GB2365116A

GB2365116A - A hybrid photovoltaic/thermal system

Info

Publication number: GB2365116A
Application number: GB0013019A
Authority: GB
Inventors: Christopher John Verney
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-04-25
Filing date: 2000-05-31
Publication date: 2002-02-13
Anticipated expiration: 2020-05-31
Also published as: GB0009824D0; GB0013019D0; GB2365116B

Abstract

A hybrid photovoltaic/thermal system comprises an array of inter-connected individual photovoltaic cells 106 attached to a substrate 107 having a high thermal conductivity with means for cooling the said substrate 107 and means for varying the orientation of the substrate 107 to maximise the flux of solar radiation incident upon the photovoltaic cells 106. The substrate 107 may be made from copper or aluminum. The means for cooling the substrate 107 comprises a number of tubes 108 in thermal contact with the substrate 107 and means for circulating a coolant though the said tubes 108. The cooling means may consist of Peltier devices. The means for varying the orientation of the photovoltaic cells 106 comprises a solar tracking unit and means responsive to signals generated by the solar tracking unit to operate a linkage 112 adapted to vary the orientation of the photovoltaic cells. The solar tracking unit may consist of two arrays of photovoltaic cells of identical characteristics which are positioned back-to-back on a common axle. The electric outputs from the two arrays of photovoltaic cells are connected to a difference analyser which operates an electric motor which rotates the two arrays of photovoltaic cells to a position where a null point is reached. This position is then used to orientate the system.

Description

<Desc/Clms Page number 1> HYBRID SOLAR ENERGY UTILISATION SYSTEM The present invention relates to hybrid solar energy utilisation systems, that is to say solar energy utilisation systems including a component adapted to produce thermal energy and a component adapted to produce electrical energy by means of the photo-voltaic effect, and specifically, to such a system including means for maximising the output of electric energy therefrom.

A conventional thermal solar energy panel consists of a, usually flat, hollow panel through which a heat transfer medium, usually water, can be circulated. One major surface of the panel is transparent with a non reflecting surface, or is blackened to increase the absorption of solar energy and usually a number of such panels are mounted on the roof of a building, preferably with a north-south orientation or as near to that as can be achieved, and plumbed into the hot water system of the building concerned. Photo-voltaic solar cell panels consist of arrays of elements made of a photovoltaic material such as silicon or germanium, connected in series. A number of such panels may be connected in series, parallel, or seriesparallel arrangements depending on whether the main consideration is the generation of relatively high voltages or the supply of electric current. It is known to mount the photo-voltaic cell panels on rotatable mountings so that the orientation of the panels can be varied so as to maximise the overall energy density of the solar radiation incident on the solar cell panels, and hence the electrical output of the solar cell panel. It is known also, that the electrical conversion efficiency of photo-voltaic cells is an inverse function of the temperature of the photo-voltaic material used in the cells, ie the cooler the temperature of the cells, the higher the output efficiency.

and so systems for the cooling of the photo-voltaic material used in the cells may be provided.

It is an object of the present invention to provide an improved hybrid solar energy utilisation system.

According to the present invention there is provided a hybrid solar energy utilisation of the type described wherein the component adapted to produce electrical energy comprises an array of interconnected individual photovoltaic cells attached to a substrate having a relatively high thermal conductivity, means for cooling the said substrate and means for varying the orientation of the substrate to maximise the flux of the solar radiation incident upon the photo-voltaic cells.

Suitable materials for the substrates are copper or aluminium. Alternatively, the substrates can be made of combinations of metals so arranged that the Peltier effect can be used to cool the photo-voltaic cells. Although the means for varying the orientation of the substrates may be mechanical, or electromechanical in nature, a preferred substrate drive system includes a subsidiary photo-voltaic solar tracking device, the output from which is used to control the action of an electric motor adapted to alter the orientation of the substrates to follow the action of the solar tracking device.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a schematic plan view of an embodiment of the invention,

and Figure 2 is a schematic view of the drive mechanism for altering the orientation of the panels of photo-voltaic solar cells shown in Figure 1.

