Demand charges are not the same as energy charges
Many commercial tariffs bill both kilowatt-hours and a charge based on the highest measured demand during a billing interval or defined period. A project can reduce annual energy use substantially yet save little on demand charges if the site’s monthly peak happens after solar production falls.
Start with interval data
Monthly bills alone rarely show when peaks occur. Obtain interval load data—often 15-, 30- or 60-minute depending on the tariff—and identify recurring peak events, seasonal changes and operational causes. Compare those timestamps with expected PV production before assigning savings to a battery.
Battery power can matter more than battery energy
Peak shaving may require a battery to deliver high power for a relatively short interval. A system with plenty of kWh but insufficient inverter or battery kW may miss the peak. Conversely, a high-power system with too little energy can exhaust its reserve if peaks last longer or repeat.
Dispatch strategy must protect the next peak
Using the battery for self-consumption or energy arbitrage can leave insufficient state of charge for a later demand event. Controls need a clear priority and reliable load forecasting. Backup reserve adds another competing objective, so the financial model should not assume the same stored energy is available for every service simultaneously.
Model the actual tariff rules
Use commercial demand-charge battery sizing and time-of-use planning. Confirm ratchets, seasonal windows, taxes and capacity terms from the current utility tariff before turning modeled peak reduction into a savings forecast.