Every few months, the same story surfaces in an off-grid forum. A homeowner posts photos of a $40,000-plus system — new panels, a wall of batteries, a five-star installer with a state license and a surety bond — that sailed through its first summer and then buckled in the first real winter. Three weeks of overcast, a battery bank that couldn’t recover, a generator nobody had wired to autostart, and a propane bill that ate the savings the system was supposed to deliver. The installer wasn’t a scam. He was licensed, bonded, well-reviewed, and had built maybe two off-grid systems before this one — both smaller cabins with a fraction of the load.
None of that — the license, the bond, the reviews — was ever built to catch this. A contractor’s license mostly certifies electrical code compliance on grid-interactive work, and on a grid-tied system the utility itself acts as a second, silent inspector: it won’t energize a bad interconnection. Off-grid has no such backstop. Nobody checks the sizing math but the person who did it. Which means the real vetting question isn’t “is this installer legitimate” — a license mostly answers that — it’s “has this installer actually solved the specific, harder problem of running a house on stored sunlight through its worst week of the year.” These ten questions, with the numbers behind each one, are how you find out before the contract is signed instead of after the first bad winter.
The 10 Questions — and the Numbers Behind Each One
Bring this list to every quote you collect. A confident installer answers all ten without blinking; a lot of quotes go quiet after four.
Jump to a question
1. How many true off-grid systems have you installed — and can I see one that’s survived two winters?
Grid-tied and true off-grid are different disciplines wearing the same “solar installer” sign. Grid-tied sizes to an annual bill offset and leans on the grid as backup; off-grid sizes to your single worst week with nothing behind it. Ask for a number, not a vibe — “we do off-grid too” can mean two jobs in ten years. Then ask to see one, not hear about one: a system at least two winters old, because year one runs on fresh-battery headroom and hides undersizing. Degradation and bad worst-month math both surface in year two.
2. What’s your license and bond or insurance — and what does it actually protect me from?
In the US, that’s a state contractor or electrical license backed by a surety bond — often $10,000–$25,000 (California’s CSLB solar bond sits at $25,000) — plus, separately, $1M+ general liability insurance worth asking for by name. In Europe, there’s no single license: it’s a national trade certification (France’s RGE label, a German electrician’s Elektrofachkraft sign-off) paired with professional liability insurance — responsabilité civile professionnelle, Betriebshaftpflichtversicherung — the rough equivalent of a US bond. Either way, that credential protects you from an abandoned job or unsafe wiring. It says nothing about whether they can size a battery bank for your December.
| What to check | United States | Europe |
|---|---|---|
| Core credential | State contractor / electrical license | National trade certification (e.g. RGE in France, Elektrofachkraft sign-off in Germany) |
| Financial backstop | Surety bond, commonly $10k–$25k | Professional liability insurance (responsabilité civile / Betriebshaftpflicht) |
| What it covers | Unfinished work, unpaid subcontractors | Damage or injury claims tied to the installer’s work |
| Tied to incentives | Some state rebate programs require a licensed installer | Most national subsidy schemes require the certified-installer label — no label, no aid |
| What it does not cover | Off-grid sizing competence, battery chemistry choice, worst-month design math | |
3. Walk me through how you sized my battery bank. Show me the worst-month number.
A real proposal names three things: worst-month sun-hours for your specific site (not the annual average — December across much of the northern US and Europe can run 2–3 peak sun-hours a day against a 5–6 hour annual average), a stated days-of-autonomy target (2–4 days is typical for a primary residence with generator backup), and a depth-of-discharge assumption tied to chemistry (LiFePO4 commonly cycled to 80% DoD, older lead-acid closer to 50%). One annual-average number and a battery size with no autonomy or DoD stated means they sized it off a rule of thumb, not your roof. Run your own numbers first with our free sizing calculator so you can check theirs instead of taking it on faith.
Key number
2–3 peak sun-hours a day. That’s a realistic December output across much of the northern US and Europe — against the 5–6 hour annual average a lot of sales quotes actually use. It’s the one number that separates a system sized for your roof from one sized for a spreadsheet.
4. What’s the battery warranty — and does it come from you or the manufacturer?
Ask for the manufacturer’s own warranty, not the installer’s. Quality LiFePO4 packs built for stationary duty commonly carry 8–10 year manufacturer warranties; budget cells can run as short as 3–5. That warranty survives even if the install shop doesn’t — small solar outfits close constantly, and a manufacturer warranty is the only paper that outlives them. Get the inverter’s warranty in writing too; it’s the other component that tends to fail first, and terms vary widely by brand and tier, commonly 5–10 years.
