GB2506333A

GB2506333A - Receiver for a solar concentrator having a heat exchanger with plural fins

Info

Publication number: GB2506333A
Application number: GB1212074.7A
Authority: GB
Inventors: Graham Paul Ford; Jonathan Edward Ford
Original assignee: JEAN PIERRE DEWERPE; LUCIEN BASTIANELLI
Current assignee: JEAN-PIERRE DEWERPE; LUCIEN BASTIANELLI
Priority date: 2012-07-06
Filing date: 2012-07-06
Publication date: 2014-04-02
Also published as: GB201212074D0

Abstract

A receiver (131 fig1) for light from a solar concentrator (133 fig1) and for outputting heated fluid comprising a solar absorber, a heat exchanger thermally coupled to the solar absorber 101 and arranged to heat a heat transfer fluid, an inlet duct 111 disposed along the length of the receiver for receiving heat transfer fluid, an outlet duct 110 disposed along the length of the receiver where the heat exchanger comprises a plurality of thermally conductive fins 106 (119 fig 5) extending across the width of the receiver between an outer edge and the centre line of the receiver, the outer edge of the fins are coupled to the inlet duct and inner edges at the centre line to the outlet duct such that the heat transfer fluid flows between the fins from the inlet to the outlet. The inlet duct preferably surrounds the outlet duct with the fins allowing fluid to pass between the two. The solar absorber is preferably curved and the fins are curved to be in contact with the solar absorber from the outer edge to the centre line. The solar absorber preferably includes a glass cover 104. The outlet duct may include a central divider 103 along the centre line of the receiver.

Description

Receiver For A Solar Concentrator

FIELD OF THE INVENTION

This invention relates to a receiver for a solar concentrator, particularly the type known as a Linear Fresnel concentrator, in which a series of long, narrow, parallel mirrors are arranged so that they focus light onto a long receiver situated stationary above the mirrors and parallel to them. They mirrors are tilted and rotate about their long axes so as to focus the reflected rays of direct sunlight off them and onto the receiver.

BACKGROUND OF THE INVENTION

Solar concentrators are used for producing heat at temperatures sufficiently high such that the heat can be captured to boil water or some other fluid in order to drive a turbine and produce power. Linear Fresnel concentrators have been used to raise steam directly from water flowing through pipes located in the receiver. Other forms of solar concentrator, such a parabolic trough type, will general use a thermally stable oil to capture the heat. That oil is then pumped to a boiler to raise the steam or organic vapour at pressure to drive a turbine.

Power plants that utilise solar concentrators are best located in arid, sunny places on earth, which receive a high level of direct sunlight. Direct sunlight is light that comes directly from the sun without being scattered by cloud or dust, and can be focussed by either lenses or mirrors. While the potential for power production from sunlight by solar power plants is vast -several times the power the world currently consumes for both electrical power generation and transport -the use of solar concentrators for power production remains limited. This is principally because the high capital cost of solar concentrators, together with the associated equipment used to store the heat so that the turbines can run at night as well as during the day.

The costs of a solar power plant are the sum of four main items of cost: the mirror, the structure for holding the mirror so that it will reflect light accurately onto the receiver and resist wind loads, the receiver and the heat store. To reduce the overall cost of a solar power plant therefore requires a configuration that will enable the overall cost of these four items to be minimised.

Linear Fresnel reflectors have been developed to reduce the cost of the mirror, compared to parabolic trough solar concentrators. Parabolic trough plants typically use relatively expensive glass mirrors which must first be formed at high temperature into the required shape, and highly accurately, whereas Linear Fresnel mirrors can use commercially available mirrored-glass made in volume from thin float-glass, a standard and low cost manufacturing process.

However, linear Fresnel solar concentrators suffer from two problems. First, they generally produce heat at a lower temperature than parabolic trough plants can. An attempt to produce heat at higher temperatures has, until now, reduced the heat capture efficiency of the plants and made them uneconomic. Second, the lower temperature of heat capture means that they are generally designed to use boiling water (at high pressure) as the working fluid. To store heat with this heat transfer fluid for long periods (say several hours) requires a phase change material that will absorb or release latent heat as it melts or solidifies at or near the boiling point of the water. In practice such materials -generally mixtures of inorganic salts -are quite expensive and have poor thermal conductivity, making the storage system expensive and rendering the solar power plant uncompetitive relative to the alternative options.

