A home paying $160 a month for power in Arizona needs a solar system of roughly 6.1 kW to cover its yearly use, would save about $1,920 in the first year, and would earn back a $15,981 installation in about 7.7 years, before any rebates. The 30% federal tax credit that used to shorten that payback is gone for homeowners: under Public Law 119-21, it does not apply to residential systems whose installation was completed after 31 December 2025, according to the Congressional Research Service.
The free solar panel savings calculator below runs those numbers for any US state or 13 Indian cities. Enter your monthly bill or kWh and it suggests a system size, then estimates generation, savings, payback, 25-year savings and CO2 avoided. For India it fills in the PM Surya Ghar subsidy. Every formula is set out below the tool.
Sizing a System, the End of 25D and PM Surya Ghar’s ₹78,000 Cap
- System size (kW) = yearly kWh use ÷ (peak sun hours × 365 × performance ratio).
- The Section 25D residential credit does not apply to expenditures made after 31 December 2025, and an expenditure counts as made when installation is complete, so most 2026 home installs get 0%.
- PM Surya Ghar pays ₹30,000 per kW for the first 2 kW and ₹18,000 for the third, so the subsidy tops out at ₹78,000 for a 3 kW home system.
- Electricity price rises matter: in our Arizona example, a 3% yearly rise lifts 25-year net savings from about $29,200 to $49,500.
Solar Panel Savings Calculator
Size a rooftop system from your bill, then see generation, savings, payback and CO2 avoided over 25 years.
Runs in your browser. Nothing you type is sent anywhere.
Location and Usage
System and Cost
Incentives
System size
–
Suggested from your use
Year-1 generation
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kW × sun hours × 365 × PR
Year-1 savings
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At today’s rate
Cost after incentives
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Gross cost minus incentives
Payback
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When cumulative savings pass the cost
25-year net savings
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Savings minus cost after incentives
CO2 avoided
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Over 25 years
Year-by-Year Table
| Year | Generation (kWh) | Rate | Savings | Cumulative net |
|---|---|---|---|---|
| Run the calculator to fill this table. | ||||
An estimate, not a quote. Sun hours are annual averages and real output depends on roof angle, shade and weather. The calculator runs in your browser and stores nothing.
Solar Savings Formulas Used in This Calculator
The calculator follows these steps, in order:
- Monthly use from a bill: kWh per month = monthly bill ÷ rate per kWh. Leave out fixed charges and taxes.
- Yield per kW: kWh per kW per year = peak sun hours × 365 × performance ratio.
- Suggested size: system kW = (monthly kWh × 12 × share of use to cover) ÷ yield per kW. A size you type in replaces the suggestion.
- Cost: gross cost = kW × 1,000 × cost per watt. Net cost = gross cost − (gross × credit %) − fixed subsidy.
- Generation in year n: kW × yield per kW × (1 − degradation)^(n − 1).
- Savings in year n: the generation you use yourself (up to your yearly consumption) × rate × (1 + price rise)^(n − 1), plus any surplus × your export credit, raised by the same factor.
- Payback: the point at which cumulative savings equal the net cost, interpolated within the year it happens.
- 25-year net savings: the sum of 25 years of savings minus the net cost.
- CO2 avoided: total kWh generated × the grid emission factor in kg per kWh ÷ 1,000 = tonnes.
Payback is the same break-even logic a business applies to any capital purchase.
Worked Example: An Arizona Home Paying $160 a Month
Arizona’s average residential rate was 14.91 cents per kWh in 2024, according to the EIA’s state table, and the preset uses 7 peak sun hours. Add $2.60 per watt, an 82% performance ratio, 0.5% yearly degradation and a 3% yearly price rise. Load Arizona Example reproduces these figures.
| Step | Working | Result |
|---|---|---|
| Monthly use | $160 ÷ $0.1491 | 1,073 kWh |
| Yearly use | 1,073 × 12 | 12,877 kWh |
| Yield per kW | 7 × 365 × 0.82 | 2,095 kWh |
| System size | 12,877 ÷ 2,095 | 6.15 kW |
| Installed cost | 6,146 W × $2.60 | $15,981 |
| Year-1 savings | 12,877 kWh × $0.1491 | $1,920 |
| Payback | Cumulative savings pass $15,981 | 7.7 years |
| 25-year net savings | $65,456 saved − $15,981 | $49,475 |
| CO2 avoided | 303,336 kWh × 0.672 kg | 203.8 tonnes |
With flat prices instead of a 3% rise, payback stretches to 8.5 years and 25-year net savings drop to about $29,200. If an installer’s production estimate for your roof differs, adjust the sun hours until year-1 generation matches it.
Worked Example: A 3 kW Rooftop System in Delhi
Take a Delhi household using 350 units a month at ₹8 per unit, quoted ₹60,000 per kW for a 3 kW system (both are illustrative figures; use your own bill and vendor quote). Delhi NCR’s preset is 4.7 peak sun hours. With the PM Surya Ghar subsidy ticked:
| Step | Working | Result |
|---|---|---|
| Yearly use | 350 × 12 | 4,200 kWh |
| Year-1 generation | 3 × 4.7 × 365 × 0.82 | 4,220 kWh |
| Gross cost | 3,000 W × ₹60 | ₹1,80,000 |
| Central subsidy | 2 × ₹30,000 + 1 × ₹18,000 | ₹78,000 |
| Net cost | ₹1,80,000 − ₹78,000 | ₹1,02,000 |
| Year-1 savings | 4,200 kWh used × ₹8 | ₹33,600 |
| Payback (2% yearly tariff rise) | Cumulative savings pass ₹1,02,000 | 3.0 years |
| CO2 avoided over 25 years | 99,409 kWh × 0.727 kg | 72.3 tonnes |
Without the subsidy, payback takes about 5.2 years. The 20 kWh surplus earns nothing here because the export credit is blank; enter your discom’s net-metering rate to value it. If you also want backup power, size the battery separately with our guide to inverter battery backup time.
