Donato Melchiorre

Feasibility of using electric vehicles as domestic storage systems

Low-carbon grids are becoming increasingly prevalent, especially in developed countries, as a transition is under way towards renewable energy sources. Solar photovoltaics and wind are the most mature and predominant technologies with the highest growth rates in the renewable sector. Both suffer from intermittency issues, and the question of large-scale short- and long-term electricity storage grows as the renewable share in generation continues to rise, reaching 29.5% in the UK in 2017. Simultaneously, the transport industry is going through electrification, predominantly the personal vehicle sector. Currently, lithium-ion batteries dominate the electric vehicle (EV) market and this technology is predicted to continue doing so. Furthermore, EV batteries are performing much better than expected, meaning optimising battery utilisation will increase value for money for owners and benefit society.

By combining these trends, a new area of technologies known as Vehicle-to-Grid (V2G) has arisen. Using EV batteries for storage could help the grid by alleviating some of the intermittency issues, through load balancing. However, V2G research has focused on the systemic point of view and often failed to consider consumer interests. In contrast, Vehicle-to-Home (V2H) is more customer-centric as it aims to shift domestic electricity consumption from peak to off-peak periods, which also helps the grid. This makes sense if the consumer is on a time-of-use tariff. An increased focus on demand side management measures will lead to a greater presence of such tariffs. The purpose of this dissertation is to determine the feasibility of using EV batteries for domestic electricity storage in the UK. The economic and technical aspects of a V2H system will be assessed against domestic battery solutions.

To carry out the comparison, a UK average EV and domestic battery have been established, called CamEV and CamBat respectively. The CamEV characteristics were determined by taking a weighted average from the five highest selling EVs in the UK. An arithmetic mean was found for the individual CamBat features from seven models available on the UK market. The CamEV and CamBat were compared under four scenarios. These are Ofgem’s two domestic electricity profile classes (PC1, PC2) and two existing time-of-use tariffs, one with two and the other with three rates during a day.

Maximum annual savings on electricity bills for consumers were estimated to be around 35% and 57% for the EV and battery, respectively. However, not all scenarios yielded savings and with the highest battery degradation rate, the consumer lost up to 15% for EV and 13% annually for battery use. Savings on the three-rate tariff were higher than on the two-rate tariff for both EV and battery. Battery degradation cost was the major parameter in calculating the economic feasibility of V2H and domestic batteries, but these costs are expected to continue to fall. Suitable time-of-use tariff design is the key to maximising consumers’ savings of these systems.