Why the 15-minute peak is the number to calculate
In German commercial electricity billing you do not only pay for the energy you consume, but also for how hard your worst quarter-hour was. The meter forms an average value every 15 minutes, and the grid operator bills the demand charge against the single highest 15-minute average of the billing period. One spike sets the price for the whole period.
This is why the calculation matters: reducing your annual kWh consumption barely moves the demand charge, while shaving a few kilowatts off that one peak quarter-hour directly lowers the billed power (Bemessungsleistung). Peak shaving targets exactly that measured maximum, not the average load.
How peak shaving with a battery works
A battery storage system (BESS) covers the short load spikes out of stored energy instead of drawing them from the grid. When load approaches your defined threshold, the battery discharges to keep the metered 15-minute average below it, then recharges during quieter periods.
According to Stromfee, this lowers the Bemessungsleistung — but only when three things line up: correct sizing, a load forecast, and priority logic that decides when the battery discharges. A battery that is too small, or that is already empty when the peak arrives, will not cap it.
Calculating the two sizing dimensions: power and energy
Battery sizing has two separate values. The power rating (kW) must cover the gap between your load peak and the threshold you want to hold. The energy capacity (kWh) must cover that gap for the full duration of the peak event — a spike that lasts several quarter-hours needs more stored energy than a single short one.
Stromfee delivers turnkey systems from 100 kWh up to 100 MWh, and cites a typical BESS size of 2–5 MWh for the hotel use case. The reported peak-shaving effect is a saving of 30–50% of the demand-charge (Leistungskosten) portion, and up to 35% on grid fees (Netzentgelte) in the hotel energy-chain example. These ranges depend on your specific load profile, so the actual figure comes from your own measured data.
Combining peak shaving with Day-Ahead arbitrage
The same battery that caps peaks can also trade. Between peak events it charges when prices are low and discharges (or sells) when they are high — arbitrage on the Day-Ahead and intraday markets. Stromfee cites a usable spread of 50–80 €/MWh and, for intraday EPEX SPOT ID1/ID3 trading, an arbitrage yield of up to 80,000 € per year per MWh.
The calculation for a combined system therefore weighs two revenue streams against each other: the guaranteed demand-charge reduction from peak shaving, and the variable arbitrage margin. Priority logic has to reserve enough state-of-charge for the forecast peak before it commits capacity to trading, otherwise a profitable trade can leave the battery unable to cap the next spike.
What data the calculation needs
A reliable peak-shaving calculation is built on your actual 15-minute load profile over a full billing period, your grid operator's demand-charge tariff, and a load forecast to anticipate when peaks occur. From these you derive the threshold, the required power and energy, and the resulting reduction in billed power.
Stromfee packages this into a feasibility study (Machbarkeitsstudie) covering BESS sizing with capex and payback, a spike-based recalculation against your specific grid operator (Spitzabrechnung), and a Day-Ahead remuneration comparison. That turns the sizing question into a numbers-backed business case rather than a rule of thumb.
FAQ
Which value does peak shaving actually reduce?
It reduces the Bemessungsleistung — the highest 15-minute average power in the billing period — which sets the demand-charge (Leistungspreis) part of your grid fees. It does not reduce your total energy consumption.
How large does the battery need to be?
Two dimensions matter: power (kW) to cover the gap between your peak and your threshold, and energy (kWh) to hold that gap for the full duration of the peak. Stromfee builds from 100 kWh to 100 MWh; a typical hotel BESS is 2–5 MWh, but your load profile determines the exact size.
How much can peak shaving save?
Stromfee reports a saving of 30–50% of the demand-charge portion and up to 35% on grid fees in the hotel example. The real figure depends on your measured load profile and grid operator tariff, which is why a feasibility study calculates it against your own data.
Can the same battery do peak shaving and arbitrage?
Yes. Between peaks the battery trades on the Day-Ahead and intraday markets — Stromfee cites a usable spread of 50–80 €/MWh and up to 80,000 €/year per MWh via EPEX SPOT ID1/ID3. Priority logic must reserve state-of-charge for the forecast peak before allocating capacity to trading.