How a battery really makes money

Five value pools, four scalable markets

A battery monetises constrained optionality: its ability to change its physical position quickly, within finite power, energy and contractual limits.

Revenue is not margin

A battery imports 40 MWh at £35/MWh. With 90% AC-to-AC round-trip efficiency, 36 MWh is available for sale at the grid boundary. It sells at £100/MWh.

The £3,600 receipt is turnover. The £2,200 is gross energy margin before trading fees, network charges where applicable, optimiser fees, auxiliary consumption, degradation and other operating costs.

What each market actually pays for

Energy trading

The optimiser buys and sells energy before Gate Closure. Public prices show opportunities, while the site's complete trade book, transfer prices and portfolio hedges remain private.

Balancing Mechanism

At Gate Closure, the intended physical profile becomes the Final Physical Notification, or FPN. NESO can accept a bid or offer that changes the unit from that position.

• Bid: consume more or generate less.
• Offer: consume less or generate more.

An accepted price does not reveal profit. The economic result depends on the underlying contracted position, stored-energy value, later rebalancing, imbalance effects and costs.

Balancing services and Capacity Market

Balancing services procure qualified capability, with availability, utilisation and performance treatment defined by each product. The Capacity Market pays against de-rated capacity and creates delivery obligations during system stress.

The five-part stacking test

A 50 MW battery is scheduled to export 30 MW and has sold 20 MW of positive reserve. A new opportunity would increase export by another 10 MW. There is enough stored energy. Can it accept?

No, under the stated assumptions. A full reserve call would require 60 MW against a 50 MW export limit. The failure is instantaneous power, even if the energy arithmetic works.

1. Power: do simultaneous commitments fit within import and export limits?
2. Energy: can state of charge support duration and recovery?
3. Rules: is the combination permitted?
4. Performance: can response, ramping, metering and availability be met?
5. Opportunity cost: which compatible alternative is displaced?

What public data can prove

A defensible asset analysis labels each statement as observed, calculated, inferred or unknown. This prevents a plausible estimate from being presented as an audited fact.

The correct mental model

The optimiser sells constrained optionality and repeatedly decides whether to use flexibility now or preserve it for later.

That option is bounded by import and export power, usable energy, state of charge, efficiency, ramp rate, grid limits, degradation, existing commitments, telemetry and pre-qualification.

Energy markets and the cost of moving energy

Positions can be established in day-ahead and intraday markets up to Gate Closure. A portfolio can trade centrally and notify individual units according to an internal dispatch plan, so a physical notification is related to the trade book without being the same record.

At £50/MWh charging and 88% round-trip efficiency, the energy-only break-even discharge price is £56.82/MWh. Fees, auxiliary load and degradation increase it.

Measurement boundary

Efficiency can be quoted at cell, DC block, inverter or grid connection. A credible calculation states the boundary, auxiliary treatment, assumed efficiency curve, degraded available capacity and treatment of remaining inventory.

Cashflow and inventory

Importing 50 MWh at £35/MWh costs £1,750. At 90% AC-to-AC efficiency, the 45 deliverable MWh carry £38.89/MWh of charging-energy cost. If 30 MWh is sold for £3,300, only £1,166.67 of cost is allocated to that sale. The remaining 15 MWh carry £583.33 into the next decision.

The Balancing Mechanism

The BM baseline is the Final Physical Notification. A bid moves the unit towards more consumption or less generation. An offer moves it towards less consumption or more generation.

NESO selects actions using price, technical capability and system needs. Location and constraints can justify selecting a higher-priced action. An accepted instruction becomes a Bid Offer Acceptance and is settled using the relevant submitted bid or offer price.

Why visible turnover can mislead

An accepted offer for 10 MWh at £200/MWh creates a visible £2,000 cashflow. Profit still depends on the pre-existing energy contract, stored-energy cost or opportunity value, imbalance settlement, later state-of-charge restoration, degradation and optimiser fees.

Balancing services

NESO procures response and reserve products with product-specific rules. Two concepts recur:

• Availability: payment for maintaining qualified capability during a contracted window.
• Utilisation: payment associated with delivered action where the product provides for it.

An award consumes option value. Depending on product and direction, the site may need power headroom, a state-of-charge range, energy for a stated duration, recovery capability, metering, telemetry and a compliant physical position.

Trading around an award can remain possible when the physical position and current rules permit it. The award constrains optimisation rather than automatically stopping every other action.

Capacity Market

The Capacity Market supports security of supply. Successful providers receive an agreement linked to a delivery obligation and face applicable penalties for failure during a system stress event. T-1 and T-4 auctions generally procure one and four years ahead.

Storage is de-rated to reflect its expected security-of-supply contribution. Nameplate MW or MWh is therefore not automatically the paid quantity, and duration matters commercially.

Register discipline

Pre-qualification, auction entry, agreement award, delivery year, milestones, termination and current status are different facts. Limit the conclusion to what the record proves.

Route-to-market contracts

Labels do not settle the economics. The contract must specify dispatch rights, availability guarantees, degradation allowances, excluded markets, index definitions, credit support, imbalance responsibility and termination rights.

Co-optimisation and opportunity cost

A simplified storage model updates energy through time:

Energy remains between zero and usable capacity. Charging and discharging remain within import, export and connection limits. Service awards, ramp rates, warranties and availability create further constraints.

Opportunity cost

Holding 20 MW for reserve displaces any incompatible use of that power. Discharging now also consumes energy that might be worth more later. Opportunity cost is the value of the best compatible alternative displaced by the chosen action.

Perfect foresight

A historical optimisation that knows every later price and activation is an upper-bound benchmark. Real operators submit positions under uncertainty and face outages, liquidity, execution, telemetry and forecast errors.

What the public record can support

1. Observed: the record shows an accepted offer volume and price.
2. Calculated: a stated method gives an estimated cashflow.
3. Inferred: the physical profile is consistent with a strategy.
4. Unknown: the trade book and owner margin are private.

Worked case: Northbank BESS

This synthetic case tests market and physical reasoning. It does not reproduce a particular NESO service.

1. Charging cost and inventory

Charging costs £1,750. The 45 deliverable MWh carry £38.89/MWh of energy cost.

2. Scheduled stack

A full reserve call reaches 50 MW. Energy use is 30 MWh baseline plus 10 MWh reserve, leaving 5 MWh from the charged inventory. Both tests pass.

3. Additional BM opportunity

A new action would increase export by 10 MW for 30 minutes. The energy total reaches exactly 45 MWh, while simultaneous power under a full reserve call reaches 60 MW. The action fails the power test.

4. Realised energy margin

The remaining 15 MWh carries £583.33 of charging-energy cost. Service cashflow is added only after recognising availability, any utilisation, stored-energy cost, later position effects, deductions and fees.