Free peak-shaving calculator: size a business battery

Two ways to use it

• Quick estimate: five numbers from the bill and a quote. It treats every peak as a rectangle of the same height and length, and says so next to the result.
• Upload a load profile: a CSV, Excel, MSCONS or Green Button file with 15-minute or hourly data. The file is read and the year is simulated in your browser, with Zorowatt's rule-based battery controller and a plain peak-charge tariff you set. Nothing is uploaded or stored, and it does not use up a site analysis.

Open the free peak-shaving calculator next to this article and follow along.

The arithmetic of the quick estimate

1. Shaved power = today's peak × the share you want to cut. 400 kW × 15% = 60 kW, so the new peak is 340 kW.
2. Usable energy = shaved power × how long the peaks last ÷ 0.95, the discharge efficiency the calculator assumes (an estimate). 60 kW × 2 h ÷ 0.95 ≈ 126 kWh.
3. Investment = usable energy × the installed price per kWh. 126.3 kWh × €450 ≈ €56,800.
4. Savings = shaved power × the peak charge per kW per month × 12. 60 × €8 × 12 = €5,760 a year.
5. Simple payback = investment ÷ savings. €56,800 ÷ €5,760 ≈ 9.9 years.

These are the calculator's default inputs and they are illustrative, not a real site. The €450/kWh is a placeholder for your own quote.

What the quick estimate leaves out

• Real peaks differ in height and length. The day with the longest peak sets the energy the battery needs.
• Recharging: the battery has to refill below the new peak before the next one, or it arrives half empty.
• Losses: charging and discharging lose energy, which costs money on the energy part of the bill.
• Everything except the peak charge: no energy savings, no solar, no arbitrage, no connection limit.
• Ageing, replacement and the time value of money.

The load-profile mode covers the first three. The Workspace covers the rest: the site's real tariff, the bill rebuilt month by month against the invoices, solar, NPV and IRR with degradation, and a report.

What the load-profile mode does

1. Reads the file: finds the header, the delimiter, the date order, kWh or kW, a cumulative register and daylight-saving days, and shows what it assumed.
2. Searches a grid of battery sizes (energy × power) and runs each through every interval of the year with a rule-based controller: a monthly peak threshold, a reserve, recharging below the threshold.
3. Bills each size under a plain tariff: your €/kW/month charge on the month's highest interval plus €0.15/kWh for energy, so losses cost something.
4. Returns the peak before and after, the savings a year, the investment and the payback, or "not within 15 years". The finance uses Zorowatt's default assumptions (15 years, 7% discount rate, 2% price escalation, 1% a year calendar fade), which are estimates.

If the file has gaps, duplicates or a kW / kWh mix-up, the result inherits them. Run it through the free meter data checker first; it needs 12 months with at least 90% of the intervals measured before it calls the data good enough for a study.

Which €/kW figure to enter

The calculator asks for a charge per kW per month. Where the tariff states it differently, convert it:

Run the default example through those rates and the payback moves a long way (illustrative, peak charge only):

• Liander, kWmax only: 60 × €3.57 × 12 = €2,570 a year; €56,800 ÷ €2,570 ≈ 22 years.
• Liander, kWmax and contract: 60 × €5.86 × 12 = €4,219 a year; about 13.5 years, if the battery holds the lower contract in every quarter-hour of the year.
• NEW Netz above 2,500 hours: 60 × €118.34 = €7,100 a year; about 8 years, if the battery holds the peak on every day of the year.

That spread is why the German case is usually built on the Leistungspreis and the Dutch one on the connection (see Netcongestie and the 2028 kWmax). pv magazine puts the range where peak shaving can pay off at €60–120/kW and calls it usually limited below €60/kW (pv magazine).

Two traps in Germany

• The Leistungspreis is set by the year's single highest quarter-hour. The calculator bills the peak month by month, so for a German site it is optimistic: if the battery misses one day, the real saving for the whole year is what it held on that day. Zorowatt's German tariffs in the Workspace bill the annual peak.
• Full-load hours are annual kWh ÷ annual peak kW. Cutting the peak raises them, and a site just below 2,500 hours can cross the threshold, where the kW price is higher and the kWh price lower. The Workspace's German tariffs switch at 2,500 hours; the calculator does not.

More in German grid charges and the 2,500-hour rule and how to size a battery for peak shaving.

Other free calculators

Zorowatt's is not the only one. Two we know of, from their own pages:

• The VDI 4657-3 web tool (Germany, published November 2025 with the guideline): upload your own load profile and see the effect of storage sizes on the maximum peak, with an economic evaluation of investment and electricity costs (Solarserver, 24 Nov 2025).
• JouleIO's peak shaving calculator (US): paste 15-, 30- or 60-minute kW readings and get a battery size in kWh, a payback and the share of the demand bill cut, in US terms ($/kW-month) (JouleIO).

Both were read on 2026-10-28. If one of them answers your question, use it; the numbers above work the same way whichever tool you use.

When the calculator is not enough

A quick estimate is a first look, enough to decide whether a full study is worth doing. A client deciding on a battery needs more:

• 12 months of 15-minute data, checked, and the invoices for the same months.
• The bill rebuilt under the operator's actual tariff and set against those invoices, line by line.
• The battery simulated through the year, billed by the same engine, with solar or a new load where there is one.
• NPV, IRR and payback with degradation and replacement, and every assumption visible.

Sources

• Liander, tariffs for connection and transport, large consumers 2026
• Stedin, tariffs 2026 large consumers
• Enexis, large-business tariffs from 1 Jul 2026
• NEW Netz, Preisblatt Strom 2026
• MET Romania, regulated tariffs from 1 Jan 2026
• pv magazine on when peak shaving pays
• Solarserver on the VDI 4657-3 web tool, 24 Nov 2025
• JouleIO peak shaving calculator

Last checked: 2026-10-30. Facts about other tools were read on 2026-10-28 from the pages linked next to them; prices and features change, so check the vendor's page before you rely on one. Examples marked illustrative are not real customers. Tariffs change every 1 January; check the current sheet before you use a rate.