Comparing Solar Quotes Line by Line: What Actually Matters

A solar proposal is a designed document, and the thing it’s designed to do is get signed. That’s not a conspiracy — every industry’s sales materials work the same way — but it has a practical consequence for anyone holding three of them. The numbers printed largest and earliest, the twenty-five-year savings total and the monthly payment that lands just under your current bill, are the marketing layer. The numbers that would actually let you compare one quote against another are usually scattered across later pages, tucked into footnotes, or missing entirely. So when you set three proposals side by side and try to pick, you’re not comparing three systems. You’re comparing three sales strategies, each optimized to look best on its own terms. To compare the systems underneath, you have to do a little work the proposals don’t do for you: rebuild each one into the same handful of numbers, on the same basis, and only then decide. It takes maybe half an hour, and it changes which quote wins more often than you’d think.

Rebuild every quote into the same few numbers

The first problem is that proposals quote different system sizes, which makes the headline totals meaningless against each other. A $21,000 system and a $27,000 system tell you nothing until you know how much each one produces, and the cleanest common denominator is price per watt. Take the gross price — the full price before any incentive is subtracted — and divide it by the system size in watts of DC panel capacity. A 7.2 kW system at $23,000 works out to $3.19 per watt. Do that for every quote and suddenly they all sit on one scale you can read at a glance. As a reference point, installed residential prices have generally landed somewhere between roughly $2.50 and $4.00 per watt before incentives, so a figure sitting well outside that band is a prompt to ask hard questions — a suspiciously low number invites scrutiny of the equipment and warranty just as much as a high one invites scrutiny of the margin. The reason cost per watt works as the great equalizer is precisely that it strips away system size, which is the variable installers most often use to make an apples-to-oranges comparison feel like a fair fight.

Three traps sit in the way of doing this cleanly, and all three are common enough to assume they’re deliberate until proven otherwise. The first is net versus gross. Some proposals lead with the price after the 30% federal tax credit is subtracted, and a few go further and fold in hypothetical “utility savings” too, so the number you’re reading isn’t a price at all but a projection. Always rebuild from the gross price. The federal credit is yours to claim on your own return regardless of which installer you choose, so letting one proposal bake it into the headline just makes that quote look artificially cheaper than an identical one that quoted honestly. The second trap is DC versus AC sizing. Use the DC panel rating — panel count multiplied by each panel’s wattage — consistently across every quote, because a proposal that quotes the smaller AC system size will look artificially cheap per watt against one using DC. The third, and the most expensive, is that a financed price is not a cash price. Solar loans very commonly embed a dealer fee that can add a substantial percentage to the total in exchange for the attractive advertised interest rate, and that fee is buried in the price rather than shown as a line. Ask every installer for the cash price and the financed price separately, in writing. If they differ by thousands of dollars, that gap is the real cost of the loan, no matter how low the rate looks, and comparing one company’s cash price against another’s financed price will steer you badly wrong.

Price per watt tells you what you’re paying; it says nothing about what you’re getting, and for that you need the estimated year-one production in kilowatt-hours. Every serious proposal should carry this figure, and it should be derived from your actual roof — its orientation, tilt, and shading — rather than a regional average dropped in from a database. The quick quality check is to divide estimated annual kWh by system size in kW, which gives you what the industry calls specific yield. Most US roofs land somewhere around 1,100 to 1,600 kWh per kW per year depending on region and shading, so if one installer’s estimate for the exact same roof runs fifteen percent higher than everyone else’s, someone is modeling optimistically — and it’s almost never the low one that’s off. Optimistic production is the quietest way to inflate a proposal, because it makes every downstream number look better, from annual savings to payback period to that cheerful “cash-flow positive from day one” chart, while costing the installer nothing, since production usually isn’t guaranteed in the contract. A quote that’s honest about production is often less flashy and more trustworthy than one that isn’t.

While you’re checking production, confirm the system is sized to your usage rather than to your roof’s maximum capacity or your loan approval’s ceiling. Pull twelve months of kilowatt-hours from your utility account and check the proposal’s “offset” claim against your real consumption, and sanity-check the sizing independently with the solar panel size calculator so you have a number that didn’t come from someone trying to sell you more panels. Oversizing is a common and quiet way to raise the ticket, since a bigger system means a bigger contract, and a household that ends up exporting a large share of its generation at reduced rates is subsidizing the installer’s revenue rather than its own savings. From there, read the equipment as line items. You don’t need to become a panel connoisseur, but the quote should specify exact model numbers for both panels and inverters — “Tier 1 panels” is a marketing phrase describing a bank’s financing list, not a spec. Most mainstream panels are far closer in real-world quality than the sales pitches imply, and a twenty-five-year product warranty is now common, so a big price premium justified by small spec differences deserves skepticism. The inverter choice is usually the largest genuine hardware difference between competing quotes, with real trade-offs in how the system handles shade, how long the warranty runs, and what a repair costs, so it deserves a deliberate decision rather than defaulting to whichever brand the installer happens to stock. Look, too, at what’s included beyond the hardware: permitting, interconnection paperwork, a main electrical panel upgrade if your service needs one, roof work, and any trenching. One quote’s mysterious extra $2,000 sometimes turns out to cover a panel upgrade that another quote will bill as a change order after you’ve signed, so knowing roughly where installation money actually goes helps you judge whether a line item is padding or substance.

