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Berkeley ENE,RES C200 - Micro-hydropower - status and prospects

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Micro-hydropower: status and prospectsO PaishIT Power Limited, The Manor House, Chineham Court, Luytens Close, Chineham, Hants, UKAbstract: Hydropower on a small scale, or micro-hydro, is one of the most cost-effective energytechnologies to be considered for rural electri cation in less developed countries. It is also the mainprospect for future hydro developments in Europe, where the large-scale opportunities either have beenexploited already or would now be considered environmentally unacceptable. Whereas large hydro schemesoften involve the construction of major dams and the  ooding of whole valleys, micro-hydro is o ne of themost environmentally benign energy technologies available. The techn ology is extremely robust and systemscan last for 50 years or more with little maintenance.Keywords: hydropower, micro-hydro, mini-hydro, water powerNOTATIONgacceleration due to gravityHpressure headkWh kilowatt hournrotational speed (r=min)Nsspeci c speedPpowerTWh terawatt hourZhydraulic ef ciencyrdensity of water1 INTRODUCTIONHydropower is another form of solar energy. Of t he Sun’sradiation that enters the Earth’s atmosphere, about half isconverted into heat directly at the Earth’s surface, a quarteris re ected back into space, and the re maining quarter isspent in evaporating water, mostly from the oceans. It is thissolar en ergy, convert ed into the latent heat of evaporation ofwater, that powers the hydrological cycle on which hydro-power depends.Hydro-electricity is usually associated with the buildingof large dams. In the 20th century, hun dreds of massivebarriers of concrete, rock and earth were placed across rivervalleys worldwide to create huge arti cial lakes. While theycreate a major, reliable power supply, plus irrigation and ood control bene ts, dams necessarily  ood large areas offertile land and d isplace many thousands of local inhabi -tants. In many cases, rapid silting up of the dam has reducedits productivity and lifetime.Hydropower on a small-scale, or micro-hydro, is theexploitation of a river’s hydro potential without signi cantdamming, an d is one of the most environmentally benignenergy options available.1.1 Small-scale hydroHydropower has variou s degrees of ‘smallness’. To datethere is still no internationally agreed de niti on of ‘small’hydro; the upper limit varies between 2.5 and 2 5 MW. Amaximum of 10 MW is the most widely accep ted valu eworldwide, although the de nition in China stands of ciallyat 25 MW. In the jargon of the industry, ‘mini’ hydrotypically refers to schemes below 2 MW, micro-hyd robelow 500 kW and pico-hydro below 10 kW. This paperfocuses mainly on schemes below 500 kW, alt hough this isan arbitrary div ision and many of the principles involvedwill also apply to larger schemes.Micro-hydro is in most cases ‘run of river’; in otherwords, any d am or barrage is quite small, usually just a weir,and generally little or no water is stored. The civil workspurely serve the function of regulating the level of th e waterat the intake to the hydro-plant. Therefore run-of-riverinstallations do not have the same kinds of adverse effecton the local environment as large hydro.Micro-hydro started with the wooden waterwheel. Water-wheels of various types had been in use in many parts ofEurope and Asia for some 2000 years, mostly fo r millinggrain. By the time o f the Industrial Revolution, waterwheeltechnology had been developed to a  ne art, and ef cienciesapproaching 70 per cent were being achieved in the manytens of thousands of waterwheels that were in regular use.Improved engineering skills during the 19th century,combined with the n eed to develop smaller and higherThe MS was received on 22 May 2001 and was accepted after revision forpublication on 8 November 2001.SPECIAL ISSUE PAPER 31A04201 # IMechE 2002 Proc Instn Mech Engrs Vol 216 Part A: J Power and Energyspeed devices to generate electricity, led to the developmentof modern-day turbines, presen ted in section 4.2 WORLD POTENTIALHydropower, large and small, is by far the most important ofthe ‘renewables’ for electrical power production. TheWorldHydropower Atlas 2 000[1], published by th eInternationalJournal of Hydropower and Dams, reported that the world’stechnically feasible hydro potential is estimated at14 370 TWh=year, which equates to 100 per cent of today’sglobal electricity demand. The e conomically feasible propor-tion of this is currently considered to be 8080 TWh =year.The hydropower potential exploited in 1999 was2650 TW h=year, providing 19 per cent of the planet’selectricity from an installed capacity of 674 GW. Of newhydro capacity, 135 GW is expected to be commissioned inthe period 2001–2010. All other renewables combinedprovided less than 2 per cent of glob al consumption. Asillustrated in Fig. 1, North America and Europe havedeveloped most of their economic potential, but hugeresources remain in Asia, Africa and South America.Small hydro (< 10 MW) currently contributes over40 GW of world capacity. The global small hydro potentialis believed to be in excess of 100 GW. China alone hasdeveloped more than 15 GW and plans to develop a further10 GW in the next decade.2.1 EuropeHydropower provides about 17 per cent of EU electricitysupply. Small hydro provides over 8 GW of capacity andthere is an estimated 18 GW of further small hydropotential, including refurbishment projects. The EuropeanCommission has an nounced a target to increase small hydrocapacity by 4500 MW (50 per cent) by the year 201 0.The UK has 100 MW of small hydro capacity operatingfrom approximately 120 sites. Most of the remaining poten-tial of interest is located in Scotland and Wales, althoughEngland has many tens of thousands of small low head sites,previously watermills, which in aggregate amount to over50 MW of further potential.3 PRINCIPLES OF MICRO-HYDROHydro-turbines convert water pressure into mechanical shaftpower, which can be used to drive an electricity generator orother machinery. The power available is proportional to theproduct of pressure head and volume  owrate. The generalformula for any hydro system’s power output isP ˆ ZrgQHwherePis the mechanical power producedat the turbineshaft(watts),Zis the hy draulic ef ciency of the turbine,ris thedensity of water volume (kg=m3),gis the acceleration dueto gravity (m=s2),Qis the  owrate passing through theturbine (m3=s) andHis the effective pressure head of


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