Patent Publication Number: US-2011048502-A1

Title: Systems and Methods of Photovoltaic Cogeneration

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of Provisional U.S. Application Ser. No. 61/275,394, filed Aug. 28, 2009, and titled “System and Method for Novel Solar Panel Cogeneration and Efficiency Enhancement,” incorporated herein by reference. 
    
    
     FIELD OF THE TECHNOLOGY 
     At least some embodiments of the disclosure relate to photovoltaic systems in general, and more particularly but not limited to, improving the energy production performance of photovoltaic systems. 
     BACKGROUND 
     Photovoltaic cell efficiency decreases with increasing temperature. This effect can be mitigated by removing thermal energy from the photovoltaic cells. At the same time, cooling systems often use electricity or mechanical energy to generate cool air or fluid. However, some cooling systems use heat or thermal energy as the energy input. These cooling systems are useful where power is inconsistent or where there is an abundance of excess heat (e.g., turbine exhausts). Absorption chillers are one example of such cooling systems. 
     SUMMARY OF THE DESCRIPTION 
     Systems and methods to cool solar cells and a structure using an absorption chiller to achieve both goals are described herein. Some embodiments are summarized in this section. 
     Solar cells generally work more efficiently when cooled to an optimum operating temperature. This disclosure discusses systems and method for removing excess heat, or thermal energy, from solar modules comprising solar cells and using that thermal energy for various applications. For instance, the thermal energy removed from a solar module can be used to drive a heating and cooling apparatus that uses thermal energy as an energy input. The thermal energy can also be used to directly heat a structure, object, or space (e.g., a home, office, or swimming pool, to name a few). The thermal energy can also be stored and used at a later time. 
     In one embodiment, a system can include a photovoltaic module, a thermal path, and an apparatus. The photovoltaic module can co-generate thermal energy (generate electricity and thermal energy). The thermal path can remove a portion of the thermal energy from the photovoltaic module. The apparatus can be at least partially driven by the portion of the thermal energy from the thermal path. 
     In another embodiment, an apparatus can include a photovoltaic module, a thermal energy absorption enclosure, and a heating fluid. The photovoltaic module can generate electricity and thermal energy. The thermal energy absorption enclosure can be in contact with the photovoltaic module. The heating fluid can pass through the thermal energy absorption enclosure and be configured to absorb a portion of the thermal energy and remove the portion of the thermal energy from the thermal energy absorption enclosure. 
     In another embodiment, a method includes removing thermal energy from a photovoltaic module and using the thermal energy to drive an apparatus. 
     Other embodiments and features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG. 1   a  illustrates a system that includes a photovoltaic cogeneration unit thermally connected to a heating and/or cooling apparatus. 
         FIG. 1   b  illustrates an embodiment of the photovoltaic cogeneration unit  110  illustrated in  FIG. 1 . 
         FIG. 2  illustrates a system including an absorption chiller having a generator that is heated via thermal energy drawn from a photovoltaic module. 
         FIG. 3  is a detail view of an embodiment of the photovoltaic cogeneration unit illustrated in  FIG. 2 . 
         FIG. 4  illustrates one embodiment of an absorption chiller. 
         FIG. 5  illustrates a system including an absorption chiller located adjacent to a structure, and having a thermal energy input provided by a heating fluid that is heated via a photovoltaic cogeneration unit. 
         FIG. 6  is a detailed embodiment of the photovoltaic cogeneration unit illustrated in  FIG. 5 . 
         FIG. 7  illustrates an embodiment of a system for cooling a photovoltaic module. 
         FIG. 8  illustrates a method for cooling a solar module. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding. However, in certain instances, well known or conventional details are not described in order to avoid obscuring the description. References to one or an embodiment in the present disclosure are not necessarily references to the same embodiment; and, such references mean at least one. 
     Photovoltaic systems tend to operate effectively in sunny locations (e.g., California, Arizona, Colorado, to name a few). Sunny locations also tend to be warm and utilize large amounts of electricity to power air conditioning or other cooling systems. Thus, cooling systems and photovoltaic systems are often found in the same locations, and often the photovoltaic systems generate the electricity that drives the cooling systems. 
     While sunlight provides energy to solar cells of photovoltaic systems, sunlight also decreases solar cell efficiency by heating the solar cells. As the semiconductors in solar cells are heated, solar cell voltage drops and less power can be generated. Natural convection cooling from the air generally fails to sufficiently cool solar cells. Solar cells can operate more efficiently if thermal energy (or heat) is removed from them. At the same time, there are cooling devices that use heat as an input rather than mechanical energy or electricity. One such category of cooling systems is an absorption chiller. By drawing heat out of solar cells and using that heat to drive an absorption chiller, solar cells can operate more efficiently and a cooling system can run off excess thermal heat that otherwise would not be used. 
       FIG. 1   a  illustrates a system  100  that includes a photovoltaic cogeneration unit  110  thermally connected to a heating and/or cooling apparatus  120 . The photovoltaic cogeneration unit  110  includes a photovoltaic module  104  for generating electricity via absorbing incident light  102 . The photovoltaic module  104  also generates thermal energy since not all of the absorbed light  102  is converted to electricity. This thermal energy can decrease the efficiency of the photovoltaic module  104 , so a portion of the thermal energy can be transported (or removed or conveyed) to the heating and/or cooling apparatus  120 . The heating and/or cooling apparatus  120  can use the portion of the thermal energy to drive a cooling cycle. In an embodiment, the heating and/or cooling apparatus  120  can use the portion of the thermal energy to drive a heating cycle or to directly heat a structure, object, or space. Removing the portion of the thermal energy from the photovoltaic module  104  and conveying the portion of the thermal energy to the heating and/or cooling apparatus  120  can control the temperature of the photovoltaic module  104 . The heating and/or cooling apparatus  120  can generate cool fluid to be used to cool a structure, object, or space. The heating and/or cooling apparatus  120  can be at least partially driven by or use the thermal energy as an energy input rather than mechanical or electrical energy. Examples of such heating and/or cooling apparatuses include absorption chillers, adsorption chillers, solar air conditioning desiccant systems, and the heating and/or cooling apparatuses disclosed in at least the following: U.S. Pat. No. 4,438,633, U.S. Pat. No. 4,123,003, U.S. Pat. No. 4,007,776, and U.S. Pat. No. 4,023,948, the disclosures of which are incorporated herein by reference. The system  106  may also include a thermal energy absorption enclosure  106  in contact with the photovoltaic module  104 . A heating fluid can pass through the thermal energy absorption enclosure  106  and absorb a portion of the thermal energy from the photovoltaic module  104 . The heating fluid can then remove the portion of the thermal energy from the thermal energy absorption enclosure  106 . The portion of the thermal energy can be transported from the photovoltaic cogeneration unit  110  to the heating and/or cooling apparatus  120  via a thermal path  112 . The thermal path  112  can be a conduit (e.g., pipes) for the heating fluid. 
