SolarCalcLab

Size your solar with your roof's real sunlight.

Free solar and electrical calculators that use measured sun data for your location, and show the formula and sources behind every result.

Find my system size Browse all calculators
Popular: Solar panel Battery size Wire size Watts to amps

Sun data from PVGIS and NREL. Tariffs from US EIA, Ofgem, AER and Destatis.

Quick system estimate

Try a city
$180
$40$400
13.4 kWp
system size
32
panels at 430 W
24,080 kWh
output per year
Monthly outputpeak 2,890 kWh
Yield 1,750 kWh per kWp, tariff $0.17 per kWh, approximate Use my exact address

Start with the question you have.

How big a solar system do I need?
Solar panel calculator How many panels Panel output Panel angle Peak sun hours
Will solar pay for itself?
Solar cost Payback and ROI Net metering STC rebate Electricity cost
What battery should I buy, and how long will it last?
Battery size Battery life Amp hours Backup time Solar generator
Is my wiring and inverter the right size?
Voltage drop Wire size Inverter size MPPT controller String size

Every calculator, in one place.

29 free tools, grouped by the job they do.

All calculators

Solar sizing6

Cost and savings5

Batteries5

Wiring and design5

Converters8

Quick conversions, right here.

Watts, amps, kWh and battery units. Type a number and read the answer, no page load.

Amps to watts kW to amps kVA to kW mAh to Wh Ah to Wh Watts to kWh

Watts to amps

W
12.50 A
I = P ÷ V = 1500 ÷ 120

The rules change at the border.

The 30% federal credit for homeowners ended on 31 December 2025.

Savings now depend on your state: net metering rules, state rebates and sales or property tax exemptions. Leases and power purchase agreements can still pass on a business credit through the installer.

Net metering calculator Solar tax credit 2026, explained

How a result is made, step by step.

  1. 1

    Your inputs

    Address, usage and equipment, in your own units.

  2. 2

    Location data

    Hourly sunlight from PVGIS or NREL for that exact spot.

  3. 3

    Open formula

    The equation and a worked example sit under the result.

  4. 4

    Standards check

    Limits from NEC, BS 7671 and IEC, named on the page.

  5. 5

    Sources and date

    Every tool links its key sources and shows when it was last checked.

New guides

All guides
What size wire for a 40 amp breaker: 8 AWG copper cable connected to a 40 A breaker

Wiring and electrical, 7 min read

What Size Wire for a 40 Amp Breaker?
Diagram of rooftop solar panels on a home feeding a two-way meter, with arrows showing solar exports to the grid and electricity imports back to the house

Savings, 10 min read

What Is Net Metering and How Does It Work for Solar?

Questions people ask first.

Still stuck? Ask the team

Are the SolarCalcLab calculators free?

Yes. Every calculator is free to use, with no sign-up and no limit on how many times you run it. The math runs in your browser, so the numbers you type stay on your device.

How accurate are the solar estimates?

The solar tools use measured sunlight for your location from PVGIS and NREL, typical system losses and the formula shown under each result. Treat the output as a planning estimate. Shading, panel temperature and wiring can move the real figure, so confirm a final design with a licensed installer.

How many solar panels does a typical home need?

It depends on how much power you use and how much sun you get. A home using 10,500 kWh a year in a spot that yields 1,400 kWh per kWp needs about 7.5 kWp, or 18 panels at 430 W. The how many solar panels calculator runs this for your own numbers.

Do the calculators work outside the United States?

Yes. The tools handle US, UK, Australian and German defaults, including AWG and mm² wire sizes, 120 V and 230 V mains, local electricity prices and the NEC, BS 7671 and IEC limits that apply in each country.

Where does the data come from?

Sun data comes from PVGIS and NREL, and electricity prices from the US EIA, Ofgem, the AER and Destatis. Each calculator names its sources and the date they were last checked. The full list is on the data sources page.