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Solar Panel Calculator

Design your solar system step by step

Location & Solar Resource
Energy Consumption
System Design
Financial
Advanced Settings
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5
Step 1 of 5: Location & Solar Resource

Location & Solar Resource

Your location determines available sunlight and optimal system design

Quick Orientation

°
%
hrs/day

Steps

Results

25-Year Net Savings

$62,396

Payback in 6.8 years|383% ROI|7.6 kW system
System Size

7.6 kW

Panels

19

Year 1 Production

15,368 kWh

Year 1 Savings

$2,459

Payback Period

6.8 yr

ROI

383%

LCOE

$0.062/kWh

CO₂ Offset (25yr)

95.2 tons

Cost Breakdown

Solar Panels
$12,540
Inverter & BOS
$5,700
Installation
$4,560
Permits & Fees
$500
Total System Cost
$23,300
Federal Tax Credit (ITC)
−$6,990
Net Cost$16,310

First Year Savings

Electricity Bill Savings
$2,400
Net Metering Credits
$59
Total Year 1 Savings
$2,459

Monthly Production (Year 1)

Jan

867

kWh

Feb

1,001

kWh

Mar

1,267

kWh

Apr

1,467

kWh

May

1,628

kWh

Jun

1,668

kWh

Jul

1,641

kWh

Aug

1,548

kWh

Sep

1,361

kWh

Oct

1,134

kWh

Nov

961

kWh

Dec

827

kWh

Environmental Impact (25 Years)

95.2

tons CO₂ offset

366,323

total kWh produced

Frequently Asked Questions

Q

How many solar panels do I need for my home?

The number of solar panels depends on your monthly electricity usage, local peak sun hours, panel wattage, and roof orientation. A typical US home using 900 kWh/month in a sunny state needs about 16-20 panels (400W each) for a 6-8 kW system to offset 100% of electricity use.

  • Divide annual kWh by (365 × peak sun hours × system efficiency) to get system size in kW
  • Divide system size by individual panel wattage to get panel count
  • Account for roof orientation, shading, and inverter losses
  • Consider 100-110% offset to cover future usage growth
Home SizeMonthly kWhSystem SizePanels (400W)
Small600 kWh4-5 kW10-13
Medium900 kWh6-8 kW15-20
Large1,500 kWh10-12 kW25-30
Very Large2,500 kWh16-20 kW40-50
Q

What is the payback period for solar panels?

The average solar panel payback period in the US is 6-12 years, depending on your state, electricity rate, system cost, and available incentives. States with high electricity rates like California and Hawaii see payback in 5-7 years, while states with lower rates may take 10-15 years.

FactorFaster PaybackSlower Payback
Electricity rate$0.20+/kWhUnder $0.12/kWh
Peak sun hours5.5+ hours/dayUnder 4 hours/day
State incentivesSRECs + rebatesFederal ITC only
Net meteringFull retail creditReduced or no credit
Q

How does the federal solar tax credit (ITC) work?

The federal Investment Tax Credit (ITC) allows you to deduct 30% of the total installed cost of your solar energy system from your federal taxes. This applies to both residential and commercial systems installed through 2032. The credit steps down to 26% in 2033 and 22% in 2034.

  • Covers panels, inverters, battery storage, installation labor, and permits
  • Must be claimed in the tax year the system is placed in service
  • Can be carried forward if your tax liability is less than the credit amount
  • No maximum dollar limit on residential systems
  • Battery storage added to existing systems also qualifies
Q

What is LCOE and why does it matter for solar?

LCOE (Levelized Cost of Energy) is the total lifetime cost of your solar system divided by total lifetime energy production, expressed in $/kWh. It represents your effective cost of solar electricity and allows direct comparison with your utility rate. A lower LCOE than your grid rate means solar saves you money.

For residential solar, typical LCOE ranges from $0.04-$0.08/kWh after incentives, compared to the national average grid rate of $0.16/kWh. This means solar electricity costs 50-75% less than grid electricity over the system lifetime. LCOE accounts for the initial investment, maintenance costs, degradation, and total energy produced over 25 years.

Q

Should I buy or lease solar panels?

Buying solar panels (cash or loan) typically provides the highest long-term savings and ROI because you own the system and receive all incentives including the federal tax credit. Leasing requires no upfront cost but offers lower total savings since the leasing company keeps the tax credits and charges an escalating monthly fee.

