Solar in Napa County

What net billing changes about the equipment

Storage stops being a preference. A battery charges from the array during the hours when exported energy is worth least and discharges into the house during the hours when imported energy costs most. That is the mechanism, and it is why most serious proposals here now include storage.

Inverter architecture stops being a preference too. A string inverter treats a group of modules as one circuit, so the weakest module sets the pace for the rest of the string. Microinverters and DC optimizers work module by module. On a flat valley-floor roof with one clean plane and nothing above it, a string design is defensible. On a hillside parcel under the Mayacamas or across on the Howell Mountain side, where a ridge takes the sun off part of the roof and a mature oak shades another section at a different hour, module-level electronics recover production a string design gives away.

Whether the inverter can accept batteries at all is the next question. A hybrid inverter charges and discharges DC storage directly. A standard grid-tied inverter does not, so adding storage two years later means AC coupling it: a second box on the wall and a second conversation with the utility.

All of it lands on the electrical service. A grid-tied array back-feeds the main panel, and there is a hard limit on how much back-fed current a panel can accept. It is a function of the busbar rating and the main breaker size, and it gets checked before a permit issues rather than after. In the older neighborhoods of the city of Napa, in the upvalley town cores, and on rural parcels built out in stages across decades, we routinely open panels that were adequate for the house as built and are not adequate for the house plus an array plus a battery plus a car. Sometimes the answer is a supply-side connection ahead of the main breaker. Sometimes it is a service upgrade, which is electrical work we do ourselves in Napa County rather than hand off.

Permits in Napa County go through six front doors

A Napa County address does not tell you who issues the permit. Five incorporated jurisdictions run their own building departments: the cities of Napa, American Canyon, St. Helena and Calistoga, and the Town of Yountville. Everything outside those city limits, including Angwin, Pope Valley, Chiles Valley, Deer Park, Oakville, Rutherford and the parcels out toward Lake Berryessa, falls to the Building Division of Napa County Planning, Building and Environmental Services, whose permits page describes a division "responsible for managing the construction permitting process."

What keeps that from becoming six sets of rules is state law. Government Code section 65850.5 required that "on or before September 30, 2015, 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." It also removes discretion: "a city or county shall administratively approve applications to install solar energy systems through the issuance of a building permit or similar nondiscretionary permit." A jurisdiction does not weigh whether it likes your array. It measures the installation against a published standard.

The statute reaches into process as well. Each jurisdiction "shall adopt a checklist of all requirements with which small rooftop solar energy systems shall comply to be eligible for expedited review," and each "shall allow for electronic submittal of a permit application and associated documentation, and shall authorize the electronic signature on all forms, applications, and other documentation." So the real differences between Calistoga and American Canyon are differences of checklist and portal, not of philosophy. County submittals run through an online permit center shared by every division of the department.

The building permit is only half the approval. The jurisdiction signs off on the installation; PG&E grants permission to operate. An array that has passed final inspection still cannot legally run until the utility side closes out. We carry both and tell you where the project stands in each queue.

One thing worth separating: California's Building Energy Efficiency Standards, with the 2025 edition effective January 1, 2026, set what new construction must include. They do not create a retrofit obligation on a house that already stands.

When it makes sense to replace an existing array

An aging system usually announces itself in the numbers rather than with any visible failure: a true-up bill that climbs year over year with no change in how the house is used, an inverter that has gone offline or shows recurring faults, or electronics so old that no manufacturer supports them anymore.

Replacement makes sense in three situations: the system was sized for a smaller household than the one living there now, its electronics are obsolete and unsupported, or the roof underneath is due, in which case re-roofing first and installing the new array on the new covering is almost always the cheaper order. A replacement system also lands on the current net billing tariff, which changes the right design, so the new array is sized to what you consume rather than to what the old one exported.

What drives the cost of a Napa County solar project

None of it is mysterious, and none of it is per-watt. The roof is the first variable: composition shingle, tile and standing-seam metal each mount differently, and tile takes more labor. Pitch, height, the number of separate roof planes and the condition of the covering all move the number. If the covering is near the end of its life, removing and resetting an array later is a real cost you are choosing to defer.

The electrical side is the second: size and age of the existing service, distance from panel to array, whether a supply-side connection or a full upgrade is required, and whether feeders have to be trenched to a detached structure. On rural parcels with a shop or pump house, that trench is often the largest single line item.

