Different savings does not mean the lower one is the honest one
Homeowners often see two polished proposals for the same roof with two different monthly savings numbers. It is tempting to treat the conservative one as “real” and the generous one as “sales.” Sometimes that is true. Sometimes the conservative quote is simply overpriced, or undersized, or missing a battery you actually wanted.
The useful question is not “which savings number is smaller?” It is “which assumptions are each number standing on?”
Four levers that move the story
Production, utility-rate growth, incentives, and financing can each swing lifetime savings without changing the panels on the roof.
- Production: shading, tilt, and yearly kilowatt-hours.
- Utility-rate growth: 2.5% per year and 6% per year are different products.
- Incentives: a tax credit that has expired will still inflate a 2026 savings chart if someone left it in.
- Financing: charges added to the loan (dealer fees) and interest change what you pay, even when the monthly number looks friendly.
Price can hide in the “better” savings quote
A proposal can show modest monthly savings and still be a poor price for the hardware. Another can show large savings because it assumed your electric bill climbs quickly for 25 years. Neither pattern, by itself, tells you which deal to take.
What to do with two quotes
Line up system size, equipment, cash price, financed amount, annual energy production, and the assumed yearly increase in electricity prices. Where they differ, ask why. An independent review does that against data rather than against the other salesperson.
Build an apples-to-apples comparison
Illustrative example: multiplying 10,000 kWh by $0.20 gives $2,000, while $0.25 gives $2,500. That $500 difference comes from the price assumption alone. Neither calculation is a complete bill-savings estimate: export compensation, when you use electricity, fixed charges, and financing can change the result.
The FTC notes that future utility rates are difficult to predict. A savings chart is therefore conditional on its assumptions. FTC: Solar Power for Your Home (U.S. consumer guidance, April 2022)
- Label every difference before comparing the final savings total.
- Ask the seller to show a scenario using matching assumptions.
- Treat the result as an estimate with limits, not a promise.
| Input | Question |
|---|---|
| Scope | Same system size, equipment, battery, and building work? |
| Energy | Same yearly production and shading assumptions? |
| Bill savings | Same tariff, export rate, fixed charges, and rate growth? |
| Purchase | Same cash price basis, financing terms, and eligible incentives? |