How does the day-ahead energy market work?
The Day-Ahead Market (DAM) is the wholesale electricity market where electricity suppliers and large consumers purchase electricity for the following day. Every day at 12:00 p.m., EPEX Spot publishes hourly prices for the following day. These prices reflect the expected balance between supply and demand.
| Time | Typical Day-Ahead price | Reason |
|---|---|---|
| 2:00 a.m.–6:00 a.m. (night) | €5–€25 per MWh | Low consumption, high wind power generation |
| 7:00–9:00 a.m. (morning rush hour) | €60–€150 per MWh | High consumption, low solar generation |
| 11:00 a.m.–2:00 p.m. (sunny afternoon) | €0–€30 per MWh (summer) | High solar power generation, low industrial consumption |
| 5:00 PM–8:00 PM (evening rush hour) | €50–€120 per MWh | High residential consumption, setting sun |
| 9:00 PM–12:00 AM | €20–€60 per MWh | Declining consumption, stable wind power generation |
How significant are the arbitrage profits in practice?
For the sake of honesty, we must distinguish between theoretical potential and realistic returns:
Theoretical maximum (2022, extreme volatility)
In 2022, price differences were extreme due to the energy crisis. The average spread between the cheapest and most expensive hours on the DAM was €120 per MWh. A 500 kWh battery that completed one full cycle every day could theoretically earn €500 × €0.12 = €60 per day = €21,900 per year.
Realistic average (2024–2025)
In a typical market year, the average usable spread is approximately €25–€50 per MWh. Taking into account charging losses (10%), inverter losses (5%), and the fact that optimal arbitrage is not possible every day, a realistic net result for a 500 kWh system is:
| Parameter | Value |
|---|---|
| Average net spread | €30 per MWh |
| Daily loading capacity | 450 kWh (after a 10% charging loss) |
| Real daily savings | €13,50 |
| Operating days per year | 300 (excluding maintenance and periods of low spreads) |
| Realistic annual return on arbitrage | €4.050 |
That is relatively modest for a 500 kWh system. As a result, arbitrage is rarely the primary business case—it is a supplementary revenue stream in addition to peak shaving and self-consumption.
When does arbitration become the primary driver?
There are situations in which energy arbitrage is the dominant source of revenue:
- Systems primarily designed for balancing markets (FCR/aFRR): Larger systems that are part of an aggregation pool can earn significantly more through frequency control than through pure day-ahead arbitrage.
- Periods of extreme volatility: during cold spells, heat waves, or when large wind farms go offline, price differences can become so significant that a single day can generate months’ worth of normal returns.
- Locations with a highly competitive dynamic contract: companies that actually pay the hourly market price (including surcharges) can achieve larger arbitrage margins than companies with a partially fixed contract structure.
Dynamic vs. Fixed-Rate Energy Contracts: Weighing the Options
| Criterion | Permanent contract | Dynamic contract | Dynamic + battery |
|---|---|---|---|
| Price certainty | High | Low | Medium |
| Arbitrage potential | None | High (but risky) | High (controlled) |
| Impact of peak shaving on the bill | Limited | Large | Large |
| Risk associated with extreme prices | None | Large | Small (battery as a backup) |
| Suitable for? | Risk-averse companies | Companies with flexible processes | Most business customers |
How does Boltainer automate energy arbitrage?
Boltainer’s EMS software automatically downloads the published Day-Ahead prices for the following day (at 12:30 p.m.) on a daily basis. Based on those prices, the EMS calculates the optimal charging and discharging strategy for the next 24 hours, taking into account:
- Available battery capacity and current charge level
- The projected peak shaving requirements
- Expected solar yield (weather data)
- Any FCR or congestion management obligations
The result is an optimized daily schedule that addresses all your goals at once without you having to lift a finger.
Frequently Asked Questions About Energy Arbitrage
What is energy arbitrage in simple terms?
Electricity isn’t always expensive. At night and on sunny afternoons, electricity is cheap. During morning and evening rush hours, electricity is expensive. Energy arbitrage involves buying cheap electricity, storing it in a battery, and using it instead of expensive electricity. The price difference is your profit.
Do I need a dynamic contract for energy arbitrage?
Technically speaking, yes—with a fixed-rate contract, the price differences benefit your supplier, not you. But even without a dynamic contract, a battery can have a direct impact on your bill through peak shaving. Energy arbitrage is a bonus that is most valuable with a dynamic contract.
Is energy arbitrage legal?
It’s completely legal. You buy electricity at one time, store it, and use it later. You pay the market price at the time of purchase. There are no legal restrictions on using a battery for this purpose.
What are the risks of energy arbitrage?
The main risks are: a market with low volatility (small price differences = small profits), increased battery wear due to more charge cycles, and the risk that the arbitrage profit will be insufficient to offset the additional charge cycles. Boltainer’s EMS automatically takes these factors into account and only executes arbitrage if the expected profit exceeds the cost of wear and tear.