Storage is third, driven by usable capacity, how many circuits get backed up, and where the battery can go. Shading is fourth, since terrain and trees are answered with either more modules or module-level electronics. Access is fifth, and it is why the photo above shows fall protection: steep pitch, two stories and a hillside driveway change how a crew works. Jurisdiction is sixth, because review depth and inspection cadence are not identical across six departments. If spreading the project helps, we offer financing.

Incentives and program status

Napa County's community choice electricity provider is MCE, not Sonoma Clean Power. That distinction matters, because a great deal of North Bay solar content is written for Sonoma County and lists programs a Napa address cannot enroll in. Delivery is PG&E countywide regardless of who generates the power.

MCE's heat pump rebates are the local program most likely to sit alongside a solar project here, covering heat pump water heaters and heat pump heating and cooling. The conditions are the ones that catch people: you have to have owned and lived in a single-family detached home in MCE territory for at least twelve months, a participating contractor has to file the paperwork on your behalf, and MCE states that its "rebates cannot be applied to a project retroactively."

One condition is specific to solar households. MCE notes that "if your home has solar or EV charging, the equipment must have been installed for at least 12 months," so an array installed recently can sit between you and a heat pump rebate purely on timing. If both are on the plan, the order is worth settling at the start.

The larger economic lever in this county is not a rebate at all. It is the export-versus-self-consumption question at the top of this page, and design decides it.

Program terms move. We confirm what is genuinely open when we write your quote.

Outages, backup, and what solar alone will not do

This is the most common misunderstanding about residential solar, so plainly: a grid-tied array without storage does not power your house during an outage. When the grid drops, the inverter disconnects and stops producing, because energizing a line a utility worker believes is dead would be dangerous. The sun can be blazing on a full roof of modules and the lights will still be off.

Backup requires storage, an inverter capable of islanding, and a backup panel separating the circuits you want carried. That is designed before installation, not switched on later. It matters here because PG&E may turn off power during severe weather through its Public Safety Power Shutoff program to help prevent wildfires, and the hillside and rural parts of the county carry more exposure than the valley floor towns. A property on a well feels it harder, since no power means no water at all.

Where a battery is not the whole answer, a standby generator is. We are a Certified Generac Generator installer, and on rural parcels with a deep well pump, the combination of solar, a modest battery and a standby generator is often more practical than solving everything with storage. Generator work also touches gas or propane piping, which is plumbing scope we hold in-house.

The areas of Napa County we work in

The county is a long, narrow valley with mountains on both flanks, and conditions are not the same end to end. American Canyon and the Carneros end sit closest to San Pablo Bay, run cooler and windier, and hold the newest housing: simpler roof planes, larger services, the most straightforward installs.

The city of Napa is the mixed case. Older neighborhoods near downtown and along the river have smaller original services, more roof planes, more mature trees and more surprises inside the panel. Postwar and later tracts on the north and east edges behave like American Canyon. Two houses two miles apart can need completely different electrical scopes.

Yountville, Oakville and Rutherford are small cores surrounded by agricultural parcels, where distance from the service point to the outbuilding is often the defining constraint. Upvalley, St. Helena and Calistoga run the hottest summers in the county and carry the strongest cooling loads, exactly the profile that pairs well with an array and a battery. Their town cores are older, so panel capacity comes up early.

The hill country is its own category: Angwin and the Howell Mountain side, Atlas Peak and the Vaca range east, Spring Mountain and Diamond Mountain on the Mayacamas side west, and the Pope Valley and Lake Berryessa country beyond. Terrain shading is real, trenching runs long, wells and septic are the norm, and outage exposure is why most of these projects include storage.

How to choose a solar contractor for this work

Ask who holds the electrical license and who is actually doing the panel work, because that is where solar jobs stall. Ask for a production estimate showing hourly or monthly shape rather than an annual total, since annual totals hide the entire net billing problem. Ask what the estimate becomes if a tree is not removed. Ask whether the proposed inverter can take a battery later, and get that in writing. Ask who pulls the permit, in which jurisdiction, and who chases interconnection through to permission to operate.

Then ask the unglamorous question: who will be here in eight years when a connector fails. An array is a twenty-five-year asset bolted to a roof, sold in a market where companies appear and vanish. Ongaro & Sons has worked on North Bay homes since 1932, we are Diamond Certified, and we hold a BBB A+ Rating. What customers say about the work is on our reviews page.

What North Bay homeowners say

Two recent notes from customers, in their own words: