Predictive energy balance for solar hot water systems

Abstract

Solar hot water systems necessarily require storage due to a time difference between solar supply and hot water demand. Typically the storage vessel uses an auxiliary heater to maintain a volume of hot water during periods of low insolation. The operation of this heater is controlled by a reactive device called a thermostat. This paper presents an advanced control solution to allow the thermostat to operate with discretion so that less solar energy is displaced by the operation of the auxiliary heater. The control algorithm is based on a predictive energy balance, although its behaviour may be modified by human input.