This paper develops an optimal control (OC) model of a heat pump water heater (HPWH) supplied by a wind generator-photovoltaic-grid system. The objective function is energy cost minimization, taking into account the time-of-use electricity tariff (TOU), which is an important control parameter. The control variables are the supply switch to the HPWH and the power from the grid, while the hot water temperature inside the tank is the state variable. The model meets both the HPWH's technical and operational constraints in providing hot water at a desired temperature and achieves load shifting. This problem is solved using a mixed integer linear program. The results show a 70.7% cost reduction upon implementation of this intervention. A case study is done and the OC shows significant potential in energy and cost saving when compared to the digital thermostat controller used currently in most HPWHs. The economic analysis is presented in this paper as well. Nomenclature P w (t) wind generator power output (kW) P pv (t) photovoltaic power output (kW) P g (t)grid power (kW) P hp heat pump water heater power demand (kW) COP coefficient of performance u(t) heat pump power supply switch control variable (0 or 1) T (t) hot water temperature inside the tank ( • C) T low and T up lower and upper hot water temperature set points (

Today, as a consequence of the growing installation of efficient technologies, such as com-12 bined heat and power (CHP) as a co-generation, the integration of electricity through grid 13 supply, Photovoltaic (PV) and energy storage systems as an integrated network is attracting a 14 lot of attention in smart grid applications. To model the interaction among electricity and nat-15 ural gas, the energy hub framework is adopted to determine a modelling procedure for such 16 multi-carrier energy systems. This paper presents a residential energy hub model for a smart 17 home as a modified framework of conventional energy hubs in a smart grid with considera-18 tion of heat pump water heater, coordination of sources and carbon emissions. Therefore, this 19 study is twofold; the first part optimizes the operation of the combined CHP, Photovoltaic and 20 storage system under time-of-use tariff. Since residential load management plays a key role 21 in realizing household demand response programs in a smart grid, performing optimal load 22 management in the proposed residential energy hub model is also studied in this paper. To 23 achieve this, the optimization problem is extended by considering modelling of a heat pump 24 water heater. It is also found out that CO 2 signal could give customers an environmental 25 motivation to shift or reduce loads during peak hours, as it would enable co-optimization of 26 electricity consumption costs and carbon emissions reductions.

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 consists 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 to the HPWH. The objective function of the model is to minimize energy and fuel cost while maximizing PV energy trade-off for incentives. The TOU is an important control parameter in this model. The power flows from each power source are the control variables. The optimal control shows a great potential to realize a practical net zero-energy building and demand side management. This model meets both the technical and operational constraints. A case study is done based on a 3x16kW HPWH installed at a Pretoria hotel in South Africa. Simulations run over a year on selected seasonal dates using the actual measured demand of the HPWH. The optimal control problem is solved using a mixed integer non-linear program and the results show how TOU affects the power dispatch to the HPWH. The energy and cost savings are presented in this paper.

This paper presents an optimal energy management strategy for a grid tied photovoltaic-wind-fuel cell hybrid power supply system. The hybrid systems meets the load demand consisting of an electrical load and a heat pump water heater supplying thermal load. The objective is to minimize energy cost and maximize fuel cell output, taking into account the time-of-use electricity tariff. The optimal control problem is solved using a mixed integer linear program with the supply switch to the heat pump water heater and the power from the grid, power to/from inverter, power to electrolyzer and from fuel cell the control variables. The hot water temperature inside the water storage tank and the hydrogen in the storage tank are the state variables. The performance of the proposed control strategy is tested by simulating different operating scenarios: with and without renewable energy feed-in, and the results confirm the effectiveness of the proposed control strategy, as it increases the supply reliability of the system. Keywords

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