     The thermal energy absorption enclosure  106  can be configured to absorb a portion of the thermal energy from the photovoltaic module  104 . The thermal energy absorption enclosure  106  is an apparatus able to allow the heating fluid to absorb the portion of the thermal energy while passing through the thermal energy absorption enclosure  106 . In an embodiment, the thermal energy absorption enclosure  106  has input and output conduits configured to circulate the heating fluid into, through, and out of the thermal energy absorption enclosure  106 . In an embodiment, the thermal energy absorption enclosure  106  is heating-fluid filled space between two plates. One of the plates can be made of a thermally-conductive material (e.g., steel or copper, to name two) and can be connected to or in contact with the photovoltaic module  104 . In an embodiment, the thermal energy absorption enclosure  106  is a series of parallel, criss-crossing, or meandering conduits connected to the photovoltaic module  104 . In an embodiment, the thermal energy absorption enclosure  106  is a part of the photovoltaic module  104 . In an embodiment, a thermally conductive material or structure can be arranged between the photovoltaic module  104  and the thermal energy absorption enclosure  106 . The thermally conductive material or structure can enhance the transfer of thermal energy between the photovoltaic module  104  and the thermal energy absorption enclosure  106 . For instance, thermal paste or metallic heat fins can be arranged and in contact with the photovoltaic module  104  and the thermal energy absorption enclosure  106 . Other materials and structures are also possible. While the heating fluid may fill the entire thermal energy absorption enclosure  106 , this is not required. The pressure from the circulating heating fluid may be such that the heating fluid only partially fills the thermal energy absorption enclosure  106 . 
     In an embodiment, the thermal energy absorption enclosure  106  is part of the heating and/or cooling apparatus  120 . For instance, the heating and/or cooling apparatus  120  can be an absorption chiller, and the thermal energy absorption enclosure  106  can be a generator of the absorption chiller. Alternately, the thermal energy absorption enclosure  106  can have a heating fluid circulating through it that absorbs a portion of the thermal energy from the photovoltaic module  104 . The heating fluid can circulate between the thermal energy absorption enclosure  106  and the heating and/or cooling apparatus  120  via the thermal path  112 , thus transporting the portion of the thermal energy from the thermal energy absorption enclosure  106  to the heating and/or cooling apparatus  120 . In an embodiment, the thermal path  112  comprises one or more conduits. The heating fluid circulates through the conduits and circulates between the thermal energy absorption enclosure  106  and the heating and/or cooling apparatus  120 . Non-limiting examples of the heating fluid include water and steam. 
     In an embodiment, the heating and/or cooling apparatus  120  can remove the portion of the thermal energy from the photovoltaic module  104 . In an embodiment, the heating and/or cooling apparatus  120  can be used to cool a structure, object, or space using the portion of the thermal energy as an energy input. In an embodiment, the heating and/or cooling apparatus  120  can be a heat exchanger for conveying the portion of the thermal energy from the photovoltaic cogeneration unit  110  to a structure, object, or space. In an embodiment, the heating and/or cooling apparatus  120  is an absorption chiller and includes a generator. The thermal energy absorption enclosure  106  can absorb the portion of the thermal energy from the photovoltaic module  104  via the heating fluid. The heating fluid can circulate between the thermal energy absorption enclosure  106  and the generator of the absorption chiller thus transporting the portion of the thermal energy from the thermal energy absorption enclosure  106  to the generator. The absorption chiller can use the portion of the thermal energy to remove thermal energy from a structure, object, or space (or to generate cool fluid used to cool a structure, object, or space). 
     In another embodiment, the generator can replace the thermal energy absorption enclosure  106 . In other words, the generator can be integrated or attached to the photovoltaic module  104 . The generator can control the temperature of the photovoltaic module  104  by absorbing the portion of the thermal energy from the photovoltaic module  104 . The generator can use the portion of the thermal energy to separate a refrigerant and an absorbent via boiling the refrigerant out of solution. The generator can then transport the gaseous refrigerant back to a condenser of the absorption chiller via a gaseous refrigerant output conduit. The generator can transport the liquid refrigerant back to an absorber of the absorption chiller via a liquid absorbent output conduit. 
     In an embodiment where the heating and/or cooling apparatus is an absorption chiller, the portion of the thermal energy from the photovoltaic module  104  may not be sufficient to boil the refrigerant out of solution in the generator. The heating and/or cooling apparatus  120  can then include a heat exchanger (e.g., a solar collector or a solar thermal collector, to name two) that can absorb additional thermal energy from an external environment and transport the additional thermal energy to the generator. The combination of the portion of the thermal energy from the photovoltaic module  104  and the additional thermal energy from the heat exchanger may be sufficient to boil the refrigerant out of solution. 
     In an embodiment, the active means of controlling the temperature of the photovoltaic module  104  can be implemented. For instance, the temperature of the photovoltaic module  104  can be monitored via one or more sensors adjacent to, incorporated into, or attached to, the photovoltaic module  104 . A temperature sensor could also be adjacent to, incorporated into, or attached to the thermal energy absorption enclosure  106 . 
     Although the thermal energy absorption enclosure  106  is described in the singular, two or more thermal energy absorbing cavities  106  can also be implemented. 
     Thermally connected, or a thermal connection, or a conductive thermal connection can include any connection through a medium having a thermal conductivity similar to or greater than thermal conductors such as steel, copper, silver, thermal paste, diamond, to name a few. Thermally connected, or a thermal connection, or a conductive thermal connection do not include connections through a medium having a thermal conductivity similar to thermal insulators such as atmospheric air, polymers, polystyrene, silica aerogel, xenon, wood, rubber, cement, to name a few. 
