Because the earths surface made of different types land and water,it absorbs the suns heat at different rates. One example of this uneven heating can be found in the daily wind cycle.
And another thing about wind energy is. During the day the air above the land heats up faster then the air over water.
The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place creating wind. At night, the winds are reversed because the air cools more rapidly over land then over water. And