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Tidal energy is one of the oldest forms of energy used by humans. Indeed, tide mills, in use on the Spanish, French and British coasts, date back to 787 A.D.. Tide mills consisted of a storage pond, filled by the incoming (flood) tide through a sluice and emptied during the outgoing (ebb) tide through a water wheel. The tides turned waterwheels, producing mechanical power to mill grain. We even have one remaining in New York- which worked well into the 20th century.

Tidal power is non-polluting, reliable and predictable.Tidal barrages, undersea tidal turbines - like wind turbines but driven by the sea - and a variety of machines harnessing undersea currents are under development. Unlike wind and waves, tidal currents are entirely predictable.

A tidal range of at least 7 m is required for economical operation and for sufficient head of water for the turbines

Tidal turbines look like wind turbines. They are arrayed underwater in rows, as in some wind farms. The turbines function best where coastal currents run between 3.6 and 4.9 knots (4 and 5.5 mph). In currents of that speed, a 49.2-foot (15-meter) diameter tidal turbine can generate as much energy as a 197-foot (60-meter) diameter wind turbine. Ideal locations for tidal turbine farms are close to shore in water 65.5–98.5 feet (20–30 meters) deep

Method Cents/kW-h Limitations and Externalities WindCurrently supplies approximately 1.4% of the global electricity demand. Wind is considered to be about 30% reliable. 4.0 - 6.0 Cents/kW-h Wind is currently the only cost-effective alternative energy method, but has a number of problems. Wind farms are highly subject to lightning strikes, have high mechanical fatigue failure, are limited in size by hub stress, do not function well, if at all, under conditions of heavy rain, icing conditions or very cold climates, and are noisy and cannot be insulated for sound reduction due to their size and subsequent loss of wind velocity and power. GeothermalCurrently supplies approximately 0.23% of the global electricity demand. Geothermal is considered 90-95% reliable. 4.5 - 30 Cents/kW-h New low temperature conversion of heat to electricity is likely to make geothermal substantially more plausible (more shallow drilling possible) and less expensive. Generally, the bigger the plant, the less the cost and cost also depends upon the depth to be drilled and the temperature at the depth. The higher the temperature, the lower the cost per kwh. Cost may also be affect by where the drilling is to take place as concerns distance from the grid and another factor may be the permeability of the rock. HydroCurrently supplies around 19.9% of the global electricity demand. Hydro is considered to be 60% reliable. 5.1 - 11.3 Cents/kW-h Hydro is currently the only source of renewable energy making substantive contributions to global energy demand. Hydro plants, however, can (obviously) only be built in a limited number of places, and can significantly damage aquatic ecosystems. SolarCurrently supplies approximately 0.8% of the global electricity demand. 15 - 30 Cents/kW-h Solar power has been expensive, but soon is expected to drop to as low as 3.5 cents/kW-h. Once the silicon shortage is remedied through alternative materials, a solar energy revolution is expected.

Tide 2 - 5 Cents/kW-h Blue Energy's tidal fence, engineered and ready for implementation, would provide a land bridge (road) while also generating electricity. Environmental impact is low. Tides are highly predictable.

Method Cents/kW-h Limitations and Externalities 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.

The geothermal energy process extracts heat from the Earth for the purpose of generating electricity to power homes. Most development in this area is concentrated at where tectonic plates meet, such as the western coasts of North and South America, the Mediterranean and east coast of Africa and East Asia.

The U.S. could have as much as 10 gigawatts of geothermal power at its disposal if current projects under development are completed, according to a new report.

U.S. geothermal infrastructure manages 3,100 megawatts, the new projects could add an additional 7,100 megawatts, or 7 gigawatts, of energy output.

BC Hydro’s 2002 Green Energy Study for BC estimated the realistic energy potential for tidal current energy generation in BC to be 20 TWhrs/year. The estimated cost was 11 cents/kWhr for a large (800 MW) site, and 25 cents/kWhr for a small (43 MW) site. The best sites are in the Strait of Georgia and Johnstone Strait, which are both relatively close to the main centers of consumption.

A fuel cell converts the chemical energy in hydrogen and oxygen into direct current electrical energy by electrochemical reactions. Fuel cells are devices that convert hydrogen gas directly into low-voltage, direct current electricity. The cell has no moving parts.

The process is essentially the reverse of the electrolytic method of splitting water into hydrogen and oxygen. In the fuel cell, the cathode terminal is positively charged and the anode terminal is negatively charged. These electrodes are separated by a membrane. Hydrogen gas is converted into electrons and protons (positive hydrogen ions) at the anode. The protons pass through the membrane to the cathode, leaving behind negatively charged electrons. This creates a flow of direct current electricity between the terminals when connected with an external circuit. This current can power an electric motor placed in this circuit. The hydrogen ions, electrons, and oxygen combine at the cathode to form water, the only byproduct of the process.

