Is your panel solar-ready?
Adding solar means adding a back-fed breaker to your panel. NEC 705.12(B)(3) and PG&E interconnection rules dictate what your panel needs to qualify — most older Marin panels need work before solar can connect.
By Steven Lockhart · Reviewed by Alex Towery, C-10 #989290
Updated 2026-06-16
A solar-ready electrical panel needs three things: (1) busbar rating that accommodates the 120% rule (main breaker + solar breaker ≤ 120% of busbar rating), (2) available breaker space for the solar back-fed breaker (typically 30-60A double-pole), (3) main breaker on the opposite end from the solar breaker to satisfy the 'opposite-end rule.' Most older Marin panels (100A service from before 2000) don't meet these criteria and need panel upgrade or supply-side connection before solar interconnects.
01The three solar-ready requirements.
First, busbar capacity. NEC 705.12(B)(3) — the 120% rule — limits how much current can be back-fed into a panel relative to its busbar rating. For a 200A panel, main + solar breaker amperage cannot exceed 240A (120% of 200A). A 200A main with a 40A solar breaker is fine (200+40=240, equal to the limit). A 200A main with a 60A solar breaker (200+60=260) violates the rule and requires panel upgrade or a different interconnection method. Older 100A panels are especially constrained — a 100A main allows only 20A solar breaker, far below most modern solar installations.
Second, breaker space. Solar interconnects through a dedicated back-fed breaker, typically 30-60A double-pole depending on system size. Your panel needs two adjacent open breaker spaces at the opposite end of the busbar from the main breaker. Full panels (every breaker space used) need panel upgrade or breaker consolidation before solar can connect. Third, the opposite-end rule: solar breaker must mount at the far end of the busbar from the main breaker, ensuring the busbar between them carries the full sum of main and solar currents.
02Common Marin panel scenarios.
Modern 200A panel, room to grow
Built 2000+, 200A busbar, available breaker space, modern make (Square D, Eaton, Siemens, GE). Solar-ready as-is for most residential systems. Direct interconnection works.
Modern 100A panel, tight on capacity
Built 1990-2010, 100A service, limited busbar headroom. Solar systems above ~20A back-feed require panel upgrade to 200A OR supply-side connection (taps before main breaker). Common Marin scenario.
Federal Pacific or Zinsco panel
Built pre-1990, known safety concerns, solar interconnection not recommended through these panels. Panel replacement is the right answer — solar contractor typically requires it before installing.
03What we do for solar interconnection prep.
When a homeowner is planning solar, we inspect the panel for solar-readiness during the quote. We verify busbar rating, count available breaker space, identify panel make/model, and check the main breaker position relative to the proposed solar interconnect point. We document findings and present three options if the panel isn't solar-ready: panel upgrade (200A modern), supply-side tap connection (works for some scenarios without panel upgrade), or panel replacement (for Federal Pacific, Zinsco, or panels with other issues).
Most modern solar contractors include a panel review in their site visit but don't always identify nuanced issues. We work with the solar contractor (or independently if homeowner prefers) to ensure panel-side work is done correctly and timed appropriately — panel upgrade typically precedes solar installation by 2-4 weeks to allow inspection and PG&E meter coordination.
Common questions.
Can I add solar without upgrading my panel?
Depends on your panel's solar-readiness. Modern 200A panels usually accommodate residential solar without upgrade. Older 100A panels often need upgrade for solar systems above ~20A back-feed. Supply-side tap connection (an alternative that doesn't use a panel breaker) works in some scenarios and avoids panel upgrade — discuss with solar contractor and us during the planning phase. Federal Pacific/Zinsco panels require replacement before solar regardless.
Will my solar contractor handle the panel upgrade?
Some do, many don't. Solar contractors with in-house electrical departments handle panel upgrades; pure solar contractors subcontract or refer to us. Either way works fine — what matters is that panel work is done by licensed C-10 electrician with proper permitting and the panel meets PG&E interconnection requirements before solar inspection. We coordinate directly with solar contractors on Marin projects regularly.
What's a supply-side tap?
An alternative to panel breaker interconnection where solar connects to the service-entrance conductors between the meter and the main breaker. Bypasses the 120% rule because it doesn't add load to the busbar. Useful when panel upgrade is undesirable but solar exceeds back-fed breaker capacity. Adds cost ($800-$2,000) over standard breaker interconnection and requires specific install conditions. Not all panels support clean supply-side tap installation.
How long does panel upgrade for solar take?
2-4 weeks from contract signing including permit pull, PG&E meter coordination, install day (8-10 hours, power off), and final inspection. The panel upgrade typically completes 2-3 weeks before solar installation begins so the solar contractor has a permitted, inspected panel to interconnect with. We coordinate timing with the solar contractor's schedule.
How do you handle pricing — flat fee or hourly?
Both, depending on scope. Routine service calls and predictable scope (panel replacement, EV charger install, transfer switch install, fixture replacement) are flat-fee quoted up front. Diagnostic visits and emergency scope are hourly because we don't know what we'll find. Either way, you get a written quote before work starts on anything significant, and we don't proceed beyond the quote without your sign-off.
How quickly can you schedule?
Depends on scope and season. Emergency dispatch: same-day across Marin County (1-3 hours business hours, 1-4 hours after-hours). Same-day standard service: 3-6 hours from call when capacity allows; otherwise next business day. Scheduled service work: 1-3 weeks typical. Larger projects requiring permits and PG&E coordination: 4-12 weeks depending on scope. We're upfront about timeline at the quote stage.
What warranty do you offer on work?
Our standard residential warranty: 2 years on labor, manufacturer warranty on parts (varies by product — typically 1-10 years). Major installs (panels, generators, EV chargers) often have longer manufacturer warranties (5-10 years). If there's an issue with our work in the warranty period, we come back and fix it at no cost. We also stand behind work past warranty — repeat customers and referrals matter more than a transactional fix.
Are you licensed and insured?
Yes. California State License Board C-10 Electrical Contractor #989290, in good standing. Carry general liability insurance and workers' compensation insurance as required by California law. Bondable on projects requiring it. Happy to provide proof of insurance to clients or property managers on request. License lookup: cslb.ca.gov.
Schedule a consult before storm season.
Best window for prep work: October before Marin's atmospheric-river season starts. Beat the rush, lock pricing.