There are two distinct goals of solar systems: a) generate electricity b) produce hot water
Electricity producing photo-voltaic cells not only produce electricity for the house, but also, produce excess electricity (co-generation) to "sell" back to the utility company. The payback of electricity producing systems typically has about a 10 year payback for residential installations
There are two types of hot-water producing systems a) high volume; small temperature differential b) low volume; high efficiency (temp differential)
High volume, small temperature differentials are relatively inexpensive to install and are typically used for swimming pools (black panels at right). The square feet of panels is typically about the surface square footage of the swimming pool. The technology is straightforward - water is pumped to the bottom of each panel and then forced up through a series of black thin channels. Surfacing at the top of the panel, all exits are routed to the highest point in the system and then returned to the pool.
Domestic hot water heating requires higher efficiency, glass and copper pipe systems in order to heat the water to typically 160 degrees. A couple hundred feet of panels on an appropriately south-facing roof is all that is needed to heat most residences. A boiler is required to supplement the solar heating in winter or during periods of unfavorable sun.