Solar starts at the panel, not the roof
Most homeowners picture solar as panels on the roof. Electrically, the project lives or dies at the main panel — that is where the solar system's power enters your home's wiring, where the utility interconnects, and where inspectors look first. Check these four interfaces before you sign a solar contract.
The four interfaces
Illustrative photo- Busbar rating and the 120% rule. The panel's busbar can only carry so much combined current from the utility plus your solar. Under the well-known 120% rule, a 200A busbar with a 200A main breaker typically allows up to a 40A solar breaker. Older 100A panels with 100A mains often allow little or nothing — which is why panel upgrades and solar projects so often go together.
- Spare breaker spaces for the solar breaker. The solar system needs its own dedicated two-pole breaker. A full panel with no spaces — or a panel full of double-tapped breakers — has nowhere to land it. Sometimes a quad breaker or subpanel solves it; sometimes only a panel upgrade does.
- Service size and the utility's interconnection capacity. Your utility (SCE or SDG&E) must approve the interconnection, and approval depends on your service size plus local grid conditions. An undersized service can cap your system size or trigger utility-side upgrade costs — under utility rules for customer-driven work, those costs typically fall on the customer.
- Grounding, rapid shutdown, and monitoring readiness. Current code requires module-level rapid shutdown, proper equipment grounding, and a production monitoring setup. Older panels and services often need grounding updates to pass inspection with solar attached. These are not optional extras — the inspector will check them.
Planning solar? Send us three panel photos — exterior, label, main breaker — plus your city and roof direction. We will give you a free preliminary assessment of whether your panel is solar-ready (not a final quote).