A photovoltaic power plant (25, 32, 33, 34, 35) comprising one or more photovoltaic devices (27), each device comprising at least two terminals (30, 31) wherein one or more of the terminals (30, 31) is connected to a switch (12, 13) which is in turn connected to a point (10, 15, 16) held at a voltage relative to ground (11) and at least one switch (12, 13) is controlled in response to one or more parameters, and a method of controlling such a power plant (25, 32, 33, 34, 35).