400W panel preset
Solar Calculator for 400 Watt Panels
Start with 400W panels pre-filled — the default planning reference for many U.S. residential systems.
Use this preset as a practical residential baseline when an installer quote uses 400W-class modules or a nearby nameplate rating.
Estimate preview
Panels, cost, savings
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Estimate solar with 400W panels
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.
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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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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
Same inputs, different state data: 400 W panels, 900 kWh/month, low shade, 100% offset target, partial export credit, and no ZIP-level PVWatts override. This makes the state-rate and production assumptions visible before a quote.
| 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 |
400W is a common planning default for residential solar in the U.S. It balances panel count, roof layout, and equipment availability on many modern quotes.
Use this preset when an installer proposal references 400W-class modules. Change state, shade, and offset to match your home before comparing gross $/W.
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
Is 400W a standard panel size?
400W is a common planning reference, but actual modules may be 390W, 405W, or another nameplate rating. Use the exact wattage from the quote when checking price per watt.
How does 400W compare with 450W?
Higher wattage usually reduces panel count for the same system kW, but roof obstructions and product availability still matter.
What to do next
After calculating, save the estimate assumptions, check incentive status, and compare installer quotes against the same baseline.