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...

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