Solar concentrating power plants of the Linear Fresnel type could therefore be made less costly and make power more competitively if the temperature at which they captured heat was raised, and the storage media for the heat store was reduced in cost.

Parabolic trough plants are also expensive, partly because the efficiency of the thermal power plant is limited by the maximum operating temperature of the heat transfer fluid, the thermal oil that is used to carry the heat from the solar concentrator receivers to the boiler. Even the best heat transfer oils are limited to a maximum operating temperature under 400C. This should be compared to current coal-fired steam plant practice where the steam enters the steam turbine at a temperature in excess of 5002C. The lower the steam temperature, the lower is the thermal efficiency (i.e. the ratio of power out / heat in) of the power plant, and so the less power is generated for a given area of solar concentrator mirror.

To overcome some of these issues, there have been attempts to use an inert non-condensing gas as the heat transfer fluid. The most temperature stable fluids are gases. However gases suffer from low density and low thermal conductivity, so large duct areas and extended heat transfer surfaces are required to make gases effective as heat transfer fluids, particularly at atmospheric pressure, the safest pressure to operate at.

With local intensities of radiant energy being absorbed on a single axis solar receiver as high as 50 kiloWatts per square metre of receiver absorber area, the fin design and the way it connects to the absorber surface is critical to the efficient operation of a receiver, as temperature excursions of the absorber substantially above the operating temperature of the gas could damage the selective coating on the absorber surface leading to much increased radiative losses.

Selective coatings are easily damaged by excessive temperatures. This temperature sensitivity of the coating also prevents a material, coated with a selective coating, from being welded or brazed to fins to extend its surface area. So, a method is required to mechanical connect an absorber surface to an arrangement of fins behind it such that the components remain in close thermal contact for the lifetime of the receiver.

Furthermore, the fins must be proportioned such that the gas flowing through the fins does not give rise to excessive pressure drop and hence excessive pumping power required to circulate the gas, which has a high volume flow rate due to its very low density at atmospheric pressure. Similarly the fin height and thickness must be selected to avoid excessive temperature drop across the fin, and sufficient fin surface area must be presented to enable effective heat transfer. The fin material also needs to an economic choice and able to resist creep at the operating temperatures.

Nevertheless, the use of inert gas as the heat transfer fluid in solar concentrators offers the potential of low cost solar power, for two reasons. Firstly, inert gas makes an excellent heat transfer fluid for transferring heat into a packed bed, an insulated bed of crushed and graded stones that store heat as they are heated up and release it again as they cool down, giving up their heat via the gaseous heat transfer fluid to a boiler.

This thermal storage medium is widely abundant, low in cost and easily sourced. It is one of the lowest cost heat storage materials available suitable for heat storage over a length of time from a few hours to a few tens of hours. The use for inert gas as the heat transfer medium for this purpose is low in cost.

Inert gas does not chemically degrade at the temperatures that can be achieved in a solar concentrating power plant (up to 60OC). Therefore using inert gas as the heal transfer fluid removes one of the barriers to solar energy being captured at a temperature similar to that current used in coal-fired steam power plant practice, with a resulting potential substantial improvement in power plant thermal-to-power conversion efficiency. Such a step would substantially advance the state of the art of concentrating solar power plant.

The aim of the present invention is to alleviate some of the problems described above and achieve the requirements required of an effective receiver for a Linear Fresnel solar concentrator using an inert gas transfer fluid.

SUMMARY OF THE INVENTION

The present invention therefore provides a receiver for receiving light from a solar concentrator and for outputting a heated heat transfer fluid, the receiver comprising: a solar absorber for absorbing heat from light incident on the absorber; a heat exchanger thermally coupled to the solar absorber and arranged to provide heat to a heat transfer fluid when in contact with the heat exchanger; an inlet duct disposed along a length of the receiver, and coupled to an inlet for receiving a heat transfer fluid, the inlet duct being coupled to the heat exchanger for supplying the heat exchanger with a received heat transfer fluid; an outlet duct disposed along a length of the receiver, the outlet duct being coupled to the heat exchanger for receiving a heated heat transfer fluid, and the outlet duct being coupled to an outlet for outputting the heated heat transfer fluid; wherein the heat exchanger comprises a plurality of thermally conductive fins extending across a width of the receiver between an outer edge adjacent an outer edge of the receiver and substantially a centre-line defined along the length of the receiver, and wherein the outer edge of the plurality of thermally conductive fins adjacent the outer edge of the receiver are coupled to the inlet duct for receiving a heat transfer fluid, and inner edges of the plurality of thermally conductive fins adjacent the centre-line of the receiver are coupled to the outlet duct such that a received heat transfer fluid flows from an outer edge of the receiver towards a substantially centre-line of the receiver.

