Solar panel calculator
Estimate how many panels you need, what size system fits your usage, and how the cost/payback range looks.
Best starting point when you want one homeowner estimate that ties panel count, system size, cost, savings, and roof space together.
No email required
Enter monthly kWh or electric bill. The calculator uses state-level assumptions and shows the math behind the result.
Your estimate
Example resultEstimated system size: 6.8 kW. This is an estimate, not an installer quote.
Confidence
Medium
Planning estimate only — not an installer quote, engineering design, or tax advice.
Payback uses gross system cost before verified incentives, financing fees, batteries, and roof work.
Annual usage: 10,800 kWh
Annual production target: 10,800 kWh
State rate: 34.74 cents/kWh
Export assumption: Partial export credit
Direct solar use: 5,940 kWh
Modeled exports: 4,860 kWh
Panel count view
15-19 panels
Estimate shape
Privacy note: the printable report link stores estimate inputs in the URL, including ZIP and usage or bill values. Keep it private if those details are sensitive.
Local scenarios
Compare a few assumptions without creating an account.
Saved scenarios stay in this browser only and may include ZIP, bill, and usage inputs. SolarCalcNow does not sync them or send those values to analytics.
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Confidence drivers
Expected production: 10,800 kWh
System loss: 14%
Export value: Partial export credit
Direct solar use: 5,940 kWh
Modeled exports: 4,860 kWh
State production default: 1,595 kWh/kW/year
EIA Electric Power Monthly, Table 5.6.A — June 2026 - 2026-09-04
NLR PVWatts V8 · author-selected reference point - 2026-09-04
EnergySage marketplace + SolarCalcNow cost scenario - 2026-09-04
Production evidence: California has a saved full PVWatts response; eight states have successful API yields recorded to two decimals. Colorado, Illinois and Pennsylvania retain explicit author assumptions. The download distinguishes these evidence levels.
$0.3474/kWh
34.74 ¢/kWh
EIA Table 5.6.A, June 2026 residential column; published August 26, 2026. Divide the published cents/kWh by 100. This preliminary statewide average is a fallback, not your utility tariff. Use your bill's energy-only rate; fixed charges remain payable.
1,595.2 kWh/kW/year
kWh/kW/year
PVWatts V8 typical-weather model at an author-selected reference point in the state: 4 kW DC, roof mount, 20° tilt, 180° azimuth, 14% system losses. Annual AC kWh ÷ 4 gives kWh/kW/year. Losses are already included and are not deducted again. Neither a statewide average nor a ZIP or roof survey. Shade and ±10% production bounds are separate author scenarios.
$1.98–$2.98/W
$2.48/W × 0.8…1.2
EnergySage's state marketplace average, table updated August 28, 2026. We calculate an author-selected range of average × 0.8 to average × 1.2, rounded to cents/W. This ±20% scenario is not an observed price distribution or confidence interval. Cash solar only, before incentives; compare like-for-like local quotes.
SolarCalcNow provides planning estimates only. Results are not installer quotes, engineering designs, tax advice, financing recommendations, or utility interconnection approval.
Optional next step
Your estimate stays visible. This form is optional and uses explicit consent.
Installer quote matching is not active yet. You can still calculate, save, and print your estimate before contacting installers directly.
For a home using 900 kWh per month in California, the default planning estimate is a 6.8 kW system with 15-19 panels at 400 W each, producing about 10,800 kWh per year and needing roughly 411 sq ft of roof. Estimated gross cost is $13,405-$20,176 before incentives, with simple payback of 5.1 years-7.6 years. The estimate uses EIA Electric Power Monthly, Table 5.6.A — June 2026 (updated 2026-09-04) and NLR PVWatts V8 · author-selected reference point (updated 2026-09-04).
SolarCalcNow provides planning estimates only. Results are not installer quotes, engineering designs, tax advice, financing recommendations, or utility interconnection approval.
Worked scenarios, not measured households
900 kWh/month · 400 W
Author-created California scenarios using the current source snapshots, low shade and no incentives. Except for the variable shown, inputs stay fixed: 100% annual energy target, 55% direct use and export at 35% of retail. Compare your utility and roof before using the result.
| Changed input | Calculated output |
|---|---|
| 350 W | 20 Likely panel count |
| 400 W | 17 Likely panel count |
| 450 W | 16 Likely panel count |
The sizing target uses continuous DC kW; panel count rounds up. Actual module dimensions, setbacks and roof planes can change the layout. The 21 ft² per panel × 1.15 spacing model is an author assumption, not a building-code clearance.
Calculated baseline
This baseline uses the site default 900 kWh/month example. Change usage, state, shade, or panel wattage in the calculator to match your home before comparing quotes.
| State | System | Panels | Gross cost | Payback |
|---|---|---|---|---|
| California | 6.8 kW | 15-19 | $13,405-$20,176 | 5.1 years-7.6 years |
| Texas | 6.6 kW | 15-19 | $11,764-$17,579 | 9.7 years-14.4 years |
| Massachusetts | 8.3 kW | 19-23 | $19,294-$28,900 | 8.5 years-12.8 years |
This calculator is designed for early planning. It translates monthly usage or monthly bill into an estimated system size, then converts system size into panel count, roof space, gross cost, savings, and payback.
The result is intentionally shown before any quote request. If you want installer quotes, the optional form appears after the estimate and requires explicit consent.
Same calculator engine with a different starting assumption. Useful before comparing installer quotes.
Monthly usage presets
Panel wattage presets
State calculators
FAQ
Yes. Enter your monthly electric bill and state, and the calculator estimates kWh from the state residential rate.
No. It is a planning estimate. A site survey can change system size, panel count, roof layout, and cost.
This page compares how 350 W, 400 W and 450 W modules change panel count for the same energy target. Start with twelve months of usage, then check the count against actual module dimensions and the roof layout.
After calculating, save the estimate assumptions, check incentive status, and compare installer quotes against the same baseline.