Referring to the drawings, a hybrid thermal and photo-voltaic solar energy utilisation system consists of a panel 100 made up of number of rectangular hollow flat units 101, one major surface of each one of which is blackened to absorb solar radiation, or transparent with a non-reflecting surface so that solar radiation can enter the unit 101 directly. The units 101 are connected in parallel to water inlet and outlet manifolds 102, 103, respectively, and thence to the hot water supply and/or central heating system of a building (not shown in the drawing) in the normal way.

A second photo-voltaic panel 104, not necessarily associated with the panel 100, consists of a number of units 105 each of which consists of a number of standard photo-voltaic cells 106 mounted on a substrate 107 made of a material with a high thermal conductivity, such as copper. The photovoltaic cells 106 on each substrate 107 are connected in series, and the units 105 are connected in parallel via blocking diodes, again in the conventional way or by use of a D/C-D/C converter to obtain a required voltage. Attached axially to the rear of each unit 105 is a straight tube 108 made of a metal of high thermal conductivity, such as copper. The tubes 108 are a working fit on other copper tubes 109 which are connected in parallel to inlet and outlet manifolds 110 and 111, respectively, and thence to a coolant circulating system. The working fit between the tubes 108, 109 enables the units 105 to be rotated about the tubes 108, while maintaining a reasonable thermal contact between the tubes 108 and 109, and hence the substrates 107 of the

units 105. The thermal contact between the tubes 108 and 109 can be improved by providing the ends of the tubes 108 with rotatable seals and filling the space so enclosed with a heat transfer medium..

The units 105 are joined at one end by a linkage 112 which is connected to a reversible electric motor drive unit 113 such that the units 105 can be moved in concert through an arc of some 120 degrees. The drive unit 113 is connected to a subsidiary solar cell sun tracking unit 114 via a controller 115. A number of suitable solar cell powered sun tracking units exist and therefore the sun tracking unit 114 is not described in detail. The output signal from the sun tracking unit 114 is utilised by the controller 115 to cause the units 105 to be so positioned as to maximise the solar flux upon the photo-voltaic cells 106.

The actuating mechanism for the units 105 is shown in more detail in Figure 2, which shows the theoretical manner of operation of the linkage 112, but could be altered or improved. The linkage 112 consists of a flat bar 116 in which there is a series of holes 117. The appropriate ends of the tubes 108 are fitted with pegs 118 that engage with the holes 117 in the bar 116. The bar 116 has a rack 119 formed at one end which engages with a pinion 120 on the end of an electric motor 121 which is controlled by the electric motor drive unit 113. As the bar 116 is moved by the motor 121, the interaction between the holes 117 in the bar 116 and the pegs 118 causes the substrates 106 to be rotated accordingly. The bar 116 or one of the substrates 107 can be fitted with a limit contact which engages when the angle of the substrates corresponds to the declination of the sun at about sunset for the location of the equipment and causes the motor controller 115 to rotate the substrates 106 in the reverse direction to that travelled during

the day so as to cause the orientation of the photo-voltaic cells 106 to be appropriate for sunrise. An alternative option would be to include a photoelectric cell to operate a spring-return mechanism in order to achieve the above function at or about dusk (more applicable to UK and low sun hours countries). The inlet and outlet manifolds 110 and 111 can be connected to a heat exchanger and cooling unit, or in a simpler system they can be connected via a pump to a reservoir, not shown in the drawing. During the night, the temperature of the water circulating through the system will fall, providing a reservoir of cooler water which can then be circulated through the cooling tubes 108 during the day, cooling the photo-voltaic cells 106. The store of cool water can be increased by connecting the thermal panels 100 to the cool water reservoir once the temperature of the water circulating through the thermal panels 108 has dropped to a predetermined value (normally at nightime periods). Alternatively, the photo-voltaic cells 106 can be arranged to be cooled by a Peltier effect device, although this will reduce the overall efficiency of the system as power has to be supplied to operate them. If this system is adopted, then the substrates 107 have to be made of two different metal strips which are electrically isolated except for a junction region under each of the photo-voltaic cells 106. A Peltier effect cooling system could be used in conjunction with a water-cooling system such as that described, or on its own. A more sophisticated sun-tracking system, which is not illustrated has two arrays of photo-voltaic cells of normally identical characteristics which are positioned back-to-back on a common axle. The electrical outputs from the two arrays of photo-voltaic cells are connected to a difference analyser which operates an electric motor, which rotates the two arrays of photovoltaic cells until a null point is reached. At this position the two arrays of

