Under PG&E’s current solar billing structure, a kilowatt-hour of solar electricity has a different value depending on what happens to it. Using it in your home offsets electricity you’d otherwise buy at the retail rate. Sending it to the grid earns an Energy Export Credit that varies by time of day and season. That gap is exactly why solar panel energy storage is worth a serious look for Cupertino homeowners. A battery doesn’t change how much sunlight reaches the roof, but it can change when your household uses the electricity your panels produce.
We’ve served Bay Area solar customers since 2003 and have completed more than 3,500 photovoltaic installations. For homeowners evaluating a new system or a battery addition, the important question isn’t whether storage has value in the abstract. It’s how your home uses electricity after solar production declines.
What PG&E’s Solar Billing Plan Actually Changes
PG&E’s Solar Billing Plan uses California’s Net Billing Tariff, the statewide framework that took effect for new solar customers on April 15, 2023. Under it, customers are billed for electricity imported from the grid and receive credits for excess solar exported to it, but those two numbers aren’t equal.
Time of Use rates make evening grid purchases more costly than daytime purchases. Export credits also shift over time, so a solar-only household can end up receiving less for midday production than it pays for electricity later in the day. Instead of treating each exported kilowatt-hour as a direct offset against later consumption, homeowners need to look at when solar production occurs and when the home actually draws from the grid.
Customers with legacy NEM 2.0 treatment should review their interconnection status before applying these rules to an existing system. Adding storage doesn’t automatically mean losing legacy treatment, but equipment changes and utility requirements should be confirmed before work begins.
Why Battery Storage Changes the Equation
A battery energy storage system stores electricity for later use. For a solar household, that typically means charging from excess midday production and discharging after the sun drops, when household demand continues and grid electricity costs more. Excess solar that would otherwise be exported at a comparatively low rate can instead power evening loads. The exact outcome still depends on a household’s production, consumption, rate structure, and battery settings.
A home without a battery uses solar power during the day and exports whatever exceeds household demand. With storage, Cupertino households can hold part of that excess for later. The battery may discharge into evening cooking, air conditioning, lighting, laundry, electric vehicle charging, or other loads that run after solar production drops, reducing how much electricity the home imports at those higher-cost hours.
Bill management and backup power are related but separate design goals. Load shifting helps a home use more of its own solar energy; backup power keeps selected equipment running during an outage. A battery configured for outage protection holds a reserve rather than discharging everything for daily bill management. Backup duration depends on usable battery capacity, the critical loads selected, and how much those loads draw. Refrigeration and lighting require a very different design from whole-home backup that includes large heating, cooling, or vehicle charging loads.
How to Evaluate Whether a Battery Makes Sense for Your Home
There isn’t one universal savings number for a battery because no two load profiles are identical. A home with significant electricity use after sunset has a different storage opportunity than one where occupants use most power during solar-producing hours. For a meaningful review, hourly electricity data matters more than a single monthly bill total. Production estimates should also account for roof orientation, shading, panel capacity, and seasonal variation.
Key inputs to review:
- Hourly Electricity Use: Identify when the home uses power, particularly during evening and overnight periods.
- Solar Production Pattern: Compare expected midday production with daytime household demand and potential excess generation.
- Battery Usable Capacity: Focus on the energy available for use, not only the battery’s nameplate capacity.
- Major Electrical Loads: Account for electric vehicle charging, air conditioning, heat pumps, pool equipment, and other large loads.
- Rate Plan Assumptions: Confirm the Time of Use schedule used in the analysis and how it affects imported electricity costs.
Cupertino homeowners should also identify whether their electricity supply arrangement includes community choice aggregation, a program where a local public agency procures electricity supply while PG&E continues to deliver power and maintain the grid. Supply rates and billing assumptions can affect a proposal’s analysis, so they should be visible rather than assumed.
Solar Only vs. Solar Plus Battery
A solar-only system reduces grid purchases while the panels are producing and exports surplus to PG&E. Its financial performance depends largely on how much solar electricity the household consumes directly rather than sends to the grid. A solar plus battery system retains some of that excess for later use, shifting midday power into evening hours when demand rises. The Solar Billing Plan makes this distinction more consequential for new customers, though a battery doesn’t produce a certain financial result. Utility rates change, export credit values vary, and battery operation shifts depending on backup preferences.
Solar Only
A solar-only design may fit a home with strong daytime self-consumption, modest evening usage, or a primary goal of reducing daytime grid purchases. It generally exports more production when household demand is low.
Solar Plus Storage
A solar plus storage design may fit a home with meaningful evening demand, a need for selected backup power, or a goal of shifting more solar electricity into later hours. Battery capacity and reserve settings shape how much energy is available for each purpose.
Questions to Ask Before Choosing a Battery System
A proposal should show its assumptions, not just present a projected outcome. Asking direct questions helps homeowners compare designs built on different equipment, operating strategies, and rate assumptions.
Questions to bring to a battery review:
- Which PG&E Rate Plan Is Assumed? Confirm the Time of Use rate schedule and export credit assumptions used in the analysis.
- How Much Usable Capacity Is Included? Ask for the battery’s usable capacity, round-trip efficiency, and expected operating limits.
- When Will the Battery Charge and Discharge? Review the planned operating schedule for daytime charging, evening loads, and seasonal production changes.
- What Happens During an Outage? Identify the backup circuits, reserve setting, and expected duration under different household loads.
- Who Handles Utility Coordination? Clarify responsibilities for permitting, interconnection, inspections, monitoring, and utility documentation.
- What Warranty and Support Apply? Review equipment warranty terms, labor coverage, maintenance options, and post-installation support.
Battery design is most useful when it starts with the home’s actual energy pattern rather than a generic savings estimate. The timing of production, consumption, exports, and backup needs determines whether a storage system is sized and configured for the way the household actually lives.
We help Cupertino homeowners evaluate solar and energy storage designs using production estimates, load information, in-house CAD resources, and utility coordination. Cobalt Power Systems Inc has served the Bay Area since 2003.
Reach our team at (650) 817-7791 or contact us online to discuss a battery system designed around your property’s energy use.