A National Aeronautics and Space Administration (NASA) sponsored report in 1976 surveyed solar energy system applications of air conditioning.
Indirect photovoltaic power for air conditioners consists of whole-house or whole-building solar which, traditionally for most users, has also meant net metering to the grid.
Solar in this case is inverted to alternating current (AC) to run the appliances in the house or building, including the air conditioner(s).
The advantage of this is the air conditioners don’t need any special electronics to accommodate solar, so it’s a simple implementation.
The advantage of these inverter DC air conditioners is the lower cost, while the disadvantage is that they have no way to run without solar unless they're plugged in.
Both of these systems make use variable refrigerant flow technology, with high-efficiency variable-speed DC motors and compressors to require very little run power, and both also offer heat in addition to air conditioning.
A third type of unit is available for larger, usually commercial, buildings and offers both grid and battery backup as well as optional net metering.
New versions of phase-change indirect evaporative coolers use nothing but a fan and a supply of water to cool buildings without adding extra interior humidity (such as at McCarran Airport Las Vegas Nevada).
A less-expensive partial-power photovoltaic system can reduce (but not eliminate) the monthly amount of electricity purchased from the power grid for air conditioning (and other uses).
With American state government subsidies of $2.50 to US$5.00 per photovoltaic watt, the amortized cost of PV-generated electricity can be below $0.15 per kWh.
Since the U.S. Department of Energy was created in 1977, their Weatherization Assistance Program has reduced heating-and-cooling load on 5.5 million low-income affordable homes an average of 31%.
A solar chimney or photovoltaic-powered fan can be used to exhaust undesired heat and draw in cooler, dehumidified air that has passed by ambient Earth temperature surfaces.
This concept is cost-effective, as long as the location has ambient earth temperature below the human thermal comfort zone (not the tropics).
The desiccant is then regenerated by using solar thermal energy to dehumidify, in a cost-effective, low-energy-consumption, continuously repeating cycle.
[4] A photovoltaic system can power a low-energy air circulation fan, and a motor to slowly rotate a large disk filled with desiccant.
In theory packed towers can be used to form a counter-current flow of the air and the liquid desiccant but are not normally employed in commercially available machines.
Solar thermal energy can be used to efficiently cool in the summer, and also heat domestic hot water and buildings in the winter.
In large scale installations there are several projects successful both technical and economical in operation worldwide including, for example, at the headquarters of Caixa Geral de Depósitos in Lisbon with 1,579 square metres (17,000 sq ft) solar collectors and 545 kW cooling power or on the Olympic Sailing Village in Qingdao/China.
These projects have shown that flat plate solar collectors specially developed for temperatures over 200 °F (93 °C) (featuring double glazing, increased backside insulation, etc.)
The Audubon Environmental Center at the Ernest E. Debs Regional Park in Los Angeles has an example solar air conditioning installation,[12][13] which failed fairly soon after commissioning and is no longer being maintained.
Solar Collectors from Sopogy and Cogenra were installed on the rooftop at the ERC and are producing cooling for the building's air conditioning system.
The ISAAC uses a parabolic trough solar collector with a compact and efficient design to produce ice with no fuel or electric input, as well as with no moving parts.
[22] Concerning industrial applications, several studies in the recent years highlighted that there is a high potential for refrigeration (temperatures below 0 °C) in different areas of the globe (e.g., the Mediterranean,[23] Central America[24]).
However, this can be achieved by ammonia/ water absorption chillers requiring high temperature heat input at the generator, in a range (120 ÷ 180 °C) which can only be satisfied by concentrating solar collectors.
In hot climates with significant degree days of cooling requirement, leading-edge solar air conditioning will be an increasingly important critical success factor.