A few years ago, estimating the return of an industrial battery fitted in a spreadsheet: a price per kWh, a price per kW, a few assumptions. In 2027, in French-speaking Switzerland, that no longer holds. The parameters have multiplied and they interact.
Six parameters that change everything
1. Peak power price. CHF 0.80 to 16.97 per kW per month in 2027, depending on the DSO and voltage level.
2. Billing window. The peak is billed for 1 month at BKW, Romande Energie, Viteos, Gruyère Energie, SEFA and (per its sheet) SIL, and for a rolling 12 months at Groupe E and Oiken. One missed +100 kW peak lasting 15 minutes costs CHF 369 to 1,447 in the first case, up to CHF 10,080 in the second.
3. Tariff product. Lowering the peak raises utilisation hours. At Oiken MV, tariff B becomes cheaper than tariff A above about 2,470 hours, so the battery can change the optimal tariff.
4. Solar feed-in tariff. Falling and more variable: each kWh stored rather than exported is worth the avoided purchase price minus the lost feed-in price.
5. Quarter-hour market. From 3 November 2026 the Swiss spot market has 96 prices a day instead of 24, exposing intra-hour price spreads: a battery’s natural time scale.
6. Flexibility services. Hours when the battery is not shaving peaks can serve suppliers or balance groups, without compromising peak shaving.
Why they do not simply add up
These uses compete for the same stored energy. Adding up each use in isolation always overstates profitability. What is needed is an optimisation that decides, quarter-hour by quarter-hour, the best use of the battery over its lifetime.
Our method
calc.optimalenergy.ch (Optimal BESS Sizer) starts from the site’s real 15-minute curves, applies the DSO’s real tariff (2022–2027, 10 DSOs) with its billing window, co-optimises self-consumption, peak shaving and flexibility over 20 years, sweeps battery sizes to find the optimum, and computes NPV, IRR and payback in a traceable report.
Sources: official 2027 tariff sheets (checked 09.10.2026); written confirmations from Oiken (12.10.2026), SEFA and Romande Energie (15.10.2026); EPEX SPOT, “15-minute products in Market Coupling”.
