Solar Panel Installation in Napa, CA

What we look at on the first visit

Remaining roof life. A composition shingle roof ages out on a schedule and an array is built to sit for decades. If your covering has a few years left, the sensible sequence is roof first, since removing and resetting a full array later means paying that labor twice and cutting a second set of penetrations.

Material and structure. Composition shingle is the straightforward case. Tile means tile hooks, replacement tiles and slower going. The older homes near downtown often have steep pitches, several small planes, dormers and skylights, which cuts usable area and pushes labor up. We get into the attic to read rafter size and spacing, since framing sized for its original load sometimes needs blocking or sistering before it carries an array.

Shading. This varies block to block. The mature oaks and street trees that make the older neighborhoods pleasant throw long afternoon shadows, and the hillside streets pick up shade from terrain as well as canopy. We model each roof plane across the year, because one chimney can take a string offline during exactly the hours you were counting on.

Electrical. We open the main panel and read the busbar rating, the main breaker, the free spaces and the meter position. On the older streets near downtown we routinely find services sized for a much smaller house, panels with no room left, and legacy branch wiring never meant to sit alongside a modern interconnection. In the newer south and east Napa subdivisions we more often find a 200-amp panel in the garage with space to work in.

What is coming next. We ask what else you plan to add: a heat pump, an electric water heater, a car, a pool pump, a well pump. A system sized on last year's bills alone is undersized the week you electrify something.

Sizing to your usage, not your square footage

Good sizing starts with twelve months of metered usage. Two homes on one street with the same floor plan can differ by a factor of two depending on occupancy, pool, and whether the heat is gas or electric. Under net billing the shape of that usage matters as much as the total, so we look at when you draw power and not only how much.

Then we layer in the loads you are likely to add, which is where Napa homeowners undersize themselves. The Bay Area Air Quality Management District's Regulation 9, Rule 6 set zero-NOx requirements for residential water heaters with point of sale standards phased across 2027 and 2031 by equipment type, so they reach what may be sold and installed rather than the unit already in place, and Napa sits fully inside that district. No existing gas water heater is banned, and we confirm the current requirement at project time. For sizing, the point is that a meaningful share of local water heating will move onto electricity, and today's array should have that in the arithmetic. The same holds for heat pump heating and cooling and heat pump water heaters.

On the code side, California's 2025 Building Energy Efficiency Standards took effect January 1, 2026, per the California Energy Commission. Those govern new construction and certain alterations. They place no retrofit obligation on an existing Napa house.

Permits, and the two approvals people confuse

California does not leave solar permitting to local discretion. Government Code 65850.5 directs that "every city, county, or city and county... shall adopt an ordinance... that creates an expedited, streamlined permitting process for small residential rooftop solar energy systems," and requires jurisdictions to "administratively approve applications to install solar energy systems through the issuance of a building permit or similar nondiscretionary permit." Review is limited to health and safety, which makes it ministerial. The statute defines the small residential category, including a ceiling of "10 kilowatts alternating current nameplate rating or 30 kilowatts thermal" on a single or duplex family dwelling. An application meeting the published checklist is deemed complete, and once confirmed complete the jurisdiction is to approve it and issue the permits.

Inside city limits that permit comes from the City of Napa Building Division. Outside city limits it goes through Napa County Planning, Building and Environmental Services, along with any extra review that applies on rural or hillside parcels. We handle either path, and the unincorporated side is covered on our Napa County solar page.

The approval people forget is the utility one. PG&E's interconnection application runs on its own schedule, and permission to operate is what allows the system to export. A permit lets your array be built legally. Permission to operate turns it on.

Plan review also shapes something homeowners do not anticipate: roof access pathways and setbacks near ridges are part of the layout, so a sound design rarely covers every square foot of a complex roof. On the cut-up planes common in the older parts of town, those clearances often set the final module count.

Inspection, interconnection, and switch-on

The building inspector checks mounting and flashing, conductors and overcurrent protection, disconnects, grounding and bonding, the rapid shutdown provision and the labeling. We meet the inspector rather than leaving a homeowner to explain someone else's work.

Once that signs off, the package goes to PG&E and the system waits. Until the release arrives the array stays off, and people occasionally hear they can quietly run it in the meantime. No licensed contractor should suggest that. At release we commission the system: verify every module reports, compare production against the modeled curve for that time of year, register your monitoring account, and walk you through the disconnects.

What fails on a home solar system over time

Panels themselves rarely fail. Almost everything around them can.

Inverter faults. A string inverter is the shortest-lived major component in a typical system and eventually needs replacing. Microinverters fail one at a time and show up as a single module missing from monitoring rather than a dark system.

Monitoring dropping offline. The most common reason a system looks dead is a changed Wi-Fi password or a replaced router. The array is fine, the reporting path is not.

Production drift. Soiling, a tree that grew, a critter nest under the modules. Local summers are dry and dusty and the film that settles between rains takes a real bite. Winter rain does most of the cleaning at no charge, but a system nobody has looked at in eight years usually has something to find.

Smoke. In smoke-heavy stretches we watch production sag on customer monitoring for days and then recover. That is atmospheric, not a defect.

