Solar Panel Count

Free Solar Panel Count calculator with clear step-by-step results.

About Solar Panel Count

Sizes an array from consumption rather than roof space. Specific yield - the kilowatt-hours a kilowatt-peak produces annually in your location - is derated for shading and orientation, and the required capacity is divided by panel rating and rounded up to whole modules.

Formulas

Required capacity

kWp = consumption x offset target / (specific yield x (1 - shading loss))

Panels required

Panels = ceil(required kWp x 1000 / panel watts)

Worked example

With the default values below, Solar Panel Count returns Panels required of 10. Change any input above and every figure here is recalculated in your browser.

Inputs used

Annual electricity consumptionminimum 1 kWh: 4,800 kWh
Share of consumption to offsetaccepts 1–150 %: 80 %
Specific yield for your locationminimum 200 kWh/kWp/year: 1,050 kWh/kWp/year
Panel ratingminimum 50 W: 430 W
Shading and orientation lossaccepts 0–60 %: 8 %

Results

Panels required: 10 panels
System size: 4.300 kWp
Expected annual generation: 4,154 kWh
Consumption actually offset: 86.5% %

Step by step

1Values used
2Required capacity
3Panels required
4Panels required= 10 panels
5System size= 4.300 kWp
6Expected annual generation= 4,154 kWh
7Consumption actually offset= 86.5 %

Assumptions and limits

The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What specific yield applies to me?

Roughly 750-950 kWh/kWp in northern Europe, 1,100-1,400 in southern Europe and the northern US, and 1,500-1,800 in desert climates. National solar irradiance tools give a site-specific figure.

Why not offset 100% of consumption?

Because generation and consumption are out of phase. Without storage or a generous export tariff, oversizing simply exports more energy at a low price.