The Federal 25D Solar Tax Credit After 2025
The Section 25D Residential Clean Energy Credit was worth 30% of the cost of home solar. Public Law 119-21 ended it for expenditures made after 31 December 2025. The CRS note flags the detail that catches people out: an expenditure counts as made when installation is complete, not when you sign or pay, so a system started in 2025 and finished in 2026 does not qualify. Unused credit from an earlier qualifying install can still be carried forward.
So the credit field defaults to 0%. Leased systems and power purchase agreements are a separate route: EnergySage notes that lease and PPA projects still qualify for the federal credit. Any state, city or utility rebate you are offered goes in the fixed subsidy field.
PM Surya Ghar Subsidy Amounts by System Size
PM Surya Ghar Muft Bijli Yojana pays central financial assistance on home rooftop solar, in slabs listed by the Delhi government’s solar portal.
| System Size | How It Is Calculated | Central Subsidy |
|---|---|---|
| 1 kW | 1 × ₹30,000 | ₹30,000 |
| 2 kW | 2 × ₹30,000 | ₹60,000 |
| 2.5 kW | ₹60,000 + 0.5 × ₹18,000 | ₹69,000 |
| 3 kW or more | ₹60,000 + ₹18,000, capped | ₹78,000 |
| Group housing societies and RWAs | ₹18,000 per kW for common facilities, up to 500 kW | Varies |
Because the subsidy stops at 3 kW, every kilowatt above that is paid in full, so extra capacity pays back more slowly. If your state adds its own top-up, untick the central scheme box and enter the combined amount in the fixed subsidy field.
Sun Hours, Degradation and CO2 Factors Behind the Presets
- US peak sun hours: each state preset shows the range published by SolarReviews, whose map draws on NREL’s National Solar Radiation Database for 1998 to 2016. The calculator uses the low end, because states such as Texas (4 to 7.5 hours) span very different climates.
- Indian cities: annual average peak sun hours for 13 cities from Heaven Green Energy, which lists typical yields of about 1,400 to 1,750 kWh per kWp a year from the Global Solar Atlas. The same page uses a performance ratio of 0.82, our default.
- US rates: 2024 state averages from EIA Table 5A. Your own bill rate is better.
- Degradation: a review of nearly 2,000 measured rates found a median loss of 0.5% a year (Photovoltaic Degradation Rates: An Analytical Review).
- US CO2 factor: 0.672 kg per kWh, the figure the EPA’s equivalencies calculator uses for avoided electricity, based on eGRID 2022 data (1,405.3 lb CO2 per MWh).
- India CO2 factor: 0.727 kg per kWh, the Central Electricity Authority’s weighted average for 2023-24 as reported by SolarQuarter.
Why Real Solar Savings Can Fall Short of the Estimate
- Export credits below retail: if your utility pays less for exported power than it charges, enter that lower export rate or cover less than 100% of use.
- Fixed charges in the bill: a bill that includes connection fees and taxes overstates your kWh. Compare yours with the average electricity bill in your state.
- Financing costs: loan interest is not included. Work out the monthly payment with our EMI guide and compare it with your monthly savings.
For more free calculators, see the Bizolaunch tools page.
This calculator and article are for information and education only and are not investment, tax or financial advice. Figures were checked on 30 October 2026; confirm current incentives, tariffs and quotes with the official source, your utility or a registered adviser before acting.
Is the 30% Credit Gone and How Many Panels You Need
Is the 30% Solar Tax Credit Still Available in 2026?
Not for systems homeowners buy and install in 2026. The Section 25D credit does not apply to expenditures made after 31 December 2025, and the expenditure date is when installation is complete. Carryforwards from earlier qualifying installs can still be used.
How Do You Calculate Solar Panel Payback?
Add up each year’s savings until they equal the installed cost minus incentives. With flat prices and no degradation it is net cost ÷ yearly savings: $15,981 ÷ $1,920 is about 8.3 years.
How Much Subsidy Is Available for a 3 kW Rooftop Solar System in India?
₹78,000 under PM Surya Ghar: ₹30,000 per kW for the first 2 kW and ₹18,000 for the third. Systems larger than 3 kW receive the same ₹78,000.
How Many Solar Panels Do I Need?
Divide the system size by the wattage of the panel your installer quotes. A 6.15 kW system built from 400 W panels needs 6,150 ÷ 400 = 15.4, so 16 panels.
What Are Peak Sun Hours?
The daily sunlight on a surface expressed as hours at 1,000 watts per square metre. Five peak sun hours equals 5 kWh per square metre per day.
CRS on the 25D Credit, Delhi’s Subsidy Portal and Sun Hour Data
- Congressional Research Service: Expiration and Carryforward Rules for the Residential Clean Energy Credit (IN12611, 25 September 2025)
- Government of NCT of Delhi, Solar Portal: Central subsidy under PM Surya Ghar
- EnergySage: Solar panel cost in 2026
- U.S. Energy Information Administration: Table 5A, 2024 Average Monthly Bill, Residential
- SolarReviews: Peak sun hours by state
- Heaven Green Energy: Peak sun hours and yield for Indian cities
- OSTI: Photovoltaic Degradation Rates, An Analytical Review
- US EPA: Greenhouse Gas Equivalencies Calculator, Calculations and References
- SolarQuarter: CEA CO2 Baseline Database figures
