Presentation on theme: "Renewable Energy Resources"— Presentation transcript:
1Renewable Energy Resources HYDROELECTRIC ENERGYRenewable Energy Resources2008António F. O. Falcão
2SOLAR ENERGY flux on the Earth surface: About 25% consumed in evaporation of waterAlmost all this energy is released in water vapour condensation (clouds, rain) & radiated back into outer spaceOnly 0.06% remains as potential energy stored in water that falls on hills and mountainsHYDRO ENERGY RESOURCETotal resource: (about 15 times total world hydroelectric productionTechnical potential: about:Total world electricity consumption: TWh
415,8% of world electrical energy consumption Regional hydro potential outputRegionTechical potential TWh/yearAnnual output TWh/yearOutput as % of technical potentialAsia509357211%South America279250718%Europe270672927%Africa1888804,20%North America166866540%Oceania2324017%World14379259315,8% of world electrical energy consumptionBased on average outputSource: G. Boyle, Renewable Energy, 2004.
8Large hydro Small hydro Mini-hydro 10 MW 500 kW 100 kW Micro-hydro Note: there are other definitions.
9Small hydroelectric plants (< 10 MW) World totalsInstalled capacity (GW)Annual production TWh/yearTotal (large + small)740 2700Small (< 10 MW)50 a 60 150Small/total6 a 7% 6%Installed capacity (GW) in small hydroelectric plants:China 26Japan 3.5Austria, France, Italy, USA > 2 eachBrazil, Norway, Spain > 1 cadaPortugal 0.3 (about 100 plants)TOTAL to 60 GW
10Installed capacity and production of SHPs (<10MW) in 30 European countries
11L = losses in canal, pennstock, in metres B= gross head(altura de queda bruta)Turbine= gross head (altura dequeda bruta) in metresL = losses in canal, pennstock, in metres= net head (altura de queda disponível)Q = flow rate or intake (caudal), in m3/s= gross power (potência bruta), in Watts= power available to turbine= turbine power outputturbine efficiency= electrical power outputelectrical efficiency
12Ω is directly related to geometry (type) of turbine H = (net) headQ = flow rateN = rotational speedHydraulic turbineQratedN, H = constantDimensional analysis(Dimensionless) specific speedΩ is directly related to geometry (type) of turbine
13Rotors of hydraulic turbines with different specific speeds Ω. PeltonFrancisKaplanRotors of hydraulic turbines with different specific speeds Ω.
14and type of hydraulic turbine (Pelton, Francis, Kaplan) Correspondence between specific speed Ωand type of hydraulic turbine (Pelton, Francis, Kaplan)
20Reversible Francis pump-turbine In times of reduced energy demand, excesselectrical capacity in the grid (e.g. from wind turbines) may be used to pump water, previously used to generate power, back into an upper reservoir.This water will then be used to generate electricity when needed. This can be done by a reversible pump-turbine and an electrical generator-motor.
22Kaplan turbine Electrical generator Blade angle can be controlled spiral casingGuide vanesBlade angle can be controlledrunnerElectrical generator
23Simple control: rotor blades are fixed Kaplan turbineDouble controlGuide-vane controlRotor-blade controlPropeller turbine (small power plants)Simple control: rotor blades are fixed
24A variant of the Kaplan turbine: the horizontal axis Bulb turbine Used for very low heads, and in tidal power plantsTidal plant of La Rance, Franceguide vanes
25Cross-flow turbine (also known as Mitchel-Banki and Ossberger turbine) Used in small hydropower plants.The water crosses twice (inwards and outwards) the rotor blades.Cheap and versatile.Peak efficiency lower than for conventional turbines.Favourable efficiency-flow curve.Explicar princípio de funcionamento; discutir a definição
28Ranges of application of Pelton, Francis and Kaplan turbines (adapted from Bureau of Reclamation, USA, 1976). Recommended rotational speeds are submultiples of 3000 rpm, for sinchronous generators.Q (m3/s)H (m)
29How to estimate the type and size of a turbine, given (rated values of): H = (net) head,Q = flow rate,N = rotational speed ?Type (geometry)
31Francis and Kaplan turbines Specific diameter(dimensionless)
32Part-flow efficiency of small hydraulic turbines Cross-flowPeltonKaplanFrancisPropeller0.00.20.40.60.81.0EfficiencyFlow rate as proportion of design flow rate
33HYDROLOGY Watershed (of hydropower scheme) (bacia hidrográfica) Flow (rate) (caudal)Basic hydrological data required to plan a (small) hydropower scheme:Mean daily flow series at scheme water intake for long period (~20 years).This information is rarely available.Indirect procedures are often necessary.
