The Solar Panel Cost Calculator sizes a home solar system from your electricity bill and prices it: annual usage in kWh, the system size (kW) needed to offset the share of that usage you target, the panel count and roof area that implies, gross cost at your cost per watt, estimated annual savings, and the simple payback those savings imply. Note upfront: the calculator applies no federal tax credit for purchases in its current model, because the residential Section 25D credit expired for 2026 installations; read the incentives section before comparing quotes that still advertise one.
How It Works
Gross cost is size x 1,000 x cost per watt. Panels assume 400 W each, roof area 20 square feet per panel, and annual savings value the offset production at your electricity rate (capped at your usage). The production factor, annual kWh per installed kW, defaults to 1,300 and is the input that carries your climate: roughly 1,000 to 1,100 in cloudy northern regions, 1,400 to 1,600 in the sunny Southwest.
Parameters
| Input | Required | Meaning | |---|---|---| | Monthly bill | Yes | Average electric bill | | Electricity rate | No | 0.17 | | Offset % | No | Share of usage to cover, default 100% (up to 200%) | | Cost per watt | No | Installed 2.95 | | Production factor | No | kWh per kW per year, default 1,300 | | Ownership | No | Buy or lease (lease economics explained below) |
Worked examples
With defaults: a 0.17 rate implies 14,118 kWh a year; a 100% offset needs 10.86 kW, costing **2.95 per watt, using 28 panels and about 560 square feet of roof, and saving about 180 bill at 16,343, and saving $2,160 a year for a payback near 7.6 years. The pair teaches the central solar lesson: payback is driven less by sunshine than by the retail price of the electricity you stop buying, which is why identical hardware is a great investment in California or Hawaii and a marginal one where grid power is cheap.
Sizing judgment: offset, roof, and the export problem
A 100% offset on annual energy is a starting point, not an optimum. Production peaks at midday and in summer while consumption often peaks in the evening and winter, so exported surplus is typically credited at less than the retail rate under modern net-billing rules, which quietly devalues the last, largest slice of an oversized system; many households now size to 80 to 90% of usage, add load shifting (timers on water heating, EV charging at noon), or pair a smaller array with a battery whose economics this calculator does not model. Roof area is the other hard constraint: the panel count's 20 sq ft per panel excludes setbacks, vents, chimneys, and shading gaps, so treat the roof figure as a minimum and a south-facing unshaded plane (in the northern hemisphere) as the scarce resource the whole design competes for.
Incentives, leasing, and the honest cost basis
The purchase path in this calculator is deliberately unsubsidized at the federal level (Section 25D's expiry), but state and utility incentives, property-tax exemptions, and SRECs still exist in many jurisdictions and can remove thousands from the net cost; they are jurisdiction-specific enough that the calculator leaves them out rather than guessing yours. Under lease and PPA structures the provider owns the system and claims the commercial credit (Section 48E) itself, passing value through as a lower monthly payment: you never see a gross cost or a credit, you see an escalator clause, so compare a lease by its year-one payment, its annual escalator, and the total of payments over the term against the purchase payback above. In all structures, get the production estimate in writing with its factor stated, since the difference between a 1,150 and a 1,450 factor is the difference between the two worked examples' paybacks.
Limitations
A sizing and simple-payback model: it assumes your bill is entirely usage-driven (fixed connection fees survive solar and lengthen real payback slightly), values savings at a constant rate (rate inflation improves real returns; export-credit rules worsen them), and omits panel degradation (about 0.5% a year), inverter replacement around year 12 to 15, roof condition and re-roofing, shading analysis, batteries, financing interest, and home-value effects. Simple payback is not a return on investment; treat it as screening arithmetic before a site-specific quote.
Frequently Asked Questions
Why is there no 30% federal credit in the result?
Because the calculator models current law for purchases: the residential clean energy credit (Section 25D) expired for systems placed in service from 2026, so the credit amount is zero and net cost equals gross cost. Quotes showing a 30% credit on a 2026 purchase should be questioned; state incentives may still apply and are not modeled here.
What production factor should I enter?
Your installer's estimate for your roof, or by region: about 1,000 to 1,100 for the Pacific Northwest and Great Lakes, 1,200 to 1,350 for much of the Midwest and Northeast, 1,400 to 1,600 for the Southwest and interior California. The factor swings the required system size proportionally, so it is worth getting right.
Is a shorter payback always better?
Mostly, but payback ignores what happens after it: a system with a 9-year payback and 25-year warranted life leaves 16 years of near-free power, while lease structures never reach an ownership payback at all. Compare payback alongside the ownership endgame, not instead of it.