Energy & Sustainability. Lecture 12: Hydroelectricity February 19, 2009

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1 Energy & Sustainability Lecture 12: Hydroelectricity February 19, 2009

2 Estimating the Power Before Decision to Build Empirical relationships between flow rate and either water depth or speed (in particular for developed countries such data has been accumulated for years) Alternative method: determination of annual precipitation, particularly suitable for large systems, need to take into account losses due to evaporation, leakage, vegetation (as much as three quarters) Time variations Protection against 100 year flood

3 Francis turbine Picture: Grand Coulee dam By far the most common type in present day medium or large scale plants Used in installations where head is as low as 2 m or as high as 300 m Radial flow turbines, water flow is inwards towards the center

4 Francis turbine Picture: Three gorges dam Completely submerged Runs equally well with horizontal or vertical axis

5 In medium or high head turbines: flow is channeled though a scroll case (volute), curved tube of diminishing size (snail shell) with the guide vanes set in its inner surface Guide vanes guide water towards the runner

6 Francis turbine Picture: Three gorges dam Completely submerged Runs equally well with horizontal or vertical axis Shape of the guide vanes, runner blades, and the speed of the water are critical: run most efficiently when blade speed only slightly less than water speed As water crosses the curved blades it is deflected sideways, losing its whirl motion Water also deflected to the turbine axis where it finally flows out of the central draft tube (see sketch on last slide) Pushes blades in the opposite direction: this reaction force transfers energy and maintains the rotation Water arrives at the runner under pressure > pressure drop through the turbine accounts for large part of the delivered energy

7 Maximizing efficiency Efficiencies as high as 95%, but only under optimum conditions Maintaining the right speed and direction of the water relative to the runner blades is important But: suppose the demand falls Output power can be reduced by reducing the water flow In Francis turbines this is done by turning the guide vanes, but > changes the angel at which the water hits the moving blades > efficiency falls Other efficiency loss: flowing water carries away kinetic energy > partial remedy: flare the draft tube + volume flow stays the same > speed of water decreases > pressure back at the exit of the tube is reduced > pressure drop across it increases > energy extracted increases

8 Limits of the Francis Turbine Low head situations and high head situations High head: mean high water speeds > high rotation speeds > for sites with very highheads Francis turbine becomes unsuitable > impulse turbine Low head: low water speeds, large volume > larger input area required and adaptation of blades to the reduced speed > wide turbine entry and increasingly twisted blades > propeller turbine

9 Propeller turbine Axial flow turbine Area through which water enters as large as can be: it is the area swept by the blades Suitable for very large volume flows and propellers have therefore become usual for very low heads of a few meters

10 Propeller Turbine

11 Propeller turbine Technically simpler to improve efficiency by varying the angle of the blades when power demand changes => Kaplan turbines Blade speed is >> water speed (as much as twice as fast) Blade angle needs to increase with distance from center because outer parts move faster => twisted shape Semi Kaplan: guide vanes are not adjustable

12 Impulse turbines For sides with heads > ~250 m: Pelton wheels A set of double cups or buckets mounted around the rim A high speed jet of water, formed under the pressure of a high head, hits the splitting edge between each pair of cups and in turn as the wheel spins The water passes round the curved bowls and gives up almost all its kinetic energy Power can be varied by adjusting the jet size or by deflecting the entire jet away from the wheel

13 Impulse turbines Efficiency of a Pelton wheel is greatest when the speed of the cups is half the speed of the water Cup speed depends on the water speed and the wheel diameter and the water speed depends on the head > optimum relation ship between those three factors Difference to reaction turbines before: is not submerged and doesn t work based on the pressure difference, operates in air at normal atmospheric pressure, driven by the impulse of the water from the jet

14 Pelton Wheel Input Power Potential energy of water mass M and height H: MgH, g acceleration due to Gravity If all potential energy is converted into kinetic energy: MgH = ½ M v 2 => v = (2gH), so the volume flow of an effective head H is Q=A (2gH) so the input power is P (kw)=1000 A (2gH) g H = 45 A H 3 Number of jets is j: P(kW)=45 j A H 3

15 Pelton Wheel Input Power

16 Ranges of Application

17 Specific Speed N S = n P H 2 H n: rotation rate in rpm P: available power in kw H: effective head in m Type of Turbine Range of specific speeds Francis Propeller or Kaplan Pelton 10 80

