Solar Cooling
. Solar energy can also be used for cooling. An absorption air conditioner or refrigerator uses a large solar collector to provide the heat that drives the cooling process (see Refrigeration ). Solar heat is applied to the refrigerant and absorbent mixture, which is combined under pressure in a container called a generator or boiler. The Sun’s heat brings the mixture to a boil. The refrigerant (often ammonia) vaporizes, rises as a gas, and reaches the condenser. There it gives off heat and returns to liquid form. As the drops of pure refrigerant fall, they trickle into the evaporator (freezing unit) where they evaporate vigorously. Evaporation requires heat energy, which comes from the surroundings, and results in cooling: The refrigerant absorbs heat from the unit and cools the space. The refrigerant, now a gas again, rejoins the mixture in the boiler to restart the process. Absorption coolers must be adapted to operate at the normal working temperatures for flatbed solar collectors—b