Operation cost and energy usage minimization of a hybrid solar/electrical water heating system

Approximately 40% to 60 % of the total energy consumed by a traditional household in South Africa can be allocated to the heating of water. Furthermore, most of water heating takes place during peak electricity consumption periods, where electricity costs are highest. In this paper, the optimal energy management of a hybrid solar electric water heater (HSWH) is presented. The hybrid system consists of an indirect flat plate collector coupled to an electric storage tank water heater (ESTWH). The electric resistive element inside the storage tank water heater serves only as an auxiliary heater when solar irradiance is insufficient. A typical medium density household within the Mangaung municipality area in the city of Bloemfontein, South Africa is considered. The aim is to evaluate if an optimal control approach can be used to effectively shift the energy usage profile of the system under the residential Time-of-Use (TOU) tariff enforced by the electricity supplier, while maintaining a comfortable thermal level of the hot water user. The secondary aim is to reduce the energy required to increase the thermal level of the water compared to a baseline water heater. The proposed water heating system with optimal control is modelled and simulated using Matlab OPTI-Toolbox. The control variable was successfully solved with switching taking place during off-peak periods while maintaining the desired temperature of the hot water consumer.