For a PG&E homeowner comparing solar-plus-battery PPAs, storage can make daytime solar useful later in the day. A useful proposal should also account for the energy consumed in charging, storing and delivering that electricity. Ask where the PPA measures billable energy and whether the savings estimate includes battery losses.
This helps you compare the complete service: solar generation, useful stored energy, backup capability and ongoing payments.
Why efficiency matters on PG&E's Solar Billing Plan
PG&E's Solar Billing Plan distinguishes electricity purchased from the grid from surplus solar exported for credits. A battery can shift solar use into later hours, reducing some grid purchases. The value depends on when that energy is used and the applicable import prices and export credits.
Ask the provider to model your actual rate plan and generation provider, including a community choice provider where applicable. An existing NEM household needs a comparison under its own billing rules. Do not assume a generic annual solar-production total describes either household's bill.
Compare the same energy pathway
Round-trip efficiency describes how much energy emerges after a specified charging-and-discharging pathway. It is different from storage capacity, maximum power or a battery's current charge percentage.
For a manufacturer example, Tesla's Powerwall 3 specifications list 89% solar-to-battery-to-home/grid round-trip efficiency. The stated conditions are beginning of life, 77°F and 3.3 kW charging/discharging, for a typical solar-shifting use case. The same page lists 97.5% for the different solar-to-home/grid pathway, tested with CEC weighted methodology.
Those figures should not be interchanged. Ask which pathway and test conditions the proposed equipment's estimate uses, and how the model accounts for operating conditions and aging. A published specification is not a promise that every home's daily result will match it.
A simple example of the payment question
Assume, solely for illustration, that a contract bills 10 kWh before storage at $0.20 per kWh, and the modeled path from that billing point to household loads returns 90% of the energy. The payment for those 10 kWh is $2; the modeled delivered energy is 9 kWh. Dividing $2 by 9 gives about $0.222 per delivered kWh, before other costs.
These are invented assumptions, not a PG&E rate, an available PPA offer or a Powerwall performance estimate. A different billing measurement point changes the calculation. The example is also not a whole-system cost: some solar may serve the house directly, some may be exported, and battery fees and remaining utility charges still matter.
Request a written explanation of the billing meter, treatment of storage losses and any separate battery charge. Our guide to solar production and exports explains why those energy quantities differ.
Keep backup and contract terms in the comparison
PG&E's battery guidance covers storage for bill management and outages. Ask the model to reflect your intended backup reserve as well as daily energy shifting. Supported loads, available charge and equipment limits determine outage performance; solar replenishment requires suitable sunlight and compatible operating equipment.
A qualifying no-upfront PPA can make a professionally installed system accessible without buying it outright. The CPUC solar guide explains provider ownership and ongoing payments for generated electricity. Confirm qualification, the billing definition, rate, any escalator, term, battery ownership and fees, maintenance, replacement and home-sale transfer provisions. No upfront purchase does not mean free electricity or guaranteed savings.
Bring your PG&E bill and proposal to West Coast Alternatives to discuss a solar-and-battery comparison that accounts for both useful energy and the full payment structure.