A fueled generator provides a constant supply of power as long as it is fueled, so you don't have to worry about the sun or the wind.
It is useful in the early game when you can't afford renewable energy or if you can't make batteries yet. Its inventory holds 75 wood, refueled by haulers. It consumes 22 wood every day, so a fully fueled generator will provide power for about 3 days 9 hours. It provides heat, but less than a campfire.