1. Renewable Energy Resources
HYDROELECTRIC ENERGY
Renewable Energy Resources
2008
António F. O. Falcão

2. 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

3. Prefixes:

4. 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
Source: G. Boyle, Renewable Energy, 2004.

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

6. 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)

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

9. 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 to 60 GW

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

11. L = losses in canal, pennstock, in metresB
= 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

12. 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

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

14. and type of hydraulic turbine (Pelton, Francis, Kaplan)
Correspondence between specific speed Ω
and type of hydraulic turbine (Pelton, Francis, Kaplan)

15. Pelton turbines (low Ω)
Usually:
High H
Small Q

16. Twin jet Pelton turbine
wheel or runner
nozzle
pennstock

17. Large Pelton turbine
Vertical axis
6 jets (6 nozzles)

18. Francis turbines (medium Ω)

19. Francis turbine
Spiral casing
Guide vanes
runner
draft tube

20. 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.

21. Kaplan turbines (high Ω)
Usually:
Low H
Large Q

22. Kaplan turbine Electrical generator Blade angle can be controlled
spiral casing
Guide vanes
Blade angle can be controlled
runner
Electrical generator

23. 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

24. 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

25. 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

26. Cross-flow turbine

27. Head-flow ranges of small hydro turbines

28. 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)

29. 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)

30. Pelton turbine D
Diameter D

31. Francis and Kaplan turbines
Specific diameter
(dimensionless)

32. 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

33. 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.

34. 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

35. 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.

36. 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

37. 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.

38. 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.

39. 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)

40. 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.

41. 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).

42. 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

43. 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.

44. 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 .

45. 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

46. 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.

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

48. Total electrical energy produced in one year:
Exercise

49. 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

50. 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

51. The two largest hydropower plants in the world
Three Gorges Dam, China
Itaipu, Brazil-Paraguay

52. 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

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

54. Itaipu hydropower plant, Paraná River, Brazil-Paraguay
Construction:
Reservoir area: 1350 km2
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

55. 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

56. 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).

57. 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.

58. 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.

59. Range of costs for small hydropower projects.
kW installed
US$/kW

60. Small hydropower : specific costs of installed capacity
Head (m)
€/kW

61. 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.

62. 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.

63. 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).