SOLAR TAX CREDITS can be claimed on special membranes put on roofs underneath solar panels, but only on the incremental cost above what replacing the roof would cost, the IRS said.

The IRS made the statement in a private letter ruling that it made public in December. The ruling is Private Letter Ruling 201450013.

A company asked the IRS whether it could claim an investment tax credit on a solar commercial rooftop system that it purchased. The system uses bi-facial solar panels that absorb sunlight on both sides of the panels. A special membrane is put on the roof to reflect sunlight to the backside of the panels. The panels are up to 40% more efficient than regular panels. The membrane covers 96% of the roof.

The IRS confirmed the membrane is considered part of the solar system, but said the company had to back out the cost of putting a new roof on the building without the reflective feature.

Keith Martin in Washington