Battery storage and carbon impact: How we measure this and why

‘If you can’t measure it, you can’t improve it’ as the saying goes. At Field we think batteries have enormous potential to improve our electricity system and help us get to net zero by reducing carbon intensity.

But, in order to work out the impact our batteries are having, it’s critically important that we measure that impact accurately.

We track the carbon impact of our battery storage sites very closely, looking at two things:

1. The realised carbon impact of each site on a day-to-day basis as it meets the needs of the grid
2. A full cradle-to-grave carbon life cycle assessment, which forecasts the impact of our projects over their 20-year lifespan

So, what goes into our life cycle assessment and how do we go about it?

Firstly, our life cycle assessments are independently verified. We always want our calculations and assumptions to stand up to external scrutiny.

Secondly, they’re fully cradle-to-grave – measuring the inputs and outputs from procurement, through construction, to the end of life and recycling stages.

When calculating carbon emissions from building each of our sites, we look at the impact of manufacturing the battery energy storage systems and balance of plant systems, transport to the site, and construction of the site, including cables and building work.

Operational impact is measured through a consistent, clear set of metrics, based on the carbon arbitrage we calculate from a battery’s trading activity. Carbon arbitrage gives us an idea of how much carbon we expect our batteries to help the system avoid producing.

This sounds complicated, but is fairly easy to calculate. We take the difference between the following:

1. The grid’s carbon intensity when a battery imports power
2. The grid’s carbon intensity when a battery exports supplies to the grid

This calculation accounts for round trip efficiency losses - the amount of energy it takes to withdraw or add to a battery’s power - to make sure we don’t overestimate the impact of our sites.

End of life then looks at the disposal and recycling of the batteries, as well as decommissioning of the site.

What does Field’s life cycle assessment look like so far?

We’re early on in our journey. Our first battery site, in Oldham, has been running for nearly a year, but life cycle assessments are typically calculated over the full lifetime of the asset. As a result, we need to pair the actual carbon we have incurred (during construction for instance), with a detailed forecast of how we will operate our asset in the future in order to avoid carbon.

Oldham’s LCA below (independently validated by DNV) shows the expected impact over a lifetime of a site and its significant carbon saving potential.

We have several more sites in construction that will start operating in 2024. Each and every one will have a life cycle assessment undertaken and independently verified.

Whenever new data becomes available, such as new emissions figures from equipment manufacturers, we update a site’s assessment to reflect it.

How do the different uses of our sites create a different carbon impact?

Batteries are responsible for a fair amount of the power sector’s emissions reduction.

Frequency response or ancillary services, including dynamic containment, can help the system operator resolve disruption faster and more cheaply, sometimes ahead of faults happening, while cutting the emissions associated with fossil fuel plants performing the same role.

A lot of our Oldham battery site’s early work was providing ancillary services.

These charges or discharges of the battery support the smooth, reliable running of the grid, and replace a role traditionally played by much more carbon intensive “gas peaker” plants.

However, our life cycle assessment currently assumes we are always displacing gas peaker plants when we discharge the battery, and assumes we are always acting in the wholesale markets (in order to simplify the forecast a little). This action is where price is highly correlated with carbon arbitrage.

In reality, Oldham is and will continue to perform in the Ancillary Services markets over the next 1-2 years, until moving more into an energy arbitrage strategy. The timing of these services is not correlated at all to carbon arbitrage.

This is why, counterintuitively, our Oldham site gained carbon, rather than avoided it, in its first few months of operation.

Some have suggested assigning a value for avoided carbon to ancillary services, which is something we’re exploring too. After all, we’re eliminating the expensive need to turn on a gas peaker and need to be able to track the full value of bringing more batteries onto the system.

More broadly, Oldham (and other batteries) are starting to do more work in the Balancing Mechanism (National Grid’s marketplace for balancing electricity supply and demand in real time). With more batteries in this marketplace, we will need fewer fossil fuel plants to switch on when demand is high or supplies are tight.

As a result of Oldham’s increasing role in the Balancing Mechanism, the site’s carbon impact is now falling and will keep falling towards ‘carbon negative’ territory. Over time, this will enable us to build a clearer, more accurate picture of how batteries are helping reduce emissions and drive progress on our path to Net Zero.