The promises are the last layer, and they matter more than they look. Warranties come in stacked pieces — the panel product warranty, the panel performance warranty, the inverter warranty, and the installer’s own workmanship warranty covering the labor and the holes they drilled in your roof. That workmanship warranty is the one that varies most between companies, anywhere from one year to twenty-five, and it’s also the one you’re most likely to actually use, since roof leaks and wiring faults are installation problems, not manufacturing ones. It’s only as good as the company standing behind it, which is why the installer’s track record, licensing, and local history belong in the comparison right alongside the numbers — vetting the company is its own exercise, and a slightly higher price from a firm likely to exist in a decade can be the better buy. Two questions, asked of every installer in writing, separate the serious quotes from the rest better than any brochure page: who do I call if my production comes in twenty percent below your estimate in year two, and who pays the labor on a warranty equipment swap. The quality and specificity of those answers tells you a great deal about what you’re really buying.

A worked comparison, and stress-testing the winner

Numbers make this concrete, so take two illustrative quotes for the same roof and run them through the rebuild.

	Quote A	Quote B
Size (DC)	7.0 kW	8.4 kW
Gross price	$21,700	$27,300
Price per watt	$3.10	$3.25
Est. year-one production	9,100 kWh	10,400 kWh
Yield (kWh/kW)	1,300	1,238
Inverter	String	Microinverters
Workmanship warranty	10 years	25 years

At first glance Quote B costs $5,600 more, and if that were the whole story you’d choose A and move on. But the rebuild reframes the gap entirely. Quote B is also 1.4 kW larger, carries panel-level electronics instead of a single string inverter, and backs its labor for two and a half times as long. Per watt, the difference between them is fifteen cents, not $5,600 — the bulk of that headline gap is simply buying more system. Whether the extra is worth paying comes down to three things the table can’t decide for you: your usage, since the value of Quote B’s additional production depends entirely on whether you actually need those extra kilowatt-hours or will export them cheaply; your roof, since microinverters justify their premium on a shaded or multi-orientation roof and buy far less on a clean open one; and your read on each company, since a twenty-five-year workmanship warranty from a firm you’re unsure will survive is worth less than a ten-year one from a local outfit with a decade of references. That’s a real, defensible decision. “B costs more” was never the decision at all — it was the illusion the un-normalized numbers created.

One kind of quote resists this whole exercise, and it’s worth recognizing so you don’t waste an afternoon trying to force it onto the same scale: the lease or power-purchase agreement. A lease doesn’t sell you a system at a price per watt at all — it sells you the electricity the panels make, usually at a per-kilowatt-hour rate that escalates each year, with the leasing company keeping ownership and, critically, the federal tax credit. You can’t compute a meaningful price per watt for it because you never pay one, and a lease sitting in a stack of cash and financed quotes will often show the lowest monthly number precisely because it’s a fundamentally different product. Compare leases against each other on their rate and escalator, and compare ownership quotes against each other on price per watt, but don’t let a low lease payment masquerade as the cheapest way to own solar, because it isn’t ownership at all. The same discipline that normalizes two purchase quotes — insisting on the same basis before comparing — is what keeps a lease from winning a contest it isn’t actually entered in.

Once you’ve picked the leading quote on that basis, run its gross price and production through the solar panel cost calculator and see whether the payback story the proposal tells still stands up under your own assumptions rather than the installer’s. Pay particular attention to the utility-rate escalator, the assumed annual increase in electricity prices that quietly inflates every long-term savings figure. Proposals love to assume four or five percent a year compounding forever, which makes distant savings balloon; plug in a flatter, more conservative rate and watch how much of the twenty-five-year headline survives. If the deal only works with aggressive assumptions — steep rate inflation, zero degradation, perfect production, no maintenance — that fragility is itself the proposal telling you something. A quote that still clears your bar under pessimistic inputs is one you can sign with a clear head, and the half hour of rebuilding is what earns you that confidence.

The contract terms that sit outside the savings math deserve a last read across quotes, because they’re where a good price can quietly curdle. Look at the deposit each installer wants and what happens to it if you cancel — a large non-refundable deposit changes the risk of signing. Check whether the price is firm or subject to change once the site survey or permitting turns up something, since a quote that can be revised upward after you’ve committed isn’t really the quote you compared. Note the estimated timeline from signing to permission-to-operate, and whether there’s any production guarantee or just an estimate, because “we estimate 10,400 kWh” and “we guarantee at least 9,500 kWh or we compensate you” are very different promises hiding behind similar-looking numbers. None of these appear in the price-per-watt comparison, but they can separate two quotes that looked identical on the spreadsheet, and the installer more willing to put firm terms in writing is usually the one more confident it can deliver. Read the whole document, not just the numbers you extracted from it, before the rebuild’s winner becomes the signature’s.