34Indirect procedure:Usually consists of transposition of sufficiently long (≥20 years) flow-records from other watershed (bacia hidrográfica) equipped with a stream-gauging station (estação de medição de caudal).Watershed of hydropower scheme and water shed of stream-gauging station should be located in same region, of similar area, with similar hydrological behaviour (similar mean annual rain fall level) and similar geological constitution.Rain gauges (medidores de precipitação) should be available inside (or near) both watersheds, and be used for simultaneous rain-fall measurements.Stream-gauging stationPower plant
35Relation between annual precipitation and runoff at stream-gauging station (per unit watershed area) By transposition → relationship between annual precipitation and power-plant flow rate at hydro-power scheme.
36Mean annual flow duration curve Dimensionless form of the mean annual flow duration curveTime fraction flow rate is equalled or exceededmean annual flow rate
37ENERGY EVALUATION – CASE 1 Water reservoir has small storage capacity.Run-of-the-river plant (central de fio de água).Case of many (most?) small hydropower plants.Storage capacity is neglected.Energy evaluation from the flow duration curve.No time-series (day-by-day prediction) of power output.At most, seasonal variations are to be predicted.
38Run-of-river plant and flow duration curve. Time-fraction flow rate is equalled or exceededMax. turbine flowMin. turbine flowEcological flowRun-of-river plant and flow duration curve.
39Required data for energy evaluation: Flow duration curve for hydropower scheme.Maximum and minimum turbine flow rates (to be specified from turbine characteristic curves).Ecological discharge (and others, required for the consumption between the weir and the turbine outlet).Head loss L in diversion circuit as function of flow rate.Efficiency curves of turbine and electrical equipment.Run-of-river hydropower plant (fio de água)
40Part-flow efficiency of small hydraulic turbines Cross-flowPeltonKaplanFrancisPropeller0.00.20.40.60.81.0EfficiencyFlow rate as proportion of design flow rateMaximum and minimum turbine flow rates to be decided based on turbine size and efficiency curve.
41ENERGY EVALUATION - CASE 2 Second case: water reservoir (lagoon) has significant or large capacity.Case of some small and most large hydropower plants.Storage capacity must be taken into account.Energy evaluation is based on the simulation of a scenario: daily (or hourly) flow-series and exploitation rules.Basically the computation consists in the step-by-step numerical integration of a differential equation (equation of continuity).
42Required data for energy evaluation: Time-series of flow into the reservoir (simulated scenario).Maximum and minimum turbine flow rates (to be specified from turbine characteristic curves).Ecological discharge (and others, required for the consumption between the weir and the turbine outlet).Head loss L in diversion circuit as function of flow rate.Efficiency curves of turbine and electrical equipment.Reservor stage-capacity curve (surface elevation versus stored water volume).Exploitation rules (e.g. concentrate energy production in periods of higher tariff or higher demand).Hydropower plant with storage capacity
43Exercise Assume: Annual-average flow into reservoir. Consider a small run-of-river hydropower plant.Specify the turbine type and size.Evaluate the annual production of electrical energy.Assume:Annual-average flow into reservoir.Flow duration curve.Gross head Hb .Loss L in hydraulic circuit.Efficiency curve of turbine, and rated & minimum turbine flow.Efficiency of electrical equipment.Ecological flow rate.
44Exercise or F(q) is fraction of time q is exceeded. Time fraction flow rate is equalled or exceeded τExerciseorF(q) is fraction of time q is exceeded.is probability density function.= probability of occurrence of flow between q and q + dq .
45Choice of function F(q) ExerciseChoice of function F(q)kc0,50,500000,550,587400,60,664640,650,731920,70,790000,750,839880,80,882610,90,950401,01,000001,11,036361,21,063091,31,082751,41,097191,61,115361,81,124502,01,12838Weibull distribution (widely used in wind energy):c = scale parameterk = shape parameter
46ExerciseChoice of efficiency-flow curve for turbine (typical small Francis turbine)Set a minimum value for the turbine efficiency, e.g. 20% efficiency.Set the minimum value of the turbine flow rate accordingly.
