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HYDROELECTRIC ENERGY. Renewable Energy Resources 2008. António F. O. Falcão. 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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Hydroelectric energy

HYDROELECTRIC ENERGY

Renewable Energy Resources

2008

António F. O. Falcão


Hydroelectric energy

  • HYDRO ENERGY RESOURCE

  • Total resource: (about 15 times total world hydroelectric production

  • Technical potential: about:

  • Total world electricity consumption: 16 400 TWh

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


Hydroelectric energy

Prefixes:


Hydroelectric energy

15,8% of world electrical energy consumption

Based on average output 1999-2002

Source: G. Boyle, Renewable Energy, 2004.


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Technical potential

Economic potential

Exploited potential

North & Central

America

Australasia/

Oceania

Europe

Asia

South America

Africa

Exploited hydro potential by continent


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Weir and intake (dique ou açude)

Canal

(canal)

Forebay tank

(câmara de carga)

Penstock

(conduta forçada)

Power house

(casa das máquinas)

Small hydro site layout


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Large hydro

10 MW

Small hydro

500 kW

Mini-hydro

100 kW

Micro-hydro

Note: there are other definitions.


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Small hydroelectric plants (< 10 MW)

World totals

  • 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


Hydroelectric energy

Installed capacity and production of SHPs (<10MW) in 30 European countries


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A

= gross head (altura de

queda bruta) in metres

Canal

= gross head

(altura de queda bruta)

L = losses in canal, pennstock, in metres

Pennstock

= net head (altura de queda disponível)

Turbine

B

Q = flow rate or intake (caudal), in m3/s

= gross power (potência bruta), in Watts

= power available to turbine

turbine efficiency

= turbine power output

= electrical power output

electrical efficiency


Hydroelectric energy

Hydraulic turbine

rated

H = (net) head

Q = flow rate

N = rotational speed

N, H = constant

Dimensional analysis

Q

(Dimensionless) specific speed

Ω is directly related to geometry (type) of turbine


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Francis

Pelton

Kaplan

Rotors of hydraulic turbines with different specific speeds Ω.


Hydroelectric energy

Correspondence between specific speed Ω

and type of hydraulic turbine (Pelton, Francis, Kaplan)


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Pelton turbines (low Ω)

  • Usually:

  • High H

  • Small Q


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Twin jet Pelton turbine

wheel or runner

nozzle

pennstock


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  • Large Pelton turbine

  • Vertical axis

  • 6 jets (6 nozzles)


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Francis turbines (medium Ω)


Hydroelectric energy

Francis turbine

Spiral casing

runner

Guide vanes

draft tube


Hydroelectric energy

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.


Hydroelectric energy

Kaplan turbines (high Ω)

  • Usually:

  • Low H

  • Large Q


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Kaplan turbine

Electrical generator

Blade angle can be controlled

spiral casing

Guide vanes

runner


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Propeller turbine (small power plants)

Simple control: rotor blades are fixed

Kaplan turbine

Double control

Guide-vane control

Rotor-blade control


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A variant of the Kaplan turbine: the horizontal axis

Bulb turbine

Used for very low heads, and in tidal power plants

guide vanes

Tidal plant of La Rance, France


Cross flow turbine also known as mitchel banki and ossberger turbine

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.


Cross flow turbine

Cross-flow turbine


Hydroelectric energy

Head-flow ranges of small hydro turbines


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H (m)

Q (m3/s)

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.


Hydroelectric energy

  • 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)


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Pelton turbine

D

Diameter D


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Francis and Kaplan turbines

D

Specific diameter

(dimensionless)


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1.0

Pelton

0.8

Cross-flow

Efficiency

0.6

Kaplan

Francis

Propeller

0.4

0.2

0.0

0.0

0.2

0.4

0.6

0.8

1.0

Flow rate as proportion of design flow rate

Part-flow efficiency of small hydraulic turbines


Hydroelectric energy

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.


Hydroelectric energy

Power plant

Stream-gauging station

  • 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.


Hydroelectric energy

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.


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Mean annual flow duration curve

mean annual flow rate

Time fraction flow rate is equalled or exceeded

Dimensionless form of the mean annual flow duration curve


Hydroelectric energy

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.


Hydroelectric energy

Run-of-river plant and flow duration curve.

Max. turbine flow

Min. turbine flow

Ecological flow

Time-fraction flow rate is equalled or exceeded


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Run-of-river hydropower plant(fio de água)

  • 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.


Hydroelectric energy

Maximum and minimum turbine flow rates to be decided based on turbine size and efficiency curve.

1.0

Pelton

0.8

Cross-flow

Efficiency

0.6

Kaplan

Francis

Propeller

0.4

0.2

0.0

0.0

0.2

0.4

0.6

0.8

1.0

Flow rate as proportion of design flow rate

Part-flow efficiency of small hydraulic turbines


Hydroelectric energy

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).


Hydroelectric energy

Hydropower plant with storage capacity

  • 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).


Hydroelectric energy

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 Hb .

  • Loss L in hydraulic circuit.

  • Efficiency curve of turbine, and rated & minimum turbine flow.

  • Efficiency of electrical equipment.

  • Ecological flow rate.


Hydroelectric energy

Exercise

or

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

is probability density function.

Time fraction flow rate is equalled or exceeded τ

= probability of occurrence of flow between q and q + dq .


Hydroelectric energy

k = shape parameter

c = scale parameter

Exercise

Choice of function F(q)

Weibull distribution(widely used in wind energy):


Hydroelectric energy

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.


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Exercise

Annual-averaged electrical power output (SI units):


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Exercise

Total electrical energy produced in one year:


Hydroelectric energy

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


Hydroelectric energy

Some results from Exercise

Ecological flow rate = 0

Head losses = 0

k = 1.6 shape parameter of Weibull distribution

Cross-flow turbine

Francis turbine

rated

rated

annual-averaged

Annual-averaged

Annual-averaged

Francis

Cross-flow


Hydroelectric energy

The two largest hydropower plants in the world

Three Gorges Dam, China

Itaipu, Brazil-Paraguay


Hydroelectric energy

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


Hydroelectric energy

Three Gorges Dam hydropower plant

  • Installed power: 22500 MW

  • 34×700 MW Francis turbines


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Itaipu hydropower plant, Paraná River, Brazil-Paraguay

Construction: 1984-91

Reservoir area: 1350 km2

Total dam length: 7235 m

Dam height: 196 m

Installed power: 12870 MW

18 Francis turbines of 715 MW


Hydroelectric energy

  • 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


Hydroelectric energy

  • 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).


Hydroelectric energy

  • 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.


Hydroelectric energy

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.


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US$/kW

kW installed

Range of costs for small hydropower projects.


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Small hydropower : specific costs of installed capacity

€/kW

Head (m)


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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.


Hydroelectric energy

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 flowsdownstream 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.


Hydroelectric energy

  • 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).


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