In the land of the midnight sun we use just that, the sun, as the main power supply for our riggs. During the period from early may to late September we will get all our energy from the sun.
We are in the mist of constructing a solar farm twice the size we need. Why? So that we can trade our execs solar energy during the bright summer days for water powered energy during the dark winter month (and as a backup)
The cold weather is also to our benefit when it comes to cooling the riggs there by reducing the need for power and maitenens