       FIG. 1   b  illustrates an embodiment of the photovoltaic cogeneration unit  110  illustrated in  FIG. 1 . The photovoltaic cogeneration unit  110  includes the photovoltaic module  104 , the thermal energy absorption enclosure  106 , and a heating fluid  108 . The photovoltaic module  104  can generate thermal energy. The thermal energy absorption enclosure  106  can be in contact with or be a part of the photovoltaic module  104 . The thermal energy absorption enclosure  106  can remove a portion of the thermal energy from the photovoltaic module  104 . The heating fluid  108  can pass through the thermal energy absorption enclosure  106  (either clockwise or counterclockwise despite the arrows in the illustrated embodiment). While passing through the thermal energy absorption enclosure  106  the heating fluid  108  can absorb the portion of the thermal energy and remove the portion of the thermal energy from the thermal energy absorption enclosure  106 . 
     The photovoltaic cogeneration unit  110  can also include at least two heating fluid input/output conduits  140 ,  150 . At least one heating fluid input/output conduit  140 ,  150  can be configured to transport the heating fluid  108  at a first temperature into the thermal energy absorption enclosure  106 . At least one heating fluid input/output conduit  140 ,  150  can be configured to transport the heating fluid  108  at a second temperature out of the thermal energy absorption enclosure  106 . The second temperature can be higher than the first temperature since the heating fluid  108  absorbs a portion of the thermal energy from the photovoltaic module  104  as the heating fluid  108  passes through the thermal energy absorption enclosure  106 . The illustrated embodiment uses arrows to indicate one direction that heating fluid  108  could travel while passing through the thermal energy absorption enclosure  106 . However, it should be understood that this is illustrative only, and that other directions of heating fluid  108  travel as well as other numbers and configurations of the heating fluid input/output conduits  140 ,  150  is also possible. 
     In an embodiment, the thermal energy absorption enclosure  106  or the heating fluid input/output conduits  140 ,  150  can be used to provide thermal energy. For instance, they could be used to melt snow or ice on the photovoltaic module  104 . They could also be used to provide direct thermal energy to a structure, object, or space. These embodiments can be controlled by a controller that both monitors temperatures and determines when thermal energy is to be released into the structure, object, or space. 
       FIG. 2  illustrates a system  200  including an absorption chiller  220  having a generator that is heated via thermal energy drawn from a photovoltaic module. The photovoltaic module (see  FIG. 3 ) is part of a photovoltaic cogeneration unit  210 . The photovoltaic module absorbs incident light  202  and generates electricity and excess thermal energy. The photovoltaic module is thermally connected to a generator (see  FIG. 3 ) of the absorption chiller  220 . The generator removes thermal energy from the photovoltaic module and uses the thermal energy as an energy input to run the absorption chiller  220 . By removing thermal energy from the photovoltaic module, the solar cells within the photovoltaic module are cooled, which allows the solar cells to run more efficiently. The system  200  is thus able to generate electricity more efficiently than if a non-cooled photovoltaic module was used, and able to generate cool air to cool a structure  204  (or other entity requiring cooling) without using electricity. 
     The absorption chiller  220  includes an evaporator  222 , an absorber  224 , the generator, and a condenser  226 . In an embodiment, the evaporator  222  removes heat from the structure  204  and transfers the heat into the refrigerant. The refrigerant starts in a liquid state, but the heat from the structure  204  causes the liquid refrigerant to evaporate or boil. Once converted to a gaseous state, the refrigerant is transferred to the absorber  224  where it is absorbed into the absorbent to form a liquid absorbent-refrigerant solution. The liquid absorbent-refrigerant solution is a liquid in which the refrigerant gas has been absorbed into the liquid absorbent. The liquid absorbent-refrigerant solution is then transferred to the generator via a liquid absorbent-refrigerant input conduit  228 . The generator uses thermal energy from the photovoltaic module to boil the absorbent-refrigerant solution and thereby separate the refrigerant and absorbent. Since the refrigerant has a lower boiling point than the absorbent, the refrigerant boils while the absorbent remains primarily liquefied (some absorbent adheres to the vaporizing refrigerant and the combination forms gas-filled bubbles). The liquid absorbent is then transferred back to the absorber  224  via a liquid absorbent output conduit  230 . The refrigerant, now in a gaseous state and called a gaseous refrigerant, is transferred to the condenser  226  via a gaseous refrigerant output conduit  232 . The condenser  226  removes heat from the gaseous refrigerant (e.g., via a heat exchanger) causing the gaseous refrigerant to condense into a liquid refrigerant. The liquid refrigerant can be transferred back to the evaporator  222  where the cycle begins anew. 
     The absorption chiller  220  uses thermal energy instead of mechanical energy (e.g., a compressor) to cool the structure  204 , a space, or an object. In an embodiment, the absorption chiller  220  includes an absorbent and a refrigerant. Examples of absorbent-refrigerant combinations include water and liquid ammonia, and Lithium Bromide (LiBr) and water. An absorbent can extract one or more substances from a fluid (gas or liquid) medium on contact. In the process, the absorbent generally undergoes a physical and/or chemical change. A refrigerant is used to provide cooling in the absorption chiller  220 . The refrigerant absorbs thermal energy during a gas to liquid phase transformation in the evaporator  222 . The refrigerant releases thermal energy during a gas to liquid phase transformation in the condenser  226 . 
     While the absorption chiller  220  has been described as having four distinct chambers or compartments (i.e., the evaporator  222 , the absorber  224 , the generator, and the condenser  226 ), it should be understood that any one or more of these compartments can reside within the same chamber or compartment. For example, the evaporator  222  and the absorber  224  can be within the same chamber. In such an embodiment, the evaporator  222  can include a series of meandering pipes, or a heat exchanger, used to cool warm air from the structure  204 . The absorber  224  can comprise a pool of absorbent residing in the same chamber as the meandering pipes that make up the evaporator  222 . The refrigerant could be dripped or sprayed onto the heat exchanger causing the refrigerant to boil, and the gaseous refrigerant could diffuse through the chamber and come into contact with and be absorbed by the pool of absorbent. This is a non-limiting example solely intended to show that one or more of the evaporator  222 , the absorber  224 , the generator, and the condenser  226  can exist in a single compartment or chamber. 
     In the illustrated embodiment, the absorption chiller  220  is distributed between two locations: a location adjacent to and level with the structure  204 , and a location within the photovoltaic cogeneration unit  210 . In other words, the generator and the rest of the absorption chiller  220  are in different locations. In another embodiment of the absorption chiller  220 , the evaporator  222 , absorber  224 , generator, and condenser  226  can be in the same location. For instance, all four components can be located atop or affixed to the structure  204 . Alternatively, two or more of the four components of the absorption chiller  220  can be distributed in separate locations. 
