"Businesses may deduct from net income, for state excise tax purposes, costs incurred from the installation of any "solar or wind powered climatic control unit and any solar or wind powered water heating unit or any other type unit or system powered thereby." The installation must be located in Massachusetts and used exclusively in the trade or business of the corporation. A system or unit that qualifies for this deduction will not be taxed under the tangible property measure of the state's corporate excise tax. The exemption is in effect for the length of the equipment's depreciation period" (DSIRE site).
For more information visit Corporate Deduction.