The size of the peak matters
Many commercial tariffs include a demand charge tied to peak power over a defined billing interval. The exact interval, season, demand definition and any ratchet provisions depend on the tariff. Review the bill and tariff together.
Solar does not erase every peak
A facility can use solar throughout the day and still set its monthly peak during a cloudy period or after sunset. Annual production alone does not show how a project affects billed demand.
Storage has a specific job
A battery may discharge during a peak and charge at another time. The result depends on power, energy capacity, available state of charge and controls. Backup reserves can reduce the capacity available for economic dispatch.
Ask for the right evidence
Request an interval-load analysis, the actual tariff and a comparison of the modeled bill with and without the system. Include equipment losses and operating constraints. A smaller peak is useful only if it reduces the billed metric.
Further reading
U.S. Department of Energy — On-Site Energy Storage Decision Guide ↗