Understanding combined solar-plus-storage payback
How combined payback compares to solar alone
A 150 kW solar system at $1.60/W plus a 200 kWh battery at $550/kWh costs $350,000 gross, or $245,000 after a 30% ITC. With $28,000 a year in usage-charge savings from solar and $15,000 a year in demand-charge savings from the battery, the combined $43,000 in annual savings produces a payback of about 5.7 years. Compare that against the solar-only payback in the commercial solar payback calculator to see exactly how much the battery adds to the timeline, and the rebate plus ITC combined calculator in our rebates and incentives section if a state or utility rebate stacks with the federal credit here too. Once you have a size in mind, the loan payment calculator in our Financing section can help you compare loan, lease, and cash purchase options for the system you just sized.
Why add a battery on top of solar at all
Solar handles usage-charge savings well but does little for demand charges unless your peak happens to fall during sun hours. A battery adds a second, more reliable savings stream from demand charge reduction, plus resilience during outages, which together often justify the additional upfront cost even though the battery alone typically pays back slower than solar alone. NREL's own REopt analysis of commercial solar-plus-storage economics found the combination provides meaningful energy-charge savings on top of demand-charge reduction, and that the benefit holds regardless of how variable a building's load profile is. The peak demand battery offset calculator can help quantify that second savings stream on its own.
Whether the battery needs to match backup power sizing
Not necessarily. A battery sized purely for demand charge reduction can be smaller than one sized for extended backup power, since peak shaving only requires enough capacity to cover the highest demand event, not hours of full facility operation. If backup power is also a goal, size the battery to the larger of the two requirements using the battery storage sizing calculator, and the battery storage size calculator in our battery storage section for the underlying capacity math at a residential and small-scale angle.
What happens if the battery is added later
The battery's own payback is calculated independently from that point forward, using only the battery's cost and its own savings stream, typically demand charge reduction. Adding storage later doesn't reset or improve the solar system's original payback, but it does let a business spread out capital spending across two separate decisions, each of which can be tracked with the battery demand charge payback calculator on its own. The Department of Energy's end-use load profile data is a useful reference if you want to sanity-check typical commercial load patterns against your own utility bills either way.