Read a Solar Quote Like an Engineer, Not a Salesperson
Three solar quotes can differ by $12,000 for the same roof. The gap is almost never the panels; it's assumptions buried in the production estimate and the payback slide.
A solar quote is a financial document dressed up as a hardware list. The panels are commodities; what you are actually buying is a 25-year production estimate and a set of assumptions about what electricity will cost in 2045. Two installers can honestly land $8,000 apart on the same roof; a third can land $12,000 apart by being less than honest. Sorting them out takes a spreadsheet and four hours.
Start with what your roof can physically do
Note the azimuth of each roof plane (180 degrees is due south; east and west lose 10 to 20 percent), the pitch, and anything that shades the roof between 9 a.m. and 3 p.m. Plug those into a free production estimator for a kWh-per-year baseline. Any quote more than 8 percent above it needs an explanation.
Normalize price to dollars per watt
Divide the pre-incentive price by the system’s DC size in watts. A 7.2 kW system at $21,600 is $3.00 per watt. Most 2026 installs land between $2.50 and $3.75; a steep roof or a main panel upgrade pushes higher. A quote at $4.50 with nothing special on the roof is padded. Confirm it includes permits, interconnection, and electrical work.
Check the production estimate, not just the size
Divide annual kWh by system kW for specific yield. A well-oriented Southwest roof produces 1,600 to 1,800 kWh per kW per year; the Northeast runs 1,100 to 1,350. A quote claiming 1,650 in Ohio has ignored shading. Check degradation too: 0.5 percent per year is realistic, and assuming zero overstates year-25 output by about 12 percent.
Understand the inverter choice
A string inverter is one box on the wall, cheapest, and fine for a single unshaded plane. Microinverters sit under each panel, cost $0.20 to $0.40 more per watt, and keep one shaded panel from dragging down the string. They carry 25-year warranties; string inverters run 10 to 12, so one replacement belongs in your 25-year cost.
Question the escalator and the tariff
The payback slide assumes electricity prices rise every year. Salespeople love 4 to 6 percent; the 20-year national history is closer to 2 to 3. Rerun payback at 2.5 percent — if it still lands inside 10 to 12 years, it’s solid. Then pull your utility’s tariff: retail net metering credits exports at what you pay; net billing may credit a third of that, which swings payback by years.
Run the payback with your numbers
Net cost after incentives divided by first-year savings gives simple payback. Then extend it: add an inverter replacement at year 12, subtract 0.5 percent production per year, use your realistic escalator, and compare 25-year net savings, not sticker price. A $3,000 pricier system with a 25-year workmanship warranty often wins on that page.
Solar is a 25-year commitment; your roof may not be. If your shingles are past 12 to 15 years, re-roofing first beats pulling and resetting panels later at $2,000 to $5,000. Verify the installer, not a subcontractor, holds the electrical license and the workmanship warranty, and get the roof penetration warranty in writing.
You are not buying panels. You are buying a production estimate and a set of assumptions.
After you sign
Ask for the as-built production model once the design is engineered, and check your monitoring app against it after the first full year. Within 5 percent is doing its job; 15 percent under is a shading or wiring problem a good installer fixes under warranty. Keep every spec sheet — the buyer of your home in 2035 will want them.
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