The flow direction of the gas flow along the fins is from the outer edges of the receiver towards the centre line of the receiver, where the received radiant energy is most intense. This flow pattern minimises the mean temperature of the receiver and hence thermal losses from the absorber surface of the receiver. The short gas path (half the width of the receiver) enables the receiver to be designed so that the pressure drop required to maintain the gas flow rate through the receiver is sufficiently low to keep the power required for pumping the gas through the fins low enough so that it is merely a small proportion of the heat energy collected by the gas.

In embodiments, the outlet duct comprises a dividing wall along a length of the outlet duct to divide the outlet duct into first and second outlet ducts, and wherein the dividing wall is disposed substantially along the centre-line of the receiver. Preferably, the outlet duct is disposed within the inlet duct.

By separating the outlet duct into two outlet ducts, differences in illumination of the receiver (resulting in different temperature and/or velocity measurements in the output heated heat transfer fluid) can be detected, allowing a solar concentrator to be angled correctly to produce a more balanced output.

In embodiments, the heat exchanger comprises a plurality of thermally conductive short fins, each of the short fins interposed the plurality of fins and extending from the centre-line of the receiver along a portion of the width of the receiver. Since the heat is most intense at the centre-line of the receiver, the additional fins extending along a portion of the width of the receiver enable more heat to be transferred to the fluid. Preferably, the fins are substantially parallel with one another.

In embodiments, a lower portion of the fins has an arcuate form between the inner edge adjacent the centre-line of the receiver and the outer edge.

In some embodiments, the absorber layer comprises a substrate mechanically connected to the plurality of fins. Preferably, the substrate comprises a plurality of grooves, each groove being shaped to receive one of each of the plurality of fins in a mechanical connection. In embodiments, the substrate may be corrugated.

In embodiments, the receiver comprises a rear outer casing, and wherein a gap between the rear outer casing and the outlet defines the inlet.

In further embodiments, the receiver comprises an optically transparent front face for receiving light incident on the receiver, and wherein the solar absorber is arranged within the receiver to be exposed to light received by the front face.

In some embodiments, the outlet is coupled to a temperature and/or velocity sensor for detecting a temperature and/or velocity of an output heated heat transfer fluid. The inlet may also be coupled to a temperature sensor for detecting a temperature of a received heat transfer fluid.

Preferably, the heat transfer fluid is a gas such as Nitrogen.

The present invention also provides a solar concentrator system, comprising: solar concentrator means for receiving incident light and for outputting a concentrated light output; and a receiver as described above, the receiver being arranged to receive the concentrated light output, and for outputting a heated heat transfer fluid.

In such embodiments, the solar concentrator system further comprises a heat store for storing heat, the heat store being coupled to the receiver for receiving the heated heat transfer fluid and being configured to extract heat from the heated heat transfer fluid for storing.

We therefore describe a receiver for a linear Fresnel solar concentrator consisting of a gaseous, chemically inert, non-condensing, heat transfer fluid, flowing between the thermally conductive parallel fins of a heat exchanger in a direction from the outer long edges of the receivers light absorbing surface towards its long-axis centreline, the gas exiting the heat exchanger near the centreline and in a direction away from the face that is absorbing the reflected rays of concentrated direct sunlight energy.

Concentrated sunlight reflected by the mirrors of a linear Fresnel concentrator, or similar, enters through a glass window before being absorbed by an optically absorbing surface.

Creating such a surface is a known technique; it may be made as a thin, microscopically layered material or mixture of materials arranged so that it forms a solar selective absorbing surface -i.e. one that absorbs sunlight with a high efficiency, or high absorbance, but is a poor emitter of radiant energy at much longer wavelengths of electromagnetic energy.

The light entering the window may be guided by mirrors running parallel with the long axis of the receiver, to guide or even slightly concentrate further the light before it is absorbed.

