What Is Solar Irradiance and Why Does It Matter?

Solar irradiance is the measure of how much sunlight energy falls on a surface per unit area — expressed in watts per square metre (W/m²). For solar panel owners and anyone planning a solar installation, the most useful version of this measurement is Peak Sun Hours (PSH).

Peak sun hours represent the number of hours per day when solar irradiance averages 1,000 W/m² — the standard condition at which solar panels are rated. A city with 5 peak sun hours means a 1kW solar panel will generate approximately 5 kWh of electricity per day. It is the single most important number when sizing a solar system or estimating savings.

Our solar irradiance checker uses long-term average data for 50+ cities worldwide — accounting for typical cloud cover, seasonal variation, and local weather patterns — to give you realistic, reliable estimates rather than ideal-condition figures.

How to Use the Solar Irradiance Checker

Example: A 5kW system in Mumbai (5.5 peak sun hours) generates 5 × 5.5 = 27.5 kWh per day — roughly 825 kWh per month.

Compare: the same 5kW system in London (2.8 hrs) generates just 14 kWh/day — showing how dramatically location affects solar economics.

Peak Sun Hours — How Do Cities Compare?

Solar potential varies enormously by location. Desert cities near the equator lead the world in solar irradiance, while high-latitude cities in northern Europe receive significantly less. Here is how major cities stack up:

Solar Irradiance — Common Questions

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