If the solar market fails to light up, it won't be for a lack of sun-drenched spaces. The Energy Foundation scouted out the country's best commercial and residential roof space and found there's enough to support 710,000MW of solar power. So what makes a roof prime PV real estate? We asked Ed Kern, president of Lincoln, Mass.-based Irradiance and a frequent PV design consultant, what to shop for.

Roof grade — Even the slightest tilt will force you to make surface penetrations to anchor the system. You can get away with just ballasts on flat roofs.

Surface — Roofs with an EPDM membrane will resist corrosion and unintentional penetrations. Water tends to collect under ballast trays, and tar and gravel surfaces are much more susceptible to water damage.

Layout — Avoid sites with skylights and roof-mounted HVAC systems because they can be difficult to work around. Wide open spaces are best.

Height — The taller the building, the windier the roof and the more ballast you'll need. And building codes for load-bearing capabilities get complicated for buildings over 60 feet, so steer clear of the highrises.