18 Small Scale Hydroelectricity (SSH) Prevailing view: <~ 10 MW, in the US: <30 MW Can also be classified by the available head Many SSH plants are run of river with heads of only a few meters Nowadays: MW are the norm for power stations (large scale) Renewed interest in SSH different reason in different regions: Industrialized countries: Environmental issues Developing countries: stepwise electrification (local grid systems) Renewed interest lead to technical improvements (standardization of components, electronic controls => off the shelf systems at reduced costs and more reliable)

19 World SSH Data SSH capacity and output is rising But how rapidly not easy to estimate No reliable data especially from remote areas China s SSH plants (reported in the early 1990s) have become (2003) WEC survey: by the end of 1999 installed capacity of SSH (<10 MW) is 18 GW in 38 selected countries, includes Americas and Europe, but not China World wide increase estimates: 1 2 GW/year Estimated operational capacity in 2003: GW, about 1% of the world electricity generation

20 SSH in China 300 million people derive their electricity from SSH (here defined as < 25 MW capacity) Intense program of local electrification over the past few decades, in early 2002: total installed capacity >26 GW China distinguishes micro (<100 kw), mini ( kw), and small ( MW) plants Of the plants: 90% micro or mini but ¾ of the total output comes from the 10% of small installations > raising concern because of environmental impacts of these

21 SSH in the Rest of the World > 26 GW from installation with <10 MW, 10 GW in western Europe, 3.5 GW in Japan SSH in most contexts is more costly than electricity from conventional sources IEA 2003: it is claimed that technical improvements will bring the costs to a level which makes SSH competitive in suitable locations Still many European countries concentrate on other renewables like wind power and solar PV

22 SSH in the Rest of the World Elsewhere in the world: considerable SSH potential remains unused Concept of complete water to wire systems at remote sites is estimated to represent a worldwide market of up to $5 billion and has attracted manufacturers in Europe, the U.S. etc

23 SSH in the Rest of the World Local manufacturers have been encouraged as well: ex. Nepal: many mountain streams are suitable for high head plants > development of local industry producing extremely smallscale systems, transportable by a single person on foot Peltric turbo generator set: tiny Pelton wheel driving a simple generator Operates under heads of 50 70m, output: ~ 1kW Copied in other countries Unfortunately encouraging development came to a halt, because of social unrest and total operational capacity has fallen below 13 MW recorded in 2000 (WEC)

24 Environmental Considerations First quote: The environmental impacts of a hydroelectric project must be thoroughly analyzed since, after it is completed, they are essentially irreversible Energy Resources and Policy, R.C. Dorf, 1978

25 Environmental Considerations Second quote: The ecological damage per unit of energy produced is probably greater for hydroelectricity than for any other energy source Final Report of the Committee on Nuclear and Alternative Energy Systems (CONEAS), 1979

26 Environmental Considerations Third quote: carefully planned hydropower development can, and does, make a great contribution to improving electrical system reliability and stability throughout the world. [It] will play an important role in the improvement of living standards in the developing world, [and] make a substantial contribution to the avoidance of greenhouse gas emission and the related climate change issues Survey of Energy Resources, Hydropower,WEC, 2003

27 Benefits of Hydro electricity No CO 2 No particulates or chemical compounds such as dioxins that are harmful to human health No emission of radioactivity No major explosions or fire Often associated with positive environmental effects such as flood control or irrigation Valued amenity or even a visual improvement of landscape

28 Deleterious Effects Hydrological effects water flows, groundwater, water supply, irrigation etc. Other effects of large dams and reservoirs Social effects

29 Hydrological Effects Diverting rivers: The Gabcikovo Nagymaros Project

30 The Gabcikovo Nagymaros Project Danube is already used for hydroelectricity but this project on the Slovak Hungarian border has been controversial 1977: Agreement on a 880 MW scheme including a reservoir and a canal to carry diverted water to a power plant in Gabcikovo and a second barrage and plant at Nagymaros Work proceeded for a decade Late 1980s: political changes, increasingly vocal opposition on environmental grounds 1989: construction stopped on Hungarian side May 1992: cancellation Newly established Slovak state declared cancellation illegal

