The chart shows insolation on a tilted surface by hour-of-day for the selected date. Depending on the orientation and slope of the surface (e.g. a roof or slope in a garden), the insolation will vary significantly across the day.

What does it tell me?

• How the amount and intensity of sunlight varies through the day
• e.g. At what time will the sun stop shining through a skylight?

Note: the chart does not account for shade from structures or objects (e.g. buildings or trees) or cloud cover.

Insolation is a measure of the power of sunlight reaching a surface. It is usually given for a period of time, e.g. per hour, per day, per month.

Horizontal insolation is a good measure of the overall sunlight potential for the location. The direction in which you are facing does not affect its value.

Generally, you will see higher 'horizontal' (i.e. flat ground) insolation in summer months, and lower values during winter months. Latitudes closer to the equator and those lying at higher elevations typically see higher insolation values.