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Construction & Homeenergy

Solar Panel Sizing Calculator

Solar array sizing from daily consumption. Peak sun hours are the equivalent hours at full rated irradiance, not hours of daylight, which is the input people get wrong by a factor of two.

Also called: solar system size calculator, how many solar panels.

kWh
%
W
m²
System size
3

3 kW to cover 12 kWh a day at 5 peak sun hours with 20% losses. That is 6 panels of 550 W over 15.6 m², costing about 1,65,000 and paying back in 4.71 years. Peak sun hours are equivalent hours at full irradiance, not hours of daylight.

Panels needed
6
Roof area needed
15.6
Installed cost
1,65,000
Annual generation
4,380
Annual saving
35,040
Payback period
4.71
On peak sun hours
Peak sun hours are equivalent hours at full irradiance, not hours of daylight.
On regulation
This is a sizing estimate. The applicable wiring or building regulation governs and overrides any figure here.
How this is calculated
Method and background

How this is calculated

A panel is rated at 1,000 watts per square metre of irradiance, and peak sun hours are how many hours of that a location receives in energy terms per day. A place with twelve hours of daylight might have five peak sun hours. System losses of fifteen to twenty-five percent cover inverter efficiency, temperature derating, wiring, soiling and mismatch, and panels perform worse hot than cold, which is why a hot climate does not gain as much as its sunshine suggests.

peak sun hours are the equivalent hours at full rated irradiance, not hours of daylight
E
Daily energy
h
Peak sun hours
L
System losses

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

a 12 kWh a day household

Daily consumption
12 kWh
Peak sun hours
5
System losses
20%
Panel rating
550 W
Area per panel
2.6 m²
Installed cost per watt
55
Electricity rate
8

System size3

12 / (5 x 0.8); 3000/550 rounded up

Open this example

no losses needs a smaller array

Daily consumption
12 kWh
Peak sun hours
5
System losses
0%
Panel rating
550 W
Area per panel
2.6 m²
Installed cost per watt
55
Electricity rate
8

System size2.4

boundary

Open this example

Method and limits

What it assumes

  • Unshaded panels at a reasonable tilt and orientation.

What it deliberately does not model

  • Shading is not linear: one shaded panel can pull down a whole string without optimisers.
  • Peak sun hours vary by season, so a system sized on the annual average underperforms in winter.
  • Net metering rules decide whether excess generation is worth anything.

Formula version 1.0.0 · definition 1.0.0 · India · Report a problem with this calculator

Frequently asked questions

What are peak sun hours?
The equivalent hours of full rated irradiance, not hours of daylight. Twelve hours of daylight might be five peak sun hours, and using the daylight figure oversizes by more than double.
Why are system losses so high?
Inverter efficiency, temperature derating, wiring, soiling and panel mismatch all take a share. Fifteen to twenty-five percent is normal and not a sign of a bad system.