Abstract: A merchant and a customer have an agreement for the trading of energy units wherein the customer pays a contracted sum and the applicable wholesale market pool price for excess units of energy and receives the wholesale market pool price for unused units of energy. A system monitors and controls the energy usage of the customer. The system includes a metering means (105), a communication means (123, 124) receiving pricing information, a computing means (103) accumulating information from the metering means and communication means and determining a preferred trading outcome, and switching means controlling energy supply to the energy consuming devices to achieve the preferred trading outcome.