Hydro power is now almost exclusively used for the generation of electricity. In 1994, it accounted for approximately 18% of the world's electricity generation. Hydro power generation world-wide far outstripped any other renewable resource and it is likely to do so in the foreseeable future. Because of its very nature, hydro power is not evenly distributed world wide. For example in 1994, 95% of electricity generation in Brazil was from hydro whereas in England it only accounted for 0.1 %. The largest remaining areas for economically feasible pure hydro power development are in China, Brazil and Russia, respectively.
Pure hydro power exploits the potential energy of water in one of two ways: either by impounding it by means of a dam, and hence concentrating and releasing the potential energy at a chosen point, or by circumventing a region of large losses in potential energy, for example, a waterfall, rapids or river horseshoe. In many instances, there is insufficient water at one site for economic development, in which case the water is diverted and collected from diverse sites by channels, pipelines and tunnels to a common point. Water thus collected or impounded is directed by pressure pipelines (called penstocks) to the power-houses hydraulic turbines. Pure hydro power projects are often staged, the outfall of one facility being the head water of the next. For low head applications power-houses are typically situated at the base of dams. Power-houses in high head facilities are often underground.
The water channels and pipelines have to be designed for the hydraulic transients resulting from the change of flow rate of the water. Surge tanks, overflows and pressure relief valves are used extensively. Hydro facilities have to accommodate maximum predicted floods and are normally equipped with spillways, often gated. Water flow in complex scheme is controlled with hydraulic valves and gates, which are also used for isolation during maintenance. Depending on climate and location, the facility may be equipped to deal with ice floes and large amounts of vegetation. Where water-borne silt is a problem upstream, settling beds are provided.
Pumped storage hydro projects have little or no natural water inflow. Water is pumped from a lower to a higher reservoir during periods of low electrical demand and released through turbines during periods of high demand. As such, pumped storage is the only practical method of substantial energy storage, permitting thermal power stations to operate at base load. The upper and lower reservoirs of pumped storage facilities are often completely man made. A large percentage of pumped storage facilities use reversible pump turbines. However, there are also many facilities where the pump and turbine share the same shaft, which in turn is connected to the motor/generator. During turbine operation, the pump is dewatered and vise versa during pump operation. Alternatively, the two are isolated with mechanical couplings. For high head pumped storage schemes, multi stage pumps or pump turbines are used.
Because of the relatively fast response of hydro units, hydro power can be very effective as spinning reserve and peaking duty on a large generating system. In some instances hydro spinning reserve can be advantageously coupled with synchronous condenser operation of the associated hydro generators, for electrical system compensation. In a micro or macro form, relatively small hydro units can be installed to serve isolated communities, obviating the need for long and expensive transmission lines.
Power from a pure hydro facility is not constant and varies according to the availability of the water. Water flows tend to be seasonal (spring runoffs and monsoon) and, although the creation of large reservoirs alleviates this problem, they cannot completely eliminate it. Dependability of hydro power is also reduced if the scheme is multi purpose, providing water for irrigation or acting as flood control. In both cases the release of water could be dictated by factors other than the power demand (see also Water).
The initial capital outlay for a large hydro scheme can be substantial and difficult to arrange. The amount of construction work is usually considerable. Both of these factors give hydro projects a substantially longer lead time than an equivalent thermal generating facility. The development of large river schemes involving the flooding of substantial tracts of land upstream of the dam is disruptive to both the local environment and populace, especially if large communities have to be relocated. High head schemes are also environmentally contentious as they tend to be located in areas of natural beauty. Accordingly, it is increasingly difficult to obtain both approval and financing for the creation of new hydro power facilities and recent efforts have concentrated on the refurbishing of existing hydro developments.
Gummer, J. H., Barr, D. M, and Simms, G. P. (1993) Evaluation Criteria for Upgrading Hydro Powerplants, International Water Power and Dam Construction, v. 45-12.
International Water Power & Dam Construction Handbook, (1994) Reed Business Publishing, London, ISBN 0617 00548 6. DOI: 10.1016/0148-9062(95)99254-U
Mosonyi, E. (1991) Water Power Development, Akademiai Kiado, Budapest, ISBN 9630542706.
