Abstract
Due to the need for energy security, increasing demand for renewable electricity, and mitigation of the effects of natural disasters, microgrids are being deployed for a decarbonized and decentralized electricity grid. The variability of both renewable energy sources and electricity demand creates a significant supply-demand mismatch in microgrids. This is normally dealt with battery storage systems coupled with microgrids to reduce intermittency by storing surplus generated energy for later use. However, batteries are expensive and have a limited lifecycle. It becomes pertinent to explore other affordable options with an extended lifespan. This thesis aims to assess the storage potential of domestic hot water cylinders as part of a residential microgrid comprised of a cluster of 19 households with solar photovoltaic (PV) supply.
To carry out an analysis of this potential, this thesis develops a physical model of a hot water cylinder that simulates the hot water electricity demand of the households under different control conditions. This simulation is based on a novel approach that determines hot water flow based on reverse engineering measured electricity data. The electricity demand data and PV supply data were based on data collected previously in the GREEN Grid project in New Zealand. Four performance metrics including system efficiency, self-sufficiency, solar PV self-consumption, and percentage reduction in battery capacity were used to compare two systems with and without domestic hot water cylinder storage under 10 scenarios.
The results showed that the system that includes domestic hot water cylinder storage required from 37-78% less battery capacity for the same percentage of self-sufficiency. Results of the systems also indicated that scenarios that meet 100% of the demand with solar PV are less efficient than scenarios that import a fraction of their supply from the utility grid to meet demand. We thus conclude that domestic hot water cylinders are useful for storing energy to reduce the size of batteries and increase PV self-consumption in the microgrid. We also found that microgrid systems connected to the utility grid are more efficient than stand-alone microgrids.