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Materials

Solar and batteries

California's 2025 Energy Code requires rooftop solar on new single-family homes and new detached ADUs, but most very small homes fall under the 1.8 kW exemption. MicroHom plans 2–4 kW anyway.

When solar is required

All newly built single-family homes, including new detached ADUs, must install PV sized at the smaller of the solar-access roof area × 18 W/sq ft (14 W/sq ft for low-slope roofs), or the Table 150.1-C formula. No PV is required if the solar-access roof area is under 80 contiguous sq ft or the required size is under 1.8 kWdc. A battery of at least 7.5 kWh reduces the required size by 25%. Tiny homes on wheels are recreational vehicles under HCD rules, so this housing rule does not apply to them as such.

Required PV size for small homes, by example climate zone
Climate zone200 sq ft home400 sq ft home
CZ3 (SF Bay coast)1.25 kW, exempt1.37 kW, exempt
CZ9 (LA foothills)1.48 kW, exempt1.61 kW, exempt
CZ12 (Sacramento)1.52 kW, exempt1.65 kW, exempt
CZ13 (Fresno)1.69 kW, exempt1.87 kW, required
CZ15 (Imperial / Coachella)1.78 kW, exempt2.09 kW, required

MicroHom arithmetic with the Table 150.1-C factors for one dwelling unit. An energy consultant must confirm the size for a real permit.

Typical system and cost

  • One south-facing roof plane on a 400 sq ft home fits about 3.5–4 kW; on a 200 sq ft home, about 1.8–2 kW.
  • Installed: California average $2.52 per watt (EnergySage, Oct 2026), so about $5,000 for 2 kW and $10,100 for 4 kW; small systems often price higher, $2.50–3.50 per watt.
  • Battery: about $1,037 per kWh installed, so a 13 kWh battery is about $13,500.
  • Panels add about 3–4 psf of dead load, delivered as point loads at the attachments, so the roof framing must be checked.

Federal tax credit ended. The section 25D residential clean energy credit is not allowed for expenditures made after December 31, 2025. For new construction, the expenditure counts when the owner's original use of the home begins.

Solar and battery suppliers

Sources

  1. California Energy Commission, 2025 Energy Code Support Center: single-family solar PV FAQ. Checked Oct 17, 2026.
  2. California Energy Commission, 2025 Energy Code guide for ADUs (Apr 2026). Checked Oct 17, 2026.
  3. 2025 California Energy Code, Section 150.1 (gocodebook). Checked Oct 17, 2026.
  4. California Energy Commission, What's New for 2025: Single-Family. Checked Oct 17, 2026.
  5. HCD Information Bulletin 2016-01, tiny homes. Checked Oct 17, 2026.
  6. EnergySage, solar panel cost in California (Oct 2026). Checked Oct 17, 2026.
  7. EnergySage, energy storage cost in California (Oct 2026). Checked Oct 17, 2026.
  8. OC Solar, solar panel cost in California 2026 guide. Checked Oct 17, 2026.
  9. SEAU, "Will your roof support solar panels?". Checked Oct 17, 2026.
  10. IRS, FAQs for modification of sections 25C, 25D, 25E, 30C, 30D, 45L, 45W and 179D under Public Law 119-21. Checked Oct 18, 2026.
  11. 26 U.S.C. § 25D, Residential clean energy credit (subsection h, termination). Checked Oct 18, 2026.

Last updated Oct 18, 2026. Each source above was checked on the date shown.