Phil, my reply was referenced to the potential development of non-nuclear, sustainable, cheap and safe energy sources.
While having a very occasional game in a very small group while at uni in 1996 we hit on the idea of 'magma milking'.
How it works is that one finds a volcano and sinks a shaft to tap the magma.
Salt water is then pumped in to produce steam and of course salt.
Salt is extracted and used for other needs, while steam powers the turbines.
There was a LOT of steam, so eventual condensation also produces large amounts of desalinated water, which in that particular adventure was the shortage on a recently opened planet, and out contract was to provide the recently established colony with water. 'Trucking' the water in proved expensive.
The planet was somewhat Earthlike (somewhat less water as I remember), but geography was such that habitable areas were relatively lacking in consumable water (including irrigation)
On Earth there are several regions with volcanic activity reasonably close to surface.
In fact in the United States such a project would be in the interests of national security because if the Yellowstone Caldera ever blew, the West Coast and large parts of the Mid-West can be written off for habitability for about a century.
Siphoning off energy from that magma 'ball' would comfortably power everything in North and South Americas for several thousand years without need for other sources of power production.
In Russia the Kamchatka region could power Russia and all of East Asia for a similar period.
The principal problems are water and salt recycling back into the echo-sphere and availability of superconductors to actually transmit the power into the power grids efficiently.
Greg