Solar air conditioning is any technology that uses energy from the sun to cool down the environment inside of a structure. There are a number of ways that solar energy is used to achieve a cooling effect, including adsorption heat pumps and thermal cycling using desiccants. Each of these types of solar air conditioning employ different methods to cool down air using heat energy. Photovoltaic (PV) systems can be used to generate electricity, which can then power any type of traditional air conditioning system. Passive cooling can also be used to reduce the temperature inside a building during warm conditions, though it does not directly use the energy of the sun to cool the structure.
One main way that the energy of the sun can be used to cool a structure is solar thermal cooling. These systems typically involve using the sun to heat water or another liquid solution, which passes under solar collectors through a pipe system. This very hot liquid can then be used to extract heat from inside a structure using an absorption or adsorption chiller device commonly known as a heat pump. The liquid can then be recirculated through the system to the solar collectors, heated back up, and passed back into the chiller.
Another way that solar air conditioning can be achieved is through the use of desiccants, such as silica gel. In these systems, the silica gel is used to draw moisture out of the air inside a structure. The act of extracting this moisture can also have a cooling effect, resulting in lower ambient temperatures. Heat from solar energy can then be used to warm up the desiccant materials and dry them out. The desiccants are then free to draw more moisture out of the air inside the structure, continuing the cooling effect.
Solar air conditioning can also be achieved with photovoltaic panels, which are used to generate electricity. If this power is then used to directly operate a traditional cooling unit, that is another form of solar air conditioning. Compressor style air conditioning units tend to be less efficient than other designs, but powering them with photovoltaics can reduce energy uses from other sources.
Passive cooling may not technically qualify as air conditioning and does not actually use the energy of the sun to achieve a cooling effect. This method of cooling structures is typically implemented when a building is designed and constructed. Passive solar building design can keep a structure cooler in the summer months by keeping heat out, but it can also provide warmth in colder months by effectively trapping and storing solar energy.