How do you size a BTM battery system for a commercial building?
Proper sizing requires analyzing the building's 15-minute interval data, utility rate structure, and any on-site solar — balancing power capacity (kW) and energy duration (kWh) to maximize savings without overspending.
Sizing a BTM system starts with understanding the building's load profile — how its electricity consumption varies hour by hour across the year. The key inputs are interval meter data (typically 15-minute readings), the utility rate structure, and whether on-site solar is part of the equation.
For demand charge reduction, the battery needs enough power capacity (kW) to shave peaks and enough energy capacity (kWh) to sustain that output long enough. A building with short, sharp peaks might only need a 1-hour battery, while one with broad afternoon peaks might need 2–4 hours of duration.
For TOU optimization, duration matters more. The battery needs to cover the entire on-peak window, which can be 4–6 hours depending on the rate schedule.
When paired with solar, the battery also needs capacity to absorb excess generation that would otherwise be exported at low value, then discharge it during expensive periods.
Most commercial BTM systems today fall in the range of 50 kW to 500 kW of power capacity, with 1–4 hours of duration. Oversizing wastes capital; undersizing leaves savings on the table. Good engineering uses at least 12 months of interval data and models the system against the actual rate tariff to find the sweet spot.