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Solar Panel Calculator
Estimate your solar system size, panel count, roof space, cost, savings, and payback in under a minute.
Rates and assumptions reviewed July 2026. See sources and update cadence.
Estimate preview
Panels, cost, savings
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Calculate your home solar estimate
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
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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.
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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.
Transparent formulas
Built around assumptions you can see
SolarCalcNow starts from monthly usage or bill, state electricity rate, state production assumption, panel wattage, shade, and target offset. It shows a confidence level instead of pretending every home can be estimated perfectly.
Gross cost is shown before incentives. Verified state and local incentives can be added later, but they should never be silently hardcoded into payback without source review.
See the methodologyState calculators
Start with local assumptions
FAQ
Common solar calculator questions
How accurate is this solar calculator?
It is a planning estimate, not an installer quote. Shade, roof orientation, utility rules, equipment, financing, permitting, and installer pricing can change the final result.
Do I need my electric bill or monthly kWh?
Monthly kWh is best. If you only know your monthly bill, the calculator estimates usage from the selected state's residential electricity rate.
Does the calculator include solar incentives?
The MVP shows gross cost first and does not apply incentives by default. Incentives change quickly and need source, updated date, eligibility, and active status before being used in net-cost math.
Why does the result show a panel range?
Panel count depends on panel wattage, roof layout, shading, design setbacks, and installer equipment choices. A range is more honest than a single guaranteed number.
Does roof orientation or shade change the estimate?
Yes. South-facing roofs with low shade usually produce more than east/west roofs or heavily shaded sections. SolarCalcNow uses a simple shade level, not a site-specific layout or LIDAR model.
How often are the rates and assumptions updated?
State electricity rates and production assumptions are reviewed on a published cadence, and every figure links back to its source with the date it was last checked. Utility rates and net-metering rules can still change between reviews, so confirm current terms with your utility before signing anything.