Renewable Energy Resources 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: 16 400 TWh

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15,8% of world electrical energy consumption Regional hydro potential output Region Techical potential TWh/year Annual output TWh/year Output as % of technical potential Asia 5093 572 11% South America 2792 507 18% Europe 2706 729 27% Africa 1888 80 4,20% North America 1668 665 40% Oceania 232 40 17% World 14379 2593 15,8% of world electrical energy consumption Based on average output 1999-2002 Source: G. Boyle, Renewable Energy, 2004.

Exploited hydro potential by continent Africa Asia Australasia/ Oceania Europe North & Central America South America Technical potential Economic potential Exploited potential

Small hydro site layout 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)

Large hydro Small hydro Mini-hydro 10 MW 500 kW 100 kW Micro-hydro Note: there are other definitions.

Small hydroelectric plants (< 10 MW) World totals Installed capacity (GW) Annual production TWh/year Total (large + small) 740  2700 Small (< 10 MW) 50 a 60  150 Small/total 6 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

L = losses in canal, pennstock, in metres 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 m3/s = gross power (potência bruta), in Watts = power available to turbine = turbine power output turbine efficiency = electrical power output electrical efficiency

Ω is directly related to geometry (type) of turbine 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

Rotors of hydraulic turbines with different specific speeds Ω. Pelton Francis Kaplan Rotors of hydraulic turbines with different specific speeds Ω.

and type of hydraulic turbine (Pelton, Francis, Kaplan) 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 Electrical generator Blade angle can be controlled spiral casing Guide vanes Blade angle can be controlled runner Electrical generator

Simple control: rotor blades are fixed Kaplan turbine Double control Guide-vane control Rotor-blade 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. Explicar princípio de funcionamento; discutir a definição

Cross-flow turbine

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 (m3/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 Specific diameter (dimensionless)

Part-flow efficiency of small hydraulic turbines Cross-flow Pelton Kaplan Francis Propeller 0.0 0.2 0.4 0.6 0.8 1.0 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.

Run-of-river plant and flow duration curve. 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 0.0 0.2 0.4 0.6 0.8 1.0 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 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.

Exercise or F(q) is fraction of time q is exceeded. 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 .

Choice of function F(q) Exercise Choice of function F(q) k c 0,5 0,50000 0,55 0,58740 0,6 0,66464 0,65 0,73192 0,7 0,79000 0,75 0,83988 0,8 0,88261 0,9 0,95040 1,0 1,00000 1,1 1,03636 1,2 1,06309 1,3 1,08275 1,4 1,09719 1,6 1,11536 1,8 1,12450 2,0 1,12838 Weibull distribution (widely used in wind energy): c = scale parameter k = shape parameter

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.

Annual-averaged electrical power output (SI units): Exercise Annual-averaged electrical power output (SI units):

Total electrical energy produced in one year: Exercise

Procedure (suggestion) 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 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 2009. Dam - length: 2309m; height: 185m Reservoir – length: 600km About 1.5 million people had to be relocated

Three Gorges Dam hydropower plant Installed power: 22500 MW 34×700 MW Francis turbines

Itaipu hydropower plant, Paraná River, Brazil-Paraguay Construction: 1984-91 Reservoir area: 1350 km2 Total dam length: 7235 m Dam height: 196 m Itaipu hydropower plant, Paraná River, Brazil-Paraguay Installed power: 12870 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 10 - 20 anos.

Costs of installation of small hydropower plants Comparison: cost of installation of a large onshore wind turbine (> 1MW): about 1.0 - 1.1 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. 147-194. ISBN 0-19-926178-4. M. Manuela Portela, “Hydrology”, in: Guidelines for Design of Small Hydroplants (Helena Ramos, ed.), 2000, p. 21-38. ISBN 972-96346-4-5 (available at CEHIDRO, IST).