The gas flows in a closed loop, through an inlet port along an inlet duct that connects to the two long edges of the array of parallel fins. An outlet duct connects to the central region of the fins where the gas leaves the heat exchanger and guides the gas from the fins to an exit port.

The fins are either made from, or coated with, a material that is soft and highly thermally conducting at the operating temperature and does not cause any embrittlement of the materials. Either copper or an aluminium or aluminium-silicon alloy coating has these characteristics. The absorber layer is attached to each fin by forming a mechanical pinch of the lower edge of each fin within in a groove in the absorber layer. The mechanical pinch onto the soft and thermally conducting material of the fin forms a thermally conductive connection between each fin and the absorber.

Both the lower edge of the fins and the absorber are formed in a low arch across the receiver and is pressed into mating abutments at each end formed or cut into each fin.

The resulting compression load created in the absorber as the assembly is heated ensures that the absorber stays mechanically and thermally engaged or connected with each and every fin, as each fin heats up to their operating temperature and then cools down. The material of the fin and the material of the absorber are made of either the same material or, if different, have coefficients of thermal expansion that are closely matched.

The hot gas duct that carries the now heated gas away from the fins is filled with a dividing plate that divides the duct longitudinally into two, substantially equal halves. In the event that the radiant energy of the incoming sunlight is not equal either side of the centre line of the divider, the side of the receiver that receives more radiation will have a higher gas temperature (assuming that the gas mass flow rate is arranged to be equal each side of this central divider). A temperature difference will then result in the gas streams that flow either side of the central divider. At the exit port a temperature probe and a velocity sensor, such as a pitot-tube, in each gas stream either side of the divider, measures the exit gas temperature and the exit gas velocity. A further temperature probe measures the temperature of the gas entering the receiver through the inlet port.

From these five measurements (inlet temperature, two outlet temperatures and two outlet velocities) an approximate estimate can be made of the heat being received by each half of the receiver, either side of the divider plate.

Any difference in the product of temperature rise times velocity ((To-Ti) x V) in the gas streams will indicate that the receiver is not being equally illuminated either side of the central divider. This difference can then be used by the software of an automatic controller to align the location of the concentrated sunlight coming into the receiver by way of adjusting or trimming the focus position and achieve balanced illumination of the two sides of the receiver. In a typical linear Fresnel solar concentrator the focus is formed by a group of mirrors whose angle is driven by an electrical actuator, whose position is determined by this automatic controller.

This balanced illumination will generally correspond to the most efficient operating point for the receiver. Were one side of the receiver to be more illuminated than another side, then one side would run hotter, resulting in an overall greater heat loss from the absorber. This is because the heat loss from a radiant object increases with the fourth power of the absolute temperature. So, if half of the receiver is running hotter, and the other half is running correspondingly cooler, then the overall radiant heat loss from the absorber would be greater than if both sides of the receiver were operating at the same temperature.

Typical practice in a concentrated solar system is to guide the mirrors by either measuring the optical intensity of the focal band at the edges of the receiver (steering the mirrors to minimise any difference in these signals), or by calculating the sun angle from the time of day and the calendar and hence set the required mirror angle.

The ability to measure the income gas temperature and the outgoing gas temperatures and velocities either side of the central divider at the exit port allows either control method be improved so that the primary mirrors reflect the light accurately towards the centreline of the receiver with a minimum of offset.

The gas flowing to transfer heat from the fins should be an inert, low cost, readily replaceable gas that does not corrode either the metal components or degrade the selective coating. Nitrogen is the preferred candidate, as it is readily extracted from the air and purified and is inert at the temperatures at which a single axis solar concentrator can efficiently operate up to 50020.

This configuration provides several advantages that substantially improve the cost effectiveness of the solar concentrator power plant.

In most concentrating solar plants the flow of fluid through the absorber is along the axis of the receiver. Therefore the average temperature of the receiver surface is approximately the arithmetic mean of the inlet and outlet temperatures of the heat transfer fluid. In this receiver the mean temperature of the absorber is much closer to the inlet temperature, i.e. the receiver on average runs cooler. This is because the heat transfer fluid flow is from the edges towards the centre line. The intensity of sunlight being absorbed by the receiver is high near the centre line and rapidly falls nearly to zero at the edges of the absorber. Therefore most of the temperature rise of the fluid occurs in the central region; little temperature rise occurs nearer the outer edges of the receiver. This will result in a lower heat loss for a given operating temperature, or a higher working temperature for a given heat loss.

