The chart shows insolation on a flat surface by hour-of-day for the selected date. During the course of the day, insolation increases and then decreases as the sun climbs higher and then lower.

The flat surface could be:

• A lawn or driveway
• A patio
• An interior floor or table under a skylight

What does it tell me?

• How the amount and intensity of sunlight varies through the day
• What time of day has the most intense light
• How the selected day compares with mid-summer and mid-winter

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.