3.8 Installer vetting checklist
Choosing a solar installer doesn't require a dozen checklist items — verifying these four things alone eliminates 90% of unreliable companies. Other details (insurance, years in business, sales commission, etc.) are worth asking, but none are as decisive as the four below.
1. Do they have the right license?
California law requires every solar / storage contractor to hold one of these state licenses:
| License class | What it means |
|---|---|
| C-46 Solar Contractor | Solar-specific contractor license |
| C-10 Electrical Contractor | General electrical contractor |
| B General Building Contractor | General building contractor (rarely used for solar) |
How to verify: ask the rep for the license number, then look it up at CSLB License Lookup and check:
- Status is Active
- Classification includes C-46 or C-10
- No unresolved Complaints or Disciplinary Actions
Red flag: rep can't produce the number on the spot, the number doesn't appear in CSLB, or the class doesn't include C-46 / C-10 — walk away immediately. Outside California, look up your state's equivalent regulator.
2. Will they give you the design drawings and permit paperwork?
A legal solar system must be submitted for a city permit; every drawing and document is your property, and the installer must deliver them. But in the U.S. market, many companies deliberately don't — so when you later want to switch maintainers, sell the home, expand the system, or file your tax credit, you're stuck with them.
Before signing, confirm in writing — in the contract itself — that the installer will deliver:
- Single-Line Diagram (SLD) — circuit wiring, breakers, grounding paths
- City-approved permit drawings — the version with the city stamp
- Equipment spec sheets — manufacturer PDFs for the panels, inverter, battery, etc.
- PTO Letter — utility permission to operate
- Permit Final / Inspection Sign-off
- Monitoring account + equipment serial-number list — register the monitoring app under your own email, not the installer's internal email
How to verify: write the six items into a contract clause ("Installer shall deliver to Homeowner, no later than 30 days after PTO, the following…") and hold back 10–15% of the contract price as a final payment released only upon delivery. If they refuse to put it in writing, don't sign.
Red flag: "We'll send it once the system has run stably" / "It's our internal IP" — both are stalls. See Section 2.5.1.
3. Can they show you past customers' real electric bills?
This is the single most effective real-versus-fake test.
A company that has actually installed locally should be able to produce, with customer permission, 3–5 nearby customers' real electric bills + production monitoring data from before and after install. Not a marketing slide saying "we've installed 5,000 systems" — actual side-by-side bill comparisons for a real address.
- Real bills show: pre-install
$300–500/month → post-install$15–40/month (and the True-up at year end) - Real monitoring data shows: month-by-month kWh from the customer's app, compared against the original production estimate in their contract
- You can call: the installer should be willing (with the customer's prior OK) to give you 1–2 past customers' phone numbers so you can ask them directly
Why this one matters: large sales-network companies don't volunteer the bills because their installs often underperform and their customers are often unhappy. A local company that actually does the work has past customers willing to give a reference and share the data.
How to verify: ask in person for 12-month before/after bill comparisons from 3 customers plus 2 customer phone references. If they can't produce them, be very cautious.
4. Is the quote inflated?
Solar equipment cost has dropped about 90% over 15 years — but installer quotes haven't. The difference is going to sales commissions, ad spend, and financing kickbacks.
Before signing, convert every quote into $/Watt — the only industry-standard apples-to-apples unit:
$/W = total contract price ÷ system DC kW × 1000
Reasonable 2024–2025 California $/W ranges:
| System type | Reasonable $/W (install + permits + tax included) | Over this is expensive |
|---|---|---|
| Grid-tied only (no battery) | $2.20–3.00/W | > $3.50/W |
| With battery (10 kWh+) | $3.50–5.00/W | > $5.50/W |
| Battery alone | $700–1,000/kWh of capacity | > $1,200/kWh |
How to verify:
- Get quotes from at least 3 different companies (suggest 1–2 local small/mid + 1 large for comparison)
- Convert every quote to $/W
- Compare to the median — anything 30%+ above market, ask exactly where the extra money is going
Red flag: rep emphasizes "sign today for a discount" / "price goes up tomorrow" / refuses to email a written quote. Classic high-pressure tactics designed to stop you from comparison shopping.
Standing pre-signing habit
Even if all four pass, cool off for at least 3 days before signing:
- Send the contract to a knowledgeable friend / family member / competing installer for a fresh read
- California law gives you a 3-business-day cancellation right (5 days if 65+) — high-pressure sales is specifically about getting your signature and deposit before that window matters
- Free contract reviews exist — competitors are happy to review their competitor's quote
The principle: license you can verify, paperwork they'll deliver, past-customer bills they can show, pricing that math-checks — pass all four and the smaller details rarely go wrong. Fail any one and no amount of promises matters.