5. How are you handling permits and interconnection — and is that in the price?
True off-grid usually has nothing to interconnect to, but “no utility” doesn’t mean “no paperwork.” Expect a county electrical permit and sometimes an inspection. In parts of Europe, even a fully islanded battery system still has to be registered with the national grid or market body — Germany’s Marktstammdatenregister is the standing example — despite never importing or exporting a watt. Permit and registration fees belong on the quote as a line item, not as an “oh, that’s extra” a month into the build.
6. How is the backup generator integrated, and who sized it?
Get the genset size in kW, the fuel type (propane is the common off-grid choice for its indefinite shelf life over diesel or gas), and whether autostart-on-low-battery is actually wired in — or whether you’re expected to notice and start it by hand at 2am in January. Ask what share of winter days they modeled the generator covering. If the honest answer is “could be a lot,” that’s a real running-cost number you want before you sign, not after the first propane delivery.
7. Can I call three off-grid references — not read three reviews?
Online reviews mostly come from an installer’s much larger grid-tied volume and rarely mention how a system performed in its second winter. Ask specifically for off-grid clients you can call, and ask each one the same question: “if you did it again, what would you size differently?” A confident installer sets up three calls in a day. A shaky one goes quiet or offers one carefully chosen name.
8. What’s the payment schedule — and is there a lien waiver?
Normal looks like a modest deposit (commonly 10–30%) tied to ordering equipment, progress payments at defined milestones, and a final payment held until commissioning. A deposit past half the contract before anything’s on the roof, or a demand for payment in full up front, is the red flag. Ask for a lien waiver at final payment, so a subcontractor the installer didn’t pay can’t put a claim on your property months later.
9. What happens when something fails — what’s the real response time?
Remote monitoring should be standard on a system this size; the real question is who the alert goes to (you, them, or both) and what response time they’ll commit to in writing once winter state-of-charge starts dropping fast. Ask what a service call costs after year one — some shops bundle free first-year support into the price and then charge $150–$250 or more per visit afterward.
10. What’s not in this number?
This is the question that turns a $40,000 quote into a $55,000 project. The usual gaps: trenching or conduit to a detached battery shed, tree clearing for solar access, a bigger propane tank, panel or mini-split upgrades to carry new loads, sales tax, and the permit or registration fees from question five. Get every one of those priced or explicitly excluded in writing. A verbal “don’t worry, that’s minor” is not a line item.
What a Real Off-Grid Installer Does Without Being Asked
The best sign isn’t a perfect answer to all ten — it’s how many of these already show up before you ask.
- Asks for your worst-month load, not just your square footage
- Shows the autonomy-days and depth-of-discharge assumptions behind the battery number
- Points you to a manufacturer warranty you can read yourself
- Prices the generator, propane tank and fuel run into the proposal, not around it
- Has a system of their own — or a client’s — that’s survived two winters
- Itemizes permits and registration instead of folding them into “misc”
- Puts a milestone-based payment schedule in writing
- Tells you what happens to your warranty if their company isn’t around in year six
Frequently Asked Questions
Do I legally need a licensed installer for an off-grid solar system?
It depends where you are. Many US counties require a permitted electrical install even for a system with no utility interconnection, and insurers or lenders may ask for proof of licensed work later even if the county didn’t at build time. In most of Europe, using a certified installer isn’t always legally mandatory for a private, unsubsidized install, but it’s usually the only way to access national incentive schemes — and often the only way to get insured.
How much does a professional off-grid solar installation cost in 2026?
Panels alone run roughly $2.50–$3.50 per watt installed. Add a real off-grid battery bank at roughly $800–$1,000 per usable kWh, and a complete system lands anywhere from about $35,000 for a small, efficient cabin to well over $100,000 for a full-size home carrying several days of autonomy. Batteries, not panels, are usually the majority of the number.
What’s the real difference between an off-grid and a grid-tied solar installer?
A grid-tied or hybrid installer sizes for annual bill offset and can lean on the grid as backup if they undersize. A true off-grid installer has to size for your single worst week with zero backstop — a narrower, rarer skill even within the same trade, and one a general solar license was never built to test.
Should I ever pay 100% of an off-grid contract up front?
No. A modest deposit tied to ordering equipment, milestone-based progress payments, and a final payment held until commissioning is standard. Paying in full up front removes your only real leverage if the sizing turns out to be wrong.