8/25/07 11:16 PMMicro hydropower basic: introductionPage 1 of 7http://web.archive.org/web/20070509191717/http://www.microhydropower.net/intro.htmlMicro hydropower basicsIntroduction to micro hydroOther documents in this series: Civil work components Turbines Drive systems Electrical power Measurement of head Measurement of flow further reading Within this document: General History Advantages and disadvantages From water to Watts Different sizes hydropowerinstallations Small hydropower Energy usesBack to the microhydro web portal GeneralThe basic principle of hydropower is that if water can be piped from a certain level to alower level, then the resulting water pressure can be used to do work. If the waterpressure is allowed to move a mechanical component then that movement involves theconversion of the potential energy of the water into mechanical energy. Hydro turbinesconvert water pressure into mechanical shaft power, which can be used to drive anelectricity generator, a grinding mill or some other useful device. HistoryThe use of falling water as a source of energy is known for a long time. In the ancienttimes waterwheels were used already, but only at the beginning of the nineteenthcentury with the invention of the hydro turbine the use of hydropower got a new impulse.Small-scale hydropower was the most common way of electricity generating in the early20th century. In 1924 for example in Switzerland nearly 7000 small scale hydropowerstations were in use. The improvement of distribution possibilities of electricity by meansof high voltage transmission lines caused fainted interest in small scale hydropower.Renewed interest in the technology of small scale hydropower started in China.Estimates say that between 1970 and 1985 nearly 76,000 small scale hydro stationshave been built there! Advantages and disadvantages8/25/07 11:16 PMMicro hydropower basic: introductionPage 2 of 7http://web.archive.org/web/20070509191717/http://www.microhydropower.net/intro.htmlHydropower is a very clean source of energy. It does not consume but only uses thewater, after use it is available for other purposes (although on a lower horizontal level).The conversion of the potential energy of water into mechanical energy is a technologywith a high efficiency (in most cases double that of conventional thermal power stations).The use of hydropower can make a contribution to savings on exhaustible energysources. Each 600 kWh of electricity generated with a hydro plant is equivalent to 1barrel of oil (assuming an efficiency of 38 % for the conversion of oil into electricity).The main advantages of hydropower are:power is usually continuously available on demand,given a reasonable head, it is a concentrated energy source,the energy available is predictable,no fuel and limited maintenance are required, so running costs are low (comparedwith diesel power) and in many cases imports are displaced to the benefit of thelocal economy,it is a long-lasting and robust technology; systems can last for 50 years or morewithout major new investments.Against these, the main shortcomings are:it is a site specific technology and sites that are well suited to the harnessing ofwater power and are also close to a location where the power can be economicallyexploited are not very common,there is always a maximum useful power output available from a given hydropowersite, which limits the level of expansion of activities which make use of the power,river flows often vary considerably with the seasons, especially where there aremonsoon-type climates and this can limit the firm power output to quite a smallfraction of the possible peak output,lack of familiarity with the technology and how to apply it inhibits the exploitation ofhydro resources in some areas.From water to WattsTo know the power potential of water in a river it is necessary to know the flow in theriver and the available head.The flow of the river is the amount of water (in m3 or litres) which passes in a certainamount of time a cross section of the river. Flows are normally given in cubic meters persecond (m3/s) or in litres per second (l/s).Head is the vertical difference in level (in meters) the water falls down.8/25/07 11:16 PMMicro hydropower basic: introductionPage 3 of 7http://web.archive.org/web/20070509191717/http://www.microhydropower.net/intro.htmlComponents of a typical high head hydro installation. (click for enlargement)The theoretical power (P) available from a given head of water is in exact proportion tothe head H and the flow Q.P=Q × H × c c = constantThe constant c is the product of the density of water and the acceleration due to gravity(g).If P is measured in Watts, Q in m3/s and H in meters, the gross power of the flow ofwater is:P=1000 × 9.8 × Q × HThis available power will be converted by the hydro turbine in mechanical power. As aturbine has an efficiency lower than 1, the generated power will be a fraction of theavailable gross power. Different sizes hydropower installationsHydropower installations can be classified as follows:8/25/07 11:16 PMMicro hydropower basic: introductionPage 4 of 7http://web.archive.org/web/20070509191717/http://www.microhydropower.net/intro.htmlname descriptionLarge all installations with an installed capacity of more than 1000 kW(according to some definitions more than 10,000 kW)Small general term for installations smaller than 1000 kW (or < 10,000kW). Also used for installations in the range between 500 and 1000kW.Mini capacity between 100 and 500 kWMicro hydropower installations with a power output less than 100 kW (orless then 1000 kW)Large scale hydropower stations are equipped with large dams and huge water storagereservoirs. In these reservoirs large amounts of water can be stored when supply ofwater is higher than the demand. Water from wet periods can be used in this way tosupplement water supply in dry periods (or even dry years).In the sixties and seventies large hydropower stations looked as the solution to theenergy crisis in developing countries. In that period many large scale hydro schemeswere built. Examples are Aswan in Egypt, Tarbela in Pakistan, Cabora Bassa inMozambique and Kariba in Zimbabwe.The enthusiasm for projects like those has disappeared nowadays. The extreme highsums of money involved, the long money-recovery time and the huge environmentalcosts are debit to this. Specially the high environmental costs are a point of greatconcern: losses of fertile arable land,