FactorCash PurchaseSolar LoanLease/PPA
Upfront costFull price$0 down$0 down
Tax creditYou keep 30%You keep 30%Company keeps
25-yr savingsHighestHighModerate
MaintenanceYour responsibilityYour responsibilityCompany handles
Home valueIncreasesIncreasesNo increase
Q

How much do solar panels degrade over time?

Solar panels typically degrade at 0.3-0.7% per year, meaning they produce slightly less electricity each year. Monocrystalline panels degrade slowest at about 0.4%/year, while thin-film panels degrade faster at 0.7%/year. After 25 years, most panels still produce 82-90% of their original output.

  • Monocrystalline: ~0.4%/year → ~90% output at year 25
  • Polycrystalline: ~0.5%/year → ~88% output at year 25
  • Thin-Film: ~0.7%/year → ~83% output at year 25
  • Most manufacturers guarantee 80-85% production at 25 years
  • Actual degradation may be lower than rated in mild climates
Q

Does roof orientation affect solar panel production?

Yes, roof orientation significantly affects solar production. South-facing roofs are optimal in the Northern Hemisphere, producing 100% of potential output. East and west-facing roofs produce about 85% as much, while north-facing roofs may only produce 50%. Flat roofs work well at about 90% efficiency with tilted mounting.

OrientationProduction %Recommendation
South100%Ideal — maximum production
South-East/West95%Excellent — minimal loss
East or West85%Good — worth installing
Flat90%Good — use tilted mounts
North-East/West65%Marginal — consider alternatives
North50%Not recommended in most cases
Q

Is battery storage worth the investment for solar?

Battery storage adds $8,000-$15,000 to your solar system cost but provides backup power, increases self-consumption of solar energy, and can provide additional savings in areas without full net metering. It is most valuable in areas with time-of-use rates, frequent power outages, or reduced net metering credits.

  • Qualifies for the 30% federal tax credit when paired with solar
  • Tesla Powerwall (13.5 kWh) costs ~$12,000-$15,000 installed
  • Most cost-effective in states with low net metering rates
  • Provides 8-12 hours of backup power for essential loads
  • Battery replacement typically needed at year 12-15 (at ~70% original cost)

Example Calculations

1Average California Home (Cash Purchase)

Inputs

StateCalifornia
Monthly Usage900 kWh
Electricity Rate$0.27/kWh
Offset100%
Panel TypeMonocrystalline 400W
FinancingCash

Result

25-Year Net Savings$52,847
System Size5.6 kW (14 panels)
Year 1 Production9,406 kWh
Payback Period6.2 years
ROI449%
LCOE$0.049/kWh

System size: 900 × 12 / (5.8 × 365 × 0.96) = 5.3 kW → 14 panels at 400W = 5.6 kW. Total cost: 5,600W × $3.00/W = $16,800. Net cost after 30% ITC: $11,760. First year savings: 9,406 kWh × $0.27 = $2,540. Payback: $11,760 / ~$1,900 avg annual savings ≈ 6.2 years.

2Texas Home with Solar Loan and Battery

Inputs

StateTexas
Monthly Usage1,250 kWh
Electricity Rate$0.13/kWh
Panel TypeMonocrystalline 400W
FinancingSolar Loan (6.5%, 20yr)
BatteryYes (13.5 kWh, $12,000)

Result

25-Year Net Savings$18,312
System Size8.0 kW (20 panels)
Total System Cost$36,000
Net Cost After ITC$25,200
Payback Period14.8 years
Monthly Loan Payment$188

Lower electricity rates in Texas lead to a longer payback period. The battery adds $12,000 but provides backup power during Texas grid emergencies. The 30% ITC applies to both panels ($24,000) and battery ($12,000). Monthly loan payment: $25,200 at 6.5% for 20 years = $188/month.

3Budget System in Ohio (Polycrystalline)

Inputs

StateOhio
Monthly Usage800 kWh
Electricity Rate$0.14/kWh
Panel TypePolycrystalline 350W
FinancingCash

Result

25-Year Net Savings$12,640
System Size5.6 kW (16 panels)
Total System Cost$14,000
Net Cost After ITC$9,800
Payback Period11.4 years
LCOE$0.058/kWh

Ohio has lower sun hours (3.9) and moderate rates, resulting in longer payback. Budget polycrystalline panels at $2.50/W reduce initial cost. System still provides positive ROI over 25 years with 129% return on investment.

Formulas Used

System Size Formula

System (kW) = (Monthly kWh × 12 × Offset%) / (Peak Sun Hours × 365 × Efficiency)

Calculates the required solar system size based on energy needs and location.

