Chapter 7: Hydropower

Question 1

What is the percentage of the worldwide electricity consumption in 2015 from the total primary energy consumption?

Answer 1

15.3% of almost 160 000 TWh/a primary energy consumption

Question 2

How does the worldwide electricity production mix look like in 2015?

Answer 2

In 2015, electricity production reached 24000 TWh/a, with: -Fossile fuels 67% -Nuclear 11% -Hydro 16% -Wind 3% -Solar 0.8% - Other renewables 2.1%

Question 3

How much is the net energy input form the sun onto the earth surface? and how much percent is consumed from it in form of primary energy`? of electricity?

Answer 3

• 1.1 x 10^9
• TWh 1.6x 10^5 TWh = 0.015%
• 2.6 x 10^4 TWh= 0.002%

Question 4

Okey let’s review some basics from high school, what is the hydrologic water circuit? what are its phases ?

Answer 4

1. Evaporation in form of vapour 2. Condensation in form of clouds 3. Transportation by the wind (advection) 4. Precipitation in case the wind transport the thingies up –> condensation increases 5. Rainfall reaches the ground hurraay: - Surface runoff –> collects in creeks and rivers - Infiltration/ percolation: soil moisture increases, which feeds up the groundwater table, partly re-apparition in rivers later

Question 5

What is the catchment area of a river ?

Answer 5

Area where precipitation is collected

Question 6

Theoretical potential of hydropower? How much percent does it represent from the electrical generation in 2014? ( which is 2.6 x 10^4 TWh/a)

Answer 6

Theoretical power or energy per year that results from the line potential of all creeks and rivers in the area –> 44 000 TWh/a

Question 7

Technically exploitable potential ? How much percent does it represent from the electrical generation in 2014? ( which is 2.6 x 10^4 TWh/a)

Answer 7

Power or energy per year that can be exploited if all potential hydro power plants in a region would be built, i.e. taking into account insurmountable technical (and possibly ecological and structural) barriers, such as available conversion technology, accessibility etc. –> 28 000 TWh/a

Question 8

Economically feasible potential?

Answer 8

Power or energy per year that can be exploited by building all the plants that are economically feasible at the time being, i.e. at the current energy prices, capital cost and manufacturing, capital and O&M cost

Question 9

Expression of power output of a hydro power plant?

Answer 9

P = nu ·rho ·g ·Q ·H [W] wherein: nu: total plant efficiency (approx. 0.70 .. 0.85) rho: water density (approx. 1000 kg/m3) g: gravity constant (approx. 9.81 m/s2) Q: flow rate through plant [m3/s] H: geodetic head [m] (level difference between headwater and tailwater)

Question 10

Worldwide distribution and utilisation of hydro potentials

Answer 10

• Almost half of the world’s electrical energy could be supplied by hydro power plants (economically feasibly!)
• Hydro power development in Africa, Asia and South America holds a great potential

Question 11

Electricity generation from renewable sources in Germany ?

Worldwide?

Answer 11

• Total renewable share 2015: 29.0 %
• Total renewable share 2015: 23.1 %

Question 12

Land based Hydro Power Plants (HPP’s). Draw the categories in a chart!

Answer 12

can be categorized according to two criteria:

• head: low, medium and high head plants (<25m / 25 ..250m / >250 m)
• utilisation mode: run-of-the-river plants and storage plants

The pumped storage plants which are used to store excess electrical energy belong to the storage plants.

Question 13

When are storage plants used? How do their operation schemes look like?

Answer 13

• Storage plants are mainly used to satisfy peak load demand. They have a reservoir which permits to hold back the natural inflow over a certain period of time.
• Depending on the storage capacity and the temporal usage, they are operated under a yearly, weekly or daily operation scheme, thus being termed annual, weekly or daily storage reservoirs. (Jahres- Wochen- oder Tagesspeicher)
• As the energy contained in a given volume of water is in direct proportion to the head, storage plants are normally medium or high head plants.
• The reservoir is usually created by building a dam in a suitable location of the natural river valley.
• From the reservoir, the water is conveyed by an open channel or a headrace tunnel (Freispiegelgerinne oder Druckstollen) and a usually steeply descending penstock (Druckrohrleitung) to the power house which is situated farther below in the valley.
• A further type is the barrage plant (Talsperrenkraftwerk), where the power house is integrated into the base of the dam.

