The short version
- Convert every quote to dollars per watt — a smaller system at a lower total price is not cheaper.
- Compare estimated annual kWh, not just capacity. That is what you actually buy.
- Ask what is excluded: panel upgrades, tree work, roof repair and permit fees are the usual omissions.
- Three warranties exist — product, performance and workmanship — with three different lengths.
Put every quote on the same basis
Quotes arrive in different shapes on purpose. Before comparing anything else, reduce each one to four numbers:
- Dollars per wattTotal price ÷ system size in watts. This is the only fair comparison of price. A $19,000 quote for 6 kW ($3.17/W) is worse value than a $24,000 quote for 8.5 kW ($2.82/W).
- Estimated annual productionIn kWh. Two 8 kW systems on the same roof can differ by 15% depending on panel orientation, inverter choice and how the designer handled shade.
- Dollars per annual kWhTotal price ÷ estimated yearly production. The truest single measure of what you're paying for energy.
- 25-year total costIncluding interest, dealer fees, escalators and any assumed incentive. This is where financing structure shows up.
If an installer won't give you estimated annual production in writing, that is itself a data point.
Read for what's missing
The gap between a quote and a final invoice is almost always something that wasn't in the quote. Ask about each of these explicitly:
- Main panel upgrade. Common in older homes, typically $2,000–$4,000, and frequently quoted as a later "if required" line.
- Roof work. Repairs, decking replacement or re-roofing found once they're up there.
- Tree trimming or removal. If shade is being designed around, someone has to pay for that.
- Permit and interconnection fees. Sometimes bundled, sometimes passed through at cost.
- Trenching. For ground mounts or detached garages, this gets expensive fast.
- Monitoring subscription. Free for a period, then billed — check the term.
Interrogate the production estimate
Production estimates are the easiest place for a quote to be quietly optimistic, because nobody checks them until year two. Two questions expose most of it:
- "What shading analysis did you run, and can I see the output?" A real survey produces a shade report from on-roof measurement or lidar modelling, not an eyeballed satellite image.
- "What degradation and system losses are assumed?" Soiling, wiring losses, inverter efficiency and annual degradation all belong in the model. An estimate with none of them baked in is a best case, not a forecast.
If two quotes for the same roof differ by more than about 10% on annual production, one of them is wrong. Ask both to explain the gap.
Three warranties, not one
| Warranty | Covers | Typical length |
|---|---|---|
| Product | Manufacturing defects in the panel itself | 12–25 years |
| Performance | A guaranteed minimum output at a given year | 25–30 years |
| Workmanship | The installer's labour, roof penetrations, leaks | 2–25 years |
Workmanship is the one that varies most and matters most. A 25-year panel warranty is worth little if the company that drilled your roof offers two years on their own work — and less still if they aren't trading in year six.
Check the company, not just the quote
- How long have they been installing, under this name? Solar has high company turnover. Rebrands are common.
- Are they installing, or subcontracting? Not disqualifying, but you should know who is actually on your roof and who honours the workmanship warranty.
- Licence, bonding and insurance — verifiable with your state licensing board, not just claimed on a website.
- Reviews that mention service after installation, not just the sales experience. Anyone can be pleasant before a deposit.
A workable process
- Get three quotesTwo is not enough to see an outlier; four rarely adds information.
- Insist on the same scopeSame target offset, same battery decision. Otherwise you're comparing different products.
- Build a one-page tablePrice, size, $/W, annual kWh, $/kWh, warranties, exclusions, 25-year total.
- Take a weekAny offer that evaporates if you think about it overnight was never the real price.