Energy storage co-located with EV charging infrastructure displaces the impact that cars simultaneously drawing electricity would otherwise have on the grid, particularly during peak demand periods. But for investments in energy storage co-located with EV charging to be profitable and draw investors to this emerging asset class, such systems have to be able to address several benefits and income streams.


During Energy Storage & Connected Systems, held on 6 and 7 February in London, two EV charging-plus-storage projects were presented, providing a useful way in which to compare different business models for these types of investments.

Open Energi’s David Hill presenting during Energy Storage & Connected Systems’ EV session

David Hill, commercial director at UK energy aggregator Open Energi, talked about his company’s experience of operating a battery asset co-located with fast chargers.

The aggregator owns and operates a 250kW/500kWh Tesla Powerpack battery energy storage system connected to 12 Tesla Superchargers at the South Mimms motorway services station, on the outskirts of London. Superchargers employ the EV maker’s proprietary direct current (DC) fast charging technology. Each is able to provide up to 120kW per car.

The Supercharger site at South Mimms is one of the busiest EV charging locations in the UK.

Primarily the Powerpack eases strain on the local grid, when several of the chargers are in use together, and also helps to control energy costs during peak electricity usage periods.

Hill says: “One car fast-charging has a fairly benign impact on the system but when the sixth car comes along and starts charging, along with the others, then this starts to cause issues. With the battery you can optimise the connection. However, on its own grid connection optimisation is not a business case.”

On top of its priority function the battery earns revenues from providing grid balancing services. Open Energi’s Dynamic Demand 2.0 software decides when the battery is going to bid into the market.


Grid impact from several EVs fast charging

A consequence of more EVs being driven will be the impact on electricity demand. To quote the National Grid’s numbers from the grid operator’s Future Energy Scenarios, Two Degrees analysis there are around 500,000 EVs on Britain’s roads today, which will increase to 1.6 million by 2020, rising to 9.3 million by 2030. In electricity demand terms, that’s just under 15TWh.

Open Energi is able to see the impact on electricity demand when multiple cars are charging at the same time. In under five minutes the site’s power demand can typically go from 0kW to 300kW, then to 400kW, 500kW and increasing to around 600kW during the next 10-15 minute interval.

The aggregator collects data to provide a profile of energy consumption through the week, showing when the battery is being used and how it helps to reduce the number and intensity of the highest charging peaks, which are greater than 100kW. As Hill puts it, “We are interested in the ‘spiky’ stuff.”

The company is also interested in how the battery operates in relation to the warranty. “This will get more scrutiny in future. As you start to take advantage of pricing variations, deeper discharges are required of the battery, compared with shallower ones needed for frequency regulation, so changes in how the battery is used can potentially affect the warranty,” Hill says.

Later in the session, Alex Earl, UK country manager at Alfen, a Netherlands-based provider of grid power supply equipment,

Alfen’s UK country manager Alex Earl discusses how energy storage can provide grid services and also provide other benefits, including EV charging

discussed an EV charging-plus-storage project at Car Jeans football stadium in The Hague. The company will commission the installation in the next couple of months, where several standard chargers (22kW each) are connected to a 700kW solar PV array and a 750kW/750kWh battery.

The battery reduces demand on the local network in peak times, by peak shaving, reducing grid reinforcement costs.


Revenue stacking

The battery’s owner and operator Scholt, a Dutch energy aggregator and trader, deploys the system to earn revenues from frequency response, as well as arbitrage, on the intra-day and day ahead markets.

EVs parked at the site in the evening are charged with electricity stored in the battery and from solar PV directly during the day, if need be.

Stedin, the local electricity distribution utility, is able to collect data from the project to see how the energy storage installation operates within the local grid network.

Alfen’s UK country manager, Alex Earl, says the business case for the installation does not take into consideration other possible revenue streams and savings, such as reduced energy costs through optimised solar self-consumption, or revenues from implementing a tariff for EV charging.

The projects contrast the different ways of using energy storage installed with EV chargers.

South Mimms shows the impact that fast charging has on the battery, requiring a lot of capacity to be prioritised for this function. It will inform whether EV fast charger sites could use larger batteries, to further access potential revenue streams, from grid services, for example.

In the Dutch project the smaller chargers, able to accommodate destination charging where cars are parked for several hours, place less demand on the battery than fast chargers. In combination with the bigger battery than the one at South Mimms, the system can be deployed to focus heavily on revenue streams from grid balancing and price arbitrage.


Energy Storage & Connected Systems is an annual conference and exhibition held in association with the Renewable Energy Association that brings together key industry figures to focus on the future of energy in the UK.