Roof work. A future re-roof means the array comes off and goes back on with new flashing. Plan it as a scheduled project rather than something a roofer improvises.

When an array ages out, or its original installer is gone, we design and install a replacement system sized to how the house actually runs now. If the array itself is still earning its keep, adding battery storage is an install job we take on too, because the panel and interconnection work sits under our own C-10 license.

Batteries, backup, and what to expect here

Storage does two different jobs and they deserve separate consideration. The first is economic: under the current export rules, holding midday production for the expensive evening hours captures more value than sending it out. That is what moved batteries from a luxury to a normal part of a well-designed system.

The second is riding out an outage, and here the specifics matter. A battery does not usually back up a whole house. Most installations feed a subpanel of chosen circuits: refrigeration, some lighting, internet, a few outlets, the furnace or air handler controls. Air conditioning is a large draw and backing it up meaningfully changes the sizing, so we ask what you want running and design to that list.

Runtime is a function of load. A battery that carries a light demand overnight will not carry a heavy one for three days. For households that need to stay powered through a long shutoff, a standby generator is the better tool, and we install those as a Certified Generac Generator installer.

One case comes up constantly outside the city limits. Properties on private wells lose water the instant they lose power, because the pump is electric. On those homes we treat the well pump as a backed-up circuit from the start, which is a very different sizing exercise than a house on the City of Napa water system.

What drives the cost of a solar project here

No two quotes are comparable until you know what is inside them. These are the variables that move the number:

• Array size in DC kilowatts, which follows from your usage and the loads you plan to add
• Roof material and complexity. Tile and multi-plane roofs cost more labor than a single-plane composition roof
• Roof condition, since a re-roof beforehand is a separate project and a real line item
• Structural work, if framing needs reinforcement to carry the array
• The electrical tie-in. A clean back-fed breaker is one number, a supply-side connection another, a service upgrade another again
• Conduit run length from array to inverter to panel, which your meter location sets
• Module and inverter selection, including efficiency, warranty term and shade electronics
• Storage, meaning how many units and how large a backed-up subpanel
• Detached structures or ground mounts, which add trenching and a feeder
• Permit and interconnection fees, which vary by jurisdiction and scope

All of it goes in writing before work begins, so you can see which line moved when the design moves. If spreading the cost matters, financing options come up front rather than at signing.

Incentives: what applies in Napa, and what does not

Programs in this state change often. Current status:

• MCE supplies your electricity here, and its offerings differ from what you will read about for Sonoma County. MCE's EV charging program covers workplace, multifamily properties of four or more units, and commuter parking lots. That list has no room for a single-family house. Say that precisely rather than broadly, though, because two other routes do reach one: PG&E's residential charger rebate, whose terms make Community Choice Aggregation customers eligible, and MCE Sync, which rewards smart charging rather than the purchase.
• Sonoma Clean Power programs, which surface constantly in North Bay searches, serve Sonoma County accounts and do not reach a Napa address.

The rest of the work a solar project touches

Solar rarely stays in its own lane, which is the practical argument for one licensed company across the trades.

Panel and service work. The most common companion project is a service or panel upgrade, either because the busbar cannot accept the interconnection or because the household is stacking new electric loads. We hold the C-10 and run that work ourselves.

EV charging. A charger is a large continuous load and belongs in the load calculation before the array is sized. Details are on our Napa EV charger installation page.

Heating and cooling. A heat pump reshapes summer and winter consumption both and is often the largest electrical load a Napa home adds. We are a Mitsubishi Diamond Contractor Elite and a Trane Comfort Specialist and hold the C-20.

Water heating. A heat pump water heater usually needs a dedicated 240-volt circuit, another reason panel capacity gets checked early. We hold the C-36 plumbing license for that side of the work.

Commercial and agricultural sites. Bigger roofs, bigger services and three-phase equipment change the design entirely.

Where we work in Napa

We install across the city and the surrounding county. Downtown and the streets around it hold Victorian and early-twentieth-century homes with the complex roofs and dated services described earlier. Alta Heights climbs the hills east of downtown, where terrain shading and canopy matter more than they do on flat ground. Browns Valley runs west toward the hills with a mix of eras on larger lots. South and east Napa are mostly newer subdivisions, and a simple composition roof over a 200-amp garage panel makes for the most straightforward installations we do here.

Beyond the city limits, hillside and rural parcels bring longer conduit runs, well pumps, propane instead of piped gas, and a different permit authority.

How to choose a solar contractor in Napa

Ask what happens at the main panel. If the quote does not say whether your service can accept the interconnection and what the alternative is, the design is unfinished.

Ask who performs the electrical work. Companies that subcontract that half are common, and the seams show at inspection and again when something needs attention in year six.

Ask how the shade study was done and for which months. One annual average number hides the exact problem you need to see on a treed lot.

Ask whether the company will still be reachable. Ongaro & Sons has operated since 1932 and works from Petaluma, we are Diamond Certified, and we hold a BBB A+ Rating. Every Napa job is served out of that Petaluma headquarters by our own crews, and warranty work comes back to the same company that did the install.

What North Bay homeowners say

Two reviews from customers across our service area: