What a battery actually earns: arbitrage, not generation
A grid-scale battery never creates a single watt. Here's what it's actually being paid for.
A battery is a trade, not a power station
Every other plant on the grid — coal, gas, wind, nuclear — earns money by converting something into electricity and selling it. A battery does neither. It buys electricity when it's cheap, stores it for a while, and sells it back when it's expensive. Its entire business model is the gap between those two prices, a strategy known as arbitrage — and because that gap is never guaranteed, timing a battery well is a genuinely different skill from running a thermal plant well.
Where the gap comes from
Prices move through the day largely because demand does (see our piece on why gas sets the price): overnight demand is low, so cheap baseload and renewables usually cover it and the clearing price sits low; the evening peak needs the stack pushed further up, often into gas, so the price sits much higher. A battery that charges overnight at, say, £25/MWh and discharges into the evening peak at £75/MWh has captured a £50/MWh spread — that's its entire profit, before accounting for the small efficiency loss (round-trip efficiency) every real battery has converting electricity to stored energy and back.
Why capacity isn't the whole story
It's tempting to think a bigger battery just earns more, and all else equal it does — but the spread it's chasing isn't fixed, and a battery that discharges too early (before the peak fully forms) or holds out too long (missing the peak and getting caught by a falling price afterward) gives away most of its margin regardless of size. A well-timed small battery routinely out-earns a larger one running on a lazier schedule. This is also why battery operators watch the whole day's price shape, not just the current price — the decision to hold charge back is a bet on a bigger spread showing up later.
What this means for the wider grid
Batteries charging overnight (when demand is low) and discharging into the evening peak (when demand is high) don't just make money for their owner — they genuinely flatten the demand curve a little, which is part of why grid operators and policymakers like more battery storage on the system: it reduces how often the most expensive, most polluting peaker plants need to run at all.
Try running one
In GridTradingDesk your battery can run on full auto, bidding in only when the price clears its own reserve threshold, or you can take manual control — force a charge, force a discharge, or hold it out entirely for a bigger move later. It's one of the clearest ways in the game to feel the difference between generating and trading.