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

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

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 lists its data sources and the date they were last checked.