A PG&E homeowner comparing solar-plus-battery PPAs may see a capacity in kilowatt-hours, a charge percentage and a backup-reserve percentage. Each answers a different question. Understanding all three helps turn a promising equipment package into a useful outage plan.
A qualifying no-upfront offer can make solar and storage accessible while preserving cash. Ask the provider to document how its proposed battery will support your priorities using the distinctions below. Official sources were checked September 14, 2026.
Capacity describes the battery; charge describes this moment
Request the exact model, number of units and total usable energy capacity in kWh. Have the designer identify whether a quoted capacity is total or usable, and explain the manufacturer's measurement conditions. Also request the separate continuous and starting-power limits; energy capacity alone does not establish which appliances can run together.
For example, Enphase's U.S. IQ Battery 5P launch announcement, dated May 25, 2023, describes 5 kWh of capacity and 3.84 kW of continuous power. Those are different specifications. The announcement is a product example, not a statement that a particular PPA includes that equipment.
Charge percentage describes how full the battery is now. A quote that assumes a full battery should say so. Ask for another estimate using the expected charge after an ordinary evening of household use.
Backup reserve is a setting, not today's charge reading
PG&E's residential battery guidance explains that using stored energy for bill management can leave less saved for an outage. The utility also notes that backup commonly serves selected circuits. Your circuit list and operating settings therefore belong beside the capacity figure.
A reserve setting helps retain energy for interruptions. Its behavior depends on the product. Tesla's Backup Reserve guide explains that Powerwall makes the reserved energy available during an outage and may discharge below that percentage. The setting is not an outage shutdown threshold.
For Powerwall, do not automatically subtract the reserve percentage again when estimating outage energy: that portion is intended for backup. Have your installer explain the corresponding behavior for the actual model, including any low-charge operating limits. Changing a setting also does not make an incompletely charged battery instantly full.
Compare quotes with the same starting conditions
As a simplified illustration, assume 10 kWh of usable capacity and a charge display that scales directly with it. At 80% charge, that represents 8 kWh; at 40%, it represents 4 kWh. Neither figure is yet a promise of energy delivered to appliances.
Ask the designer to account for losses, operating limits and the selected loads, without deducting allowances already included in its estimate. Request a no-solar overnight scenario and a separate daylight scenario. Outage recharging requires suitable sunlight and compatible backup equipment; finite storage does not guarantee power through every interruption.
Bring your PG&E usage history and essential-load list so both proposals use comparable assumptions.
Put the equipment and payments together
Under a PPA, the provider owns the solar system and sells its generated electricity, as the CPUC consumer guide explains. Confirm qualification for zero upfront payment, battery inclusion and ownership, backup controls, installation charges, maintenance and replacement coverage.
Review the ongoing rate, any escalator, term and home-sale provisions alongside remaining PG&E charges. Savings are not guaranteed, and no upfront purchase does not mean free electricity. Our battery service-coverage guide can help organize those questions.
Explore your homeowner journey with a proposal that names the equipment, expected starting charge and supported circuits—not just a battery count.