A.Gary Gerber, owner of Sun Light and Power, in Berkeley, Calif., responds: Actually, many people are using these solar modules — we call them building-integrated photovoltaics, or BIPVs — as roofing. Designed to replace long-lived roofing systems such as composite slate shingles, concrete tile, and standing-seam metal roofing, BIPVs are normally installed by a roofer as part of a new roof. Because most of these roofs are actually a mixture of PV modules and conventional roofing material, the roofer has to weave the two together, while a solar contractor makes the necessary electrical connections and supervises the work.

There are several reasons there are not more BIPVs. For one thing, most PV systems being installed today are for retrofit, in cases where a new roof isn't required. Second, of those homeowners who do need a new roof, many choose composition shingles, and there is no PV system that cost-effectively replaces this type of roofing. Third, an integrated PV roof is not necessarily less expensive than putting modules above the roof; often, it's actually much more costly, due to higher material costs, increased wiring costs, and smaller modules that require more total labor to install.

Fourth, long-term maintenance and repair of a BIPV system may involve removing and replacing the roof itself, a prospect that concerns some homeowners (even though the BIPV usually has a 25-year warranty). Finally, most solar companies would prefer to install their systems themselves rather than deal with the logistics and costs of hiring, training, and supervising a roofer.

BIPV makes the most sense for new construction, especially when the builder can hide the system from view in plain sight. As more new-home builders and developers get wise to the advantages of offering PV to their customers, expect to see many more of these BIPV roofs dotting the landscape (if we can spot them).