The ‘enormous’ potential of domestic batteries for FFR

At the beginning of September, Social Energy won the first ever fully domestic weekly Firm Frequency Response (FFR) contract with National Grid ESO.

This saw the energy technology company utilise its fleet of over 5,500 domestic solar and battery storage systems within its network to respond to National Grid ESO calls, providing 4MW of FFR capacity throughout the day to help the operator balance demand.

Previously, FFR capacity had largely been met by larger scale technologies, such as grid-scale batteries. But with domestic solar and battery systems becoming increasingly common – and the challenge of balancing continuing to grow as intermittent renewables take over from fossil fuels – there is an “enormous” potential for systems like Social Energy’s to help manage demand, as the company’s chief technology officer Steve Day explained to Current±.

What sort of battery system do most households within the trial use?

It's a mixture. When we launched we were offering a Duracell branded product - we still do - but that had a relatively small capacity at 3kWh. Next we introduced a SolaX product, which was slightly larger at 4.5kWh. The latest product that we offer is a 5.8kWh battery.

It offers a higher power output of 3.68kW, and is modular, meaning you can increase it in units of 5.8kWh. So you can have a 5.8kWh, or two of them together and it will be 11.6kWh, and so on, up to four units. Depending on the size of the house and the circumstances of the customer it can be sized it appropriately.

What technical challenges have there been for using domestic batteries for FFR?

There have been many of the same challenges that a grid scale battery would face, plus a few more that we had to solve. There were commercial challenges associated with getting the proposition economical for a domestic property to participate, and that meant engineering down the cost of some of the equipment that needs to go into the home to allow it to participate.

National Grid mandates that you need a certain type of metering, and you have to be able to fulfil specific technical requirements in order to deliver the service. The cost of the equipment required to do that was several thousand pounds and that pretty much ruled out domestic. We’ve now got the costs down to the point where it's a few hundred pounds for the same equipment, and we expect it to reduce further. That was one major challenge.

Other challenges are around operations. To give you some examples, in a home we have to deal with the idiosyncrasies of that environment. That can mean things like the reliability of customers broadband, or their internal home network. As a result we need a platform that is resilient enough to cope with broadband outages, unlike a grid scale battery, where it will have a dedicated data connection.

There are also issues around managing the temperature of the battery as we have less control over where the battery will be installed. This means it might go into a loft where there will experience relatively high temperatures in the summer, or it could be installed outside and see relatively low temperatures in the winter.

We thoroughly test our batteries in our labs to understand their thermodynamic behaviour, and then we use sophisticated AI manage the operation of the battery in a way that is optimised for its local conditions.

Could you tell me a little about how the trial will work in practice?

The trial has been running for a while, and is operating like a commercial service. Social Energy have been - and are - in the commercial monthly tender rounds for frequency response since last October. The trial operates in a similar way, it's run as an auction, although it's got a different clearing system as it's pay as clear rather than pay as bid and contracts run for a week at a time rather than a month. But otherwise the delivery of the service is more or less the same.

That's beneficial for us because we can participate in the two markets in parallel, the monthly tender rounds and the weekly auctions. In effect it means we get two bites of the cherry. We can bid into the monthly tenders and if we’re not successful, then we have another option to bid into four weekly auctions during that month as well. That means we have more opportunity to create value for our customers, and it also allows us to better accommodate things like changes in weather conditions.

In the monthly tenders we have to commit to providing a fixed level of response for 30 days, and it's very hard to accurately predict things like weather over that timeframe. Over a week we can better optimise how we utilise our customers’ batteries, and again that results in more value being delivered to those customers.

How big of an impact could projects like this have on balancing the grid?

I think the potential is enormous, the domestic market is a huge - 30-40% of total energy consumption in the UK, so you can't ignore it if you want to move to a truly low carbon grid.

There is plenty of latent capability to provide flexibility services there, and there's going to be more in the future. We can see that with the rollout of electric vehicles (EVs), at the moment. We talk a lot about battery storage but Social Energy also has a project pipeline that includes connecting other flexibility assets onto the platform that can deliver the same types of services, like EV chargers, hot water tanks, or heat pumps.

We're seeing an increasing number of those being installed into people’s homes. Often they're viewed as a problem for the likes of DNOs, but if they're managed appropriately they can be an integral part of the solution, and help to create a truly low carbon grid. So we believe there is enormous potential for these services to grow and to be procured from the domestic side in the future.