Solar panel calculator
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.
Estimate preview
Panels, cost, savings
No email required
Run the solar panel calculator
Enter monthly kWh or electric bill. The calculator uses state-level assumptions and shows the math behind the result.
Your estimate
Example resultYou likely need 18-22 panels
Estimated system size: 7.8 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.
- Estimated system size
- 7.8 kW
- Sized for your target offset and system loss assumption.
- Likely panel count
- 18-22
- Centered around 20 panels at 400W equivalent.
- Roof space
- 483 sq ft
- Includes a spacing factor, not a final layout plan.
- Annual production
- 10,800 kWh
- Modeled first-year output at the selected offset; not a production guarantee.
- Gross cost
- $18,445 - $23,939
- Before verified incentives, financing, or battery costs.
- Gross cost per watt
- $2.35 - $3.05
- Before incentives. Useful for comparing installer quotes.
- Annual savings
- $2,693
- Based on state residential rate and self-consumption assumption.
- Payback
- 6.8 years - 8.9 years
- Simple gross-cost payback estimate.
Annual usage: 10,800 kWh
Annual production target: 10,800 kWh
State rate: 35.25 cents/kWh
Export assumption: Partial export credit
Direct solar use: 5,940 kWh
Modeled exports: 4,860 kWh
Panel count view
18-22 panels
Estimate shape
Production, savings, and payback
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
Save estimates on this device
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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Assumptions behind this estimate
- California state-level electricity rate and solar production defaults are used.
- 100% bill offset target.
- 400W solar panels.
- 14% system loss assumption.
- Roof area uses about 21 sq ft per panel plus spacing factor.
- Gross cost range excludes verified incentives, financing, batteries, roof work, and panel upgrades.
- 55% of annual solar production is modeled as directly used before export.
- Export value assumption: Partial export credit.
- Savings are energy-only and exclude fixed charges, minimum bills, demand charges, and time-of-use detail.
- You provided monthly kWh usage.
- State production defaults are used for this estimate.
Confidence drivers
- Overall confidence: Medium.
- You provided monthly kWh usage.
- State production defaults are used for this estimate.
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: 1,600 kWh/kW/year
SolarCalcNow provides planning estimates only. Results are not installer quotes, engineering designs, tax advice, financing recommendations, or utility interconnection approval.
Optional next step
Want installer quotes based on this estimate?
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.
SolarCalcNow provides planning estimates only. Results are not installer quotes, engineering designs, tax advice, financing recommendations, or utility interconnection approval.
Real baseline
What the calculator returns for 900 kWh/month
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 | 7.8 kW | 18-22 | $18,445-$23,939 | 6.8 years-8.9 years |
| Texas | 8.4 kW | 19-23 | $19,674-$25,953 | 15.2 years-20.0 years |
| Massachusetts | 10.0 kW | 24-28 | $27,628-$36,670 | 12.3 years-16.3 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.
Compare planning presets
Same calculator engine with a different starting assumption. Useful before comparing installer quotes.
Monthly usage presets
Panel wattage presets
State calculators
Start with local assumptions
FAQ
Common solar calculator questions
Can I use this without my exact kWh?
Yes. Enter your monthly electric bill and state, and the calculator estimates kWh from the state residential rate.
Does this replace an installer site survey?
No. It is a planning estimate. A site survey can change system size, panel count, roof layout, and cost.
How is this page different from the homepage calculator?
Both use the same engine. This page focuses on panel-count and sizing intent with SEO-specific guidance, while the homepage is the general entry point.
What to do next
After calculating, save the estimate assumptions, check incentive status, and compare installer quotes against the same baseline.