17 April, 2007

Hydro Power - Introduction and Types

Hydro power has played an important historical role in the industrialization of society from grinding flour to powering industry. Hydro energy originates from the sun, and hence, is renewable and its fuel is free.
“Hydro” means “water” in Latin – so “hydro power” is made from water.Hydropower is the capture of the energy of moving water for some useful purpose.The analysis of hydroelectric generation begins with the potential energy of the water. The gravitational potential energy (PE) is defined based on a material’s mass (m) and height (H) from a reference point.
PE = m.g.H
where g is gravitational constant. The power generation (P) depends upon the period (T) over which the water is discharged through that height, often times referred to as the head.
The water mass may be expressed in terms of its density (ρ) and volume (V), i.e., m=ρV.Often,the volume of water is measured in acre-feet which is the volume occupied by a foot of water covering an acre of area; one acre-foot is equivalent to 43,560 ft³. The standard density of water is 1,000 kg/m³ or 62.4 lbm/ft³. The power can then be represented in terms of the mass flow rate or volumetric flow rate
The electric power output is reduced by the hydraulic turbine-generator efficiency.
There are many forms of water power:
  • Waterwheels , used for hundreds of years to power mills and machinery
  • Hydroelectric energy, a term usually reserved for hydroelectric dams.
  • Tidal power, which captures energy from the tides in horizontal direction
  • Tidal stream power, which does the same vertically
  • Wave power, which uses the energy in waves
Hydroelectric power
Hydroelectric power now supplies about 715,000 MW or 19% of world electricity (16% in 2003). Large dams are still being designed. Apart from a few countries with an abundance of it, hydro power is normally applied to peak load demand because it is readily stopped and started. Nevertheless, hydroelectric power is probably not a major option for the future of energy production in the developed nations because most major sites within these nations are either already being exploited or are unavailable for other reasons, such as environmental considerations.
Hydropower produces essentially no carbon dioxide or other harmful emissions, in contrast to burning fossil fuels, and is not a significant contributor to global warming through CO2.
Hydroelectric power can be far less expensive than electricity generated from fossil fuel or nuclear energy. Areas with abundant hydroelectric power attract industry. Environmental concerns about the effects of reservoirs may prohibit development of economic hydropower sources.
The chief advantage of hydroelectric dams is their ability to handle seasonal (as well as daily) high peak loads. When the electricity demands drop, the dam simply stores more water (which provides more flow when it releases). Some electricity generators use water dams to store excess energy (often during the night), by using the electricity to pump water up into a basin. Electricity can be generated when demand increases. In practice the utilization of stored water in river dams is sometimes complicated by demands for irrigation which may occur out of phase with peak electrical demands.

Tidal power
Harnessing the tides in a bay or estuary has been achieved in France (since 1966), Canada and Russia, and could be achieved in other areas with a large tidal range. The trapped water turns turbines as it is released through the tidal barrage in either direction. Another possible fault is that the system would generate electricity most efficiently in bursts every six hours (once every tide). This limits the applications of tidal energy.

Tidal stream powerA relatively new technology, tidal stream generators draw energy from currents in much the same way that wind generators do. The higher density of water means that a single generator can provide significant power. This technology is at the early stages of development and will require more research before it becomes a significant contributor.
Several prototypes have shown promise. In the UK in 2003, a 300 kW Periodflow marine current propeller type turbine was tested off the coast of Devon, and a 150 kW oscillating hydroplane device, the Stingray, was tested off the Scottish coast. Another British device, the Hydro Venturi, is to be tested in San Francisco Bay.
The Canadian company Blue Energy has plans for installing very large arrays tidal current devices mounted in what they call a 'tidal fence' in various locations around the world, based on a vertical axis turbine design.

Wave powerHarnessing power from ocean surface wave motion might yield much more energy than tides. The feasibility of this has been investigated, particularly in Scotland in the UK. Generators either coupled to floating devices or turned by air displaced by waves in a hollow concrete structure would produce electricity. Numerous technical problems have frustrated progress.
A prototype shore based wave power generator is being constructed at Port Kembla in Australia and is expected to generate up to 500 MWh annually. The Wave Energy Converter has been constructed (as of July 2005) and initial results have exceeded expectations of energy production during times of low wave energy. Wave energy is captured by an air driven generator and converted to electricity. For countries with large coastlines and rough sea conditions, the energy of waves offers the possibility of generating electricity in utility volumes. Excess power during rough seas could be used to produce hydrogen.

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