- Gummer, J. H., Barr, D. M, and Simms, G. P. (1993) Evaluation Criteria for Upgrading Hydro Powerplants, International Water Power and Dam Construction, v. 45-12.
- International Water Power & Dam Construction Handbook, (1994) Reed Business Publishing, London, ISBN 0617 00548 6. DOI: 10.1016/0148-9062(95)99254-U
- Mosonyi, E. (1991) Water Power Development, Akademiai Kiado, Budapest, ISBN 9630542706.
Sasa nguvu za maji hutumiwa karibu tu kutokeza umeme. Mwaka 1994 kilikuwa na asilimia 18 ya uzalishaji wa umeme duniani. Kwa sasa, umeme wa maji ni chanzo kikuu cha nishati duniani kote na ni uwezekano mkubwa kwamba utazidi kuwa chanzo kikuu cha nishati katika siku zijazo. Kwa sababu ya asili yake, nishati ya maji haigawanywi kwa usawa ulimwenguni pote. Kwa mfano, mwaka wa 1994, asilimia 95 ya umeme nchini Brazil ulitokana na umeme wa maji, wakati Uingereza ilitokana na asilimia 0.1 tu. Maeneo makubwa zaidi yanayobaki kwa ajili ya maendeleo ya umeme wa maji safi ya kiuchumi ni nchini China, Brazil na Urusi, kwa mtiririko huo. Nishati ya maji hutumia nishati ya maji kwa njia mbili: ama kwa kuifunga kwa njia ya bwawa, na hivyo kukusanya na kutolewa nishati ya uwezekano katika hatua iliyochaguliwa, au kwa kuzunguka eneo la hasara kubwa katika nishati ya uwezekano, kwa mfano, maporomoko ya maji, maporomoko ya maji au mto wa farasi. Katika hali nyingi, hakuna maji ya kutosha katika eneo moja kwa ajili ya maendeleo ya kiuchumi, na katika kesi hiyo maji ni kuelekezwa na kukusanywa kutoka maeneo mbalimbali na mifereji, mabomba na handaki kwa uhakika wa kawaida. Maji yanayokusanywa au kuhifadhiwa kwa njia hiyo huelekezwa kupitia mabomba ya shinikizo (yanayoitwa penstocks) hadi kwenye turbini za majimaji za umeme. Miradi safi ya umeme wa maji mara nyingi hufanywa kwa hatua, na maji ya kituo kimoja huwa maji ya kichwa cha kingine. Kwa ajili ya maombi ya chini ya kichwa nguvu-nyumba ni kawaida iko katika msingi wa mabwawa. Nyumba za umeme katika vifaa vya juu mara nyingi ziko chini ya ardhi. Mifereji ya maji na mabomba lazima kubuniwa kwa ajili ya transients hydraulic yanayotokana na mabadiliko ya kiwango cha mtiririko wa maji. Tangi surge, overflows na valves shinikizo relief ni kutumika sana. Vifaa vya maji vinapaswa kukabiliana na mafuriko makubwa ya utabiri na kwa kawaida vina vifaa vya kuvuja, mara nyingi vina milango. Mtiririko wa maji katika mpango tata ni kudhibitiwa na valves hydraulic na malango, ambayo pia ni kutumika kwa ajili ya kutengwa wakati wa matengenezo. Ikitegemea hali ya hewa na mahali, kituo hicho chaweza kuwa na vifaa vya kushughulikia barafu na mimea mingi. Mahali ambapo matope yanayotokana na maji ni tatizo juu ya mto, vitanda vya kutulia hutolewa. Miradi ya maji ya kuhifadhi maji yenye pampu ina maji machache au hayana maji ya asili. Maji hupomwa kutoka chini hadi juu ya hifadhi wakati wa mahitaji ya chini ya umeme na kutolewa kupitia turbines wakati wa mahitaji ya juu. Kama vile, kuhifadhi pampu ni njia pekee ya vitendo ya kuhifadhi nishati kubwa, kuruhusu mitambo ya umeme wa joto kufanya kazi katika mzigo wa msingi. Mara nyingi mabwawa ya juu na ya chini ya vituo vya kuhifadhi maji kwa pampu hutengenezwa kabisa na