Commercial Solar Companies and EPCs in California: Compare by Scope

A California commercial solar company can be an installer, an EPC (engineering, procurement and construction contractor), a developer or a financier, and one project often involves several of them. Compare them on scope, not size: the licensed entity that signs, completed projects like yours, an itemized cash price, a bill model built on your tariff, and who services the system afterward.

This page is part of the commercial solar guide for California businesses. Before comparing bidders, the commercial cost-per-watt benchmarks give you a published baseline to hold each price against. Shopping for your house rather than a business? Start with choosing a solar company for your home. Sources were checked September 23, 2026.

California Rate Relief is a referral service. We are not a licensed contractor. It does not rank, endorse or name any company as a preferred provider.

Installer, EPC, developer, owner: who does what

EPC describes a contracting role, not a license. The EPC engineers the system, buys the equipment and builds the job, usually under one contract for the whole scope. A residential-style installer typically sells and installs a standard package; an EPC is hired to deliver a designed project on a specific building or site.

Four roles show up on commercial deals, and sales conversations blur them:

• The developer originates the project, secures the site and interconnection path, and often arranges the financing. See what a solar developer does for how that role is paid.
• The EPC contractor performs the engineering, procurement and construction.
• The owner holds title to the system. Under a lease or power purchase agreement, that is not the business using the power.
• The service provider monitors and maintains the system after it is running. It may be the EPC, the owner or a third party.

Whatever the label, the physical work in California is done under a state contractor license. CSLB's C-46 Solar Contractor classification covers installing, modifying, maintaining and repairing photovoltaic systems, and the C-10 Electrical Contractor scope includes solar photovoltaic cells. Ask which licensed entity signs the contract and pulls the permits, then check that number yourself in the CSLB license lookup. A company that markets itself as an EPC is not automatically the licensed entity doing your work.

Six things to get in writing from every bidder

Ask each bidder to price the same scope, and get the responsible legal entities named. These six items separate a comparable proposal from a sales estimate:

A company website describes its own offering. It does not establish current license standing, capacity to take your project or the final installed price.

How to get commercial solar quotes you can compare

Most mismatched quotes start with mismatched inputs. Send every bidder the same package: twelve months of interval data from the utility, the rate schedule name, the roof plan or site plan, the size of the main electrical service, any roof work already planned, and the ownership structure you want priced (cash, loan, lease or PPA). Then ask for:

1. The DC system size and the module and inverter models.
2. A line-item cash price before any financing or tax assumption.
3. Monthly production and a monthly bill model on your actual tariff.
4. Interconnection responsibility and the assumed permission-to-operate date.
5. The service, monitoring and warranty terms, and who delivers them.

Keep tax and incentive assumptions on a separate row. The commercial quote checklist lists the line items to request.

Top, largest and best commercial solar companies: how to read the lists

This page does not name a company as the largest or the best. No dated, primary-source ranking of commercial solar companies working in California exists (checked September 23, 2026), and a ranking without one is a guess. You can still read published lists critically by asking how they were measured:

• Megawatts installed in a period is the usual metric, and it favors utility-scale builders over commercial rooftop specialists.
• Project count gives a very different order, because many small rooftop jobs can outnumber a few large ones.
• National versus California volume matters: a large national EPC may have done little work in your utility territory.
• Segment matters most. Commercial rooftop, carport, ground mount and utility scale are different businesses with different contractors.

Utility-scale EPC work is a separate market. Large facilities that sell into the wholesale market interconnect under the CAISO tariff or a wholesale distribution tariff rather than the CPUC's Rule 21, and solar facilities of 50 MW or more can use the California Energy Commission's opt-in certification program. If you are hosting a system on your own building or lot, look for commercial rooftop or carport experience instead.

