Solar Panel Calculator
Size a solar array from your daily energy use, peak sun hours and panel wattage, get the kW needed, panel count and expected production. Calculates in your browser.
Show the math
The array must cover your daily use after losses, across the available sun hours:
array kW = daily kWh ÷ (sun hours × (1 − losses))
panels = ⌈array W ÷ panel W⌉
Peak sun hours are the equivalent hours of full 1 kW/m² sunlight, typically 3–6 depending on location and season. All math runs in your browser.
What this does
A solar panel calculator sizes a PV array from your daily energy use, local peak sun hours, and panel wattage — giving the system kW, panel count, and expected production.
How to use it
- Enter your daily energy use in kWh.
- Set your peak sun hours.
- Enter the panel wattage.
- Read the array size and panel count.
How it works
Real systems lose roughly 15–25% to heat, wiring, and inverters, so the array is sized above raw demand. Production varies with season and shading.
array kW = daily kWh ÷ (sun hours × (1 − losses))
Understanding your result
The array is deliberately sized above your raw demand because real systems lose 15 to 25 percent to heat, wiring, and inverters, and production swings with season and shading. Size to your annual average rather than a single sunny day, and sanity-check the panel count against the roof area and orientation you actually have, since a perfect array that does not fit is no help.
Example
Using 30 kWh/day at 5 peak sun hours needs roughly a 7 kW array.
Sources & methodology
Last updated .
Frequently asked questions
How many solar panels do I need?
Divide daily kWh use by (peak sun hours \u00d7 (1 \u2212 losses)) to get the array size in kW, then divide by your panel wattage and round up.
What are peak sun hours?
The equivalent hours of full 1 kW/m\u00b2 sunlight per day \u2014 typically 3\u20136 depending on location and season, not the same as daylight hours.
Is my data stored?
No. Everything is calculated locally in your browser.
Related tools
Solar Payback Calculator
Work out how long a solar system takes to pay for itself from its cost, incentives, production and electricity rate, plus lifetime savings and ROI. Calculates in your browser.
Battery Storage Calculator
Size a battery bank from daily energy use and days of autonomy, allowing for depth of discharge and round-trip efficiency. Gives kWh and amp-hours. Calculates in your browser.
Off-Grid Load Calculator
Add up your off-grid appliances to find daily energy use, peak power and peak current at your system voltage \u2014 to size your inverter, battery and solar. Calculates in your browser.
Generator Sizing Calculator
Size a backup generator from your running and starting watts, accounting for the largest motor surge plus a safety margin. Calculates in your browser.