What is the ultimate energy source for most wind?

Hint: As a first step, one could recall how wind occurs, that is the basic definition of wind. Thereby, you will be able to get the first step to your answer, that is you will understand heat causes the pressure difference which results in wind. Now the ultimate source of wind energy would be the source of this heat.

Complete step-by-step solution:
In the question, we are asked about the ultimate energy source for most wind. Let us first recall what the cause of wind is. You may remember that uneven atmospheric pressure on the Earth is the cause that results in wind. This uneven atmospheric pressure further creates a pressure gradient and this later creates pressure gradient force.
What you have to understand here is the fact that this uneven atmospheric is the Heat. It is also observed that, for a constant volume under consideration, increasing the atmospheric heat further increases the pressure. This is basically the application of Gay Lussac’s law.
Now you may recall that the Sun is the source that heats the surface and thereby the air above the surface also gets warm and also moves up to the atmosphere.
Therefore, we could make this conclusion that the Sun is the ultimate source of wind energy.

 Note: A partial vacuum would be created as the result of the warm air being moved up. Now the cooler air would come so as to fill this void thus created. So this induced flow of air over earth’s surface is termed as wind. The conversion of wind energy to more useful forms of energy is termed as wind power.