Electrifying an ADU with Solar and Battery Backup: A Planning Guide
A planning guide to all-electric ADUs, solar feasibility, battery backup, utility interconnection, and incentive checks in the Bay Area.
Maor Greenberg
An accessory dwelling unit (ADU) can be planned for electric heating, hot water, cooking, and laundry from the start. Adding rooftop solar or a battery is a separate design decision: the right system depends on the ADU’s expected loads, roof and site conditions, utility connection, and how the household will use power. This guide explains what to coordinate before choosing equipment and how to evaluate estimates without assuming a guaranteed return.
Plan the ADU as an all-electric building
Common electric choices include a heat pump for heating and cooling, a heat pump water heater, an induction cooktop, and an electric clothes dryer. Select equipment around the unit’s floor plan, insulation, windows, occupancy, and hot-water needs. Coordinate mechanical locations, ventilation, condensate, noise, and service access with the architectural design.
Ask the design and construction team to identify electrical loads early. An electrician can evaluate the service and panel, planned appliances, and whether the ADU will have a separate meter or share service with the main home. The utility connection, panel capacity, wiring route, and any service work should be included in the project scope before finishes are finalized.
Coordinate solar with the roof and site
Solar feasibility depends on usable roof area, orientation, shading, roof condition, and the electrical design. A detached ADU may have limited roof area, and nearby trees or buildings can affect production. If the main house is also being considered for solar, compare both roofs and clarify which meter and loads the system is intended to serve.
Request an estimate that shows the proposed system size, expected annual production, assumptions about shade and equipment, and the utility rate plan used in any bill analysis. For customers under California’s net billing tariff, electricity exported to the grid is credited under tariff rules and may be valued differently from electricity purchased. The California Public Utilities Commission explains net billing. A production estimate alone does not establish a particular bill reduction or payback.
Decide what a battery should do
A battery can store electricity for later use and may provide backup for selected circuits when configured for that purpose. It does not automatically power the entire ADU during an outage. Ask the installer to list the backed-up loads, expected duration under stated conditions, equipment required for backup, and how the system operates when the grid is down.
Battery location and installation details need to be coordinated with the plans and reviewed under applicable building and fire requirements. The project team should confirm clearances, access, wiring, permits, utility interconnection, and any required inspections with the authority having jurisdiction and utility. Avoid treating battery backup, bill savings, and resilience as interchangeable benefits; each depends on system design and use.
Check incentives and tax rules before relying on them
Do not include the former federal residential clean energy credit in a budget for a new installation after 2025. The IRS states that Section 25D is unavailable for expenditures made after December 31, 2025; it also states that Section 25C is unavailable for qualifying property placed in service after that date. Ask a tax professional about a prior-year project or individual tax circumstances.
California and utility programs have separate eligibility and funding rules. The California Energy Commission’s HEEHRA information describes income-qualified heat-pump rebates with reservation requirements; a newly built ADU should not be assumed to qualify. The CPUC’s Self-Generation Incentive Program describes eligible storage incentives, including a residential equity category with specific eligibility and current budget limits. Confirm with the program administrator whether the property, applicant, equipment, and project timing qualify before ordering or starting work. A program’s advertised maximum is not a guaranteed award.
Compare the full project scope
Compare proposals with the same assumptions and scope. Separate ADU construction, electrical service work, solar, storage, permits, utility work, and optional backup equipment. Ask which items are included, what could change after site review, who handles interconnection, and whether incentive applications require preapproval.
For an operating-cost estimate, request the expected electric use, applicable tariff, solar production assumptions, export value, battery operating strategy, and any fixed utility charges. Actual costs and results vary with site conditions, rates, occupancy, equipment, construction scope, and program eligibility. Treat payback, rent, resale value, and emissions estimates as project-specific analyses, not guaranteed outcomes.
Bring the decisions together during design
Decide first which loads the ADU needs to serve and whether solar or outage backup is a priority. Then coordinate roof design, electrical capacity, equipment locations, utility connection, permits, and budget. If the ADU is part of a larger home project, planning these systems alongside architecture and construction can make the scope clearer before work begins. Learn about Greenberg Construction’s ADU service or contact the team to discuss a project.