Question 14

a) What are the characteristics of a high head storage plant with an open flume diversion channel?

(storage plants)

Answer 14

characteristic features:

• low dam height
• due to the way the water is withdrawn, only small reservoir level variations are permissible –> small useable storage capacity
• relatively high losses in the long channel
• not suitable fur pumping mode –> limited economic feasibility

Question 15

b) What are the characteristics of High head storage plant with headrace tunnel (Druckstollen)?

(storage plants)

Give an example for this type of storage plant!

Answer 15

characteristic features:
large level variations possible –> large useful storage capacity

Deltah/H <<1

pumping mode possible–> high economic feasibility

often realised as a cavern power plant
type power house (Kavernenkraftwerk)
in the Alpine region, these plants are often supplied from more than one water intake

Example: Malta, Rottau plant (Austria)

Question 16

c) Barrage plants (Talsperrenkraftwerke)?

(storage plants)

Give an example of this type

Answer 16

characteristic features:

• limited useful storage capacity due to
• delta H ~ delta h_OW
• pumped storage possible –> intermediate economic feasibility
• sometimes also built as a separate power house at the foot of a barrage

Example: Grand Coulee dam

H = 116m
QM = 3100 m3/s Pn = 6 800 MW
built 1933 - 1941 extended 1975

Question 17

d) Pumped storage plants?

Answer 17

• basically built like other high head storage plants
• powerhouse contains pumps and turbines or reversible pump turbines, see 2.4 and 3.5.
• waterways must be suitable for turbine and pumping flow direction!

Question 18

Run-of-river (ROR) hydro power plants?

Answer 18

are normally utilising the current discharge of the river. The purpose of their weirs and dams is to create a pressure head, but they do not create a substantial storage volume

• Often, a number of successive power stations are situated along a river, forming a chain of power plants
• A section of a river is completely utilised, when the head of the backwater (Stauwurzel) of one power station reaches up to the tailwater of the next upstream HPP.
• The individual plants can be diversion plants or river plants
  
  • diversion canal plant (Ausleitungskraftwerk): The power house is situated outside of the river bed in a diverted reach (Ausleitungskanal).
  • river hydro power plant (Stromausbau, Flußkraftwerk): Power house and weirs are situated directly inside the original river bed .

Question 19

Diversion canal plant?

Example in real life xD?

Answer 19

e.g. as lateral channel power plant (Seitenkanalkraftwerk), often to be found in older small hydro plants

advantageous: sling power plant (a, c), shortcutting a natural sinuosity (Schleifenausbau),
lower losses compared to lateral channel (b)

advantages:

• powerhouse can be built in a dry excavation pit
• bed load (Geschiebe) can be kept away from the turbine inlets
• disaster flood (Katastrophenhochwasser) remains in the original river bed
• full river width available for flood discharge over the weir

disadvantages:

• ecologic flow in the original river bed needs to be granted
• later uprating (increasing of design flow rate) is not possible due to the fixed design flow rate of the channel
• high land use

Example>

Lech canal between Gersthofen and Meitingen
canal 15 km long, 3 HPP’s, H = 7 … 10 m, P = 7 … 11.5 MW

Question 20

What are the types of River hydro power plants?

Answer 20

Power plants situated in the original river bed can be categorized as follows:

• block power plant (zusammenhängendes Kraftwerk)
• bay type (special case of 1., Buchtenkraftwerk)
• pier head plant (Pfeilerkraftwerk)
• submerged power plant (überströmbares Kraftwerk)

Question 21

a) Block power plant?

Answer 21

Block power plant (zusammenhängende Bauweise):

• Weir and powerhouse are built within the original river bed without excavating the shores to widen the bed.
• The power house can be partitioned in two parts,it can be offset against the weir field in the up- or downstream direction.
• In river bends, the powerhouse is normally situated on the outer shore, as the river carries less sediment there.
  The drawings show the HPP Oberpeiching on the river Lech. It is equipped with three Kaplan full spiral turbines.

Question 22

b) Bay type block power plant ?

Answer 22

On narrow rivers, it is often necessary to install the power house in an artificial bay outside of the original river bed. Thus the whole original bed width is available for flood release.
Often, special intake structures (Einlaufbauwerke) are required to avoid sediment deposition in the bay.

