System sizing

Solar Panel Size Calculator

Estimate the solar system size in kW that can offset your home electricity usage.

Use this page when you need the system capacity in kW first, before turning that capacity into panel count, roof area, and quote checks.

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Estimate preview

Panels, cost, savings

System size7.8 kW

Payback window5-7 yr

ConfidenceHigh

No email required

Estimate system size

Enter monthly kWh or electric bill. The calculator uses state-level assumptions and shows the math behind the result.

Monthly usage, kWhMonthly bill, $

Planning for new electric loads?

Add a simple monthly usage placeholder before sizing solar. Replace it with your actual bill or device estimate when you have it.

Need more than a placeholder? Calculate EV charging from annual miles and efficiency, then compare current and future solar size. Plan EV and other future home loads

StateZIP codeRoof typeUsed for planning context only; roof type does not change sizing or cost math without a site-specific quote.

ShadePanel wattsOffset target

Export valueAdvanced planning input. Your utility may use different net metering, net billing, or export-credit rules.Direct solar use

55%

Share of annual solar production used in the home before export. Replace this planning assumption with interval data when available.

Your estimate

Example result

You 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

Annual production target10,800 kWh

Annual savings$2,693

Payback6.8 years - 8.9 years

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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.

Optional next step

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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

System kW below scales with monthly kWh and offset target. Roof orientation, shade, and inverter clipping can change the final design after a site survey.

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

Methodology first

System size connects usage to production

Read methodology

Solar system size is measured in kilowatts. The calculator starts with annual usage, multiplies by your offset target, then divides by a state-level production estimate and adjusts for system losses.

This produces a planning-size estimate. Actual system design should account for roof azimuth, tilt, shade, inverter clipping, local code, and equipment choices.