Abstract: A control system includes one or more levels of control of power and energy. At one level, a first controller optimally divides power between two or more processes, to maximize instantaneous production, for a given amount of currently available power. In the case of EDR desalination, electric power is optimally divided between ion exchange membranes and pumps to maximize instantaneous production of desalinated water for a given amount of available electric power. Optionally, at another level, a second controller divides time-varying power between the processes fed by the first level controller and an energy storage unit, based on a prediction of future power availability and a function. In the EDR case, power generated by a photovoltaic array is divided between the EDR desalination process and a battery, based on a prediction of future PV power availability and a function, to ensure reliable water production in the future.