If no conventional heating and cooling system exists in a building, a solar energy or geothermal heating and cooling system shall be assessed to the owner of the real property on which it is located at not more than the value of a conventional system. If a solar energy or geothermal heating and cooling system is installed in addition to a conventional system in a building, the combined system may be assessed to the owner of the real property on which it is located at not more than the value of the conventional system.