Solar absorption cooling is a thermodynamic process. In other words its uses heat instead of compression like a regular air conditioner does. Since it uses heat, solar energy is the perfect source.
Absorption cooling and compressor cooling both use a refrigerant with a very low (sub-zero Fahrenheit) boiling point. Compressor air conditioners use Freon and absorption air conditioners usually use ammonia. In both types, when this refrigerant evaporates or boils, it takes some heat away with it, providing the cooling effect.
The main difference between the two types is the way the refrigerant is changed from a gas back into a liquid so that the cycle can start over again.
A compressor air conditioner, the kind most of us have, either a window unit or a central unit, uses an electric compressor to increase the pressure on the gas, and then condenses the hot high pressure gas back to a liquid by a condenser (heat exchanger). And the compressor uses lots of electricity!
Once the high pressure gas has cooled, it passes through a pressure release valve which drops the refrigerant temperature to below freezing.
The difference in absorption heat pumps is that the evaporated ammonia is not pumped up in pressure in a compressor, but is instead absorbed into water. A relatively low-power pump can then pump the solution up to a higher pressure.
The problem then is removing the ammonia from the water, and that's where the heat source comes in. The heat essentially boils the ammonia out of the water, starting the cycle again. This is where solar energy comes in, to provide the heat source. Only this energy is free!