System and method for cooling photovoltaic cells

Abstract

A cooling system for PV cells includes an evaporator configured to thermally contact the PV cells and transfer heat generated thereby to coolant in the evaporator, a condenser for receiving vaporized coolant from the evaporator and condensing the coolant to a liquid state, tubing connecting the evaporator, and the condenser in a circuit, a compressor arranged in the circuit for pumping coolant therethrough in a coolant flow direction, an active charge control apparatus arranged in the circuit between, in the coolant flow direction, the evaporator and the condenser, and a liquid flow control apparatus arranged in the circuit between, in the coolant flow direction, the condenser and the evaporator. The active charge control apparatus and the liquid flow apparatus cooperate to maintain the evaporator completely wetted by coolant and prevent coolant in the liquid state from leaving the evaporator.

1 . A cooling system for photovoltaic (PV) cells comprising:
 an evaporator configured to thermally contact the PV cells and transfer heat generated thereby to coolant in the evaporator;   a condenser for receiving hot coolant from the evaporator and extracting heat therefrom, coolant leaving the condenser in the liquid state;   conduits connecting the evaporator, and the condenser in a circuit;   a compressor arranged in the circuit for pumping coolant therethrough in a coolant flow direction;   an active charge control apparatus arranged in the circuit between, in the coolant flow direction, the evaporator and the condenser; and   a liquid flow control apparatus arranged in the circuit between, in the coolant flow direction, the condenser and the evaporator;   wherein the active charge control apparatus and the liquid flow apparatus cooperate to maintain the evaporator completely wetted by coolant and prevent coolant in the liquid state from leaving the evaporator.   
     
     
         2 . The system of  claim 1  wherein one wall of the evaporator is also a support member for the PV cells, placing the evaporator in direct thermal contact with the PV cells. 
     
     
         3 . The system of  claim 1  wherein the liquid flow control apparatus includes:
 a cylinder; and 
 a float arranged in the cylinder; 
 wherein the cylinder fills with liquid to a height determined by the amount of vaporized coolant arriving from the condenser, thereby altering a height of the float, and the height of the float determining the rate of liquid flow through the liquid flow control apparatus, and working in concert with the active charge control apparatus holds the amount of subcooling in the condenser to approximately zero, which ensures that all non-circulating liquid coolant in the system is stored in the active charge control apparatus, with the result that zero superheat is maintained in the evaporator. 
 
     
     
         4 . The system of  claim 1 , wherein the liquid flow control apparatus includes:
 an inlet tube;   an outlet tube;   an outer tube surrounding the outlet tube;   a sealed cavity containing a controlling fluid, the cavity being formed by a dome and an impervious flexible diaphragm, said diaphragm being subjected to the pressure and temperature of the incoming controlled fluid from the condenser against its underside, and said diaphragm being subjected to the temperature and pressure of the controlling fluid on its top side, such that the diaphragm responds to the temperature and pressure of the controlled fluid to flex the diaphragm upward to open the valve when there is excess subcooling of the controlled fluid, with result that subcooling of the liquid from the condenser is held within a predetermined range and the LFC apparatus cooperates with the ACC apparatus to prevent superheat in the evaporator.   
     
     
         5 . The system of  claim 4 , wherein the predetermined range is zero to eight degrees Fahrenheit, thus cooperating with the active charge control to prevent superheat in the evaporator, and therefore uniform cooling of the PV cells. 
     
     
         6 . The system of  claim 1 , wherein the evaporator includes serpentine tubing thermally bonded to a structural member which is in thermal contact with the PV cells. 
     
     
         7 . The system of  claim 1 , wherein the evaporator includes corrugated metallic panels joined to one of a flat metal panel or another corrugated metallic panel to form refrigerant passages in thermal contact with the PV cells. 
     
     
         8 . A method for cooling photovoltaic (PV) cells to increase their efficiency, and for capturing the waste heat from the PV cells, the method comprising:
 placing an evaporator in thermal contact with the PV cells; and   circulating coolant through the evaporator to remove waste heat therefrom;   wherein circulating coolant through the evaporator includes maintaining the evaporator in a wetted state with substantially no coolant superheating.   
     
     
         9 . The method of  claim 8 , wherein maintaining the evaporator in a wetted state with no coolant superheating includes minimizing subcooling in coolant supplied to the evaporator with a liquid flow control apparatus arranged between a condenser an evaporator inlet. 
     
     
         10 . The method of  claim 9 , wherein maintaining the evaporator in a wetted state with no coolant superheating further includes preventing superheating with an active charge control apparatus arrange between an evaporator outlet and a compressor inlet. 
     
