Energy profiles and electricity flexibility potential in Norwegian apartment buildings with electric vehicle charging

Abstract

Renewable energy generation and energy efficiency of buildings are central strategies for mitigating emissions, aligned with the objectives of the Paris Agreement. With an increasing share of the energy supply coming from variable sources, the demand for flexible end-use of electricity increases. Energy flexibility in buildings has the potential to reduce grid burden of neighbourhoods. However, despite its potential, the practical implementation of end-user flexibility is challenging. Integrating flexibility solutions with existing automation systems while ensuring occupant satisfaction can be a complex task and remains a main challenge for implementation. In this context, residential electric vehicle (EV) charging within apartment buildings stands out as a promising solution. Shifting the timing of EV charging from high-demand afternoons to low-load nights can minimize grid strain with little impact on resident comfort. Additionally, in many apartment buildings, EV charging is already part of an energy management infrastructure, which may ease the practical implementation of flexibility solutions. Literature reviews show an increasing research focus on residential EV charging, however there is a need for more real-world data and knowledge on EV charging behaviour and energy use in apartments buildings, and the relationship between them. This thesis focuses on exploring energy profiles and the electricity flexibility potential in Norwegian apartment buildings with EV charging. A third of the Norwegian population resides in apartments, the residential sector has an increasing demand for EV charging, and a growing solar photovoltaic (PV) utilisation. The study includes the use of comprehensive datasets of energy and EV charging from Norwegian apartment buildings. The main case study is a large housing cooperative with more than 1000 apartments, and EV charging data is analysed from 35 000 EV charging sessions in 12 residential locations in Norway. Initially, the thesis examines the energy profiles for household energy use and PV generation for apartment buildings, and how the energy profiles are influenced by climate variables such as outdoor temperature and solar radiation. In the main case study, the average annual delivered energy to the apartments was found to be about 138 kWh/m2 for heating and 51 kWh/m2 for electricity. Assuming one EV per apartment, the average electricity use for EV charging was about 25 kWh/m2, contributing to roughly 12% of the total energy use per apartment. Next, the research focuses on how user habits of residential EV charging influence the electricity load profiles. The study identified variations in residential charging behaviour between users with private charge points (CPs) at their own parking spaces and those who utilized shared CPs. Users with private CPs had an average connection time of 12.8 hours, whereas those using shared CPs had an average of 6.5 hours connection time. Data from EV charging reports provided information on session energy and plug-in times, which was then used to simulate hourly charging energy at different charging power levels. The study presents how residential charging behaviour and energy flexibility are affected by the battery capacity and charging power for the EVs. Findings indicate a significant opportunity for shifting residential EV charging in time, particularly from late afternoon and evenings to nighttime. The flexibility potential of single EV users grows with increasing charging power, connection frequency, and duration of each connection. The thesis also explores the effects of grid-connected EV cabin preheating, which is generally recommended in cold climates. EV cabin preheating typically occurs during mornings with cold outdoor temperatures, when the grid is already under pressure. During a trial involving 51 preheating sessions with five representative EV models, it was observed that most EVs used approximately 2 kWh of energy during preheating, with some sessions reaching a maximum of 5 kWh. Finally, the thesis explores the potential for electricity flexibility from EVs, in relation to nonflexible apartment loads and PV generation, in the Norwegian context. The grid burden of optimised EV charging is affected by different energy/peak tariffs, metering locations, the availability of PV systems, and vehicle-to-grid (V2G) technologies. In the simulated scenarios with apartment electricity loads and optimised EV charging, the peak loads were reduced by around 45% compared to a base case with non-coordinated EV charging. The study found that relatively few EVs were connected to the residential CPs during the day, which limits the self-consumption of PV generation for EV charging. For the simulated scenarios, a maximum of 38% of the energy load in the optimised EV charging was covered by PV generation. The study offers knowledge relevant for housing associations and building owners regarding their energy use and opportunities for end-use flexibility. Similarly, it provides insights for companies developing end-user flexibility solutions, such as charge point operators (CPOs), energy companies, and aggregators. Additionally, Distribution System Operators (DSOs), can benefit from the knowledge about how end-use flexibility in the residential sector can contribute to reduce the grid burden. Public policymakers and regulatory bodies can leverage this knowledge to drive progress in realizing end-use flexibility and meeting energy and climate objectives.