Optimal power control of grid tied PV-battery-diesel system powering heat pump water heaters

This paper develops an optimal control strategy for power dispatch of the grid tied photovoltaic (PV) - battery-diesel system to power heat pump water heaters (HPWH). The system comprises of the PV modules, grid, battery, HPWH, diesel generator (DG) and other domestic appliances. The PV can simultaneously feed-in the excess power to the grid and supply the loads. The battery is used as storage of cheaper-to-buy off peak grid energy dependent on the time-of-use (TOU) electricity tariff whilst the DG is a backup power source. The objective function of model is to minimize energy and fuel cost while maximizing PV energy trade-off for incentives. The TOU is an important control parameter in the model. The power flows from each source are the control variables. The optimal control showed a great potential for the realization of a practical net zero-energy building and as well as for demand side management, since the model meets both technical and operational constraints. A case study is done based on 3x16kW HPWH installed at Pretoria hotel in South Africa. Simulations run over year on selected seasonal dates using the actual measured demand of the HPWH. The optimal control problem is solved using mixed integer nonlinear program and the results show how TOU affects the power dispatch to the HPWH. The energy and cost savings are presented in this paper. (C) 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license