In Minnesota, solar-energy systems purchased on or after August 1, 2005, are exempt from the state's sales tax. Solar energy systems are defined as "a set of devices whose primary purpose is to collect solar energy and convert and store it for useful purposes including heating and cooling buildings or other energy-using processes." Thus the exemption is very broad and could apply to solar electric (PV) systems, solar water-heating systems and solar space-heating systems. All components of these systems are exempt, including panels, wiring, pipes, pumps and racks. Buyers must complete Minnesota Department of Revenue Form ST3 "Certificate of Exemption" in order to claim the exemption. Sellers are required to keep the form in their files for tax reference. This incentive has no expiration date.