47Annual-averaged electrical power output (SI units): ExerciseAnnual-averaged electrical power output (SI units):
48Total electrical energy produced in one year: Exercise
49Procedure (suggestion) ExerciseProcedure (suggestion)Fix annual-averaged flow rate into reservoir, e.g.Fix gross head, e.g.Fix head loss, proportional to ,e.g. such that loss equal to a few percent of gross headFix flow duration curve, e.g. based on Weibull distributionFix turbine type, turbine efficiency curve andFix minimum (dimensionless) turbine flow rateFix ecological flow rateAssumeComputeMake comparisons as appropriate; look for “optimum” value of
50Some results from Exercise Ecological flow rate = 0Head losses = 0Francis turbineCross-flow turbineratedannual-averagedAnnual-averagedFrancisCross-flowk = 1.6 shape parameter of Weibull distribution
51The two largest hydropower plants in the world Three Gorges Dam, ChinaItaipu, Brazil-Paraguay
52THREE GORGES DAM – The largest hydropower plant in the world Yangtze River, China.Construction: started in 1994; to be completed in 2009.Dam - length: 2309m; height: 185mReservoir – length: 600kmAbout 1.5 million people had to be relocated
53Three Gorges Dam hydropower plant Installed power: MW34×700 MW Francis turbines
54Itaipu hydropower plant, Paraná River, Brazil-Paraguay Construction:Reservoir area: 1350 km2Total dam length: 7235 mDam height: 196 mItaipu hydropower plant, Paraná River, Brazil-ParaguayInstalled power: MW18 Francis turbines of 715 MW
55Principais bloqueios ao desenvolvimento de PCHs na EU Processo de licenciamentoExigências específicas locaisFinanciamentoLigação à rede eléctricaVenda de electricidade produzidaQuadro regulador incertoAusência de informações correctasRecrutamento e formação de técnicos
56Principais bloqueios em Portugal (FORUM Energias Renováveis em Portugal, 2002)Dificuldades na obtenção de licenciamentos, sujeitos a um processo extremamente complexo, onde intervêm, sem aparente coordenação, diversas instituições e ministérios.Dificuldade na ligação à rede eléctrica nacional por insuficiência da mesma e, ainda, por outras dificuldades processuais e operacionais.Ausência de critérios objectivos na emissão de pareceres de diversas entidades e na apreciação dos estudos de carácter ambiental.Eventual opinião ou intervenção negativa de agentes locais.Dificuldades de maios humanos na Administração para tratamento dos processos de licenciamento."Em 2001, a situação podia resumir-e a um impasse quase completo no licenciamento das PCHs" (situação pouco diferente da actual).
57Aspectos económicosMaiores alturas de queda são factor favorável (menores caudais para a mesma potência, menores custos de equipamento).Frequentemente maiores alturas ocorrem em zonas menos habitadas (consumo local, ligação à rede).Na Europa, a maior parte dos melhores locais (maiores quedas) já estão aproveitados.Muito longo período de vida (frequentemente 50 anos) com pequenos custos de operação e manutenção. Investimentos nas grandes hídricas em geral do Estado.Mas a análise económica (investidores privados) baseia-se em amortizações em anos.
58Costs of installation of small hydropower plants Comparison: cost of installation of a large onshore wind turbine (> 1MW): about M€/MW.Note that lifespan of wind turbine (20-25 years?) is probably shorter than lifespan of a hydro plant.
59Range of costs for small hydropower projects. kW installedUS$/kW
60Small hydropower : specific costs of installed capacity Head (m)€/kW
61ENVIRONMENTAL IMPACT - 1 The impact of the large hydropower plants is probably greater (afecting larger areas) than any other power plants (not necessarily worse impact).The impact from small plants (per unit power) is not necessarily smaller than from large ones.This impact is important during construction and during operation.Do not forget that any renewable has environmental impact, namely concerning construction/production phaes (energy and materials are required).The large hydro plants change the ecology over large areas.Beneficial effects:Replaces fossile-fuel power plants (reduce greenhouse gases & acid rain).Flood control (especially plants with large reservoir).Irrigation.Valued amenity and visual improvement.
62ENVIRONMENTAL IMPACT - 2 The most obvious impact of large hydro-electric dams is the flooding of vast areas of land, much of it previously forested or used for agriculture.Large plants required the relocation of many people (Aswan, Nile river: 80000; Kariba, Zambesi river: 60000; Three Gorges Dam, Yangtze river: 1.5 million).In large reservoirs behind hydro dams, decaying vegetation, submerged by flooding, may give off large quantities of greenhouse gases (methane).Damming a river can alter the amount and quality of water in the river downstream of the dam, as well as preventing fish from migrating upstream. These impacts can be reduced by requiring minimum flows downstream of a dam, and by creating fish ladders which allow fish to move upstream past the dam.Silt (sediments), normally carried downstream to the lower reaches of a river, is trapped by a dam and deposited on the bed of the reservoir. This silt can slowly fill up a reservoir, decreasing the amount of water which can be stored and used for electrical generation. The river downstream of the dam is also deprived of silt which fertilizes the river's flood-plain during high water periods.
63Basic bibliography (in addition to pdf files available at site of Renewable Energy Resources): Janet Ramage, “Hydroelectricity”, in: Renewable Energy (Godfrey Boyle ed.), Oxford University Press, 2004, p ISBNM. Manuela Portela, “Hydrology”, in: Guidelines for Design of Small Hydroplants (Helena Ramos, ed.), 2000, p ISBN (available at CEHIDRO, IST).