Which Electric Vehicle Use Profiles Provide Optimal Building Support Opportunities?
With potentially up to 60% of total new car sales in the UK being electric vehicles (EVs) by 2030, this represents a significant draw on the UK National Grid . Element Energy predict an electricity demand increase of 30% to 86GW on peak demand from EV charging unless correctly managed charging schedules are implemented . However, whilst EVs do represent a potential future strain on the UK electricity grid, the electricity within the vehicles represents as much as 11GWh of potential energy storage capacity available for grid support services . Appropriate management strategies for EV charging and discharging are imperative to ensuring system overload does not occur, whilst guaranteeing every EV user can undertake their required journeys. Another key consideration for future EV grid support opportunities is EV availability. A field trial of nearly 200 vehicles has been used as a case study for EV use profiles, with the trial looking at private and commercial fleets. This data has been used in two forms; firstly to provide data on journey information for the two primary data sets. Secondly to act as a comparison to building energy consumption profiles to attempt a support scenario suggestions.
When we look at the journey patterns of the two data sets (Figure 1) there isn’t a noticeable difference between the commercial and private fleet in terms of total number of journeys taken by the fleet. Peak vehicle usage for the commercial fleet is between 7am and 8pm, with a sharp increase between 7am and 8am. This suggests they would be ideally placed to support grid services between the hours of midnight and 7am. However, the vehicles also require re-charging before their all day us and, this would be best placed to occur during this time, suggesting that perhaps a managed charging strategy would be more appropriate than a V2G strategy for this vehicle use profile.
Figure 1 – Number of Fleet Journeys vs. Time of Day
Conversely, the private fleet have clear peaks in vehicle use between 7am and 9pm, with increased peaks also appear between 7am and 8.30am and 4pm and 8pm. This is also when the UK electricity grid has the highest demands placed upon it, again suggesting peak grid support options may be unsuitable for the use profiles demonstrated in this data set.
Despite this, commercial building support could be possible for those vehicles not in use during working hours (traditionally between 8am and 6pm in the UK). If we look at the building demand profiles of two UK office buildings based in the north of England (Figure 2 and 3) we can see a clear increase in demand during office working hours (mean value). Assuming just 10 of the EVs from the private fleet were available at any one time during this period, the electricity savings could be as much as £1,500 per annum for each building. Assuming 10 vehicles each have an average battery availability of ~17kWh per day for V2G services, this leaves around 5-10kWh per hour for building support opportunities based upon a 5 hour availability period per vehicle.
Figure 2 and 3 – Building Demand Profiles
Assuming a 3kWh discharge rate for the vehicles, if just 10 vehicles are available to discharge into the buildings, this reduces the mean demand for the buildings to the orange line shown in Figures 2 and 3. An increase in EV numbers signed up to a V2G scheme would provide additional savings to the building.
It is worth noting at this point the alternative sale markets available for excess EV battery capacity. These are numerous and represent a complex network of ancillary services, Short Term Operating Reserve (STOR) and fast response services to the National Grid. Research suggests the future of V2G uptake will rely upon the development of a price per kWh payment for EV stored electricity in order for EV users to sign up to such a scheme. This would likely operate in a similar way to the successful PV ‘Feed-in-Tariff’ (FIT). However, complex decision making and management of disparate storage assets will be essential, with a Virtual Power Plant (VPP) being an obvious choice, providing management based upon building and National Grid demand, payment tariffs and EV availability. Here we have just explored potential building support however, there is a wide range of support opportunities available for and EV to provide electricity. Competitive pricing of the V2G tariff will be the main driver for whether the EV is used for building or grid support.
In looking at this small case study of EVs containing both private and commercial vehicle there is evidence to suggest electrical support is possible through excess EV battery storage. Based upon the building demand information evaluated there is evidence to suggest EV support could go a long way to reducing daily building demand. Commercial buildings also represent an ideal scenario due to the predictability of the vehicle location and building demand profiles.
The commercial fleet represents less of an opportunity than the private fleet, with vehicle usage dominating a large proportion of the day. Proportionally the number of vehicles in use is less than the private fleet, however the most popular time of day was during peak grid electricity demand times.
Overall, this case study indicated that generic use profiles would not be suitable in providing peak shaving services to the National Grid, however commercial buildings could see large benefits if they were to provide adequate infrastructure to support V2G technology and payment.
 Element Energy Ltd, “Pathways to high penetration of electric vehicles,” 2013.
 National Grid, “UK Future Energy Scenarios,” Warwick, 2013.
Becky Gough is a Research Engineer currently working towards a Systems Engineering Doctorate in low carbon technologies with Cenex, The Centre of Excellence for Low Carbon and Fuel Cell Technologies. Her background is in the buildings sector, graduating from Nottingham University in 2012 with a degree in Architecture and Environmental Design. As a building services engineer she began her Engineering Doctorate in 2012, looking at the interoperability of renewable technologies into domestic and commercial properties. From this her work led into the design and optimisation of hybrid heat pump and photovoltaic thermal systems in association with her first sponsor company.
Her current research looks to explore the integration of electric vehicles into the built and smart cities environment. How EVs can be used as a reserve energy store for peak shaving services in the UK is of key importance. She is involved in several Innovate UK funded projects looking to explore the role vehicle-to-grid will play in the energy supply network over coming years.