Question 23

Which one has the best inflow conditions?

Answer 23

With short pier

Question 24

c ) Pierhead power plant?

Answer 24

In pierhead power stations, the piers holding the weirs are made a bit wider, so one turbine can be installed in each pier.

Question 25

d) Submersible power plants:

Answer 25

Weir and power house are combined into one building. Controlled flap gates (Fischbauchklappen) installed on top of the power house permit headwater level regulation and flood discharge.

Often also realised with Kaplan bulb turbines
Sometimes turbines and bottom outlets
(Grundablässe) placed alternately
advantages and disadvantages:
+ aesthetically very unobtrusive (Landschaftsschutz)
+ weight widely distributed onto the soil
+ very good flood discharge characteristics
+ head augmentation possible in overflow operation
- poor accessibility for maintenance and repair of electro-mechanical equipment
- increased susceptibility to sediment accumulation

Question 26

Now we come to the third type of hydroPP: Small hydro power plants :D what’s this ?

Answer 26

There are different definitions for discerning small and large hydro plants. The common definition rates plants < 1MW as “Micro Hydro” , plants < 5MW as “Small hydro” and the rest as “Large Hydro”. This section is dealing with hydro power plants with a design power smaller than 1 MW.

• Small hydro plants with higher heads (30-250m) are normally using Pelton or cross-flow turbines. These plants are essentially downscaled versions of the plants described before.
• Very low head plants: Output power: P= nu · rho · g · Q · H
  
  • big discharge for small power
  • bigger, more expensive turbine and structure
  • higher specific installation cost [€/kW installed power
• Small plants: The specific installation cost is raising with decreasing size
  European Water Framework Directive: strong restrictions concerning ecologic compatibility
  –> appropriate technologies need to be developed, granting:
  
  • minimum environmental impact
  • fish migration up- and downstream
  • acceptable investment return periods

Question 27

Water wheels are the first type of small hydro, tell me more about them and their different types?

Answer 27

• Water wheels are a very old-established technology.
• We distinguish overshot water wheels, breast wheels and undershot water wheels
• maximum achievable efficiency for the above types is approx. 80%, 65% and 50% respectively
• discharge up to approx. 1 m3/s, max. power approx. 50 kW
• pros and cons:
  
  • • aesthetically rather pleasing
  • ± overshot wheels are fish friendly, undershot and breast wheels are not
  • very low energy density, i.e. large dimension for small power
  • icing problems in winter
  • very low speed, i.e. extreme gearbox transmission ratio needed to drive a generator.a

Question 28

Hydrodynamic screw, based on which principle does it work ?

Answer 28

reversed functional principle of Archimedes’ screw (~250 B.C.)
• H = 1 … 10 m
• Q = 0.1 … 8 m3/s
• P = 1 … 500 kW
overall efficiency 65 … 75%
pros and cons:
+ relatively cost effective
+ relatively fish friendly (some problems with eels)

• relatively low speed, i.e. large gearbox transmission ratio needed to drive a generator
• icing problems in winter
• noise emissions, especially at variable tailwater level!

Question 29

Steff and KataMax turbines what is this ? is the hamann better ?

Answer 29

Steff and KataMax turbines

• Essentially a cross-over between an overshot water wheel and a hydrodynamic screw
• No benefit to be seen, but a lot of undesirable mechanical complexity….

Hamann? > It is basically a Kaplan bulb turbine with 30 runners instead of one + missing draft tube + missing guide vanes
Big failure –> it seems a good way to create a machine with minimum efficiency, maximum fish mortality and very poor operation & maintenance characteristics…

Question 30

How about the VLH turbine (very low head turbine)?

Answer 30

• rather large runner diameter –> limited exit losses
• directly coupled, submerged, slow running, variable speed PMG
• trash rack and trash rack cleaner integrate into the turbine
• turbine can be installed in a simple flume structure without big civil engineering structures
• basically a semi-Kaplan turbine (only runner blades adjustable) without draft tube.
• hinged turbine can be swivelled out of the water for maintenance or in case of flood
• efficiency approx. 80% claimed advantages:
• • very cost effective
• • fish friendly due to low circumferential speeds

Question 31

Say something abt the movable power plant (bewegliches Kraftwerk)!

