Presentation on theme: "HYDROELECTRIC ENERGY Renewable Energy Resources 2008 António F. O. Falcão."— Presentation transcript:
HYDROELECTRIC ENERGY Renewable Energy Resources 2008 António F. O. Falcão
SOLAR ENERGY flux on the Earth surface: About 25% consumed in evaporation of water Almost all this energy is released in water vapour condensation (clouds, rain) & radiated back into outer space Only 0.06% remains as potential energy stored in water that falls on hills and mountains HYDRO ENERGY RESOURCE Total resource: (about 15 times total world hydroelectric production Technical potential: about: Total world electricity consumption: TWh
Regional hydro potential output Region Techical potential TWh/year Annual output TWh/year Output as % of technical potential Asia % South America % Europe % Africa ,20% North America % Oceania % World % Based on average output Source: G. Boyle, Renewable Energy, ,8% of world electrical energy consumption
Exploited hydro potential by continent Africa Asia Australasia/ Oceania Europe North & Central America South America Technical potential Economic potential Exploited potential
Weir and intake (dique ou açude) Penstock (conduta forçada) Forebay tank (câmara de carga) Small hydro site layout Canal (canal) Power house (casa das máquinas)
10 MW 500 kW 100 kW Large hydro Small hydro Mini-hydro Micro-hydro Note: there are other definitions.
Small hydroelectric plants (< 10 MW) World totals Installed capacity (GW) Annual production TWh/year Total (large + small) Small (< 10 MW)50 a Small/total6 a 7% 6% Installed capacity (GW) in small hydroelectric plants: China 26 Japan 3.5 Austria, France, Italy, USA > 2 each Brazil, Norway, Spain > 1 cada Portugal 0.3 (about 100 plants) TOTAL 50 to 60 GW
Installed capacity and production of SHPs (<10MW) in 30 European countries
A Canal Pennstock B = gross head (altura de queda bruta) Turbine = gross head (altura de queda bruta) in metres L = losses in canal, pennstock, in metres = net head (altura de queda disponível) Q = flow rate or intake (caudal), in m 3 /s = gross power (potência bruta), in Watts = power available to turbine = turbine power outputturbine efficiency = electrical power output electrical efficiency
H = (net) head Q = flow rate N = rotational speed Hydraulic turbine Q rated N, H = constant Dimensional analysis (Dimensionless) specific speed Ω is directly related to geometry (type) of turbine
Pelton Francis Kaplan Rotors of hydraulic turbines with different specific speeds Ω.
Correspondence between specific speed Ω and type of hydraulic turbine (Pelton, Francis, Kaplan)
Pelton turbines (low Ω) Usually: High H Small Q
Twin jet Pelton turbine wheel or runner nozzle pennstock
Large Pelton turbine Vertical axis 6 jets (6 nozzles)
Francis turbines (medium Ω)
Francis turbine Spiral casing Guide vanes runner draft tube
Reversible Francis pump-turbine In times of reduced energy demand, excess electrical 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.
Kaplan turbines (high Ω) Usually: Low H Large Q
Kaplan turbine spiral casing Guide vanes Blade angle can be controlled runner Electrical generator
Kaplan turbine Guide-vane control Rotor-blade control Double control Propeller turbine (small power plants) Simple control: rotor blades are fixed
A variant of the Kaplan turbine: the horizontal axis Bulb turbine Used for very low heads, and in tidal power plants Tidal plant of La Rance, France guide vanes
Cross-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.
Head-flow ranges of small hydro turbines
Ranges 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 (m 3 /s) H (m)
How to estimate the type and size of a turbine, given (rated values of): H = (net) head, Q = flow rate, N = rotational speed ? Type (geometry)
Pelton turbine D Diameter D
Francis and Kaplan turbines D Specific diameter (dimensionless)
Part-flow efficiency of small hydraulic turbines Cross- flow Pelton Kaplan Francis Propeller Efficiency Flow rate as proportion of design flow rate
HYDROLOGY 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.
Indirect 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 station Power plant
Relation 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.
Mean annual flow duration curve Dimensionless form of the mean annual flow duration curve Time fraction flow rate is equalled or exceeded mean annual flow rate
ENERGY 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.
Time-fraction flow rate is equalled or exceeded Max. turbine flow Min. turbine flow Ecological flow Run-of-river plant and flow duration curve.
Required 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)
Part-flow efficiency of small hydraulic turbines Cross- flow Pelton Kaplan Francis Propeller Efficiency Flow rate as proportion of design flow rate Maximum and minimum turbine flow rates to be decided based on turbine size and efficiency curve.
ENERGY 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).
Required 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
Exercise 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 H b. Loss L in hydraulic circuit. Efficiency curve of turbine, and rated & minimum turbine flow. Efficiency of electrical equipment. Ecological flow rate.
Time fraction flow rate is equalled or exceeded τ Exercise or F(q) is fraction of time q is exceeded. is probability density function. = probability of occurrence of flow between q and q + dq.
Exercise Choice of function F(q) Weibull distribution (widely used in wind energy): c = scale parameter k = shape parameter kc 0,50, ,550, ,60, ,650, ,70, ,750, ,80, ,90, ,01, ,11, ,21, ,31, ,41, ,61, ,81, ,01,12838
Exercise Choice 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.
Exercise Annual-averaged electrical power output (SI units):
Total electrical energy produced in one year: Exercise
Procedure (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 head Fix flow duration curve, e.g. based on Weibull distribution Fix turbine type, turbine efficiency curve and Fix minimum (dimensionless) turbine flow rate Fix ecological flow rate Assume Compute Make comparisons as appropriate; look for optimum value of
Some results from Exercise Ecological flow rate = 0 Head losses = 0 Francis turbine Cross-flow turbine rated annual- averaged rated Annual- averaged Francis Cross-flow k = 1.6 shape parameter of Weibull distribution
The two largest hydropower plants in the world Three Gorges Dam, China Itaipu, Brazil-Paraguay
THREE GORGES DAM – The largest hydropower plant in the world Yangtze River, China. Construction: started in 1994; to be completed in Dam - length: 2309m; height: 185m Reservoir – length: 600km About 1.5 million people had to be relocated
Installed power: MW 34×700 MW Francis turbines Three Gorges Dam hydropower plant
Construction: Reservoir area: 1350 km 2 Total dam length: 7235 m Dam height: 196 m Itaipu hydropower plant, Paraná River, Brazil- Paraguay Installed power: MW 18 Francis turbines of 715 MW
Principais bloqueios ao desenvolvimento de PCHs na EU Processo de licenciamento Exigências específicas locais Financiamento Ligação à rede eléctrica Venda de electricidade produzida Quadro regulador incerto Ausência de informações correctas Recrutamento e formação de técnicos
Principais 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).
Aspectos económicos Maiores 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.
Costs 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.
Range of costs for small hydropower projects. kW installed US$/kW
Small hydropower : specific costs of installed capacity Head (m) /kW
ENVIRONMENTAL 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.
ENVIRONMENTAL 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.
Basic 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 ISBN M. Manuela Portela, Hydrology, in: Guidelines for Design of Small Hydroplants (Helena Ramos, ed.), 2000, p ISBN (available at CEHIDRO, IST).