Batteries don't make electricity. They move it through time.
A grid battery is a warehouse for power. Electricity comes in when there's too much of it and goes out when
there isn't enough. Here's how one works, what it earns, and why Britain is building so many.
⏱ 6 min read⚡ Grid-scale storage🇬🇧 GB market
300 MWUK's largest battery (Thurrock), connected 20251
From the road, a battery site looks like a neat row of shipping containers behind a fence. Inside, six
systems work together to turn grid electricity into stored chemical energy and back again.
AC power DC power Control signals
Grid connection. Usually a 33 kV or higher substation. Grid capacity is the scarcest ingredient of any project.
Transformer. Steps voltage between the grid and the site's equipment.
Inverter (power conversion system). Batteries store DC; the grid runs on AC. The inverter converts in both directions in milliseconds.
Battery containers. Racks of lithium-ion cells (LFP chemistry is now standard). Sodium-ion and flow batteries are emerging alternatives.
Cooling and fire safety. HVAC or liquid cooling keeps cells in their ideal temperature window. Gas detection and suppression protect every container.
Energy management system (EMS). The software brain. It tracks cell health and temperature and executes the trading engine's dispatch instructions.
02
How does a grid battery work, step by step?
1
Charge
Absorb surplus power on windy nights and sunny afternoons, power that would otherwise be curtailed.
2
Store
Hold it for minutes or hours. A two-hour battery can run at full power for two hours.
3
Discharge
Release it into the early-evening peak, when demand and prices jump.
4
Support the grid
Between trades, stand ready to steady grid frequency, and get paid for being ready.
03
Why does the grid need batteries to stay at 50 Hz?
Britain's grid runs at 50 hertz. When supply and demand drift apart, frequency drifts too: down when
there's too little power, up when there's too much. Old coal and gas turbines resisted these swings with
sheer spinning mass. As they close, batteries step in. They can react in under a second, far faster than
any power station. Try tripping a power station and watch the battery catch the fall:
50.000 Hz
Standing by. Paid for being available.
Battery output: 0 MW
Simulation. The shaded band is the ±0.2 Hz operating range; the statutory limit is ±0.5 Hz. Frequency-response services pay batteries to push back against every deviation.
04
How does a battery make money?
A battery has more than one customer. The same megawatt can be sold to different buyers at different
times. The industry calls this revenue stacking. Some services pay for energy delivered; others
pay simply for being available. Select a layer of our target stack:
Spreadwatt's illustrative target revenue mix. Actual mix shifts with market conditions, and that flexibility is the point.
Stream
Paid for
Response
Typical term
Wholesale & intraday trading
Energy (£/MWh spread)
Minutes to hours
Continuous, half-hourly
Balancing Mechanism
Energy, at NESO's instruction
Minutes
Real time
Frequency response
Availability (£/MW/h)
<1 second
Day-ahead auctions
Capacity Market
Guaranteed availability (£/kW/yr)
At stress events
1–15 year contracts
Local flexibility (DNO)
Relieving local network constraints
Minutes
Seasonal tenders
Indicative GB merchant battery revenues were around £40–70k per MW per year in early 20264.
The spread between a good operator and an average one is driven almost entirely by trading skill, which is
exactly where we compete. See our methodology →
05
How big are UK batteries getting?
In 2025 National Grid connected Statera Energy's Thurrock Storage at its Tilbury substation in Essex. At
300 MW and 600 MWh it was billed as the UK's largest battery, and it sits on land that once fed the
Tilbury coal power stations1. The symbolism is hard to miss: the grid's
flexibility is moving from burning fuel to storing electrons.
Energy stored (MWh), to scale. A home battery is too small to see at this scale.
06
Own land near a substation?
The best battery sites are small and unremarkable, but they sit close to the grid. We partner with
landowners on long leases that typically pay far more per acre than farming or solar.
0.5–2acres typically needed
33 kV+substation or line nearby
25–40year lease, index-linked
18–30months from first call to first rent
Site check. We assess grid capacity, access and constraints. It's free.
Option agreement. We secure the site and pay an option fee while we plan.
Grid offer and planning. We apply for the connection and planning consent.
Build. Containers, inverters and the substation link, typically in under a year.
Lease starts. Rent flows for the life of the project.
Indicative ranges from published UK industry guidance4. Every site is different.
07
Frequently asked questions
Does a battery generate electricity?
No. It stores electricity made elsewhere and releases it later, losing roughly 10–15% on the round trip. Its value comes from when it delivers power, not from making it.
How long can a grid battery run?
It depends on its duration rating. A 100 MW / 200 MWh battery is a "two-hour" battery: it can run at full power for two hours. New UK projects are trending from one hour towards two hours and beyond.
What is revenue stacking?
Selling the same asset's capability to several markets: trading, balancing, frequency response and capacity contracts. The trick is to commit each megawatt to its most valuable use at each moment.
Is there a minimum size to take part?
Many national markets require around 1 MW or more2. Smaller assets join an aggregator's portfolio to qualify. We build at grid scale, so we trade in our own right.
How long do the batteries last?
Typically 15–20 years with careful operation. Cells degrade with every cycle, which is why our trading engine prices wear into every decision.
Are battery sites safe?
Modern sites use LFP chemistry, which is far more thermally stable than older chemistries. They add continuous temperature monitoring, gas detection, fire suppression in every container, and spacing between units, all agreed with the local fire service at planning.
Why is now the right time?
Coal is gone and wind and solar keep growing, so price swings are getting bigger and the grid needs more flexibility. Storage is how the system soaks up surplus green power instead of switching it off.