GB2504802A

GB2504802A - Cooling Photovoltaic Systems Using Capillary Fibres

Info

Publication number: GB2504802A
Application number: GB1305934.0A
Authority: GB
Inventors: Gancho Mitev
Original assignee: DIMITAR MITEV; MULTINAT EDUCATIONAL CT OF BIRMINGHAM
Current assignee: DIMITAR MITEV; MULTINAT EDUCATIONAL CT OF BIRMINGHAM
Priority date: 2012-06-22
Filing date: 2013-04-02
Publication date: 2014-02-12
Also published as: BG111244A; GB201305934D0

Abstract

A system for cooling photovoltaic cells 1 including a reservoir 4 which supplies water to capillary fibres 2 behind the PV cells. The moisture at the capillary fibres reduces the temperature of the PV cell due to evaporation. The reservoir may be located above the PV cells and may be refilled periodically. The capillary fibres may be supplied with water using nozzles to spray water onto them; an anti-drop valve provides permanent pressure in the system. The water supply may be controlled by a computerized system. The temperature surrounding the PV cell may be measured using a wet thermometer.

Description

Title: System (apparatus) and method for increasing the efficiency of photovoltaic systems through controlling the working temperature of the modules.

Field

The invention relates to the sphere of the photovoltaic (PV) system for direct transformation of the solar energy into electrical.

Background

It is known that the efficiency is main indicator of a solar cell. It is established that it is mostly dependent on the working temperature of the cell and the inclination of the photovoltaic panel towards the solar rays. Tracking the sun position is being solved with mono-axial and two-axial tracking systems. But heating during operation aggravates the transformation of solar into electrical energy on average by -0.4%/°C (temperature coefficient).

State of the Art The following patent solutions are known: USA: * 4558634 December 1985 Oshiro et al. * 5505788 April 1996 Dinwoodie * 5746839 May 1988 Dinwoodie * 6061978 May 2000 Dinwoodie et al. * 6570084 May 2003 Dinwoodie * 6750392 Photovoltaic cooling system * 7297866 Ventilated photovoltaic module frame U.S. Pat No.7297866 describes method of cooling the photovoltaic modules by means of guiding the air flow through special openings in the mounting frame.

Statement of Invention

However, none of the aforementioned inventions includes the system (apparatus) or the method outlined below. In short, that is the method of controlling the working temperature of photovoltaic modules through evaporation of water from the surface of the modules via a large number of capillary fibres.

A detailed description of the invention will now be presented by referring to the accompanying drawings: * Figure 1 -first possible installation of the system (apparatus) for increasing the efficiency of photovoltaic systems through controlling the working temperature of the modules based on an drop irrigation system (Claim 6) * Figure 2 -second possible installation of the system (apparatus) for increasing the efficiency of photovoltaic systems through controlling the working temperature of the modules based on system forwater dispersion (claims 7 and 8).

Detailed Description

The primary aim of the invention (both the apparatus and the method) is increasing the efficiency of photovoltaic systems.

The invention achieves this aim by evaporating minimum quantities of water (moisture) from the heated surface of the photovoltaic modules. Thus they are being cooled down to the temperature of the ambient (surrounding) air measured by a "wet thermometer". The "wet thermometer" temperature of the ambient (surrounding) air depends on the temperature of the ambient air, its relative humidity, its rate and speed of movement. In any case, however, the temperature "according to a wet thermometer" is lower than the temperature of the ambient air. Additionally, it is significantly lower than 60-70°C -the working temperature of the photovoltaic modules at noon on a clear summer day.

The moisture is provided through many capillary fibres, attached (stuck, hardly pressed or incorporated) to the surface of the module. The system (apparatus) and method rely on removing heat from the photovoltaic modules (respectively cooling them) and using it to evaporate the moisture. It uses the "specific heat of evaporation" of minimum quantities of water for cooling purposes. Specific heat of evaporation is a physical value -the energy (heat) required to transform a given quantity of a substance from a liquid into a gas at a given pressure (often atmospheric pressure). It is marked with the letter R, and the formula is r-Q/m (i.e. specific heat of evaporation is the energy (heat) required to evaporate liquid with a mass of m=lkg under constant temperature. For the water this energy (heat) is 2.26*106 JIkg.

To ensure an even distribution of moisture over the entire surface of the photovoltaic modules the apparatus employs a dense net of capillary fibres. Water is supplied to the net of capillary fibres either through a drop irrigation system mounted at the top (higher altitude) end of the photovoltaic module or through immersing their ends in an appropriate water reservoir.

Alternatively, water supply to the capillary fibres net is provided by dispersing nozzles (spraying) located behind the photovoltaic module. They are switched on periodically for a short duration in order to irrigate (spray) the net of capillary fibres and the heated back surface of the modules. This action is automatically controlled by a computerised module that Advantages This invention delivers a number of considerable advantages over any of the existing solutions to the problem of low efficiency of photovoltaic modules. The invention: -enables the photovoltaic panels to maintain their working temperature within the limits recommended by the manufacturer for reaching highest efficiency; -ensures efficiency of the photovoltaic modules that is close to the one under laboratory conditions due its specific design and construction; -is significantly more efficient than any alternative "water cooling" solutions (explanation follows). Standard "water cooling" solutions heat up water in order to remove heat (cool down) from photovoltaic modules. This invention evaporates water to achieve the same result. The difference in both actions (heating up and evaporating) is what makes this invention more efficient. Water cooling systems remove 10 kcal of heat from photovoltaic modules heating up 1 litre of water by 10°C, while this invention removes 539 kcal of heat from photovoltaic modules by evaporating the same amount of water. Consequently, this invention is 53.9 times more efficient than the standard "water cooling" solution.

