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It was used in the watermills along the shores of England during the Roman age and also used along the shores of France and Spain. This period was around 900 AD. The water rising from the tides was impounded in barrages and it was allowed to flow through waterwheels and other energy capturing devices thus capturing the energy and converting it into useful work used to grind grains and produce flour. The first tidal mill in the US was built in Salem, MA in 1635.

Day and night, the vast waters of the ocean press and recede along the shorelines of Earth’s every continent in accordance to the celestial movements of our planet in relation to the sun and the moon

Tidal power traditionally involves erecting a dam across the opening to a tidal basin. The dam includes a sluice that is opened to allow the tide to flow into the basin; the sluice is then closed, and as the sea level drops, traditional hydropower technologies can be used to generate electricity from the elevated water in the basin. Some researchers are also trying to extract energy directly from tidal flow streams.

Another form of ocean energy is called tidal energy. When tides comes into the shore, they can be trapped in reservoirs behind dams. Then when the tide drops, the water behind the dam can be let out just like in a regular hydroelectric power plant.

Tremendous potential exists for clean energy in waves and tides. Lockheed Martin Mission Systems and Sensors (MS2) is leveraging decades of experience in designing and developing maritime systems into wave and tidal power systems. To do that, we have strategic relationships with key wave and tidal power technology providers. They will provide the technology to convert waves and tides into energy, and MS2 will provide the expertise to help make the systems work in harsh ocean environments and scalable for large-scale production. Wave power generates electricity using special buoys that use the rising and falling of ocean waves to generate electricity. MS2 is partnering with Ocean Power Technologies, Inc. (OPT) and WaveBob LLC to develop their respective wave energy systems for use in future utility-scale power generation projects. MS2 provides its expertise in systems integration, lean manufacturing, and test and optimization analysis to enhance OPT's and Wavebob’s wave power generation technology to utility-scale. Tidal power generating systems use underwater turbines designed to capture the kinetic motion of ebbing and surging ocean tides to produce power. MS2 provides design and manufacturing support to Singapore-based Atlantic Resources Corporation (ARC), which is testing its tidal turbines at the European Marine Energy Centre in Orkney, Scotland. MS2 is also exploring related technologies that can be adapted to shallow and low-rate tidal flows.

A dam-like structure is constructed across an estuary to trap a high tide of water and then let it pass through turbines to generate electricity. The water flow can generate electricity on the falling tide only, or on the falling and rising tide.

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.

Although this source of energy shows some promise in terms of "clean", renewable energy there have been some roadblocks to widespread use of energy from the tides. This type of energy should not be put on the back burner even though there appears to be limited opportunities at this time

his is somewhat balanced out by long plant lives of 100 years for the actual barrage structure, and 40 for the equipment, as well as low operating costs.

An estimate is given by researcher Eleanor Denny. Denny estimates that in order for a facility to be profitable, its capital cost should be less than €530,000 (~$700,000 USD) per MegaWatt which with the current technology is not a realistic goal, meaning that so far the industry produces negative net benefits.50

Canada's Race Rocks site, where a single turbine generator converts 65 kW of energy, cost $4,000,000.54 This figure was met with $3,000,000 investment from project partner EnCana's Environmental Innovation Fund, and a grant of just under $1 million awarded to Pearson College and their partners in the project.

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.

Tidal energy is a form of hydropower that converts the energy of the tides into electricity or other useful forms of power. The tide is created by the gravitational effect of the sun and the moon on the earth. Tidal energy is therefore a predictable form of renewable energy, which can be harnessed in two forms:

Tidal power is a means of electricity generation achieved by capturing the energy contained in moving water mass due to tides. Two types of energy can be extracted: kinetic energy of currents between ebbing and surging, and potential energy from the difference in height (or head) between high and low water marks.

Tidal power schemes do not produce energy 24 hours a day. A conventional design, in any mode of operation, would produce power for 6 to 12 hours in every 24 and will not produce power at other times

Tidal energy is produced through the use of tidal energy generators. These large underwater turbines are placed in areas with high tidal movements, and are designed to capture the kinetic motion of the ebbing and surging of ocean tides in order to produce electricity. Tidal power has great potential for future power and electricity generation because of the massive size of the oceans. These articles explore the potential energy of tidal power technologies.

It will generate one of the most environmentally-friendly forms of energy - it makes no noise

In contrast to tidal power, ocean wave energy plants do not make use of the energy difference between high tide and low tide, but generating energy from continuous wave motion. So, wave energy generation is the conversion of the forces from the motion of waves into usable energy.

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.

Tidal stream generators look and work like underwater wind turbines. As opposed to using the rising and falling movement of the tides, tidal stream generators take advantage of the fast moving sea currents (tidal streams), which flow when tides are moving in and out. These tidal streams cause the turbines to rotate, turning the generators which generate electricity. Tidal stream generators have the advantage of being much cheaper to build, and do not have as much of an environmental impact as a tidal barrage. The turbines turn relatively slowly, hence do not affect sea life. This is different to tidal barrages which can disrupt fish migrating up rivers from the sea.