Any building or addition to a building, the construction of
which is commenced on or after October 1, 1976, and before October
1, 1991, which is equipped with a solar-energy heating or cooling
system shall be exempt from taxation to the extent of the amount by
which the assessed valuation of such real property equipped with such
solar heating or cooling system exceeds the assessed valuation of
such real property equipped with the conventional portion of the heating
or cooling system, exclusive of any portion of such system related
to solar energy, provided this exemption shall only apply to the first
15 assessment years following construction of such building or addition.