A funny thing is modification or further development of a technology originally meant for fossil fuel production would potentially be a great form of clean energy. That would be using deep boreholes to tap into geothermal energy, and done using large scale drilling rigs. But it is a bit complicated to implement, conflicts with the other use of the technology, so nobody really has invested in it. It could likely go a long way into electrical power production if it were seriously looked into. (And not quite the same as open injection or drilling into existing geysers for geothermal - which both have their own share of issues. I'm thinking more along the lines of closed loop systems that recirculate the heat transfer fluid.)