Nuclear

Micro nuclear plants, like this one from Toshiba: Toshiba 10MW nuclear plant

Pebble Bed Reactor, safer, simpler and more efficient type of fission reactor. At least one prototype currently operating.

Russian Floating Nuclear Reactors "...On April 15, 2007 the construction of the first floating Nuclear Power Station, Academician Lomonosov, started at the Sevmash Submarine-Building Plant in Severodvinsk..." The Lomonosov will carry 2 modified KLT-40S nuclear reactors (ice breaker type). Each vessel would then provide up to 70 MW of electrical or 300 MW of heat energy that are enough for a city with population of 200,000 people. It could also be modified as a desalination plant producing 240,000 cubic meters of fresh water a day.

Uranium extracted from seawater

"...It now seems quite certain that uranium can be extracted from the ocean at well below $1000 per pound ($100-800/lb in recent analysis of Japan's extraction process) and there is even some optimism that it can become competitive at current market prices ($65/lb). It is clear, then, that uranium from seawater must be considered as a completely acceptable fuel for breeder reactors, contributing less than 1% to the cost of electricity. In terms of fuel cost per million BTU, even at $400/lb the uranium cost is only 1.1 cents.

Seawater contains 3.3×10–9 (3.3 parts per billion) of uranium, whence the 1.4×10**18 tonne2 of water in the oceans contains 4.6×10**9 tonne of uranium. The energy content of uranium burned in a breeder reactor is 1 MW day/g, or 1000 GW day/tonne; at 37% efficiency, readily achievable in a breeder reactor, this is 1.0 GWe yr/tonne (GWe = GW of electricity). All of the world’s present electrical usage, 2325 GWe [372 GWe of nuclear make up 16% of world electrical supply] , could therefore be supplied by the uranium in seawater for (4.6×10**9/2325) = 1.98 million years.

At ten times the power level, it would last 198,000 years and at one hundred times it would be 19,800 years.

Rivers bring 3.2×10**13 tonne/yr of water into the oceans, and their uranium content averages 1.0×10–9 (one part per billion), whence a total of 3.2×10**4 tonne/yr of uranium enter the oceans from this source.

We can withdraw 16 000 tonne/yr of uranium from seawater continuously for hundreds of millions of years. This is enough to produce 16 000 GWe or 480 quadrillion BTU per year, which is 6 times the world’s present electricity usage, and almost the world’s present total energy consumption..."