What a solar EPC firm's contract should cover

Whether you hire an EPC directly or a developer hires one for you, the EPC contract is where the project's risks land. Read it for these terms before comparing prices:

• Scope and exclusions. What the fixed price includes, what is an allowance, and what is “by owner.”
• Milestones. Mechanical completion, substantial completion and utility permission to operate, each with its own date and definition.
• Performance test. How output is tested at handover, and the remedy if the system falls short.
• Delay terms. Who pays if the project finishes late, including any liquidated damages, and which delays (utility, permits, weather) are excused.
• Warranties. Workmanship, roof penetrations and equipment, with the entity that honors each one.
• Changes and payment. How change orders are priced, the payment schedule, and lien releases from subcontractors and suppliers.

A developer offering a PPA holds this contract itself; ask to see its warranty and performance terms anyway, because they decide how fast problems on your roof get fixed. The solar developers guide explains how the developer and EPC roles split.

How a commercial solar project runs, start to finish

1. Site and bill review. Interval data, tariff, roof or site condition and electrical service.
2. Proposal and contract. Scope, price, ownership structure and the bill model.
3. Design and engineering. Layout, structural review and electrical single-line drawings.
4. Permits and interconnection. Local building and fire review, and the utility interconnection application under Rule 21 for PG&E, SCE and SDG&E customers.
5. Procurement and construction. Equipment orders, racking or canopy, wiring and switchgear work.
6. Inspection and permission to operate. Final local inspection, then the utility's approval to switch on.
7. Operations. Monitoring, maintenance and warranty service for the life of the system.

Ask each bidder for a schedule built on those steps, with the utility and permit steps shown as dependencies the contractor does not control.

What a commercial solar energy system includes

A commercial system has the same core parts as a home system, sized and engineered for a larger service: modules, inverters, racking or a canopy, conduit and combiners, switchgear at the point of interconnection, a revenue or monitoring meter, and often a battery. Sizes vary widely. Berkeley Lab's 2026 data update reports a median non-residential system of 41 kW in 2025, with the largest median sizes at schools and industrial properties (over 100 kW) and an 85 kW median on warehouses. Roughly half of 2025 non-residential installs were on commercial buildings, a third on agricultural land and the rest at tax-exempt sites.

In California, most business systems are rooftop systems. In CRR's count of the CPUC's DGStats interconnection data, 2,583 of the 3,607 non-residential systems PG&E, SCE and SDG&E connected in 2025 were on roofs, 854 on the ground and 138 mixed. Those systems used a median module of 438 W, larger than on homes; the commercial panel wattage data shows why.

The mounting decision changes who you hire. A commercial roof project may need a roofer before the solar crew arrives, and a parking-lot carport needs structural engineering and foundations. Module choice matters too; if a bidder proposes a specific brand, such as REC's commercial panel lines, check the listing data behind it.

How much do commercial solar panels cost?

Prices vary by size, site and customer type. LBNL's Tracking the Sun 2024 summary reports that large California systems installed in 2023 had median prices of $2.3 per watt at commercial sites, $2.0 at agricultural sites and $4.1 at tax-exempt sites, before incentives. A per-watt comparison only works on the same DC system size and the same included work, so keep storage, carports, roof repairs and electrical upgrades on their own lines. Work through the commercial cost-per-watt guide, then the size-specific pages for 100 kW, 500 kW and 1 MW systems.

How commercial solar is financed

Most bidders can price the same project four ways: cash or a loan (you own it and claim the tax benefits), a lease, a power purchase agreement where a third party owns the system and sells you the power, or C-PACE, repaid on the property tax bill. The commercial financing options guide compares them, and PPA versus purchase shows how ownership moves the tax benefit.

If you are looking for a company to own the system and sell you the power, that is a PPA provider, usually a developer or its financing partner. See how to vet a commercial PPA provider. Leasing is a separate structure, and so is renting your roof to a developer; commercial solar lease programs covers both. In 2025, 751 of the 3,607 non-residential systems connected in California were third-party owned, most of them under PPAs.

