Power sources really aren't the main issue when digging holes; I mean, it's basically the least of your problems. How do you keep your digging implement sharp, essentially when hitting harder stuff? How do you deal with whatever it is you dig up? How do keep your hole stable? How do you get water and other stuff out? How do you deal with the heat further down?
... it's kinda ironic the one problem modern technology can solve fairly easily was used to "solve" their hole digging issue in a weird way ^^