Answer 31

• Developed by Hydro Energie Roth and HSI Hydro
• steel structure containing trash rack, turbine, generator and draft tube pivots around two bearings
• Kaplan bulb turbine with permanent magnet generator
• 5 sizes up to H= 8.5m, P=1.8 MW, m=125 to
• pros and cons:
  
  • • safe fish passage in downstream direction
  • • bed load flushed by raising the draft tube
  • • only feasible for relatively small units
  • • high cost of steel structure
  • • corrosion protection difficult

Question 32

The shaft hydro power plant (Schachtkraftwerk) what’s nice abt this one ?

Answer 32

• a special fish-friendly solution for low head applications developed at our institute
• • H = 1.5 … 8 m, Q = 1 … 200 m3/s, P = 10 … 800 kW
• pre-fabricated concrete module is installed in existing weir or dam
• horizontal trash rack permits
  
  • transport of bed load
  • safe fish passage in downstream direction
• plant is almost completely submerged and thus almost invisible
• power conversion is by submersible Kaplan bulb turbine(s)
• • • safe fish passage in downstream direction
• • civil engineering structure is only approx.
    25% compared to a diversion plant
    + very cost effective
    submerged turbines need to be removed for inspection / service
    trash rack cleaning technology still needs to be developed and proven.

Question 33

1- Stream turbines ?
2- How is the energy calculated for this turbine type?

Answer 33

1-

• An often cited potential technology for producing electricity out of rivers in a very environmental friendly way “without any dams or weirs”:
• a stream (or current) turbine is extracting kinetic energy out of the flow of a river.
• potential turbine types are (in descending order of sensibility)
  
  • horizontal axis stream turbine (built like a wind turbine)
  • vertical or horizontal axis Darrieus or Gorlov turbine
  • devices based on oscillating airfoils
  • devices with drag-type runner

2- Energy in a free flow: kinetic energy of free flow E = ½ . m .c² [J]

Betz limit:
Pmax,th = 0.59 · 0.5 · rho · A · c³ (like wind turbine)

–> main problem:
very low energy density at low flow velocities
economically viable only at c > 2.5 m/s (rarely to be found!)

Question 34

Small excercise for a stream turbine: With river 3m deep, 10 m wide, c= 1.0 m/s, Q=30m3/s

Calculate P for each of these cases

• 3 stream turbines D=2.5 m each:
• weir with H=1 m, 3 Kaplan turbines D=2.5m:
• weir with H=2 m, 2 Kaplan turbines D=2.5m:

Answer 34

• P = 4.3 kW
• P = 280 kW
• P = 560 kW

Question 35

How is a pumped storage plant technically realized?

Answer 35

Excess electrical energy is used to pump water into a reservoir at higher elevation (pumping operation). The energy stored as potential energy is re- converted into electrical energy when needed (turbine operation). Depending on the storage volume available, the plant may be operated on a daily, weekly or seasonal basis.

A higher head permits to:

• store more energy within a given storage volume
• produce a higher electrical power with a given cross sectional area of tunnels and penstocks.

–> normal head range of pumped storage plants: 150 – 1000m

Question 36

Expression of the efficiency nu_overall of pumped storage plants?

Give an Example of PSP!

Answer 36

Relevant losses:

• Viscous friction in tunnels and penstock H
• hydr. and mech. losses within pump and turbine
• el. and mech. losses within motor and generator

Example> PSP in Vianden, Luxembourg:
nominal power 1296 MW, Europe’s biggest PSP
head approx. 280m, head reservoir capacity approx. 6.8 mio m3, capacity approx. 5 GWh
• built 1959 to 1964
nine tertiary sets 100MW each
cavern length 330 m long, height 25 m, width 15 m
• extended 1970-1976:
one pump turbine 196MW
2009 - 2012: one further pump turbine approx. 200 MW, head reservoir level raised by 1m at the same time

Question 38

Pumped storage plants in a nutshell!

Answer 38

Question 39

Give some examples with new suggestions of PSP and explain the benefits and challenges of each!

