Sizing a C&I battery: peak shaving, self-consumption, or both?

This article was generated with AI assistance from cited sources and has not been individually reviewed by an editor.

A commercial or industrial battery should be sized to the job it is actually paid to do — peak shaving, self-consumption of on-site solar, or a mix of both. The mistake most first-time buyers make is sizing to the midday solar peak instead of the evening demand peak.

Behind-the-meter C&I storage earns its keep in three main ways: shaving demand charges (the network and capacity charges billed on your highest usage spikes), shifting on-site solar output into the hours when you actually consume it, and — in markets that allow it — participating in flexibility or ancillary-service programmes.

Start with your load profile, not your roof

The first input is a year of interval data (15-minute or hourly) showing when your site draws the most power. The battery’s power rating (kW) is set by the size of the peak you want to shave; its energy capacity (kWh) is set by how long that peak lasts. A 500 kW site with a 30-minute evening peak needs a very different battery from the same site with a three-hour evening peak.

In the C&I range, typical system sizes span roughly 100 kWh to several MWh. Our reference price bands place C&I storage at roughly €430–€560 per kWh for the 500 kWh-to-2 MWh range and €520–€680 per kWh for 100–500 kWh systems, with utility-scale references lower at €300–€420 per kWh. These are planning bands, not quotes — always price against at least three integrators.

Two jobs, two sizing rules

• Peak shaving only: size the power rating to the largest recurring peak you want to cut, and the energy capacity to cover that peak’s full duration plus a safety margin. Over-sizing the energy capacity here just adds cost with no extra demand-charge saving.
• Self-consumption only: size to the surplus your solar produces after your own load is served, measured across the year — not just in summer. A system sized to a July afternoon will sit nearly empty in winter, which is exactly the mistake residential buyers make and C&I buyers should avoid repeating.
• Combined: model the two revenue streams separately. Demand-charge savings are predictable and contracted; solar-shifting savings depend on your tariff and solar output. Stack them, but do not let one inflated assumption subsidise a weak one.

What to ask the integrator

• Ask for the monthly production curve of your roof and a dispatch model against your evening load, not an annual average.
• Ask for the demand-charge saving as a separate line item, backed by your actual tariff schedule.
• Ask what happens in winter: does the model show near-zero contribution in the dark months, or is it smearing summer savings across twelve months?
• Ask for degradation assumptions — a 10-year model with no annual capacity loss is not honest.

The honest payback test

A payback model that shows the battery earning nothing in winter and still paying back is credible. A model that spreads the summer saving evenly across the year is not. Re-run it month by month, and after the first full year, check the model against your actual bill. That first winter is where an honest sizing shows up.

Method and price bands as noted. BessCare publishes a method openly and never sells scores or rankings. No manufacturer or integrator reviewed this guide before publication.