An analysis is presented of the benefits of voluntary load shedding schemes which interrupt electricity supply when generating capacity is insufficient. Supply interruption is by ripple control, in which coded pulses are transmitted through the supply network, or by radio control. An algorithm is devised and illustrated, which evaluates the benefits of load shedding for any system, assuming fixed prices and a constant load duration curve. The algorithm is developed by calculating the expected shed load in a given period and the costs of building additional capacity to meet this load. These costs correspond to the benefits of the load shedding scheme.