Solar potential varies around the country
In many U.S. climates, a solar hot water system is a sensible way to heat water for showers and laundry. However, it usually makes less sense to use a solar thermal system for space heating.
The performance of an active solar space heating system depends on the equipment installed, the climate, the solar potential of the site, how well the house is insulated and air-sealed, and the type of heat distribution system in the house.
The National Renewable Energy Laboratory says homeowners can expect to meet up to 40% to 60% of their winter space-heating needs with solar collectors; in many climates, however, performance is likely to be lower.
An active solar thermal space heating system must be larger than the typical solar domestic hot water system, which typically requires two collectors and a 120-gallon storage tank. That means that a solar heating system requires between 4 and 20 solar collectors, and between 240 and 5,000 gallons of thermal storage capacity. Larger systems can provide a larger percentage of a home’s heating load.
The typical cold-climate solar thermal system circulates a solution of glycol (antifreeze) and water through a series of solar collectors. Most solar collectors measure 4 ft. by 8 ft. or 4 ft. by 10 ft. When the sun is shining, a pump circulates the solar fluid from the collectors to a heat-exchange coil immersed in the solar storage tank. To heat the house, the water in the solar storage tank can be circulated through hydronic tubing to baseboard radiators, to a radiant floor, or to a fan-coil unit and ductwork. A wide variety of heating appliances can be used to supply backup heat on cloudy days.
Solar hot-air collectors are simpler than solar hot-water collectors. A solar hot-air collector consists of an insulated box, painted black on the interior,…