An inverter converts direct current (DC) into alternating current (AC) by mechanical or electronic means and makes renewable resources and energy-storage systems utility interactive. Inverters are basic components on most small and large energy systems that convert low-voltage DC power generated from a renewable energy source into higher-voltage AC power required for many residential, commercial, and industrial applications. Grid-tied inverters are required in energy systems that produce or store electric energy in DC form and transfer that energy to or from an AC power system. Typical energy systems include solar photovoltaics (PV), wind turbines, batteries, and fuel cells. Grid-tied inverters were considered unreliable when they were first commercially introduced in the early 1980s. Their problems were attributed to the lack of quality control that comes from mass production.