The raw power of the sun is hard to comprehend. According to the Union of Concerned Scientists (UCS), a science-based advocacy group, all the energy stored in Earth’s coal, oil, and natural gas reserves is matched by the energy from just 20 days of sunshine! Solar energy is free and clean, and the sun has a pretty good track record of dependability.
Of course, putting it to work in our homes for HVAC use is a different animal. There are three main ways we can harness solar energy for residential HVAC applications: passive use, solar heat collectors and photovoltaics.
Passive Use: Simple design features such as properly orienting a house and using skylights, awnings and shade trees judiciously are especially useful in new construction. Thoughtful design decreases fuel consumption and increases HVAC efficiency.
Solar Heat Collectors: Most solar collectors are liquid-based and consist of pipes in a large, flat box that is painted black inside and covered with glass. The pipes carry heated liquid from the box into the building. The liquid typically transfers heat to a hot water tank or passes through radiators that heat the air.
Solar energy also powers air conditioning systems. A solar-assisted dessicant cooling system employs a combination of evaporative cooling with air dehumidification by a dessicant, such as silica gel.
In the solar powered absorption chiller, an alternative to a traditional compression chiller, solar energy heats a refrigerant under pressure, doing the job that usually requires a compressor. It’s a particularly efficient approach for office cooling since it works well during the hottest part of the day.
Solar heating or cooling systems generally require a small amount of electricity for running fans or pumps. That power can be provided by solar photovoltaic cells.
Photovoltaics: Photovoltaics (PV) is the direct conversion of light into electricity. Certain materials exhibit the photoelectric effect, which means they release electrons when exposed to light. This effect was first discovered in 1839 but not employed seriously until NASA used it to power spacecraft in the 1960s.
To make a PV cell, a thin semiconductor wafer is treated to form an electric field, positive on one side and negative on the other. When sunlight strikes the cell, electrons are knocked loose from atoms in the semiconductor material. Electrical conductors capture the electrons in the form of an electric current.
Until recently, PV systems have mostly powered off-grid applications: homes in remote locations, cell phone transmitters, road signs, water pumps, and millions of solar watches and calculators. But thanks to lower production costs, net metering policies, and government incentives, in 2005 installation of on-grid PV systems outpaced the installation off-grid systems for the first time.
It will be interesting to see whether solar power catches on as a major player in the residential HVAC market. What are your thoughts.