Solar tools

How many solar panels do I need?

Enter your location, your annual electricity use and the share you want to cover. The array size comes from long-term solar data for your own coordinate — the same model as the solar output calculator — and the panel count follows from the panel rating you choose.

How many solar panels does a home using 10,800 kWh a year need?

There is no single answer, because the number depends far more on where you live than on the panels. Covering 10,800 kWh a year needs roughly 12.7 kWp — about 32 panels of 400 W — where a kWp yields around 850 kWh a year, as it does in the UK and the Nordics, and roughly 6.4 kWp, about 16 panels, where a kWp yields around 1,700 kWh, as it does in the US Southwest. That is a factor of two for the same house. Enter your city above and the calculator replaces this range with your location’s actual long-term yield at your roof tilt and orientation. Note too that matching your annual total is not the same as being self-sufficient: production and consumption rarely line up month to month.

Enter your location and consumption

Panel count is not a fixed number: the same house needs roughly twice the array in northern Europe that it needs in the US Southwest. This tool sizes the array from long-term solar data for your own coordinate, using the same model as the solar output calculator.

Reference: array size for 100% annual offset

Illustrative specific yields spanning the realistic global range, 400 W panels, panel counts rounded up. These are reference bands for orientation only — the calculator above uses long-term data for your own coordinate rather than a band.
Typical setting	Specific yield	6,000 kWh/yr	10,800 kWh/yr	15,000 kWh/yr
Northern Europe, UK, Nordics	850 kWh/kWp	7.1 kWp · 18	12.7 kWp · 32	17.6 kWp · 45
Central Europe, Pacific Northwest	1000 kWh/kWp	6.0 kWp · 15	10.8 kWp · 27	15.0 kWp · 38
Northern US, southern Canada	1200 kWh/kWp	5.0 kWp · 13	9.0 kWp · 23	12.5 kWp · 32
Southern Europe, southern US	1450 kWh/kWp	4.1 kWp · 11	7.4 kWp · 19	10.3 kWp · 26
US Southwest, inland Australia	1700 kWh/kWp	3.5 kWp · 9	6.4 kWp · 16	8.8 kWp · 23

Why panel count is the wrong place to start

Panel count is the last step, not the first. What you actually need is a number of kilowatts-peak, and that follows from two things: how much energy you want to cover, and how much energy one kWp produces where you live. Panel wattage only decides how many physical modules make up that kWp — at 400 W it takes ten panels per 4 kWp, at 500 W it takes eight, and the production is the same.

This is also why quoted panel counts travel badly. A rule of thumb picked up from an American article assumes a specific yield that simply does not exist in northern Europe, and applying it there undersizes the array by close to half.

Annual offset is not the same as independence

An array sized to match your annual consumption will overproduce in summer and underproduce in winter. What that is worth depends entirely on your tariff: under full retail net metering the summer surplus effectively banks against winter, while under an export tariff paying a fraction of the retail rate the same surplus is worth far less and a smaller array often makes better financial sense.

Check the monthly figures in the calculator against your own monthly bills before deciding on size. If your winter consumption is dominated by electric heating, an annual-match array will still leave large winter imports.