a photovoltaic installation typically includes an array of solar panels, an inverter, rechargeable batteries (for use at night), a charge controller (a device that prevents the batteries from over-charging), two gfci circuit breakers (one before the inverter and one after), and interconnection wiring. there is sometimes also a transformer after the inverter, which can power 240 volt heavy appliances such as a clothes dryer or oven. the transformer is often part of the inverter and can't be seen. everything past the inverter (or transformer if there is one) is set up like a normal utility-fed installation (breaker panel, lights, outlets, switches, etc.). if there is no transformer, only 120 volt devices may be used. installations without a transformer must be labelled as such on the breaker panel to alert future electricians that 240 volt appliances can not be installed. some installations have direct current (dc) lighting and possibly dc appliances. the advantage of this is that for dc loads, the losses in the inverter are avoided. these installations will have a separate dc breaker panel connected before the inverter. for safety reasons, dc wiring cannot be run in the same conduit as ac wiring, and dc outlets must not accept an ac plug and vice versa.