(3) Qualifying Expenditures.

Only net expenditures paid with respect to renewable energy source property used in connection with the taxpayer's principal residence may be used to compute the amount of the credit. The term "in connection with" includes, but is not limited to, renewable energy source property in or on a principal residence or residential property.

(a) Principal residence. A taxpayer must be a resident of Massachusetts for his or her principal residence to be in Massachusetts. If a taxpayer is resident in Massachusetts and has only one place of residence, that place of residence is the taxpayer’s principal residence. If a taxpayer is resident in Massachusetts and has more than one place of residence, the determination of which place of residence is the taxpayer’s principal residence depends upon all the facts and circumstances in the case, including the number of days spent at each place of residence and the good faith representations of the taxpayer. If an owner or tenant changes his or her principal place of residence within a taxable year an energy credit may be claimed for each principal residence of the taxpayer, subject to the maximum credit amount of $1000. Subject to the requirements of this regulation, joint owners of residential property may share any energy credit claimed for renewable energy source property expenditures in the same proportion as their ownership interest in the residential property. Joint owners are subject to the maximum credit amount of $1000. Joint ownership includes joint tenancy, tenancy in common and tenancy by the entirety. An individual who is a stockholder in a cooperative housing corporation, or who is a member of a condominium association with respect to a condominium which he or she owns, may claim a proportionate share of the renewable energy source expenditure of such condominium association or cooperative housing corporation. A cooperative housing or condominium unit may be treated as a "principal residence" for purposes of the $1000 credit limitation. (b) Renewable energy source property. Only renewable energy source property used for residential purposes qualifies for the energy credit. When at least eighty percent of the use of such property is for residential purposes, the entire amount of the renewable energy source expenditure may be used to compute the credit. However, if less than eighty percent of such property is used for residential purposes, the percent of the amount of the expenditure that must be used to compute the credit is the percent of the property's residential use. Subject to the requirements of this regulation, joint owners of renewable energy source property may share any energy credit claimed for renewable energy source property expenditures in the same proportion as their expenditures for that property. Joint owners are subject to the maximum credit amount of $1000 per principal residence. A renewable energy source expenditure does not include any expenditure for any energy storage medium if the primary function of that medium is not the storage of energy. For this reason expenditures for insulation, storm or thermal windows or doors, caulking or weather-stripping, furnace replacement burners, devices for modifying flue openings, furnace ignition systems, automatic setback thermostats, energy use meters and similar devices and items are not renewable energy source expenditures. In addition, the costs of maintenance and repair of installed renewable energy source property, or of leasing renewable energy source property, are not renewable energy source expenditures.