photovoltaic-thermal collector of claim 32, wherein the thermal absorber (74) is interposed between the channel (9) and the photovoltaic cell(s) (10).

35 35· The hybrid photovoltaic-thermal collector of any of claims 32 to 34 or 25 wherein the thermal absorber (74) is in thermal communication with the channel (9).

- 31

36. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the photovoltaic cell(s) (10) comprise(s) a semiconductor material having a bandgap corresponding to a first wavelength no more than 1200 nm.

5

37. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the photovoltaic cell(s) (10) comprise(s) a semiconductor material having a bandgap corresponding to a first wavelength no more than 1170 nm.

38. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the 10 photovoltaic cell(s) (10) comprise(s) a semiconductor material having a bandgap corresponding to a first wavelength no more than 1000 nm.

39. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the photovoltaic cell(s) (10) comprise(s) a semiconductor material having a bandgap

15 corresponding to a first wavelength no more than 900 nm.

40. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the photovoltaic cell(s) (10) comprise(s) a semiconductor material having a bandgap corresponding to a first wavelength no more than 850 nm.

41. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the photovoltaic cell(s) (10) comprise(s) a semiconductor material having a bandgap corresponding to a first wavelength no more than 750 nm.

25

42. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the photovoltaic cell(s) (10) comprise(s) a semiconductor material having a bandgap corresponding to a first wavelength no more than 600 nm.

43. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the 30 photovoltaic cell(s) (10) comprise(s) a semiconductor material having a bandgap corresponding to a first wavelength and the solar thermal generator (8) can absorp radiation at a second wavelength, wherein the first wavelength lies at the second wavelength or below the second wavelength within 300 nm, preferably 200, or more preferably 150 nm.

44- The hybrid photovoltaic-thermal collector of any preceding claim, wherein the photovoltaic cell(s) (10) comprise(s) a material selected from cadmium sulphide, cadmium telluride, silicon, silicon heterojunction, copper indium gallium (di)selenide, aluminium gallium arsenide, gallium arsenide, gallium phosphide, indium phosphide, 5 perovskite, dye sensitised or organic materials.

45. The hybrid photovoltaic-thermal collector of any preceding claim, configured to be a flat panel.

10

46. The hybrid photovoltaic-thermal collector of any preceding claim, comprising reflectors.

47. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the collector (2) does not include a solar concentrator.

48. The hybrid photovoltaic-thermal collector of any preceding claim, wherein the collector (2) comprises a solar concentrator, wherein the concentration is no more than

20

49. A system comprising:

the hybrid photovoltaic-thermal collector of any preceding ciaim haring first and second ports (18,19) in fluid communication with the at least one channel (9);

a heat storage tank (17), the heat storage tank (17) having first and second ports (22, 23) and third and fourth ports (29, 30), configured to cause fluid in the tank to be 25 stratified into relatively hot fluid (84) at the fourth port at a top of the tank and relatively cold fluid (85) at a bottom of the tank; and pipes (20, 21) configured to fluidly communicate the working fluid (6) to the first and second ports (22, 23) of the tank (17).

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50. The system of claim 49, wherein the heat storage tank (17) further comprises:

a heat exchange (81) comprising a loop or coil haring first and second ends in fluid communication with the first and second ports (22, 23) of the tank (17).

51. The system of claim 49 or 50, further comprising:

35 a pump (25) arranged to pump the working fluid (6) through the hybrid photovoltaic-thermal collector at a pressure no more than 30 atmospheres.

52. The system of claim 49 or 50, further comprising:

a pump (25) arranged to pump the working fluid (6) through the hybrid solar collector at a pressure no more than 10 atmospheres.

53. The system of claim 49 or 50, further comprising:

a pump (25) arranged to pump the working fluid (6) through the hybrid solar collector at a pressure no more than 1.5 atmospheres

10

54. The system of any of claims 49 to 53 2, arranged for thermosiphoning.

55. The system of any one of claims 49 to 54, configured such that the working fluid (6) is arranged to enter the hybrid photovoltaic-thermal collector through the first port (18) and to leave the hybrid photovoltaic-thermal collector through the second port 15 (19).

56. The system of any one of claims 49 to 55 wherein the photovoltaic cell (10) is thermally anchored to the temperature of the working fluid (6) entering hybrid photovoltaic-thermal collector.

57. A method of harvesting energy using the hybrid photovoltaic-thermal collector of any one claims 1 to 47, the method comprising:

supplying cold working fluid at a first temperature and pressure to the hybrid p hoto voltai c-th ermal coll ector;

25 receiving hot working fluid at a second temperature from the hybrid photovoltaicthermal collector, wherein:

the first temperature is no more than ambient or mains-water temperature and the pressure is no more than 30 atmospheres, and

30 the second temperature is no more than 300 °C.

58. The method of claim 57, wherein:

the pressure is no more than 10 atmospheres, and the second temperature is no more than 150 °C.

59. The method of claim 57, wherein:

the pressure is no more than 1.5 atmospheres, and the second temperature is no more than 80 °C.