Solar System Size Calculator
Fill in the values and the answer updates as you type.
How the Solar System Size Calculator works
Array size (kW) = daily use ÷ (peak sun hours × (1 − losses)). Peak sun hours are the equivalent hours of full-strength sunlight your location gets per day. The panel count is rounded up so the array covers your use. Shading, roof angle, and seasons change real output, so treat this as a first estimate. Example: with the default values, required array size comes to 3.33 kW.
Inputs and results
The Solar System Size Calculator takes 4 inputs and gives 4 results.
What you enter
- Daily electricity use (kWh) — starts at 12.
- Peak sun hours per day (h) — starts at 4.5.
- System losses (inverter, wiring, heat) (%) — starts at 20.
- Panel rating (W) — starts at 400.
What you get
- Required array size (kW)
- Panels needed
- Installed array size (kW)
- Expected daily output (kWh)
Example: Solar System Size Calculator with the starting values
With daily electricity use 12 kWh, peak sun hours per day 4.5 h, system losses (inverter, wiring, heat) 20 % and panel rating 400 W, the calculator returns:
| Required array size (kW) | 3.33 |
|---|---|
| Panels needed | 9 |
| Installed array size (kW) | 3.6 |
| Expected daily output (kWh) | 13 |
Change any value above and the results update straight away.
Solar System Size Calculator FAQ
How do I use the Solar System Size Calculator?
Enter daily electricity use, peak sun hours per day, system losses (inverter, wiring, heat) and panel rating in the fields, then read required array size (kw), panels needed, installed array size (kw) and expected daily output (kwh) in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Solar System Size Calculator calculate?
Estimate the solar array size and number of panels your home needs. It returns required array size (kw), panels needed, installed array size (kw) and expected daily output (kwh) from the 4 values you provide.
What values does the Solar System Size Calculator start with?
It opens with daily electricity use 12 kWh, peak sun hours per day 4.5 h, system losses (inverter, wiring, heat) 20 % and panel rating 400 W so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Solar System Size Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Solar System Size Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.