The NAHB Research Center, on behalf of the national Partnership for Advancing Technology in Housing, is evaluating energy production and performance of solar-powered renewable energy systems in three homes in San Diego. Two of Shea Homes' High Performance Homes, which are designed to expend 30 percent less energy on space heating and cooling than would the same home built to National Model Energy Code standards, served as control homes.

Each evaluation home is equipped with roof-mounted photovoltaic (PV) systems. These comprise 12 110-watt DC panels and two inverters that convert power produced into grid-quality AC electricity. Radiant barrier roof sheathing reflects heat away from the attic, and thermal expansion valves improve HVAC system performance.

The PV system evaluation focused on how the system's physical orientation affected electricity production, the system's effectiveness at reducing a home's summer electric demand, homeowner satisfaction, and recommendations for improvement.

Findings reveal that PV systems oriented westward produced only 12 percent less electricity than southerly oriented PV systems, giving the builder greater confidence in installing the systems in a variety of orientations without sacrificing PV performance. Overall, the PV systems provided 18 percent to 26 percent of the homes' electricity, a feature homeowners appreciate when electricity bills are due.

One additional feature homeowners liked is an indoor electric meter with digital readout. The meter monitors PV power and summarizes PV energy production over a specified period of time.

For more information, visit or e-mail