-is significantly more economical than any alternative "water cooling" solution. Since this invention relies on the "specific heat of evaporation" (as described in the above point) the overall amount water required to achieve the same result is decreased 53.9 times. As a result, the costs of water (and supplying water) are significantly smaller than the income from the increased yield of electricity. Therefore, this makes our solution not only applicable but actually profitable in large photovoltaic power stations; -is high reliable and easily maintainable (due to the construction simplicity); -is accessible for the masses (individual homes, houses, apartment blocks) due to its low price; -can be mounted onto photovoltaic modules that are already installed and working.

Examples and versions of the Invention

Example I

As shown in Figure 1, a large number of capillary fibres (2) are used to transfer and distribute moisture over the entire surface of the photovoltaic module (1). In this example the fibres are firmly pressed against the heated surface of the module by a net (3). This provides the thermal contact necessary for evaporation to occur.

Additionally, this increases the surface of evaporation. The capillary effect ensures constant and evenly distributed moisture over the surface of the module. The capillary fibres are supplied by water through a drop irrigation system with a water reservoir (4) and compensated irrigation emitters with a fixed outflow of 1, 2, 4, 6 or 8 I/h.

Water supply to the reservoir (4) is controlled by an electro-mechanical switch or an electronic control panel, connected with temperature controller that do not represent part of this invention and are not shown.

Example 2

As shown in Figure 2, this version of the invention utilised dispersing nozzles, combined with anti-drop valves or low flow foggers (5), differential thermostat with sensors (7) mounted on the heated surface, a pressure pump (6) and the necessary tubing under the modules. The pump switches on every 10 minutes for 7 to 10 seconds in order to irrigate the capillary fibres and the heated surface of the modules. The anti-drop valves ensure constant pressure in the water supply system so that irrigation begins immediately when the pump switches on.

The pump is controlled by a computerised unit that does not represent part of the invention and is not shown.

Application of the invention This invention can be incorporated in photovoltaic modules during their production.

Alternatively, it can be used as an "add-on" for already installed and working photovoltaic modules and power stations.

The only requirement for the invention to function is the presence of water in the reservoir. Fortunately, this can be easily provided due to its minimal consumption -less than 10 I/h per 1 kW capacity installed.

With switched oft position of the system, the valves are closed and the photoelectric station does operate without controlling the temperature of the modules.

Upon switching on, the back surface of the module is being sprayed, begins evaporating and in this way their temperature is being lowered.

The specialist can easily accept many modifications of the preferred exemplary performance of the invention, described in details above. That is why the applicant intends to be engaged only within the scope of the applied pretensions.

Claims

Claims 1. A system (apparatus) for increasing the efficiency of photovoltaic systems through controlling the working temperature of the modules by water evaporation comprising a water reservoir, tube connections between the elements, and a large number of capillary fibres.
2. A system (apparatus) according to claim 1, in which the large number of capillary fibres is attached to the back surface of the photovoltaic modules.
3. A system (apparatus) according to Claim 1 and Claim 2, in which the large number of capillary fibres provides constant and evenly spread moisture on the back surface of the photovoltaic modules.
4. A system (apparatus) according to Claim 3, in which the moisture on the back of the photovoltaic modules is used to control the working temperature of the photovoltaic modules, thus increasing their efficiency.
5. A system (apparatus) according to Claim 3, in which the moisture on the back of the photovoltaic modules is used to adjust the working temperature of the photovoltaic modules to its optimum level, thus increasing their efficiency.
6. A system (apparatus) according to Claim 3, in which the water necessary for moisturising the capillary fibres is delivered to them through a system for drop irrigation that is being periodically filled with water (figure 1).
7. A system (apparatus) according to Claim 3, in which the water necessary for moisturising the capillary fibres is delivered to them through a system for water dispersion comprising anti-drop valves providing permanent pressure in the system, the necessary water supply and sewerage fittings, dispersing nozzles, a differential thermostat, and a pressure pump (figure 2).
8. A system (apparatus) according to Claim 3 and Claim 7, in which the frequency and duration of supplying water to the capillary fibres by the dispersing nozzles is automatically controlled by a computerised module depending on the ratio between the time required for water to evaporate under current conditions and the actual water supplying time.
9. A method for increasing the efficiency of the photovoltaic systems through controlling the working temperature of the modules.
1O.A method according to Claim 9, in which the control of the working temperature of photovoltaic modules is achieved by water evaporation from the heated surface of the modules in order to consistently keep their temperature the same as the one of the surrounding air.
11.A method according to Claim 9 and Claim 10, in which the temperature of the surrounding air is measured by a "wet thermometer".
12. A method according to Claim 9 and Claim 10, in which the water evaporation from the surface of the photovoltaic modules occurs through a large number of capillary fibres attached to the surface of the module.Amendments to the claims have been filed as follows Claims 1. A system (apparatus) for increasing the efficiency of photovoltaic systems through cooling the photovoltaic modules down to the temperature of the surrounding air, encompassing a water reservoir and tube connections to the photovoltaic modules, characterized by the fact that it evaporates water from the sweaty back surface of the modules without any chambers, capillary fibers or other tubes.2. A system (apparatus) according to Claimi, characterized by the fact that the water supplied to the photovoltaic modules is not recuperated or restored in any way.3. A system (apparatus) according to Claim 1, characterized by a layer of felt or other woven or non-woven textile (synthetic or natural) that is stuck, pressed or attached to the back surface of the photovoltaic modules.4. A system (apparatus) according to Claim 3, characterized by the fact that the layer of felt or other woven or non-woven textile (synthetic or natural) that is stuck, pressed or attached to the back surface of the photovoltaic modules, is r maintained constantly sweaty.5. A method for increasing the efficiency of the photovoltaic systems through reducing their working temperature by an uncontrolled evaporation of water from the sweaty back surface of the photovoltaic modules