     The evaporator  222  is configured to remove heat from the structure  204 . Thermal energy can also be removed from any structure, space, object, or other entity where there is a need to remove thermal energy or for cooling. The evaporator  222  can remove thermal energy from two or more structures, spaces, objects, or other entities. In an embodiment, the evaporator  222  is thermally connected to a first heat transfer unit  234 . The first heat transfer unit  234  can include heat pumps, fans, and/or other means for moving thermal energy and/or air. In an embodiment, the first heat transfer unit  234  is configured to transport cool fluid (liquid or gas) from the evaporator  222  to the structure  204 , and to transport warm fluid from the structure  204  to the evaporator  222 . The second heat transfer unit  234  is illustrated as being located adjacent to and level with the structure  204  and a portion of the absorption chiller  220 . However, this configuration is illustrative only. The first heat transfer unit  234  can be located in a variety of locations as long as it is able to transfer fluids between the evaporator  222  and the structure  204 . 
     To bring warm fluid into the evaporator  222  and to send cold fluid out, the evaporator  222  can include a heat exchanger. A heat exchanger is a device that transfers thermal energy from one fluid to another fluid without allowing the fluids to touch or mix. For instance, the heat exchanger can include a series of meandering conduits that allow a fluid to pass through the evaporator  222  and transfer thermal energy into the evaporator  222 . Other types of heat exchangers can also be used. 
     Sometimes the generator of the absorption chiller  220  does not sufficiently separate the absorbent and refrigerant. Specifically, the refrigerant can be boiled out of the absorbent, but some absorbent may form bubbles around the gaseous refrigerant. To provide further separation, the absorption chiller  220 , in an embodiment, includes one or more curving conduits between the generator and the condenser  226 . As the bubbles run into the walls of the curving conduit, the bubbles pop. The gaseous refrigerant continues to rise through the meandering conduit while the liquid absorbent returns to the generator via the force of gravity. By the time the gaseous refrigerant reaches the condenser  226 , the gaseous refrigerant is nearly pure or completely pure (free from absorbent). 
     In an embodiment, the absorption chiller  220  uses a continuous absorption cycle. In another embodiment, the absorption chiller  220  uses an intermittent absorption cycle. 
     The absorption chiller  220  includes an absorber  224 . The absorber is configured to enable the absorbent to absorb the refrigerant. When the absorbent absorbs the refrigerant, a first amount of thermal energy is released. The first amount of thermal energy can be released into an external environment—the air surrounding the system  200 . In an embodiment, a second heat transfer unit  236  can remove the first amount of thermal energy from the absorber  224  and release the first amount of thermal energy into the external environment. The second heat transfer unit  236  can be a cooling tower or any other device configured to release thermal energy into the external environment. In an embodiment, the second heat transfer unit  236  is optionally configured to remove thermal energy from the structure  204 . In this embodiment, the second heat transfer unit  236  can be an air conditioning unit, a heat pump, a cooling tower, or any other device configured to remove thermal energy from the structure  204 . The second heat transfer unit  236  is illustrated as being located adjacent to and level with the absorption chiller  220 . However, this configuration is illustrative only. The second heat transfer unit  236  can be located in a variety of locations as long as it is able to transfer fluids and thermal energy between the absorption chiller  220  and the external environment. 
     Once the gaseous refrigerant from the evaporator  222  has been absorbed in the absorber  224  to form the absorbent-refrigerant solution, the absorbent-refrigerant solution can be transported to the generator via a liquid absorbent-refrigerant conduit  228 . The liquid absorbent-refrigerant conduit  228  and the generator will be discussed further in the discussion of  FIG. 3 . The generator splits the absorbent and refrigerant and transports the gaseous refrigerant to the condenser  226  via a gaseous refrigerant output conduit  232 . The liquid absorbent is transported back to the absorber  224  via a liquid absorbent output conduit  230 . The liquid absorbent recombines with the liquid absorbent in the absorber  224  and is again used to absorb more gaseous refrigerant from the evaporator  222 . 
     The gaseous refrigerant that is transported from the generator to the condenser  226  is condensed in the condenser  226  by removing a second amount of thermal energy from the gaseous refrigerant. The second amount of thermal energy can be released into the external environment. In an embodiment, the second heat transfer unit  236  removes the second amount of thermal energy from the condenser  226  and releases the second amount of thermal energy into the external environment. 
       FIG. 3  is a detail view of an embodiment of the photovoltaic cogeneration unit illustrated in  FIG. 2 . The photovoltaic cogeneration unit  210  can be fixed to a roof or other structure  302 . The photovoltaic cogeneration unit  210  includes a photovoltaic module  304 . The photovoltaic module  304  has one or more photovoltaic cells connected in series, in parallel, or in a combination of series and parallel. The photovoltaic cells are configured to absorb the incident light  202  and convert the sun&#39;s energy into electricity. Absorption takes place via a photon absorbing side  306  of the photovoltaic module  304 . While some of the incident light  202  is converted to free carriers in the semiconductor of the solar cells some of the incident light  202  is absorbed by the photovoltaic module  304  and converted to thermal energy. This heat or thermal energy, can be removed from the photovoltaic module  304  via the back side  308  of the photovoltaic module  304 . 
     The thermal energy can pass through a thermal conductive path  314  and enter the generator  310  (the same generator previously referred to in  FIG. 2 ). The thermal conductive path  314  can create a thermal connection between the back side  308  and a wall of the generator  316 . The thermal conductive path  314  enables a first amount of thermal energy to be transferred from the back side  308  to the generator  310  and into an absorbent-refrigerant solution  312 . The absorbent-refrigerant solution  312  enters the generator  310  from the absorber  224  via the liquid absorbent-refrigerant input conduit  228 . As heat is transferred into the absorbent-refrigerant solution  312 , the temperature of the absorbent-refrigerant solution  312  rises. When the temperature of the absorbent-refrigerant solution  312  reaches a refrigerant boiling temperature (dependent upon the partial pressure within the generator  310 ), the refrigerant begins to transform from a liquid to a vapor, or a gaseous refrigerant  318 . Still liquefied and now largely free from refrigerant, a liquid absorbent can be transported back to the absorber  224  via a liquid absorbent output conduit  230 . The liquid absorbent is then reused by the absorber  224  to absorb newly evaporated refrigerant from the evaporator  222 . The gaseous refrigerant  318  can be transported from the generator  310  to the condenser  226  via a gaseous refrigerant output conduit  232 . In the condenser  226 , thermal energy is removed from the gaseous refrigerant causing it to condense into a liquid refrigerant. At this point the liquid refrigerant is free from substantially all other substances (mainly absorbent) and can be transported to the evaporator  222  to begin the absorption cooling cycle again. 
