Optimal Scheduling Strategy for a Grid-connected Photovoltaic System for Heat Pump Water Heaters

AbstractThe aim of this paper is to develop an optimal scheduling strategy model for a grid-connected photovoltaic (PV) system to power heat pump water heaters (HPWH). The system is composed of PV modules which are grid-tied. The PV is capable of supplying power simultaneously to the HPWH and domestic loads whilst the grid is a complimentary source. The cost function of this model is to minimize energy cost, while the PV power outputs to the HPWH and domestic appliances are to be maximized. The time-of-use (TOU) electricity tariff is taken into account in the optimal scheduling model. The control variables are the power flows within the branches of the system. The optimal control strategy of this grid-connected PV system can be implemented to reduce the power demand and serve as means of load shifting while meeting technical and operational constraints. This model is shown to have more economical benefits than the solar thermal heaters, because of the possibility of turning house buildings into energy positive if the feed-in tariffs become attractive. A case study was done based on 3x16kW HPWH installed at Pretoria hotel in South Africa. Simulations run over year on selected seasonal dates using actual fluctuating coefficient of performance (COP) of the HPWH. The optimal results show how solar output variation and TOU affect the scheduling strategy of the HPWH. The energy cost savings are as well presented in this paper