A common question is whether borrowing reduces the federal credit. Under 26 U.S.C. §48E(d)(2), rules similar to §45(b)(3) apply, and §45(b)(3) reduces the credit when a facility is financed with tax-exempt bond proceeds, by the lesser of 15% or the bond-financed share. The statute does not reduce the credit for an ordinary commercial loan. Confirm your own facts with a tax professional. The commercial solar tax credit guide sets out the rest of §48E, including the December 31, 2027 cutoff for solar.

Compare the business bill, not a residential average

Energy charges measure the kilowatt-hours you use. Demand charges measure your peak. SCE's business TOU page describes facilities-related demand charges, based on the highest recorded demand in each billing month, and time-related demand charges, based on the highest demand in on-peak or mid-peak hours. A solar array can cut annual purchases without touching the interval that sets a demand charge, which is why the bill model should show solar alone and, separately, solar with battery controls. A commercial battery is priced and justified on that demand line.

Commercial solar by property type

Ask whether a bidder has finished work on your property type, not only in your county. Roof structure, operating hours, refrigeration load and interconnection path differ enough that relevant experience is a real screening question:

• Warehouse solar projects: large flat roofs, membrane condition and lighting or refrigeration load.
• Retail solar projects: leased premises, landlord consent and shorter occupancy horizons.
• Agricultural solar projects: pumping loads, seasonal use and several service points.
• Multifamily solar projects: common-area versus tenant metering and allocation rules.
• Self-storage solar projects: low, flat loads with large roof area.
• School solar projects and church solar projects: tax-exempt owners and elective pay.
• Car dealership solar: big lots, canopies and EV charging.

Manufacturing and industrial projects

An industrial proposal needs your operating schedule. Identify shift changes, weekend production, process heat, compressors, refrigeration and planned equipment additions, and ask whether the model includes startup peaks and shutdowns. Separate existing loads from an expansion that has not opened, document roof access, ventilation, fire-lane and production-interruption limits, and define which loads need backup. Bill savings and outage operation are different requirements.

Industrial accounts are usually billed on demand-heavy schedules, and the plant systems connected in California in 2025 ran well above the business median. The industrial solar guide covers the rates, sizing and Energy Code questions specific to plants and manufacturers.

Turnkey commercial solar services: design, installation and maintenance

“Full-service” or “turnkey” commercial solar usually means one company sells you design, permitting, installation, utility paperwork and ongoing service under one relationship. That can be simpler to manage, but it does not mean one legal entity performs or guarantees every piece. Map each service to an entity before signing:

“Corporate solar” programs that roll the same approach across many sites need the same map for each utility territory, because rates, tariffs and interconnection rules differ by utility.

Operations and maintenance after installation

Ask for the O&M scope as its own document: monitoring, alarm response times, inverter replacement terms, cleaning, roof-leak responsibility at penetrations, and what happens if the installer stops operating. Under a PPA or lease, the owner usually carries these duties; under a purchase, you do unless you contract them out. A new-installation contractor is not automatically responsible for an existing system. For an older system, start with the original installer, the manufacturer and your records.

Regional project brief

A street address in Riverside, Los Angeles or San Diego does not identify the utility account or tariff. Give each bidder the exact address, the permit authority, the current tariff and utility account, the owner or leaseholder with authority over the roof or site, and your operating hours, and ask for written confirmation that it accepts the address and project type.

Frequently asked questions

Sources

Checked September 23, 2026.

• CSLB, C-46 Solar, C-10 Electrical and B General Building classifications; license lookup
• LBNL, U.S. Distributed Solar and Storage: 2026 Data Update (August 2026)
• LBNL, Tracking the Sun 2024 executive summary (August 2024)
• SCE, business time-of-use rate plans
• CPUC, Electric Rule 21; California Energy Commission, Opt-In Certification Program
• 26 U.S.C. §48E and §45, Office of the Law Revision Counsel (text in effect September 22, 2026)
• California Public Utilities Commission, DGStats Interconnected Applications Data Set (data through May 31, 2026); CRR count of 2025 non-residential PV systems
• CSLB, before applying for the license exam and bond requirements