Where:

Monthly kWh= Average monthly electricity consumption
Offset%= Desired percentage of electricity to offset (e.g., 100%)
Peak Sun Hours= Average daily peak sun hours at your location
Efficiency= Combined system efficiency (orientation × tilt × shading × inverter)

Payback Period

Payback (years) = Net System Cost / Average Annual Savings

Estimates how long until cumulative savings equal the initial investment.

Where:

Net System Cost= Total cost minus federal tax credit, state incentives, and utility rebates
Average Annual Savings= Electricity savings plus net metering credits, accounting for rate escalation

Levelized Cost of Energy (LCOE)

LCOE = Total Lifetime Cost / Total Lifetime Production (kWh)

The effective per-kWh cost of solar electricity over the system lifetime.

Where:

Total Lifetime Cost= Net system cost + 25 years of maintenance + battery replacement
Total Lifetime Production= Sum of annual production with degradation over 25 years

CO₂ Offset

CO₂ (lbs) = Σ [Annual Production × (1 - Degradation)^year × CO₂ Factor]

Total carbon dioxide emissions avoided by displacing grid electricity with solar.

Where:

Annual Production= First year electricity generation in kWh
Degradation= Annual panel output decline rate (e.g., 0.4%/year)
CO₂ Factor= Grid emission factor in lbs CO₂ per kWh (varies by state)

Complete Guide to Solar Panel Economics and ROI

1

How Solar Panel Systems Are Sized for Your Home

900 kWh per month — that is the average US household electricity consumption, requiring a 6–8 kW solar system with 15–20 panels at 400W each. The sizing formula divides your annual electricity usage by the product of peak sun hours, 365 days, and system efficiency. In California with 5.8 peak sun hours, 10,800 kWh annually translates to a 5.3 kW minimum system size.

Peak sun hours vary dramatically by location: Phoenix averages 6.5 hours/day, Denver gets 5.5, Atlanta sees 4.7, and Seattle manages only 3.5. This single variable determines whether you need 14 panels or 24 panels for the same 900 kWh/month consumption. The calculator adjusts for your state’s solar resource data, roof orientation losses (south-facing = 100%, east/west = 85%, flat = 90%), and typical inverter efficiency of 96–97%.

Panel wattage matters for roof space planning. Modern monocrystalline panels produce 400–430W each, covering about 17.5 square feet per panel. A 6 kW system (15 panels) requires approximately 263 square feet of unshaded roof area. Budget polycrystalline panels at 350W need 17 panels for the same output, requiring 298 square feet — a 13% increase in roof space.

*Based on 5.0 average peak sun hours; actual varies by location
Monthly UsageSystem SizePanels (400W)Roof Space Needed
600 kWh4–5 kW10–13175–228 sq ft
900 kWh6–8 kW15–20263–350 sq ft
1,200 kWh8–10 kW20–25350–438 sq ft
1,800 kWh12–15 kW30–38525–665 sq ft

Tip: Size your system for 100–110% of current usage to account for future needs like EV charging or a home addition.

2

Solar Panel Costs, Incentives, and Payback Period

$3.00 per watt installed is the 2024 national average for residential solar, making a 6 kW system approximately $18,000 before incentives. The 30% federal Investment Tax Credit (ITC) reduces that to $12,600 out of pocket — and many states add their own rebates, SRECs (Solar Renewable Energy Credits), or property tax exemptions that push net costs even lower.

Payback period is the critical metric: it tells you when cumulative electricity savings equal your net investment. In California with $0.27/kWh rates, a $12,600 net-cost system generating $2,540/year in savings pays back in 6.2 years, then generates free electricity for the remaining 19+ years of the panel warranty. In Ohio with $0.14/kWh rates, the same system takes 11.4 years to pay back — still profitable, but less dramatically.

Financing method significantly impacts total ROI. Cash purchases deliver the highest lifetime savings (449% ROI in the California example) because there are no interest charges. Solar loans at 6.5% for 20 years add $8,000–$12,000 in interest but require $0 down. Leases eliminate upfront cost and maintenance responsibility, but the leasing company keeps the federal tax credit and charges an escalating monthly fee, reducing 25-year savings by 40–60%.