31 The Gabcikovo Nagymaros Project October 1992: Slovak engineers completed the diversion into the new channel (18 km long, with walls rising 15 m above the surroundings) Effects: fall in the water table Wells drying up Vegetation dying Unique forms of wild life in danger Reaction: - Calls for legal limits to diversion - Artificial irrigation scheme : Slovakia agreed to reduce diversion

32 The Gabcikovo Nagymaros Project September 1997: International Court of Justice ruled that both countries acted illegally demanded that they should jointly negotiate a new solution demanded that this solution must accommodate both the economic operation of the system of electricity generation and the satisfaction of essential environmental concerns Status as of October 2007: negotiations between the two countries are ongoing Present half scheme with only one power station financial disaster See also:

33 Other Hydrological Effects Evaporation from exposed surface of a large reservoir may significantly reduce the availability of water supply

34 Dams and Reservoirs Construction process itself: widespread disturbance if only for a few years Effects on a fragile eco system: long lasting In any case: Significant environmental changes View depends on the situation DOE survey 2001: primary purpose or benefit of 35% of dams in the US is recreation 2% is hydroelectricity

35 During the 20 th century, some 200 dams failures outside China are thought to have resulted in the deaths of more than ten thousand people. And within China, in one year alone, 1975, it is estimated that almost a quarter of a million people perished in a series of hydroelectric dam failures ( L. Sullivan, 1995, The Three Gorges Project ) 1971 earthquake near Los Angeles: Lower San Fernando Dam damaged, had the wall been at its maximum height 15 million tonnes of water could have been released on the inhabitants in the valley below Catastrophes

36 Silt Aswan Dam in Egypt, built in the 1960s Land downstream no longer receives the soils and nutrients previously carried by the annual Nile floods > agricultural system largely been destroyed Silt reduces its useful volume and hydro potential Hoover Dam: 70 years old lost about 1/6 th of its useful storage in its first 30 years Loss rate fell when Glen Canyon was built

37 Methane CH 4 More potent greenhouse gas than CO2 Vegetables matter decays in air to CO2, but can decay anaerobically, producing methane, when large area is flooded World Commission on Dams (WCD) 2000: All large dams and natural lakes in the boreal and tropical regions that have been measured emit green house gases [ ] some values for gross emissions are extremely low, and may be ten times less than the thermal option. Yet in some cases the gross emission can be considerable, and possibly greater than the thermal alternatives Tropical climates (e.g. Brazil): large scale hydro may emit as much greenhouse gases annually as thermal alternative although data still patchy

38 Social effects Aswan and Kariba dams in Egypt: people relocated In all of China over the second of the 20 th century: 10 million people

39 Economics Relevant factors: Initial capital costs Operation and maintenance costs Predicted lifetime Load factor Discount rates Costs of borrowing money

40 Economics Expected lifetime of machinery years Expected lifetime of structures years Dominant factor however civil engineering costs which can vary greatly from site to site: accounts for 65% to 75% of the total costs Environmental and other criteria for a license: 15 20% So 85 95% are site costs Remaining: turbo generators and controlsystems (~10%) and operation and maintenance (1 2%)

41 Economics Capital costs between $1200 and $4000 per kw, depend on where ( green field ) Refurbishing about half that But hydroelectric plants have long lives, costs for a electricity produced by a plant several decades ago is very small in comparison > investing in hydroelectricity seems like a profitable investment Why are gas turbine plants preferred in many countries?

42 Economics Compare CCGT plant and hydro plant (exactly the same annual output and same total lifetime costs: construction, maintenance, operation fuel) Hydro plant has greater lifetime output But future costs and earnings are both subject to discounting Reduces fuel costs for CCGT and reduces output earnings for both Hydro appears to have higher lifetime cost later, net earnings higher for CCGT

43 The articles/talks Article: 4 pages excluding figures, double spacing, with references Talks: 10 to 15 minutes, about 10 slots available Extra Credit: You may hand in an article in addition to your talk

44 The articles/talks Introduction: What is the question/problem discussed? What is the context? Scientific background Economical background Political background Pros and cons Conclusion Base your argumentation on solid numbers for which you can give references

Chapter 5 1. Hydraulic Turbines (Gorla & Khan, pp )

Electronic Notes Chapter 5 1. Hydraulic Turbines (Gorla & Khan, pp.91 141) 1. Terminologies Related to A Hydropower Plant Hoover Dam generates more than 4 billion kilowatt-hours of electricity each year,