     
         11 . A PV cell cooling system comprising a refrigerant circuit, including a compressor, a condenser, a liquid flow control, an evaporator, and an active charge control, wherein the evaporator is in thermal contact with Photovoltaic cells for cooling the PV cells to achieve at least one of, eliminating the loss of efficiency that results from overheating of the PV cells, or reducing the temperature of the PV cells to a temperature below the ambient air temperature, to further increase efficiency and to increase the electrical output of the PV cells. 
     
     
         12 . The PV cooling system of  claim 11 , wherein the evaporator is comprised of serpentine tubing, and which tubing is thermally bonded to a structural member which is in thermal contact with the PV cells that are thereby cooled. 
     
     
         13 . The PV cooling system of  claim 11 , wherein one wall of the evaporator also serves as the support member for the PV cells, thereby placing the evaporator in direct thermal contact with the PV cells. 
     
     
         14 . The PV cooling system of  claim 13 , wherein the evaporator is comprised of serpentine tubing, and which tubing is thermally bonded to a structural member which is in thermal contact with the PV cells that are thereby cooled. 
     
     
         15 . The PV cooling system of  claim 13  wherein the evaporator is comprised of corrugated metallic panels joined to one of a flat metal panel or another corrugated metallic panel to form refrigerant passages wherein the refrigerant evaporates to extract heat from the PV cells. 
     
     
         16 . The PV cooling system of  claim 11 , wherein the liquid flow control is comprised of an inlet tube, an outlet tube, an outer tube surrounding the outlet tube, a sealed cavity containing a controlling fluid, the cavity being formed by a dome and an impervious flexible diaphragm, said diaphragm being subjected to the pressure and temperature of the incoming controlled fluid from the condenser against its underside, and said diaphragm being subjected to the temperature and pressure of the controlling fluid on its top side, such that the diaphragm responds to the temperature and pressure of the controlled fluid to flex the diaphragm upward to open the valve when there is excess subcooling of the controlled fluid, with result that the subcooling of the liquid from the condenser is held at a low and predetermined value, within a range of zero to 8 degrees Fahrenheit. 
     
     
         17 . The PV cooling system of  claim 16 , wherein the evaporator is comprised of serpentine tubing, and which tubing is thermally bonded to a structural member which is in thermal contact with the PV cells that are thereby cooled. 
     
     
         18 . The PV cooling system of  claim 16 , wherein the evaporator is comprised of corrugated metallic panels joined to one of a flat metal panel or another corrugated metallic panel to form refrigerant passages wherein the refrigerant evaporates to extract heat from the PV cells. 
     
     
         19 . A method for cooling PV cells to increase their efficiency, and for capturing the waste heat from the PV cells for useful purposes, wherein a refrigerant circuit transfers excess heat from the PV cells to a fluid such as water, glycol, air or other fluid where the useful heat is needed, and wherein a compressor pumps a refrigerant vapor into and through a condenser, wherein the refrigerant vapor condenses to a liquid as it passes through the condenser, and the liquid refrigerant leaving the condenser is then forced through a liquid flow control and on to the inlet of an evaporator, and the liquid refrigerant evaporates back to vapor as it passes through the evaporator and wherein the evaporator is in thermal contact with the PV cells, and wherein the waste heat from the PV cells is absorbed into the refrigerant as it evaporates back to a vapor, and wherein the refrigerant vapor is forced onward to the inlet of an active charge control, and wherein the active charge control works in concert with the liquid flow control to trap any liquid refrigerant that may reach the active charge when too much refrigerant is in active circulation in the system, and wherein the active charge control serves to evaporate and place more refrigerant into active circulation when too little refrigerant is in active circulation in the system and the evaporator is not fully wetted and allowing superheating to occur in the evaporator, whereby the result is that the evaporator is fully wetted for uniform cooling of the PV cells, and only vaporized refrigerant, with no superheat is forced onward from the outlet of the active charge control to the inlet of the compressor, thereby completing the cycle, while extracting waste heat from the PV cells and delivering the useful heat at the condenser. 
     
     
         20 . The method of  claim 19  wherein one wall of the evaporator also serves as the support member for the PV cells, thereby placing the evaporator in direct thermal contact with the PV cells. 
     
     
         21 . The method of  claim 19 , wherein the liquid flow control is comprised of an inlet tube, an outlet tube, an outer tube surrounding the outlet tube, a sealed cavity containing a controlling fluid, the cavity being formed by a dome and an impervious flexible diaphragm, said diaphragm being subjected to the pressure and temperature of the incoming controlled fluid from the condenser against its underside, and said diaphragm being subjected to the temperature and pressure of the controlling fluid on its top side, such that the diaphragm responds to the temperature and pressure of the controlled fluid to flex the diaphragm upward to open the valve when there is excess subcooling of the controlled fluid, and to close the valve when there is too little subcooling of the controlled fluid, with a result that the subcooling of the liquid from the condenser is held at a low and predetermined value.