Hydropower is the capture of the energy of moving water for some useful purpose. Prior to the widespread availability of commercial electric power, hydropower was used for irrigation, milling of grain, textile manufacture, and the operation of sawmills. The energy of moving water has been exploited for centuries. Imperial Rome used water powered mills to produce flour from grain, and in China and the rest of the Far East, hydraulically operated "pot wheel" pumps that raised water into irrigation canals. In the 1830s, at the peak of the canalbuilding era, hydropower was used to transport barge traffic up and down steep hills using inclined plane railroads. Direct mechanical power transmission required that industries using hydropower had to locate near the waterfall. For example, during the last half of the 19th century, many grist mills were built at Saint Anthony Falls, utilizing the 50 foot drop in the Mississippi River. A water wheel is a hydropower system; a machine for extracting power from the flow of water. Water wheels and hydropower was widely used in the Middle Ages, powering most industry in Europe, along with the windmill. The most common use of the water wheel was to mill flour in gristmills, but other uses included foundry work and machining, and pounding linen for use in paper. A water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface. Hydroelectricity is electricity produced by hydropower. Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator, although less common variations use water's kinetic energy or un-dammed sources such as run-ofthe-river, waterwheels, and tidal power. Hydroelectricity is a renewable energy source. Since no fossil fuel is consumed, emission of C O 2 is eliminated. While some carbon dioxide is produced during manufacture and construction of the project, this is a tiny fraction of the operating emissions of equivalent fossil-fuel electricity generation. The energy extracted from water depends on the volume and on the difference in height between the source and the water's outflow. This height difference is called the head. The amount of potential energy in water is proportional to the head. To obtain very high head, water for a hydraulic turbine may be run through a large pipe called a penstock. From there it runs into the blades of the turbine. ITAIPU Paraguay & Brazil The control center of the 18 generators Left half of it (in Brazil) controls the 60 Hz units, right half (in Paraguay) controls the 50 Hz units. Disadvantages Hydroelectric projects can be disruptive to surrounding aquatic ecosystems. For instance, studies have shown that dams along the Atlantic and Pacific coasts of North America have reduced salmon populations by preventing access to spawning grounds upstream, even though most dams in salmon habitat have fish ladders installed. Salmon smolt are also harmed on their migration to sea when they must pass through turbines. This has led to some areas barging smolt downstream during parts of the year. Generation of hydroelectric power impacts on the downstream river environment. Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks. Since turbines are often opened intermittently, rapid or even daily fluctuations in river flow are observed. For example, in the Grand Canyon, the daily cyclic flow variation caused by Glen Canyon Dam was found to be contributing to erosion of sand bars. Dissolved oxygen content of the water may change from preconstruction conditions. And water exiting from turbines is typically much colder than the pre-dam water, which can change aquatic faunal populations, including many endangered species. Tidal Power sometimes called tidal energy, is the power achieved by capturing the energy contained in moving water in tides and ocean currents. The efficiency of tidal power generation in ocean dams largely depends on the amplitude (height of the rise and fall) of the tidal swell, which can be up to 33 ft where the periodic tidal waves funnel into rivers and fjords and extreme water velocities can be up to 16 knots near Vancouver Island. Amplitudes of up to 56 ft occur for example in the Bay of Fundy, where tidal resonance amplifies the tidal waves. Tidal power is reliably predictable (unlike wind energy and solar power). In Europe, tide mills have been used for nearly a thousand years, mainly for grinding grains. As with wind power, selection of location is critical for a tidal power generator Therefore, a tidal energy generator must be placed in a location with very high-amplitude tides. Suitable locations are found in the former USSR, USA, Canada, Australia, Korea, the UK and other countries. Tidal energy has an efficiency of 80% in converting the potential energy of the water into electricity, which is efficient compared to other energy resources such as solar power. There are not many effects on the environment, but it can damage some fish. Barrage The barrage method of extracting tidal energy involves building a barrage and creating a tidal lagoon. The barrage traps a water level inside a basin. Head is created when the water level outside of the basin or lagoon changes relative to the water level inside. The head is used to drive turbines. The largest has been working on the Rance river (France) since 1967 with an annual production of 600 GWh (about 68 MW average power) Barrage Rance, France Tidal Power Plant Scale model cross-section of tidal power plant The basin is filled through the sluices until high tide. Then the sluice gates are closed. The turbine gates are kept closed until the sea level falls to create sufficient head across the barrage, and then are opened so that the turbines generate until the head is again low. Then the sluices are opened, turbines disconnected and the basin is filled again. The cycle repeats itself. Ebb generation (also known as outflow generation) takes its name because generation occurs as the tide ebbs. A tidal power scheme is a long-term source of electricity that decreases the output of greenhouse gases into the atmosphere. Tidal barrage power schemes have a high capital cost and a very low running cost. As a result, a tidal power scheme may not produce returns for years, and investors are thus reluctant to participate in such projects. Governments may be able to finance tidal barrage power, but many are unwilling to do so also due to the lag time before investment return and the high irreversible commitment. Wave power refers to the energy of ocean surface waves and the capture of that energy to do useful work, including electricity generation, desalinization and the pumping of water into reservoirs. Wave power is a form of renewable energy. Though often co-mingled, wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents. Wave size is determined by wind speed and fetch (the distance over which the wind excites the waves) and by the depth and topography of the seafloor. A given wind speed has a matching practical limit over which time or distance will not produce larger waves. This limit is called a "fully developed sea.“ Wave motion is highest at the surface and diminishes exponentially with depth. POWER BUOY The rising and falling of the waves moves the buoy-like structure creating mechanical energy which is converted into electricity and transmitted to shore over a submerged transmission line. A 40kW buoy has a diameter of 12 feet and is 52 feet long, with approximately 13 feet of the unit rising above the ocean surface. Using the three-point mooring system, they are designed to be installed one to five miles offshore in water 100 to 200 feet deep. Pelamis Wave Energy Converter The Pelamis is an attenuating wave device designed for survivability at sea rather than highly efficient energy conversion. This means that rather than absorbing all of the energy available in a wave, it converts only a portion of that energy to electricity. This is principally so that the device can survive in dangerous storm conditions which could do considerable damage to a wave device attempting to absorb all the available energy. The Pelamis device consists of a series of semisubmerged cylindrical sections linked by hinged joints. The wave induced relative motion of these sections is resisted by hydraulic rams which pump high pressure oil through hydraulic motors via smoothing hydraulic accumulators. The hydraulic motors drive electrical generators to produce electricity, 30 of these machines can power 20,000 Scottish homes. Several devices can be connected together and linked to shore. Its operating efficiency is approximately 15%. What’s this? Underwater Turbines Underwater turbines are being developed that can be placed in rivers that provide a constant energy flow as long as the river maintains the minimal flow required. Due to the increased density of water when compared to air, those turbines are said to be 80% more effective.