     Thermal energy and heat are used interchangeably in this disclosure. Thermal energy includes sensible energy and latent energy in a system. Sensible energy is the portion of internal energy associated with kinetic energies including molecular/atomic translation, molecular/atomic rotation, molecular/atomic vibration, electron translation, electron spin and nuclear spin. Latent energy includes the internal energy associated with the phase of a system. 
     The photovoltaic cogeneration unit  210  can be mounted flush (not illustrated) with the roof or other structure  302  or can be mounted on a supporting system/device in order to provide an air gap (as illustrated) between the photovoltaic cogeneration unit  210  and the roof or other structure  302 . The photovoltaic cogeneration unit  210  can be parallel with the roof or other structure  302  or can be mounted at an angle to the roof or other structure  302 . The photovoltaic cogeneration unit  210  can be mounted so as to face a part of the sky where the photovoltaic cells can absorb the most incident light  202 . In an embodiment, the photovoltaic cogeneration unit  210  can be movable relative to the roof or other structure  302  in order to allow tracking of the sun. In an embodiment, the photovoltaic module  304  can be movable to allow tracking of the sun, while the generator  310  can be fixed relative to the roof or other structure  302 . 
     The photovoltaic module  304  includes photovoltaic cells (or solar cells) and structural components to support and protect the photovoltaic cells and accompanying electronics. All of these components absorb some of the incident light  202  and convert the incident light  202  to thermal energy. The thermal energy, whether in the photovoltaic cells, or transferred into the photovoltaic cells from hotter portions of the photovoltaic module  304 , can decrease the efficiency of the photovoltaic cells. 
     The photovoltaic module  304  includes a photon absorbing side  306 . The photon absorbing side  306  is the side or surface of the photovoltaic module  304  that faces the incident light  202 . The photovoltaic module  304  also includes the back side  308 . The back side  308  can be the surface of the photovoltaic module  304  that is opposite the incident light  202 . In an embodiment, the back side  308  is configured to support and protect the photovoltaic cells and accompanying electronics while at the same time is configured to allow a high rate of thermal energy transfer out of the photovoltaic module  304 . Hence, the back side  308  can also be made of a material that has high thermal conductivity. In an alternative embodiment, the back side  308  can be made of materials having high thermal conductivity and materials having low thermal conductivity. 
     The third amount of thermal energy can travel from the back side  308  to the generator  310  via the thermal conductive path  314 . In an embodiment, the thermal conductive path  314  transfers the third amount of thermal energy via conduction—the transfer of thermal energy via the contact of atoms and molecules. In an embodiment, the thermal conductive path  314  transfers the third amount of thermal energy via convection—the transfer of thermal energy via the movement of atoms and molecules. In an embodiment, the thermal conductive path  316  transfers the third amount of thermal energy via radiation—the transfer of thermal energy via photons. In an embodiment, the thermal conductive path  314  transfers the third amount of thermal energy via two or more of the following: conduction, convention, or radiation. In an embodiment, the thermal conductive path  314  is a material having high thermal conductivity (e.g., thermal grease, thermal compound, thermal paste, heat paste, heat sink paste, heat transfer compound, or heat sink compound, to name a few). For instance, the thermal conductive path  314  can be thermal grease applied between the back side  308  and the generator  316 . In an embodiment, the thermal conductive path  314  is a material or substance so thin that the material does not hinder heat transfer. In other words the material or substance is so thin that it is a poor thermal insulator. 
     In an embodiment, the thermal conductive path  314  includes a wall of the generator  316 . The wall of the generator  316  is adjacent to the back side  308  and in contact with the thermal conductive path  314 . The wall of the generator  316  can be made from a material or combination of materials that do not interact with or corrode upon contact with the absorbent-refrigerant solution, the pure refrigerant (in a liquid or vapor state), or the pure absorbent (in a liquid or vapor state). In an embodiment, the back side  308  connects directly to the wall of the generator  316  and there is no thermal conductive path  314 . In other words, the generator  310  and the photovoltaic module  304  can be in direct contact. 
     Although  FIG. 3  illustrates an embodiment where the wall of the generator  316  is flat and the back side  308  of the photovoltaic module  304  is flat, other shapes and configurations are also possible. Alternative shapes and configurations can decrease the distance that thermal energy must travel between the photovoltaic module  304  and the wall of the generator  316 . Alternative shapes and configurations can decrease the thickness of material that thermal energy must travel through to reach the wall of the generator  316 . Alternative shapes and configurations can increase the surface area of the wall of the generator  316  in order to increase the rate at which the generator  310  can absorb thermal energy. Other shapes and configurations commonly used in the field of heat transfer can also be implemented without departing from the spirit of the disclosure. The square or rectangular profile of the generator  310  illustrated in  FIG. 3  is illustrative only. One skilled in the art will recognize that the generator  310  can take on other shapes and configurations without departing from the spirit of the disclosure. 
     The three conduits  228 ,  230 ,  232  can be hollow and tubular in shape, although other shapes can also be used. The conduits can be flexible, rigid, or a combination of the two. The locations and configurations of the three conduits  228 ,  230 ,  232  in  FIG. 3  are illustrative only. One skilled in the art will recognize that the conduits  228 ,  230 ,  232  can have a variety of locations and configurations. 
     When the refrigerant boils out of the absorbent-refrigerant solution  312 , a portion of the absorbent, in liquid form, can form bubbles around the gaseous refrigerant  318 . Therefore, the system  200  may include a means for separating the liquid absorbent from the gaseous refrigerant  318 . In an embodiment, after the gaseous refrigerant  318 , inside liquid absorbent bubbles, leaves the generator  310 , but before it reaches the condenser  226 , the bubbles can pass through one or more meandering (or twisting or curved or non-straight or non-linear) conduits such that the bubbles impact the sides of the meandering conduits and break. The gaseous refrigerant  318 , now pure and free from absorbent, continues to rise towards the condenser  226  while the now pure liquid absorbent drips back to the absorber  224  via the force of gravity. Thus, passing the bubbles through the meandering conduits on the way to the condenser  226  completes the process of separating the refrigerant from the absorbent. 