The cross-wise flow of gas along the heat exchanger fins of the receiver is a short length with a large cross-sectional area. This geometry permits the flow of gas without excessive or uneconomic pumping loss, an essential requirement when dealing with a low density fluid such as an inert gas at atmospheric pressure and high temperatures.

The inert gas is available to transfer its heat into a packed bed heat store without the need for any further heat exchangers, minimising the temperature difference between the receiver operating temperature and the maximum thermal store temperature. This maximises the power output potential from the heat captured by the solar concentrator.

Any leaks in the system of ducts and gas passages do not result in any environmental contamination, since any of the common inert gases that might be used, such as nitrogen or argon, are common constituents of clean air.

Finally, the temperature limit is now only set by efficiency and metallurgical considerations, not the chemical degradation of the heat transfer fluid.

LIST OF FIGURES

An example of the solar concentrator receiver embodying the invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a perspective view of the linear Fresnel concentrator, showing the location of the receiver with respect to the reflectors. (The reflectors shown in this view are the subject of another patent application); Figure 2 is a section through the receiver showing the fins, the glass, the inlet duct, the outlet duct, the divider plate and the absorber surface; Figure 3 shows one configuration of absorber and fin arrangement. Only a few of the fins are shown in the figure; Figure 4 shows another configuration of absorber and fin arrangement. Only a few of the fins are shown in the figure; Figure 5 shows the abutment plate and its arrangement within the receiver; Figure 6 shows a cutaway through the receiver, showing the parallel fins and the gas inlet and outlets for the gas flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A linear Fresnel concentrator is shown in the Figure 1 (133) which have a number of long primary mirrors (132) with parallel major axes reflecting sunlight into a receiver (131), the receiver having its major axis also parallel to the major axes of the primary mirrors.

The clear glass cover (104) shown in Figure 2 (and 128 in Figure 6) admits the concentrated sunlight which is absorbed by a solar selective layer or coating (101 of Figure 2, 113 of Figure 3, 123 of Figure 5 and 130 of Figure 6). An inert gas at approximately atmospheric pressure flows along the inlet duct (111 of Figure 2) and into the spaces between parallel fins (106) shown in Figure 2 (and 119 in Figure Sand 126 of Figure 6). The gas then is pumped between the fins (in the region between the insulation (1 08 of Figure 2) that forms the casing of the inlet duct (111) and the insulation that forms the casing of the outlet duct (109). The gas is constrained by the * absorbers at the base of the fins (112 in Figure 3, for example), by the fins themselves * (124 in Figure 5) and by the lining of the outlet duct (122 in Figure 5). Gas flowing from any one side enters the outlet duct on the same side of the central divider (103 of Figure 2, 120 of Figure 5). These two gas streams then flow along the outlet duct (110) to a common outlet port. * *a

a C. * * .* * * a The Figures 3 and 4 show two different configurations for the absorbers at the base of the fins, in section. Figure 3 shows the absorber as an extruded grooved rectangular bar that is crimped onto each fin along the fins lower edge (just two of the many fins are shown). Figure 4 gives an example of a corrugated sheet, formed to similarly crimp and grip each fin (again, only two of the fins are shown). In either example, the fins absorbers are arched, as shown in figure 6 (130) so that, when the sunlight warms the absorber, the temperature rise in the absorber cause it to increase in length -i.e. is made of a material with has a positive thermal expansion coefficient-and the absorber then presses onto abutments made within the tins via a spreader plate (105 in Figure 2 and 127 in Figure 6), which in turn presses the absorber firmly into contact with the mating lower edge of each fin, ensuring a firm mechanical and thermal contact. By this means, the absorber may be arranged to mechanically and thermally connect to each fin, without the need for any welding or soldering zone to take place in the illuminated, which would destroy the solar selective coating (113).

A casing (107 in Figure 2) provides the structure strength for the receiver, sealing of the inert gas (in conjunction with the glass cover (104) and a weatherproof containment for the receiver.