Answer 39

The circular levee store (“Ringwallspeicher”) by Dr.- Ing. Matthias Popp a pumped storage plant with an artificially created elevation

• earth removed in excavating the lower reservoir is used to create the upper reservoir
• claimed investment cost 15 € / kWh capacity
• can be built in flat country
• illustration shows projected plant with
• 215 m high levee
• 11.4 km diameter of upper reservoir
• power 2 GW
• capacity 600 GWh ?
• side benefits:
• combination with wind turbines and solar panels
• recreational use
• fisheries etc
• Hydraulic Hydro Storage (Eduard Heindl)
  
  • ​a gravity store using water as hydraulic transmission fluid
    higher energy density compared to conventional PSP’s as:
    rho_rock > rho_water
    h approx 0.5 * total height
  • challenges:
    rock sufficiently stable?
    sealing of rock piston?
    construction technology?
    safety?
    life on the piston top?

Question 40

Types of hydro turbines?

Answer 40

Impulse turbines: Pelton and cross flow turbines

Reaction turbines: Francis-, Deriaz-, Kaplan- and Kaplan bulb turbines

Question 41

Impulse turbines: Pelton and cross flow turbines, how does it work?

Answer 41

• The energy conversion within the turbine runner is performed at constant (=ambient) pressure.
• All the energy available at the pressure inlet of the turbine is converted into
• kinetic energy of the free jet leaving the nozzle.
• This kinetic energy is then converted into mechanical energy in the buckets of the turbine runner while the pressure remains constant.

Question 42

Reaction turbines (Überdruckturbinen, Reaktionsturbinen): Francis-, Deriaz-, Kaplan- and Kaplan bulb turbines

Answer 42

• The static pressure at the runner inlet is higher than at the runner exit.
• The pressure energy available at the turbine inlet is only partly converted into kinetic energy due to acceleration in the spiral case, the stay vanes and the guide vanes.
• Most of this kinetic energy and the remaining pressure energy are converted into mechanical energy in the turbine runner.
• The draft tube converts the kinetic energy remaining at the runner outlet into pressure, thus contributing to the pressure drop across the runner.

Question 43

Functional principle of water turbines?

Answer 43

• Common basic principle of all kinds of fluid machinery used in Hydro Power: (water wheels, Pelton, Francis or Kaplan turbines)
• The fluid is conveyed onto the runner in a way that it exerts a force in circumferential direction, thus producing a driving torque M = F · r
• The force can be a gravity, impulse, pressure or lifting force or a combination of these.
• The layout of the waterway can be
  
  • straight and tangential to the runner (undershot water wheel, Pelton turbine)
  • spiral-shaped around the runner (Francis and Kaplan turbine)
  • axial with a swirl around the runner axis (Kaplan bulb turbine)

Leaving aside the water wheels, we need to distinguish between impulse turbines and reaction turbines.

Question 44

What is the specific speed n_q of a turbine?

Answer 44

n_q is a parameter describing the shape of a turbine independently of its size:

n_q = Q^0.5/H^0.75

Generally, high specific speed:
+ high speed –> high energy density but
- high structural loads and cavitation risk thus:

• low head and big discharge: high specific speed nq in order to obtain a machine with high energy density.
• high head: limited specific speed to avoid cavitation

Question 45

Pelton turbines and their application range?
How are Pelton turbiones controlled?

Answer 45

Nozzle: Conversion of pressure energy into kinetic energy of a free jet
partially impacted runner, running in air: deceleration of the free jet under ambient pressure (constant pressure turbine / impulse turbine , Gleichdruckturbine)
dry buckets should not hit the tailwater surface
–> elevation above tailwater level necessary (Freihang HF)
Impeller can be impacted multiple times at the periphery

Application range

Head range: H = 150 … 1800 m
Flow rates up to 60 m3/s; multi-jet type at all the bigger flow rates
specific speed from nq=5 to nq=15.

Control
Discharge and power are controlled by a needle within the nozzle and by the jet deflector
small turbines: regulating spear, externally actuated
bigger turbines: needle controlled by hydraulic servo motors inside the valve
jet deflector: permits quick power reduction without unduly quick closing of the valve (water hammer!)

Question 46

Francis turbines

Answer 46

Francis turbines are reaction turbines, meaning that both pressure and kinetic energy are converted by the runner. The machines are completely filled with fluid and lie typically below the tailwater level to avoid cavitation. They can also be built as reversible pump turbines: By operating the runner in the opposite direction of rotation the turbine works as a pump.

