Q. Where does Neptune get most of its energy?

A. From it's extremely hot interior

That is somewhat correct.

Explanation:

The energy for such high-speed winds and ever-changing clouds is not coming from the Sun. Indeed, Neptune radiates 2.6 times as much energy as it absorbs from the Sun. Like Jupiter and Saturn, Neptune appears to have an internal heat source and so it radiates more than twice as much energy as it receives from the Sun.