The central region of the receiver is generally illuminated at a higher intensity than the edges. Consequently the heat transfer needs to be morecapable in this region, i.e. the flow of heat through the fins from the absorber surface and into the gas needs to result in a lower temperature difference for a given intensity of sunlight in this central region, in order to maximise the cooling effect of the gas for a given pumping power and pressure drop of the gas through the heat exchange fins. This can be readily achieved : * by placing a body fins closer together in the central region, in a variant of the receiver * * with the central region of the receiver being configured with fins closer together. Near the central divider, there are fins that run all the way across the receiver. lnterpos!d between each of these are shorter fins that the gas must flow past in this central region. All of the fins are mechanically connected to the absorber so that they all conduct heat generated by the absorber by the action of incoming solar radiant energy.

* ::* Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments *s*...

* 35 and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention. Any of the embodiments described hereinabove can be used in any combination.

Claims

CLAIMS: 1. A receiver for receiving light from a solar concentrator and for outputting a heated heat transfer fluid, the receiver comprising: a solar absorber for absorbing heat from light incident on the absorber; a heat exchanger thermally coupled to the solar absorber and arranged to provide heat to a heat transfer fluid when in contact with the heat exchanger; an inlet duct disposed along a length of the receiver, and coupled to an inlet for receiving a heat transfer fluid, the inlet duct being coupled to the heat exchanger for supplying the heat exchanger with a received heat transfer fluid; an outlet duct disposed along a length of the receiver, the outlet duct being coupled to the heat exchanger for receiving a heated heat transfer fluid, and the outlet duct being coupled to an outlet for outputting the heated heat transfer fluid; wherein the heat exchanger comprises a plurality of thermally conductive fins extending across a width of the receiver between an outer edge adjacent an outer edge of the receiver and substantially a centre-line defined along the length of the receiver, and wherein the outer edge of the plurality of thermally conductive fins adjacent the outer edge of the receiver are coupled to the inlet duct for receiving a heat transfer fluid, and inner edges of the plurality of thermally conductive fins adjacent the centre-line of the receiver are coupled to the outlet duct such that a received heat transfer fluid flows from an outer edge of the receiver towards a substantially centre-line of the receiver.
2. A receiver according to claim 1, wherein the outlet duct comprises a dividing wall along a length of the outlet duct to divide the outlet duct into first and second outlet ducts, and wherein the dividing wall is disposed substantially along the centre-line of the receiver.
3. A receiver according to claims 1 or 2, wherein the outlet duct is disposed within the inlet duct.
4. A receiver according to claim 1, 2 or 3, wherein the heat exchanger comprises a plurality of thermally conductive short fins, each of the short fins interposed the plurality of fins and extending from the centre-line of the receiver along a portion of the width of the receiver.
5. A receiver according to any proceeding claim, wherein the tins are substantially parallel with one another.
6. A receiver according to any proceeding claim, wherein a lower portion of the fins has an arcuate form between the inner edge adjacent the centre-line of the receiver and the outer edge.
7. A receiver according to any proceeding claim, wherein the absorber layer comprises a substrate mechanically connected to the plurality of fins.
8. A receiver according to claim 7, wherein the substrate comprises a plurality of grooves, each groove being shaped to receive one of each of the plurality of fins in a mechanical connection.
9. A receiver according to claim 7 or 8, wherein the substrate is corrugated.
10. A receiver according to any proceeding claim, comprising a rear outer casing, and wherein a gap between the rear outer casing and the outlet defines the inlet.
11. A receiver according to any proceeding claim, comprising an optically transparent front face for receiving light incident on the receiver, and wherein the solar absorber is arranged within the receiver to be exposed to light received by the front face.
12. A receiver according to any proceeding claim, wherein the outlet is coupled to a temperature and/or velocity sensor for detecting a temperature and/or velocity of an output heated heat transfer fluid.
13. A receiver according to any proceeding claim, wherein the inlet is coupled to a temperature sensor for detecting a temperature of a received heat transfer fluid.
14. A receiver according to any proceeding claim, wherein the heat transfer fluid is a gas.
15. A receiver according to claim 14, wherein the gas is Nitrogen.
16. A solar concentrator system, comprising: solar concentrator means for receiving incident light and for outputting a concentrated light output; and a receiver according to any one of claims 1 to 15, the receiver being arranged to receive the concentrated light output, and for outputting a heated heat transfer fluid.
17. A solar concentrator system according to claim 16, comprising a heat store for storing heat, the heat store being coupled to the receiver for receiving the heated heat transfer fluid and being configured to extract heat from the heated heat transfer fluid for storing.
18. A receiver or solar concentrator system substantially as herein described with reference to the accompanying figures.