Geothermal can be very practical very fast, solve our energy problems in just a few decades and keep us going for centuries. If you are interested, there's a comprehensive study on the subject: "The Future of Geothermal Energy" (2007) by the MIT.
Except it won't be allowed to happen: it's a lot like fracking, except it's long term, no instant jackpot, no support by deep-pocketed oil companies. Enough to scare politicians and investors away for the time being.
By the way, geothermal is significantly better than solar on two counts: it's constant 24 hours a day and 365 days a year (which means no coal power to back it up, no batteries, no nothing) and it doesn't require thousands of square miles.
To be fair, it has one downside to PV, and that's that it requires large amounts of water, considerably more than the equivalent fossil-fuel power plant.