Solar Powered Air Conditioning

It’s an obvious idea, really. Use solar power to provide air conditioning. When the sun’s out, you are likely to want cooling, so there is a perfect coincidence of supply (solar power) and demand (cooling).

Of course, there is a slight problem. By its nature, sunlight is more inclined to produce heating than cooling. We shouldn’t allow this to deter us, after all, it’s just a matter of engineering.

Conventional air conditioning requires electricity to power the unit, which includes a compressor to provide the work necessary for a refrigeration cycle. In a conventional air conditioner, the cooling is achieved by refrigerant evaporating inside the piping – evaporating cools a substance down, as it takes the heat from its surroundings to enable it to vaporize. The refrigerant is a high pressure liquid going into the evaporator, where it is allowed to expand and evaporate. The evaporator piping is actually in a unit that blows air into the room, so it cools the air. Refrigerant is just a chemical designed to evaporate at the best temperature and pressure for the cycle to work. When the vaporized refrigerant gets to the next part of the cycle, it is compressed with the compressor, which makes it hot and at high pressure. It goes into a condenser unit (the outside part on a split air conditioning system) where it gives up heat to the outside air, which makes it liquid again. The high pressure but cooler liquid goes back to the evaporator, where it evaporates again.

So one way to provide air conditioning with solar power is to generate electricity, and use that power to drive a conventional air conditioning system. But there is a problem because the whole traditional air conditioning system with the compressor described above is very power-hungry!. A typical 9,000 BTU air conditioning unit for a small room consumes about 850 Watts of electricity. That's a lot of electricity (and pretty expensive) to generate with solar panels! However, there are two alternatives:

• Evaporative cooling: In places with dry climate, you can use solar panels to power evaporative cooling systems for your house. These consume much less energy to operate but they do not work in humid climates.
• Absorption cycle: There is an alternative refrigeration cycle, and a Spanish company has just incorporated it into a small unit that can be used for a house. If you have an RV, you may be familiar with the refrigerator which is powered by propane gas. Refrigerators that run on natural gas have also been available for years for residential use, but never became very popular. These use a different sort of refrigeration cycle, and it uses the chemical lithium bromide as a substitute for the compressor. This is actually a chemical absorbent, so the refrigeration cycle is called an absorption cycle.
  The company has designed all this into a unit, where the heat for the absorption cycle is provided by hot water, which is generated by a solar collector. There’s just a minimal electrical requirement to run the unit, and you can have cooling from heat!

As the demand for solar powered air conditioning is going up, scientists, inventors and manufacturers will inevitably catch up with this and we will see in the near future affordable and uniformly workable units that use the power of the sun to cool our homes!