Power

The future of energy is resolving itself to a new level of clarity. We certainly need to work on the "zoom" to see exactly the mechanisms that will get us to the future, but the horizon is now visible.

To state the obvious, the energy of the future is electricity. Other mechanisms will also coexist (see below), but not predominantly. Everything from power plants to factories to cars to home heat will become electric. Because of this demand will skyrocket from the current 500 exajoules of primary energy per year to perhaps 2000 EJ by this time next century. So-called "energy intensity" (energy production/economic output) will continue to decline in industrialized countries, but overall demand will continue to increase. In the 3rd world, unfortunately, both will rocket skyward for a half century. Conservation will slow the growth perhaps but even the most asceticly stringent views could not suggest that we will reduce overall demand as billion after billion people move from subsistence to industry.

For the next 20 to 40 years, new energy generation will be nuclear. It's there, it's safe, it's cheap. This will give breathing room for R&D to successfully develop methods of harvesting energy from a very broad range of geological sources (see below). Somewhere around 2050, we'll wake up to find that geo sources account for more than 50% of total generation. At that point, the only talk about carbon- or nuclear-sourced generation will be how fast these dinosaurs can be killed with economic efficiency.

The bigger story is energy sourced from the earth and the sky. In a sense, this is the next evolution in conservation, since currently the universe wastes (well, expends anyway) inconceivable amounts of energy. Our long-term focus will be on harnessing these joules. Or would that be jewels? To quote Wikipedia (whence all good info eventually alights) the amount of solar energy intercepted by Earth every minute is greater than the energy produced by fossil fuels each year. The earth's core alone generates an incredible 140,000,000 EJ a year. It is estimated that this could easily translate into potential of 5,000 harnessed EJ of geothermal energy per year using currently-existing technologies.

Let me put this overall theory into pictures. As these are simply theories, the numbers are indicative.

Power Sources (first tab) ... and estimates (second tab):

Further reading:
http://www.fao.org/DOCREP/006/AD550E/ad550e00.pdf
http://secondlawoflife.wordpress.com/category/power-generation/
http://ies.lbl.gov/iespubs/42949.pdf
http://web.mit.edu/space_solar_power/

and, as always: http://en.wikipedia.org/wiki/Renewable_energy