5km drilling is not that excessive, the deepest is well over 20km. The cost, on the other hand, will be massive. This is the main reason why the plentiful Geothermal resources around the UK are not taken advantage of.
I worked for Southampton Geothermal for 10 years. The well is 1.8km deep. The heat is in the form of hot water which is simply pumped out, filtered, passed through a heat exchanger and then dumped into the estuary. The 'secondary water', after taking the heat from the geothermal water, was then pumped around Southampton through 23km of buried pipe work to various buildings. Basically, it's as simple as that.
The original well was drilled in the early 80's by the Council/Government who were actually looking for oil. They found Hot Water instead and capped it off.
The Southampton resource is relatively small, the water has to be lifted the last 600 meters and rely's on a turbine pump installed in the well at that depth. The water reaches surface at around 76 Degrees C but the rate of withdrawal is limited to about 20lts per second as the temperature drops if you exceed this. (That produces around 1 MW of heat). It's also too small to make recycling the waste water by pumping it back down an option. The cost of a 2nd well and the temperature reduction this would result in makes it a non runner.
Unfortunately, the turbine pump (600 meters down the well) has worn out. It now costs more in electricity to run the pump that the value of the heat it produces. I looked into the costs of replacing the pump years ago. This would have required a drilling rig type set up to withdraw the pipes to reach the pump and was proved to be non-viable.
A real shame.
Southampton Airport are toying with the idea of constructing their own Geothermal heating scheme as they sit over the same heat resource. Not sure the idea will be viable though, due to the drilling costs and the associated plant required for such a scheme. Also, they would have to be sure they make full use of the heat 24hrs a day, every day.
Hot rocks is a different story though. A higher temperature means more heat per volume of water used. As long as you are guaranteed to be able to use the energy, it is a winner. The steam can run generators to produce electricity which can be put straight into the grid. The problem being the very low value of night time electricity. The heat also needs to be used as electricity production alone will probably not pay for itself. The problem is guaranteeing the heat is used 24hrs a day, 365days a year.