     Returning to the generator  310 , the ratio of absorbent to refrigerant in the absorbent-refrigerant solution  312  can vary or have a gradient. The absorbent-refrigerant solution  312  near a top surface of the absorbent-refrigerant solution  312  can have the smallest concentration of refrigerant. This portion can be transported back to the absorber  224  via liquid absorbent output conduit  232 . In an embodiment, the liquid absorbent output conduit  232  transports pure liquid absorbent to the absorber  236 . In other embodiment, a small amount of refrigerant remains in solution and is transported back to the absorber  224  along with the liquid absorbent. 
       FIG. 4  illustrates one embodiment of an absorption chiller  400 . Absorption cooling is a process in which cooling of a space, structure, or object is accomplished by the evaporation of a volatile fluid (a refrigerant), which is then absorbed in a solution (an absorbent), then desorbed or boiled using thermal energy from a heat source (e.g., turbine exhaust, excess heat from photovoltaic modules), and then condensed. The refrigerant can be one that evaporates at room temperature such as Lithium Bromide (LiBr). Two common absorbent-refrigerant combinations are LiBr-water, and water-ammonia. 
     The absorption chiller  400  includes an evaporator  402  for cooling a space, structure or object. The absorption chiller  400  includes an absorber  404  where the refrigerant dissolves or is absorbed into the absorbent. The absorption chiller  400  includes a generator  406  for boiling the absorbent-refrigerant solution. In the generator  406 , the refrigerant turns into a gas that is primarily devoid of absorbent. However, some absorbent may remain in the form of bubbles that enclose the gaseous refrigerant. The absorption chiller  400  can therefore include a separator (not illustrated) for breaking these bubbles and completing the separation of the gaseous refrigerant from the liquid absorbent. The gaseous refrigerant is then transported to a condenser  408  where heat is removed from the gaseous refrigerant causing the gaseous refrigerant to liquefy. The liquid refrigerant is then transported to the evaporator  402  where the cycle begins again. In an embodiment, the absorption chiller  400  optionally includes an expansion valve  410  that allows the liquid refrigerant to be released back into the evaporator  402  at lower pressure. 
     The absorption cooling cycle begins with the refrigerant in a liquid state evaporating in the evaporator  402 . When the liquid refrigerant boils, this phase change removes a first amount of thermal energy Q in     —     1  from the space, structure, or object that the absorption chiller  400  is intended to cool. This can be done via the use of a heat exchanger located inside or adjacent to the evaporator  402 . Cooling pipes snaking through the evaporator  402  are one example of a heat exchanger. 
     The gaseous refrigerant is then absorbed in an absorbent at the absorber  404 . The refrigerant has a high affinity for the absorbent. Affinity is the probability of a chemical dissolving into another chemical. As such, when the refrigerant, in a gaseous state, comes into contact with the absorbent, in a liquid state, the refrigerant is absorbed into the absorbent. The resulting solution is called a liquid absorbent-refrigerant solution. This absorption process releases a second amount of thermal energy Q out     —     1  that can be released into an external environment, for instance via a cooling tower. 
     The liquid absorbent-refrigerant solution generally will not boil at a low enough temperature to be useful for cooling. Thus, the two chemicals are separated in the generator  406 . A third amount of thermal energy Q in     —     2  is added to the liquid absorbent-refrigerant solution. Since the refrigerant has a lower boiling temperature than the absorbent, the refrigerant escapes from the absorbent as a gas. The third amount of thermal energy Q in     —     2  can be provided by a variety of sources or multiple sources. Some examples include excess hot water or steam from an industrial plant, hot water heated by the sun, or as this disclosure describes, heat removed from solar cells. 
     The gaseous refrigerant rises in bubbles formed from a small amount of absorbent. To complete the separation of refrigerant and absorbent, the rising bubbles pass through a series of twisting conduits causing the bubbles to impact the conduits&#39; sides and break the bubbles. As a result the absorbent trickles down the conduits and is returned to the absorber  404 . The gaseous refrigerant continues to rise through the twisting conduits. The twisting conduits can be referred to as a separator (not illustrated). 
     Now that the gaseous refrigerant has been purified (or substantially purified), the gaseous refrigerant is condensed in the condenser  408 . This is done by removing a fourth amount of thermal energy Q out     —     2 . The fourth amount of thermal energy can be removed via a heat exchanger. The fourth amount of thermal energy Q out     —     2  can be released into an external environment, for instance via a cooling tower. The liquid refrigerant is then ready to be fed into the evaporator  402  again. 
     Substituting thermal energy for mechanical compression means that absorption chillers can use much less electricity than mechanical compressor chillers. Absorption chillers can be cost-effective when the thermal energy they consume is less expensive than the electricity that is displaced. 
       FIG. 5  illustrates a system  500  including an absorption chiller located adjacent to a structure  504 , and having a thermal energy input provided by a heating fluid that is heated via a photovoltaic cogeneration unit  510 . The system  500  is similar to the system  200  discussed with reference to  FIGS. 2-3  in that excess thermal energy is removed from a photovoltaic module in order to cool the photovoltaic module and drive an absorption chiller  520 . However, since the absorbent, refrigerant, and possibly other chemicals in an absorption chiller  520  can be harmful or dangerous to humans and the structure  504 , the system  500  utilizes an absorption chiller that is entirely separate from the structure  504  and incapable of spilling onto the structure  504 . Rather than transferring thermal energy directly from the photovoltaic module to the generator as described with reference to  FIGS. 2-3 , the system  500  absorbs thermal energy from the photovoltaic module in a heating fluid (e.g., water) and transports the heating fluid to the absorption chiller  520  where the thermal energy is conveyed to the generator  525 . Heating fluid is any liquid or gas having a high heat capacity, posing little danger to humans, and possessing low corrosive characteristics. 
