GasCurrently supplies around 15% of the global electricity demand. 3.9 - 4.4 Cents/kW-h Gas-fired plants and generally quicker and less expensive to build than coal or nuclear, but a relatively high percentage of the cost/KWh is derived from the cost of the fuel. Due to the current (and projected future) upwards trend in gas prices, there is uncertainty around the cost / KWh over the lifetime of plants. Gas burns more cleanly than coal, but the gas itself (largely methane) is a potent greenhouse gas. Some energy conversions to calculate your cost of natural gas per kwh. 100 cubic feet (CCF)~ 1 Therm = 100,000 btu ~ 29.3 kwh. CoalCurrently supplies around 38% of the global electricity demand. 4.8 - 5.5 Cents/kW-h Increasingly difficult to build new coal plants in the developed world, due to environmental requirements governing the plants. Growing concern about coal fired plants in the developing world (China, for instance, imposes less environmental overhead, and has large supplies of high sulphur content coal). The supply of coal is plentiful, but the coal generation method is perceived to make a larger contribution to air pollution than the rest of the methods combined. NuclearCurrently supplies around 24% of the global electricity demand. 11.1 - 14.5 Cents/kW-h Political difficulties in using nuclear in some nations. Risk of widespread (and potentially lethal) contamination upon containment failure. Fuel is plentiful, but problematic. Waste disposal remains a significant problem, and de-commissioning is costly (averaging approximately US $320MM per plant in the US).

A reason many energy experts are looking at what tidal may be able to contribute, compared to other renewable sources like wind power, is that the amount of energy generated from a power-generating turbine is proportional to the density of the fluid that flows back and forth – meaning a water turbine has several hundred times the power of an air turbine.

Seawater is denser than air; a lot denser – 832 times to be exact, meaning an 8 knot tidal current has more energy than a 380kph wind. This means a wave farm of ‘sea snakes’ – devices built by Scotland’s Pelamis Wave Power – covering half a square mile of ocean could produce 30 MWh of power, which is estimated to be enough for 20,000 homes. A wave farm covering 472 square miles could supply 24 million households – enough for the entire UK.

Records of ocean power conversion date back to 900A.D. where the power of tidal movement was used to grind grains. The first modern commercial tidal power was installed off the coast of St. Malo, in Northern France. Installed in 1965, it has been operating continuously since then, producing 240 MW with every tide.

While there are non-tidal based ocean currents such as the Gulf Stream, those are usually too diffuse to be a practical energy source. The tides cause water to flow inwards from the ocean twice a day during flood tides, and outwards during ebb tides. Additional monthly and annual cycles vary the strength of this current on a monthly and annual basis. Narrow and shallow constrictions produce the fastest and most powerful movements, whose energy can be captured using submerged turbines.