• Head range: H = 30 … 800 m
• Flow rates up to 800 m3/s
• specific speed from nq=20 to nq=100
• normally executed with a spiral casing,
• SHP plants sometimes still use the early pit turbine concept without spiral case
• power and flow control is by adjustable guide vanes (wicket gate, Leitschaufeln)
• a draft tube decelerates the runner exit flow and recuperates the kinetic energy in the exit velocity

Question 47

Low specific speed Francis turbines ?

Medium specific speed Francis turbines?

High specific speed Francis turbine?

Answer 47

Low specific speed Francis turbines

• Highest head and smallest discharge in the Francis turbine range
• Flat, disc-shaped runner: flow is in is mainly in a radial (inward) direction (radial turbine)
• High pressures: thick-walled, strong spiral case

Medium specific speed Francis turbines

• Runner flow is in radial-axial (diagonal) direction

High specific speed Francis turbines

• Lowest head and greatest discharge in the Francis turbine range
• Runner flow is in radial-axial (diagonal) direction

Question 48

Kaplan Turbines

Answer 48

for different application ranges are built in the following variants:

• Kaplan full spiral turbines , nq: 90 .. 180 , H = 75 .. 15 m
• Kaplan semi spiral turbines nq: 150 .. 280 , H = 40 .. 5 m
• Kaplan bulb turbines nq: 220 .. 320 , H = 20 .. 2 m

They are normally double-regulated, i.e. guide vane and runner blade angle are separately adjustable. Thus, a high efficiency over a wide range of flow rates is achieved.

Question 49

Kaplan S-turbine?

Answer 49

only used for small turbines due to unfavourable energy conversion in the draft tube
external generator driven via straight shaft
often with adjustable runner vanes and fixed guide vanes
special design by Sulzer Hydro: CAT (Compact Axial Turbine) with upstream shaft for small hydro plants

Question 50

Kaplan bulb turbine with rim generator (Straflo turbine)?

Answer 50

• application range as Kaplan bulb turbine
• slender bulb contains bearings only
• rim generator on the periphery of the runner
• problematic seal on the ring gap (to keep the generator dry) because of high peripheral velocity –> normally only executed with fixed runner blades and adjustable guide vanes (Kaplan propeller turbine)

Question 51

Comparison between all turbine types?

Answer 51

• each of the turbine types shown can reach a peak efficiency between 92 and 96 %
• Francis turbine: closing the guide vanes changes the inflow angle to the runner blades —> reduced efficiency in part load
• double regulated Kaplan turbine: runner blades are adjusted to suit inflow angle
• semi-Kaplan turbine (only runner regulated): wider useful range than a low-head Francis turbine
• Kaplan propeller turbines (fixed runner blades) have a very peaky efficiency curve
• Pelton turbine: flow angle and velocity are almost independent of the nozzle opening
• -> flat efficiency curve

Question 52

Which turbines are best suitables for PS sets?

Usage in Ternary set differences between both turbines?

Answer 52

head range of PSP’s: 100m to 1000 m
–> only Francis and Pelton turbines are suitable

• with Francis turbines: usually horizontal shaft
• with Pelton turbine: always vertical shaft. The turbine needs to be above and the pump below the tailwater level (cavitation!)
• same sense of rotation in pumping and turbine mode: quick changes between modes of operation

Question 53

What kind of Storage pumps are used for pumped storage?

Answer 53

• turbo machines used for pumped storage are large centrifugal pumps
• with respect to cavitation, centrifugal pumps can only reach a delivery head of 150 to 200m per stage–> most storage pumps are of the multi-stage type.
• even then, the pumps requires a high pressure at the inlet of the first stage to avoid cavitation: pump needs to be set far below the tailwater level
• often designed as double flow pumps to avoid high axial forces

Question 54

What is a reversible Reversible pump turbine (Pumpturbine, Pumpenturbine) ?

Answer 54

Francis turbine that is designed to operate as a centrifugal pump when the rotation is reversed
advantage: only one hydraulic machine needed
disadvantages:
hydraulic design needs to compromise between the requirements of pump an turbine
 slightly lower efficiency
changing sense of rotation:
 design of bearings, slower change from pumping to turbine mode and back