How does Station A calculate the financials for a solar plus battery storage system?

We determine the financials for a solar plus battery storage system by calculating the battery energy limit, battery subsidies, battery lost electricity cost, and savings in addition to modeling the stand-alone assets.

Our model for solar and battery storage reuses some key components from our solar model and our battery model, so we will not re-copy those models here. Shared methodologies include:

  • Solar technical potential
  • Physical limits on battery size, both indoor and outdoor
  • Solar CAPEX
  • Battery CAPEX, except for subsidy calculations
  • Battery bill savings
  • Energy savings
  • GHG emissions savings

There are also substantial new calculations that are done only for solar + batteries, which are described further below:

Battery Energy Limit

When paired with solar, we relax the limit on battery power capacity from 50% of the building's annual peak to 100% of annual peak. We add a new limit: the battery capacity in kWh may not exceed 4 times the capacity of the solar array in kW.

Battery Subsidies

In areas where California's Self-Generation Incentive Program (SGIP) applies, we apply a $250/kWh subsidy to the cost of the battery (not solar) when paired with solar (Rather than $350, as we do for stand-alone). We limit the SGIP subsidy to covering 50% of CAPEX, so in cases where battery costs are < $500/kWh, we assume that SGIP subsidizes 50% of cost.

We assume that the Investment Tax Credit subsidy of 26% of CAPEX applies to both the solar and the battery when they are sited together.

Battery Lost Electricity Cost

When operating with solar, we assume that a battery cycles 250 times per year, as opposed to 100 when operating alone. This results in a lost electricity cost of:



We calculate the solar and battery savings by the same methods that we use when modeling them as stand-alone assets.