By Kelley Electrical Contracting, LLC. Published October 16, 2026. Educational information, not a substitute for an on-site inspection.
Why solar touches your electrical panel
Solar produces power that has to feed into your home's electrical system, and that connection is made at the main service panel. The panel's busbar (the metal strip the breakers attach to) has a rating, and the code limits how much combined current can feed it.
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The 120% rule in plain English
A common way to meet this is the so-called 120% rule: the main breaker plus the solar breaker can add up to no more than 120% of the busbar rating. For example, a 200 amp busbar can generally carry a 200 amp main plus up to 40 amps of solar backfeed. If your numbers do not fit, options include a panel upgrade, a smaller main breaker, or other connection methods your electrician and installer will evaluate.
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Utility interconnection
Before a solar system is turned on, the local utility (for example PG&E or Southern California Edison) must approve it, and the work needs a permit and inspection. This step is often called permission to operate. Electrical problems found late can delay it, so a panel check up front saves time.
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Batteries and EV chargers
Adding a battery or EV charger on top of solar changes the load picture again. Plan the panel for everything you intend to add, not just the system going in today.
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Frequently asked questions
Does solar always require a panel upgrade?
No. Many homes have enough busbar capacity. Older, smaller or crowded panels are the ones that most often need work.
Who approves my solar system to turn on?
Your local building department inspects the work, and your electric utility gives final permission to operate.
Can an electrician check my panel before I sign a solar contract?
Yes, and it is a good idea. A pre-check can reveal upgrade costs before you commit.
Call (559) 940-1939Questions? Talk to a licensed electrician.
Sources and further reading
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Licensed California electrical contractor, license #1111378, bonded and insured. Serving Fresno, Clovis and Madera.