wanadamu. Asilimia kubwa ya vifaa vya kuhifadhi pampu hutumia turbines pampu reversible. Hata hivyo, kuna pia vifaa vingi ambapo pampu na turbine kushiriki shaft moja, ambayo kwa upande ni kushikamana na motor / jenereta. Wakati wa turbine operesheni, pampu ni dewatered na vice versa wakati wa operesheni pampu. Vinginevyo, mbili ni kutengwa na couplings mitambo. Kwa ajili ya mipango ya kuhifadhi pumped juu ya kichwa, pampu multi hatua au pampu turbines ni kutumika. Kwa sababu ya majibu ya haraka ya vitengo vya maji, nguvu ya maji inaweza kuwa na ufanisi sana kama hifadhi ya mzunguko na kazi ya kilele kwenye mfumo mkubwa wa kuzalisha. Katika baadhi ya matukio hydro spinning hifadhi inaweza kuwa advantageously pamoja na synchronous condenser operesheni ya kuhusishwa hydro jenereta, kwa ajili ya mfumo wa umeme fidia. Katika fomu ya micro au macro, vitengo vidogo vya maji vinaweza kuwekwa ili kuhudumia jamii zilizo mbali, kuondoa haja ya mistari mirefu na ghali ya usafirishaji. Nguvu kutoka kituo cha maji safi si ya mara kwa mara na inatofautiana kulingana na upatikanaji wa maji. Mtiririko wa maji huwa wa msimu (mvua ya majira ya kuchipua na mvua ya mvua) na, ingawa uundaji wa mabwawa makubwa hupunguza tatizo hili, hawawezi kuondoa kabisa. Utegemezi wa umeme wa maji pia hupunguzwa ikiwa mpango huo ni wa madhumuni mengi, kutoa maji kwa ajili ya umwagiliaji maji au kutenda kama udhibiti wa mafuriko. Katika visa vyote viwili kutolewa kwa maji inaweza kuwa dictated na mambo mengine kuliko mahitaji ya nguvu (tazama pia Maji). Utekelezaji wa mtaji wa awali kwa mpango mkubwa wa maji unaweza kuwa mkubwa na ngumu kupanga. Kwa kawaida kazi ya ujenzi ni kubwa sana. Sababu hizi zote mbili kutoa miradi ya maji muda mrefu sana kuongoza kuliko kituo sawa cha kuzalisha joto. Maendeleo ya mifumo mikubwa ya mto inayohusisha mafuriko ya maeneo makubwa ya ardhi juu ya mto wa bwawa ni ya kuharibu mazingira ya ndani na watu, haswa ikiwa jamii kubwa zinapaswa kuhamishwa. Mipango ya vichwa vya juu pia ni ya utata wa mazingira kwani huwa iko katika maeneo ya uzuri wa asili. Kwa hivyo, ni vigumu kupata idhini na ufadhili kwa ajili ya uundaji wa vifaa vipya vya umeme wa maji na juhudi za hivi karibuni zimezingatia ukarabati wa maendeleo ya umeme wa maji yaliyopo. G. H. Gummer, J. H. Barr, D. M. na G. P. Simms, Tathmini ya Upgrading Hydroelectric Power Plants, International Hydroelectric Power and Dam Construction, v. 45-12 (International Hydroelectric Power & Dam Construction Handbook, 1994) na Reed Business Publishing, London, ISBN 0617 0548 (Kutoka kwa Uholanzi: Mfumo wa Usalama wa Maji, Mfumo wa Usalama wa Maji, Mfumo wa Usalama wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji). G. H. Gummer, J. H. Barr, D. M. na G. P. Simms, 1993: Criteria za Tathmini ya Upgrading Hydro Power Plants, International Hydro Power and Dam Construction, v. 45-12. International Water Power & Dam Construction Handbook, (RED Business Publishing, London, ISBN 0617 05486) ni kitabu cha kimataifa cha ujenzi wa mabwawa ya maji. (Kutoka kwa Uholanzi: Mfumo wa Usalama wa Maji, Mfumo wa Usalama wa Maji, Mfumo wa Usalama wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji, Mfumo wa Maji).