Solar Payback Period by StateYears15129635.5Hawaii6.2California8.5Texas11.4Ohio14.8WashingtonUnder 8 years8–10 years10+ years
3

Cash vs Loan vs Lease: Financing Comparison

$52,847 in 25-year net savings for a cash purchase versus $18,312 with a solar loan — financing method is the second-biggest factor (after location) in determining your solar ROI. Each option trades upfront cost against long-term return, and the best choice depends on your available capital, tax situation, and appetite for ownership.

Cash buyers keep 100% of the 30% ITC, pay zero interest, and own the system outright from day one. A $16,800 system with $5,040 ITC costs $11,760 net and generates $52,847 in savings over 25 years — a 449% return on investment. The only downside is opportunity cost: that $11,760 invested in the S&P 500 at historical 10% returns would grow to approximately $127,000, though solar savings compound as electricity rates rise 3–4% annually.

Solar loans at 6.5% for 20 years require $0 down and still qualify you for the ITC (you own the system). Monthly payments of $188 for a $25,200 net-cost system are typically less than the electricity savings, making it cash-flow positive from year one. Leases and PPAs (Power Purchase Agreements) require no upfront cost and no maintenance, but the leasing company captures the tax credit and charges an escalating rate that reduces your total savings by 40–60%.

*Based on 5.6 kW system in California at $0.27/kWh
FactorCashSolar LoanLease/PPA
Upfront cost$11,760$0$0
You keep ITC (30%)YesYesNo
25-year savings$52,847$18,312$8,000–$15,000
MaintenanceOwnerOwnerCompany
Home value impact+$15,000–$25,000+$15,000–$25,000None
Best forMax ROI$0 down ownershipNo hassle
4

Panel Degradation, Maintenance, and 25-Year Performance

0.4% per year — that is the typical degradation rate for monocrystalline solar panels, meaning your system produces 90% of its original output at year 25. Over a 25-year lifetime, a 5.6 kW system in California produces approximately 210,000 kWh of electricity, displacing over 150,000 lbs of CO₂ emissions compared to grid power.

Maintenance costs are minimal: $100–$300 per year for occasional cleaning and inspection, plus a potential inverter replacement at year 12–15 costing $1,500–$3,000. String inverters last 10–15 years, while microinverters and power optimizers typically last 20–25 years with individual panel-level monitoring. Total 25-year maintenance costs typically run $3,000–$7,000 — a fraction of the $50,000+ in electricity savings.

The LCOE (Levelized Cost of Energy) captures all costs — installation, maintenance, degradation — divided by total lifetime production. A typical residential LCOE of $0.04–$0.08/kWh after incentives compares favorably to the national average grid rate of $0.16/kWh, making solar electricity 50–75% cheaper than utility power over the system lifetime. Use our ROI calculator to compare solar against other investment options.

  • Monocrystalline panels — 0.4%/year degradation, 90% output at year 25, best efficiency per square foot
  • Polycrystalline panels — 0.5%/year degradation, 88% at year 25, 10–15% lower cost per watt
  • String inverter replacement — $1,500–$3,000 at year 12–15; microinverters last the full 25 years
  • Annual cleaning — $100–$300 per visit; panels in dusty or pollen-heavy areas need 2–3 cleanings per year
  • Monitoring system — most modern systems include free app-based monitoring to detect output drops instantly
5

Battery Storage: When It Makes Financial Sense

$12,000–$15,000 installed — that is the cost of a Tesla Powerwall (13.5 kWh) or comparable home battery in 2024. The 30% federal ITC applies to batteries paired with solar, reducing net cost to $8,400–$10,500. Whether batteries make financial sense depends entirely on your utility’s net metering policy and rate structure.

In states with full retail net metering (like California under NEM 2.0 grandfathering), batteries add minimal financial value because excess solar production earns full credit. Under NEM 3.0 or reduced net metering, batteries become valuable by storing daytime solar production for evening use when rates are highest. Time-of-use rate arbitrage can save $30–60/month, potentially paying back the battery in 12–18 years.

Beyond economics, batteries provide 8–12 hours of backup power for essential loads during grid outages. In areas with frequent storms or unreliable grid infrastructure, this resilience value often justifies the investment. Battery replacement typically occurs at year 12–15 at approximately 70% of original cost, adding $6,000–$8,000 to the 25-year total if full backup capability is maintained. Check the EV savings calculator if you are also considering an electric vehicle — solar plus EV plus battery maximizes your energy independence.

Tip: Battery storage is most cost-effective in states that have reduced or eliminated full retail net metering — check your utility’s current policy before deciding.

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Last Updated: Mar 26, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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