How many solar panels do I need? Plug-in kit size calculator
Find the kit size and number of panels needed to cover part of your home’s electricity use.
Plug-in solar kits are small, so they usually cover only part of a home’s electricity use. Enter your monthly usage from your bill and the share you would like solar to cover. Every assumption is explained below the calculator.
Advanced assumptions
How the calculator works
- Daily use = monthly kWh × 12 ÷ 365. For example, 900 kWh a month ≈ 29.6 kWh a day.
- Daily solar target = daily use × the share you want to cover.
- Kit size needed = daily target ÷ (peak sun hours × system efficiency).
- Panels = kit size ÷ wattage of one panel, rounded up to a whole panel.
The assumptions, explained
| Input | Default | Why |
|---|---|---|
| Monthly use | 900 kWh | A placeholder only. Use the kWh figure from your own bill. |
| Share to cover | 10% | Plug-in kits are small, so covering part of your use is a realistic starting point. |
| Panel wattage | 400 W | A common size for a single panel. Use the rating from the kit listing. |
| Peak sun hours | 4.5 | A middle-of-the-range starting point. Check your real value with PVWatts. |
| System efficiency | 80% | Covers typical inverter, temperature, wiring and soiling losses. |
Frequently asked questions
Can a plug-in kit power my whole home?
Usually not. Plug-in kits are designed to supply part of your everyday use, such as the fridge, router and other appliances that run during the day.
Why does the calculator round up?
You can only buy whole panels, so the calculator rounds up to the next panel. That is why the share covered can be a little higher than your target.
Should I size the kit for summer or winter?
Use a yearly average for sun hours and usage. Production is higher in summer and lower in winter, so a yearly average gives the most realistic size.
Is this electrical advice?
No. It is a simple estimate. Follow the manufacturer’s instructions and local code, and ask a licensed electrician about your circuits.