     System  500  includes an absorption chiller  520  having an evaporator  522 , an absorber  524 , a generator  525 , and a condenser  526 . In an embodiment, the absorption chiller  520  can use water as a refrigerant and lithium bromide as an absorbent. The evaporator  522  removes heat from the structure  504 , space, object, or other entity requiring cooling. The thermal energy input for the generator  525  is provided by excess thermal energy absorbed in a photovoltaic module of a photovoltaic cogeneration unit  510 . Excess thermal energy in the photovoltaic module is absorbed in a heating fluid converting cool heating fluid into warm heating fluid. Cool heating fluid is a fluid (gas or liquid) having a lower temperature than the temperature of the photovoltaic module, and thus able to absorb thermal energy from the photovoltaic module. Warm heating fluid is a fluid having a higher temperature than the cool heating fluid. The warm heating fluid is transported to the absorption chiller  520  via a warm heating fluid output conduit  532 . The thermal energy in the warm heating fluid is conveyed to the generator  525  via a heat exchanger  538 . The warm heating fluid output conduit  532  is connected between the photovoltaic cogeneration unit  510  and the heat exchanger  538  of the generator  510 . In an embodiment, the warm heating fluid (or a portion of the thermal energy) can be stored in a heating fluid storage vessel  534 , stored there temporarily, and then transported to the absorption chiller  520 . In transferring thermal energy to the generator  525 , the warm heating fluid changes to cool heating fluid. The cool heating fluid can be transported back to photovoltaic cogeneration unit  510  via cool heating fluid input conduit  528 . The cool heating fluid input conduit  528  is connected between the photovoltaic cogeneration unit  510  and the heat exchanger  538  of the generator  510 . The cool heating fluid is then used to remove more thermal energy from the photovoltaic module. 
     The absorption chiller  520  need not always be located as illustrated in  FIG. 5 . Rather the absorption chiller  520  can be located anywhere that does not pose a risk to humans or the structure  504  should chemicals in the absorption chiller  520  escape or leak. Similarly, while the illustrated absorption chiller  520  is not distributed amongst different locations (compare to the absorption chiller  220  in  FIG. 2 ), were any one or more of the evaporator  522 , absorber  524 , generator  525 , or condenser  526  distributed, they should be so distributed as to avoid endangering humans or the integrity of the structure  504  should the absorption chiller  520  leak. 
     To facilitate thermal energy transfer from the heating fluid to the generator  525 , the system  500  can include a heat exchanger  538 . The heat exchanger  538  can be connected to, or have a thermal connection to, the generator  525 . The heat exchanger  538  can convert the warm heating fluid to a cool heating fluid by transferring a second amount of thermal energy from the warm heating fluid to the generator  525 . The heat exchanger can reside within the generator  525 , connect to the generator  525 , or reside partially inside and partially outside the generator  525 . 
     The evaporator  522  is configured to remove thermal energy from the structure  504 . Thermal energy can also be removed from any structure, space, object, or other entity where there is a need to remove thermal energy or for cooling. The evaporator  522  can remove thermal energy from two or more structures, spaces, objects, or other entities. In an embodiment, the evaporator  522  is thermally connected to a first heat transfer unit  534 . The first heat transfer unit  534  can include heat pumps, fans, and/or other means for moving thermal energy and/or air. In an embodiment, the first heat transfer unit  534  is configured to transport cool fluid (liquid or gas) from the evaporator  522  to the structure  504 , and to transport warm fluid from the structure  504  to the evaporator  522 . The first heat transfer unit  534  is illustrated as being located adjacent to and level with the structure  504  and a portion of the absorption chiller  520 . However, this configuration is illustrative only. The first heat transfer unit  534  can be located in a variety of locations as long as the first heat transfer unit  534  is able to transfer fluids between the evaporator  522  and the structure  504 . 
     The heating fluid storage vessel  534  is located between the photovoltaic cogeneration unit  510  and the absorption chiller  520 . In an embodiment, the heating fluid storage vessel  534  is located atop the structure  504 . In an embodiment, the heating fluid storage vessel  534  is located adjacent to the structure  504 , not atop the structure  504 . In an embodiment, the heating fluid storage vessel  534  is located adjacent to the absorption chiller  520 . While the heating storage vessel  534  is illustrated as only being connected to the warm heating fluid output conduit  532 , in an embodiment, the heating storage vessel  534  can also be connected to the cool heating fluid input conduit  528 . In an embodiment, the heating storage vessel  534  can be a low-temperature heating storage vessel. A low-temperature heating storage vessel is a vessel having a fluid that is at a lower temperature than a temperature of the photovoltaic module. The heating storage vessel  534  need not be enclosed on at least six sides. For instance, a swimming pool is a non-limiting example of a heating storage vessel  534 . 
     The system  500  can also include a second heat transfer unit  536 . In an embodiment, the second heat transfer unit  536  can remove thermal energy from the absorber  524  and release the thermal energy into an external environment. In an embodiment, the second heat transfer unit  536  can remove thermal energy from the condenser  526  and release the thermal energy into the external environment. In an embodiment, the second heat transfer unit  536  can remove thermal energy from the structure  504  and release the thermal energy into the external environment. In an embodiment, the second heat transfer unit  536  can remove thermal energy from the external environment and transport it to the generator  525 . For instance, the second heat transfer unit  536  can include a solar thermal collector to collect thermal energy in a heating fluid and transfer the thermal energy to the generator  525  via movement of the heating fluid. The purpose of such thermal energy transfer is to supplement the thermal energy removed from the photovoltaic module. 
     In addition to using thermal energy removed from the photovoltaic module to heat the generator  525 , the thermal energy can also be used to heat rather than cool the structure  504 . To accomplish this, in an embodiment, the system  500  optionally includes a warm heating fluid conduit to the structure  538  for transferring all or a portion of the warm heating fluid in the warm heating fluid output conduit  532  into the structure  504 . The system  500  can include a first valve  540  to controllably direct warm heating fluid to the generator  525  or to the structure  504 . In an embodiment, the first valve  540  can be a two-way valve. Cool fluid can be directed back to the photovoltaic cogeneration unit  510 , from the structure  504 , via a return conduit that can connect with a second valve  542 . In an embodiment, the second valve  542  can be a two-way valve. 
       FIG. 6  is a detailed embodiment of the photovoltaic cogeneration unit  510  illustrated in  FIG. 5 . The photovoltaic cogeneration unit  510  can be fixed to a roof or other structure  602 . The photovoltaic cogeneration unit  510  includes a photovoltaic module  604 . The photovoltaic module  604  has one or more photovoltaic cells connected in series, in parallel, or in a combination of series and parallel. The photovoltaic cells are configured to absorb the incident light  502  and convert the sun&#39;s energy into electricity. Absorption takes place via a photon absorbing side  606  of the photovoltaic module  604 . While some of the incident light  502  is converted to free carriers in the semiconductor of the solar cells some of the incident light  502  is absorbed by the photovoltaic module and converted to thermal energy. This heat or thermal energy, can be removed from the photovoltaic module  604  via the back side  608  of the photovoltaic module  604 . 
