The short answer
- Many homes can add solar without a new main panel, but a larger system, a battery, an EV charger or a heat pump can push past the panel's limits.
- The "120% rule": a common 200 A panel with a 200 A main breaker can take a solar breaker of up to 40 A, about 7.6 kW of inverter output (City of Newport Beach plan-check guide).
- A main panel replacement cost a median $3,500 nationally (middle half $2,100–$5,000) in a 2026 Berkeley Lab survey (LBNL).
- Alternatives: derating the main breaker after a load calculation, a supply-side connection, or batteries and inverters with power control.
The 120% rule, plainly
The electrical code lets the breakers feeding a panel's busbar add up to 120% of its rating: 125% of the inverter's output current plus the main breaker can't exceed 120% of the busbar. For a 200 A busbar and a 200 A main, that leaves 40 A for solar (plan-check guide). Bigger systems need a smaller main breaker, a different connection, or a new panel.
What it costs
| Work | Median | Middle half |
|---|---|---|
| Main service panel replacement | $3,500 | $2,100–$5,000 |
| Customer-side service increase | $2,800 | — |
| Utility-side costs passed to the customer | $3,500 | — |
| Subpanel | $1,500 | — |
Industry-reported costs for single-family homes, national survey (Berkeley Lab, Aug 2026).
Permits
SolarAPP+ handles panel upgrades and breaker derates in most of the SoCal cities that use it, and the City of San Diego's self-issued solar permit allows upgrades up to 320 A. A service upgrade may also need the utility to change the connection; ask the installer to include that time in the schedule.
Checked against official sources on Oct 1, 2026. Sources are linked in the text. Not legal, tax or financial advice.