How a battery makes money in Spain

A battery does not produce energy: it shifts it in time and makes it available to the grid in seconds. All its revenues come from those two abilities. Which ones, and how much each weighs, depends on where it is connected.

Two ways to make money

There are two very different models:

• Grid-connected (standalone or alongside a renewable plant): it sells on the electricity markets. Its revenues are arbitrage, balancing services and, once it exists, capacity.
• Behind the meter (a factory, a farm, a building): it does not sell, it saves. It reduces contracted power, buys in the cheap periods and makes better use of its solar PV.

1. Arbitrage: buy low, sell high

The day-ahead market (OMIE) sets a price for every hour of the following day. With so much solar PV, the price collapses at midday and soars at sunset. A battery charges in the trough and discharges at the peak.

Let's run the numbers for that day for a 1 MW / 2 MWh battery with 88% round-trip efficiency. It buys 2 MWh at €20.1/MWh and sells 1.76 MWh at €251.7/MWh: a gross margin of around €403 in a single cycle.

Illustrative calculation. A single September day with a wide price spread. Some days have much smaller spreads, and grid access charges, market representation costs and degradation must be deducted from that margin. Real annual revenue comes from adding up all 365 days, not from multiplying the best one.

Besides the day-ahead market, there are the intraday auctions and continuous intraday market, where the battery can correct its position when the solar forecast or demand changes. That flexibility is exactly what a good EMS exploits.

2. Balancing services: stability in exchange for money

Red Eléctrica, as system operator, needs generation and demand to be balanced every second. To achieve this, it buys balancing services from whoever can ramp power up or down quickly. A battery responds in milliseconds, which makes it highly competitive.

• Secondary frequency control (aFRR): you are paid for keeping a reserved power band and, on top of that, for the energy activated.
• Tertiary frequency control (mFRR): manual activations to restore balance within minutes.
• Technical constraints: adjustments for local grid issues.

To take part, the installation must pass the system operator's qualification tests and act through a market participant. Systems above 5 MW must also be assigned to a control centre and send real-time telemetry, as required by RD 917/2025.

The same battery can be holding reserve capacity for the grid at ten in the morning and selling energy at nine at night.

3. Capacity: getting paid to be available

A capacity mechanism pays for each firm megawatt available at times of system stress, whether it is used or not. It is a more stable revenue than the others and highly valued by project lenders. In Spain it is still going through approval; when auctions are held, operational batteries will be natural candidates.

4. Behind the meter: savings are revenue too

In a company, the battery does not sell to the grid, but its effect on the bottom line is just as real:

• Contracted power: by shaving peaks, you can contract less power and avoid excess charges.
• Tariff periods: charges in the cheap periods (P6) and discharges in the expensive ones (P1–P2).
• Self-consumption: stores the solar surplus that would otherwise be given away or sold cheaply.
• Diesel: where there is a generator, the battery reduces its running hours.

In that example, the largest item is not arbitrage but the diesel no longer burnt. That is why every study starts with the bill and the consumption profile, not with the battery size.

Revenue stacking: the EMS's job

Revenue streams are not mutually exclusive: they combine. The hard part is deciding, hour by hour, which use is worth most without compromising the next. That is what an EMS does: it forecasts prices, generation and consumption, and allocates the battery's capacity between arbitrage, services and self-consumption.

It also looks after the asset. The 314 Ah LFP cells we integrate reach around 8,000 cycles while retaining 70% of their capacity; every cycle has a cost in lifetime, and a cycle that only earns a few euros may not be worth it. Deciding when not to cycle is also part of profitability.

Live data

Every day we publish how much a battery would have earned on the Spanish market at real prices: arbitrage by duration, price spreads, history and forecast.