The short answer
- From signing to switching on often takes one to three months: design, permit, install, inspection, then the utility's permission to operate (PTO).
- The utility step is the shortest for simple systems: SCE says simple solar-only applications may get PTO within 10 business days, and SDG&E says PTO "usually takes up to five business days".
- Batteries, panel upgrades and HOA approval add time.
- Don't turn the system on before PTO.
The steps
- Site visit and design (1–2 weeks).
- HOA approval if needed (up to 45 days by law; HOA rules).
- Permit: instant in SolarAPP+ cities, days to weeks elsewhere (permits).
- Installation: usually 1–3 days.
- City inspection.
- Utility interconnection and permission to operate.
Speeding it up
- Choose an installer that files complete applications (ask how long their recent jobs took).
- Sign the CPUC consumer protection guide promptly; SCE and SDG&E won't connect without it.
- Have your utility account number and a recent bill ready.
Checked against official sources on Oct 1, 2026. Sources are linked in the text. Not legal, tax or financial advice.