(a) The dollar limitation provided in § 203.18(a) may be increased by up to 20 percent if such an increase is necessary to account for the increased cost of the residence due to the installation of a solar energy system.

(b) Solar energy system is defined as any addition, alteration, or improvement to an existing or new structure which is designed to utilize wind energy or solar energy either of the active type based on mechanically forced energy transfer or of the passive type based on convective, conductive, or radiant energy transfer or some combination of these types to reduce the energy requirements of that structure from other energy sources and which is in conformity with such criteria and standards as shall be prescribed by the Secretary in consultation with the Secretary of Energy.