     The thermal energy can pass through a conductive heat connection  614  and can enter the thermal energy absorption enclosure  618 . The conductive heat connection  614  allows the thermal energy absorption enclosure  618  to be thermally connected to the back side  608  of the photovoltaic module  604 . More particularly, the conductive heat connection  614  creates a conductive thermal connection between the back side  608  and a wall of the thermal energy absorption enclosure  616 . The conductive heat connection  614  enables a third amount of thermal energy to be transferred from the back side  608  to the thermal energy absorption enclosure  618  and into the heating fluid  612 . The heating fluid  612  enters the thermal energy absorption enclosure  618  as cool heating fluid from the absorber  524  via the cool heating fluid input conduit  528 . As the third amount of thermal energy is transferred into the heating fluid  612 , the temperature of the heating fluid  612  rises, and the cool heating fluid is converted to warm heating fluid. This warm heating fluid is then transported to the generator  525  via warm heating fluid output conduit  532  (and optionally being temporarily stored in the heating fluid storage vessel  534 ). 
       FIG. 7  illustrates an embodiment of a system  700  for cooling a photovoltaic module. System  700  includes a photovoltaic cogeneration unit  710  that includes a photovoltaic module. The photovoltaic module converts incident light  702  into electricity. The photovoltaic module also generates heat or thermal energy from absorbed light that is not converted into electricity. This thermal energy can be removed, and thus improve the photovoltaic module efficiency, by removing the thermal energy to the heat exchanger  720 . The thermal energy can be removed via conduits transporting a heating fluid (e.g., water). En route to the heat exchanger  720 , the heating fluid can be temporarily stored in a heating fluid storage vessel  704 . The heating fluid storage vessel  704  can contain heating fluid having a temperature that is greater than, equal to, or less than the temperature of the photovoltaic module. The heat exchanger  720  can be thermally connected to a heating and/or cooling apparatus  734  and a second heat exchanger  736 . The second heat exchanger  736  can transport thermal energy to and from objects and/or structures that are to be cooled. The system may also include a controller  740 . The controller  740  can monitor voltages, currents, temperatures, fluid flow rate and other values throughout the system  700 . The controller  740  can also control fluid flow in the system  700 . In an embodiment, the controller  740  controls pumps, valves, and/or fans in the heating and/or cooling apparatus  734  and/or the heat exchanger  736 . The controller  740  can control the temperature, rate, and direction of fluid flow from the heating and/or cooling apparatus  734  via control connection  742 . The controller  740  can control the temperature, rate, and direction of fluid flow from the heat exchanger  736  via the control connection  744 . In an embodiment, the controller  740  controls a pump or valve controlling fluid flow between the heating fluid storage vessel  704  and the photovoltaic cogeneration unit  710 . In an embodiment, the controller  740  provides surplus electricity, from the photovoltaic module, to the electric grid. In an embodiment, the controller  740  uses electricity from the electric grid to power the pumps, valves, and/or fans in the system  700 . 
     In an embodiment, the photovoltaic cogeneration unit  710  can include a generator of an absorption chiller. Alternatively, thermal energy can be removed from the photovoltaic module and transported to the generator of the absorption chiller. In either case, the thermal energy from the photovoltaic cogeneration unit  710  may not be sufficient to boil the refrigerant and separate it from the absorbent in the generator. The first heating and/or cooling apparatus  734  can supplement this thermal energy by drawing a second amount of thermal energy from an external environment and transporting the second amount of thermal energy to the generator. In an embodiment, the first heating and/or cooling apparatus  734  can be a solar thermal collector. 
     It should be understood that the thermal conduits, heating fluid conduits, or arrows representing the flow of thermal energy, in  FIGS. 1-7  represent various forms of thermal energy transfer. For instance, they can represent conduits or pipes wherein a fluid passes or circulates. Alternatively, they can represent interfaces between different materials. Alternatively, they can represent the transport of thermal energy through air via convection. This short list of examples is exemplary only, and one skilled in the art will recognize that various other means of thermal energy transfer can also be implemented. 
       FIG. 8  illustrates a method  800  for cooling a solar module. The method  800  cools a solar module by removing thermal energy from the solar module and using the thermal energy to drive an apparatus. To do this, the method  800  includes a remove thermal energy from a photovoltaic module operation  802 . The method  800  also includes a use thermal energy to drive an apparatus operation  804 . Optionally the method  800  also includes a circulate a heating fluid between the photovoltaic module and an apparatus operation  806 . It should be understood that the apparatus can be a cooling apparatus, a heating apparatus, or an apparatus configured to heat and/or cool a structure, object, or space. 
     Thermal energy can be removed from a photovoltaic module via any of the methods discussed earlier in this application. For instance, the thermal energy can be used to drive an apparatus such as an absorption chiller. The heating fluid can be circulated between the photovoltaic module and the apparatus in order to transport the thermal energy from the photovoltaic module to the apparatus. In an embodiment, the thermal energy can be absorbed in the generator of the absorption chiller. The thermal energy can boil a refrigerant out of a solution of refrigerant and absorbent in the generator. Alternately, the thermal energy can be absorbed in the heating fluid and transported to the generator of the absorption chiller via heating fluid conduits. Alternately, the thermal energy can be absorbed in a heating fluid and transported to one or more heat exchangers or heating fluid storage vessels. The heat exchangers can use the thermal energy to heat a structure, object, or space (e.g., home, office, pool). The heating fluid can be stored in one or more heating fluid storage vessels to be used at a later time. 
     It is clear that many modifications and variations of these embodiments may be made by one skilled in the art without departing from the spirit of the novel art of this disclosure. For example, the absorption chiller can use different refrigerants and absorbents than those explicitly mentioned above. As another example, the entire absorption chiller can be located on the roof of a home or other structure. While the above-discussed embodiments of absorption chillers included either water and lithium bromide or ammonia and water, other refrigerants and absorbents can also be used. For instance, one absorption chiller uses air, water, and a salt water solution. These modifications and variations do not depart from the broader spirit and scope of the invention, and the examples cited herein are to be regarded in an illustrative rather than a restrictive sense.