Quick Answer: Yes — building an ADU and adding solar panels at the same time in San Jose is not only possible but financially smart. California Title 24 (Section 150.2(b)) requires that all new ADUs include a solar-ready roof and electrical infrastructure (conduit, panel space) even if solar isn’t installed immediately. Since you’re already doing this electrical work for the ADU, adding actual solar panels at the same time saves you the cost of a mobilization fee (typically $2,000-$4,000 for a solar installer to return later). The solar system should be sized to cover BOTH the main house and the new ADU’s electricity needs — an ADU typically uses 3,000-5,000 kWh per year, adding roughly 1.5-2.5 kW of solar capacity needed.
ADU + Solar Combination Guide — San Jose 2025
Helpful Resources:
- Title 24 ADU solar-ready requirement: All new ADUs in California require a solar-ready electrical system — this means a 200-amp panel (or sub-panel), conduit from panel to roof, and a reserved circuit breaker slot. This work is required regardless of whether you install solar, so installing solar at the same time costs only incremental materials, not a second mobilization
- Sizing the solar system for ADU + main house: Estimate 3,000-5,000 kWh/year for a 400-800 sq ft ADU (depending on HVAC type and tenant habits). Add this to your main house consumption. A combined 10-14 kW system (28-38 panels) typically covers both units in San Jose’s climate
- Battery storage with ADU solar: Under California’s NEM 3.0 metering, solar export credits are low (about $0.05/kWh compared to retail $0.30+/kWh). A battery (Tesla Powerwall or Enphase IQ) allows you to store ADU daytime generation for main house nighttime use — maximizing self-consumption and payback. A combined ADU + battery + solar system pays back in 8-12 years under NEM 3.0
- Separate meter for ADU: San Jose allows ADU tenants to have their own PG&E meter (ADU sub-meter) — this makes billing simple and the tenant pays their own electricity. In this case, size solar for the main house only; the ADU solar system would need to be on the ADU’s meter separately
- Permit coordination: A solar permit (City of San Jose electrical permit) and ADU building permit can be submitted together or sequentially. Coordinate with your solar installer to submit the solar permit before or concurrent with the ADU permit to avoid delays
| System Configuration | System Size | Cost Before ITC | Cost After 30% ITC |
|---|---|---|---|
| Main house only (no ADU) | 6-8 kW | $18,000 – $24,000 | $12,600 – $16,800 |
| Main house + ADU (shared meter) | 9-14 kW | $27,000 – $42,000 | $18,900 – $29,400 |
| Main house + ADU + 2 Powerwall batteries | 9-14 kW + 2 batteries | $47,000 – $74,000 | $32,900 – $51,800 |
Quartz Construction builds ADUs and coordinates solar installations throughout San Jose. Learn about ADU construction services. CSLB #1003436 | Call (650) 749-7436.
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