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Prior to the widespread availability of commercial electricity, hydropower was widely used for milling, textile manufacture, and the operation of sawmills. In the 1830s, at the height of the canal-building era, hydropower was used to transport barge traffic up and down steep hills using the technology of inclined plane railroads.
Hydropower can be far less expensive than fossil fuel or nuclear energy. Areas with abundant hydropower attract industry with low cost electricity. Increased environmental concerns have begun to outweigh cheap electricity in some countries.
A hydropower resource can be measured according to the amount of available power, or energy per unit time. The power of a given situation is a function of the hydraulic headSome dictionaries define close to thirty meanings of the word head . However, a majority of usages are associated with the connotation of forward, top, essential, control, etc. which are derived from attributes of an animal head (or brain). In anatomy, th, and rate of flow, and sometimes stream velocity. When dealing with water in a reservoir, the head is the height of the water level in the reservoir relative to its height after it has left, since Hydrostatic pressureHydrostatic pressure is the pressure exerted by a fluid due to its weight. The buoyancy force on a body fully immersed in a static fluid is attributable to the pressure, summed ( integrated) over the body's surface. The pressure is isotropic in that case at the base is a function of height only.
The amount of energy released by lowering an object of mass by a height in a gravitational field is
The energy available to hydroelectric dams is the energy that can be liberated by lowering water in a controled way. In these situations, the power is related to the mass flow rate.
Substituting for and expressing in terms of the volume of liquid moved per unit time and the density of water, we arrive at the usual form of this expression:
For in WattsThe watt (symbol: W is the SI derived unit for power. It is equivalent to 1 joule per second (1 J/s), or in electrical units, 1 volt- ampere (1 V · A). It is the rate in joules per second at which energy is being converted, used or dissipated. Equations :, is measured in , is measured in , is measured in , and is measured in meters.
Some hydropower systems such as water wheelsBerry College in Rome, Georgia A water wheel (also waterwheel Norse mill Persian wheel or noria is a hydropower system; a system for extracting power from a flow of water. It was a widely used system in the Middle Ages, powering most industry in Europe, a can draw power from the flow of a body of water without necessarily changing its height. In this case, the available power is the kinetic energyKinetic energy (also called vis viva or living force is energy possessed by a body by virtue of its motion. The kinetic energy of a body is equal to the amount of work needed to establish its velocity and rotation, starting from rest. Equations Definition of the flowing water.
Over-shot water wheels can efficiently capture both types of energy.