Even normal

gasoline vehicles can operate on a 10 percent ethanol blend with no problems. Diesel cars and trucks can run on biodiesel, though older models may need to have their fuel lines and gaskets replaced with modern synthetic materials, since biodiesel is a solvent

they generate electricity with very little pollution—much of the hydrogen and oxygen used in generating electricity ultimately combine to form a harmless byproduct, namely water.

Scientists and inventors have designed many different types and sizes of fuel cells in the search for greater efficiency, and the technical details of each kind vary

in general terms, hydrogen atoms enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The hydrogen atoms are now “ionized,” and carry a positive electrical charge. The negatively charged electrons provide the current through wires to do work. If alternating current (AC) is needed, the DC output of the fuel cell must be routed through a conversion device called an inverter.

Like electricity, hydrogen is a secondary source of energy. It stores and carries energy produced from other resources (fossil fuels, water, and biomass).

ydrogen is the simplest element. Each atom of hydrogen has only one proton. It is also the most plentiful gas in the universe. Stars like the sun are made primarily of hydrogen. The sun is basically a giant ball of hydrogen and helium gases. In the sun's core, hydrogen atoms combine to form helium atoms. This process — called fusion — gives off radiant energy.

Hydrogen gas is so much lighter than air that it rises fast and is quickly ejected from the atmosphere. This is why hydrogen as a gas (H2) is not found by itself on Earth. It is found only in compound form with other elements. Hydrogen combined with oxygen, is water (H2O). Hydrogen combined with carbon forms different compounds, including methane (CH4), coal, and petroleum.

Flash steam plants are the most common type of geothermal power plants in operation today. They use extremely hot water (above 300 degrees F (149 degrees C)), which is pumped under high pressure to the generation equipment at the surface. The hot Estimated subterranean temperatures at a depth of 6 kilometers.water is vaporized and the vapor in turn drives turbines to generate electricity

idal turbines are very much like an underwater windmill where the blades are driven by consistent, fast-moving currents.  The submerged rotors harness the power of the tidal streams to drive generators, which in turn produce electricity. Water is 832 times denser than air so consequently tidal turbine rotors can be are much smaller than wind turbine rotors generate equivalent  amounts of electricity, and they can be deployed much closer together. Devices that harness tidal stream energy present a unique set of engineering challenges in terms of design, installation and maintenance. During operation, the force of the tidal flow in Strangford Lough is equivalent to a 345 mph wind generating a 100 tonnes of thrust on the rotors. The unique SeaGen design allows capture of the maximum amount of tidal energy whilst keeping maintenance and connectivity costs low.

Tidal turbines are very much like an underwater windmill where the blades are driven by consistent, fast-moving currents.  The submerged rotors harness the power of the tidal streams to drive generators, which in turn produce electricity. Water is 832 times denser than air so consequently tidal turbine rotors are much smaller than wind turbine rotors generate equivalent  amounts of electricity, and they can be deployed much closer together. Devices that harness tidal stream energy present a unique set of engineering challenges in terms of design, installation and maintenance. During operation, the force of the tidal flow in Strangford Lough is equivalent to a 345 mph wind generating a 100 tonnes of thrust on the rotors.

idal power can be harnessed using a barrage (dam) built across an estuary that captures the potential energy generated by the change in height (or head) between high and low tides. As the tide goes in and out, the water flows through tunnels in the dam. The ebb and flow are used to either turn a water turbine or compress air through a pipe that then turns a turbine, which generates electricity. Tidal Fences and Turbines Tidal fences and turbines can also be used to capture tidal power. Tidal fences are turbines that operate like giant turnstiles, while tidal turbines are similar to wind turbines. In both cases, electricity is generated when the turbines are turned by the tidal currents that occur in coastal waters. Ocean currents generate relatively more energy than wind (air currents) because ocean water has a higher density than air and therefore applies greater force on the turbines.

Wave energy is about using the energy of ocean waves for producing electrical current. It is a renewable energy resource and often confused with Tidal Power.

Wave energy is considered a form of hydropower, although it is the wind blowing over the surface of the ocean causing waves. So in many ways, wave energy is also wind energy - with all the pros and cons.

Biofuels are basically any fuel that can be burned in air to produce heat that is produced by biological means, normally by plant growth. Currently the most prominant biofuels are ethanol and bio-deisel because these can be burned in existing internal combustion engines and are thus a direct replacement for oil. The most important biofuel historically is wood with oth

Biofuels are currently cheaper than oil although this is only because we are seeing very high oil prices at the moment. Under what might be termed more 'normal' market conditions, biofuels lack any meaningful price advantage. Biofuel production is very labor intensive and very land intensive. Production of ethanol from sugar cane was pioneered by the Brazilians in the 1970's as a solution to an oil import bill they could ill afford. It worked for them as they have plenty of land they can convert to growing sugar cane and at the time, plenty of cheap labor with which to harvest it.

he simple truth is the world does not have enough land to produce anywhere near the quantity of biofuels we need to make any dent in our oil consumption. They are only in fashion now oil prices are high and it is cost effective to produce them. Sooner or later food prices will rise to such a point that biofuel production will cease to be economic.