A photovoltaic system for residential, commercial, or industrial energy supply consists of the solar array and a number of components often summarized as the (BOS). This term is synonymous with "" q.v. BOS-components include power-conditioning equipment and structures for mounting, typically one or more DC to power converters, also known as, an energy storage device,. Most solar parks are PV systems, also known as free-field solar power plants. They can either be fixed tilt or use a single axis or dual axis. While tracking improves the overall performance, it also increases the system's installation and maintenance cost. A converts the array's power output from to, and connection to the is made through a high voltage, three phase step up.