Sizes a BESS power rating and energy capacity to shave a facility's peak demand from its current level down to a target level for a given peak duration, then estimates the resulting monthly/annual demand-charge savings, total capital cost, and simple payback period.
Standards followed
Peak-shaving BESS sizing: power = required shave × margin; energy = (required shave × duration) ÷ round-trip efficiency
What it can do
- Required shave, BESS power rating (with an inverter margin), and energy capacity (with round-trip efficiency).
- Monthly and annual demand-charge savings from the shaved kW and the utility's demand charge rate.
- Optional capital cost input for total cost and simple payback in years.
- Classification from NO REDUCTION NEEDED to LOW-BENEFIT/INFEASIBLE based on shave ratio, duration, and payback.
Example problem
1000kW peak, target 750kW, 2-hour peak duration, 90% round-trip efficiency, 10% inverter margin, $15/kW-month demand charge, $400/kWh BESS cost.
- Required shave = 1000−750 = 250kW
- BESS power = 250×1.10 = 275kW; BESS energy = (250×2)/0.9 ≈ 555.6kWh
- Monthly savings = 250×$15 = $3750; annual = $45,000
- Capital cost = 555.6×$400 ≈ $222,222; payback ≈ 222,222/45,000 ≈ 4.9 years
275kW / 555.6kWh BESS, ≈$45,000/yr savings, ≈4.9-year simple payback — STANDARD class.
This is a single-event peak-shaving sizing estimate assuming one peak period per billing cycle — actual demand-charge tariffs often have multiple peak windows (on-peak/off-peak/coincident-peak), and a full analysis needs the facility's actual interval load data, not a single peak/duration figure. Simple payback also ignores financing costs, battery degradation/replacement, and other value streams (e.g. demand response, backup power) the BESS might provide.