Electrification of Residential Heating, Cooling and Hot Water Supply – Load Smoothing Using Onsite Photovoltaics, Heat Pump and Thermal Batteries
Creators: name: Li, Yuanyuan
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401703
subject: Energy generation, conversion and storage (excl. chemical and electrical)

description: Given the pressing time frame to meet emissions reduction targets, decarbonising buildings through the electrification of heating has become a matter of urgency. However, the high energy demands of electric heating and cooling, pose a significant challenge to the electricity supply chain. Increasing the number of rooftop solar photovoltaic systems will not necessarily eliminate this problem. Cheap and safe thermal energy storage is a potentially viable solution that will allow electrical thermal comfort systems to be deployed with minimal impact on the grid. This thesis proposes an innovative system based on a combination of solar photovoltaics, a heat pump and thermal energy storage for residential heating, cooling and hot water demand. 
The research for the proposed system firstly focused on a representative Australian house located in Brisbane, where the energy consumption was previously monitored by the Australian Commonwealth Scientific Industrial Research Organisation. The work quantified the impacts of the proposed system on that specific house. The prosed system consists of a PV with a heat pump and hot and cold thermal storage (HP+PV+TES). This system was compared to a heat pump only (HP) and a heat pump with PV (HP+PV). The annual hourly thermal and domestic hot water loads were determined using building energy simulation software and verified using measured data. Combined with the measured sub-metered electrical loads of other electrical appliances, this data was used to simulate the solar system export, heat pump demand, and thermal storage system performance. Results show that by combining a 5-kW solar system, the proposed HP+PV+TES system can reduce annual grid-electricity demand by approximately 76%. This load reduction is almost twice as high as that can be achieved by a HP+PV system. By switching from HP+PV to HP+PV+TES, the savings in peak electrical load was improved from 14% to 45%, when it is calculated based on the peak load of a simple HP scenario with no PV and TES. . Furthermore, by switching from HP+PV to HP+PV+TES, solar fraction increased from 38% to 84%, and solar self-consumption increased from 27% to 56%. This study demonstrates that the proposed system is an effective means for managing electricity demand, shifting peak load and improving solar utilisation. 
The effectiveness of the system was further investigated in terms of electricity demand and solar utilisation in various geographical locations. The results illustrate that with effective controls, the proposed system can reduce a building’s annual grid electricity demand by 50–80% and increase its solar self-consumption to around 60% in the selected cities. The temporal load profile was also significantly reduced and flattened, enabling large-scale distributed photovoltaics with no negative effects on the grid. 
Furthermore, the energy performance of the electrified thermal system combined with onsite photovoltaics for a range of buildings with different thermal characteristics, orientations, occupancy profiles, and solar panel directions was investigated. This sensitivity analysis demonstrated the robustness of the potential benefits of these thermal systems when installed and operated under non-optimal conditions. The findings of this study reveal significant grid electricity savings achieved by these integrated systems, ranging from approximately 50% to 80% in both heating and cooling-dominated regions with diverse climates, even under reasonable extreme conditions. These outcomes remain consistent regardless of variations in PV direction, house thermal performance, building orientation, and occupancy profile. By utilising thermal energy storage to store surplus solar energy, the system enhanced the PV self-consumption ratio and solar fraction by approximately 30% irrespective of moderate deviations in PV direction.
An economic analysis demonstrated that these benefits can be achieved at a reasonable cost to consumers and with a positive rate of return compared with alternative options across a wide range of climate and operational conditions. In addition, by using the real-time carbon emissions data to simulate the hourly CO2 emissions, the proposed HP+PV+TES system showed a significant reduction in annual and hourly emissions compared with the conventional HP+PV system, especially during peak hours, further demonstrating the environmental benefits of the proposed system.
 This comprehensive research and analysis showed that the proposed HP+PV+TES system is a cost-effective solution to ease the stress on the grid from excessive photovoltaic power and heating- and cooling-related peak demand.