photo-voltaic cells are oriented parallel with the sun's rays. This orientation is sensed and a corresponding signal is applied to the drive motor controller 115 to cause the electric motor 121 and substrate 106 drive linkage 112 to position the substrates 106 with the photo-voltaic cells 106 uppermost and perpendicular to the plane of the two arrays of photo-voltaic cells in the sun-tracker. The system automatically tracks the sun during the day until a westerly position is reached just before sunset when a limit stop is reached. This prevents the underneath array of photo-voltaic cells being completely obscured the following morning. At the following dawn there is a large out- of-balance signal which automatically causes the substrates 106 to be returned to their start position and looking in an easterly direction.

Claims

Claims 1. One hybrid solar energy utilisation system of the type hereinbefore described wherein the components adapted to produce electrical energy comprises an array of interconnected individual photovoltaic cells attached to a substrate having a relatively high thermal conductivity with means for cooling the said substrate and mean for varying the orientation of the substrate to maximise the flux of the solar radiation incident upon the photovoltaic cells.
2. One hybrid solar energy utilisation system according to claim 1 wherein the substrate is made of copper or aluminium.
3. One hybrid solar energy utilisation system according to claim 1 or claim 2 wherein the means for cooling the substrate comprises a number of tubes in thermal contact with the substrate and means for circulating a coolant through the said tubes.
4. One hybrid solar energy utilisation system according to claim 1 or claim 2 wherein the means for cooling the substrate comprises a number of lengths of dissimilar metals attached to the substrate and adapted to provide cooling by the Peltier effect and means for supplying electrical energy to the lengths of dissimilar metals.
5. One hybrid solar energy utilisation system according to any preceding claim wherein cells can be varied in concert and there is provided means for varying the orientation of the photovoltaic cells to follow the motion of the sun and maintain the orientation of the photovoltaic cells with respect to the sun at an optimum value.
6. One hybrid solar energy utilisation system according to claim 5 wherein there is included means for returning the array of solar cells to an eastward facing orientation after a westward orientation corresponding to when local sunset has been reached.
7. One hybrid solar energy utilisation system according to claim 5 or claim 6 wherein the means for varying the orientation of the photovoltaic cells comprises a solar tracking unit and means responsive to signals generated by the solar tracking unit to operate a linkage adapted to vary the orientation of the photovoltaic cells.
8. One hybrid solar energy utilisation system according to claim 7 wherein the solar tracking unit comprises two arrays of photovoltaic cells of nominally identical electrical characteristics which are mounted back to back on a common axle, a signal difference analyser connected to the arrays of photovoltaic cells, an electric motor connected to the signal difference analyser and adapted to rotate the two arrays of photovoltaic cells until the two arrays of photovoltaic cells are orientated with their surfaces parallel to the suns rays means for determining the orientation of the photovoltaic cells in the solar tracking unit and providing output signals related thereto with means for responding to the output signals from the solar tracking unit to orient, the array of photovoltaic cells in the hybrid solar energy utilisation system with their active surfaces perpendicular to the surfaces of the photovoltaic cells in the solar tracking unit and facing the sun.
9. One hybrid solar energy utilisation system according to claim 8 wherein the solar tracking unit is adapted to respond to the occurrence of sunset and position the photovoltaic cells of the array of the hybrid solar energy utilisation system to return to an easterly location ready for the following day.
10. One hybrid solar energy utilisation system substantially as hereinbefore described and with reference to the drawing submitted.