The voltage at which the solar array will produce the maximum power output. This value will vary significantly due to environmental conditions (temperature, cloud cover, time of day, etc) and system setup (panel configuration, panel angle, etc). MPPT (maximum power point tracking) controllers such as the TriStar MPPT and SunSaver MPPT with Morningstar TrakStar™ technology are able to track this shifting value to provide the maximum amount of charging power possible.