Hydro Power

Question 1

How much of the worlds electrical consumption could be produced
by hydro power if we utilized the complete technical potential?

Answer 1

15443

Question 2

How are potential definitions (theoretical / technically feasible / economical) defined?
Can you order them by their magnitude?

Answer 2

Theoretical: Theoretical power or energy per year that results from the line potential of all creeks and rivers in the area.
Technically feasible: Power 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 barriers, such as available conversion technology, accessibility.
Economically feasible: Power or energy per year that can be exploited by building all the plants that economically feasible at the time being, i.e. at the current energy prices, capital cost and manufacturing, O&M cost.

Question 3

How do you determine the output power of a hydropower plant?

formula

Answer 3

P=ngQ*H [KW]

Question 4

In which countries do we still find the greatest unused hydro
potentials?

Answer 4

Countries in the continents of Africa, Asia and South America

Question 5

Categorization of HPPs: which two criteria are used to distinguish different types of HPPs.

Answer 5

Head range and mode of utilisation

Question 6

Why are storage plants normally high head plants?

Answer 6

High head plants are plants with a big height, and storage plants need that height to generate energy.

Question 7

Which types of high head plants do you know? What are their pros and cons?

Answer 7

Storage.
Pros: Mostly independent from daily precipitation, often high power output, very low cost of electricity, often additional benefit of flood protection.
Cons: High investment costs, high impact on nature and potentially people, construction difficult.

Pumped storage.
Pros: Efficient storage of excess from fluctuating sources, very high storage volume, high flexibility for grid stabilisation.
Cons: High investment costs, construction difficult and special site requirements needed.

Question 8

Can you sketch each of them and name their main elements?

Answer 8

Ver slide 16 e 18 aula 2

Question 9

Which types of run-of-river plants do you know?

Answer 9

Block type, diversion type, pierhead type,and submersed type.

Question 10

Pros and cons of run-of-river plants

Answer 10

Pros: Smaller units possible, medium investment costs, medium to low cost of electricity, low impact on nature.

Cons: Higher operational effort, active flood management required as often in/close to populated areas.

Question 11

Can you sketch each of run-of-river plants and name their main elements?

Answer 11

Block type
Diversion type
Pierhead type
Submersed type

Question 12

Stream turbines what is this?

Answer 12

Stream turbines use the kinetic energy of the moving water with stream turbines. Working principle identical with wind turbines as the same fluid dynamic.

Question 13

What is the main limitation of stream turbines?

Answer 13

They need much higher energy density (low power output) and often have a difficult marine environment (sand, salt, plants), which makes the accessibility for maintenance difficult.

Question 14

What is the purpose of a pumped storage plant? How big is its
cycle (turnaround) efficiency roughly? What is the main problem
in building new PSPs? Do you know of any suggestions to
overcome this?

Answer 14

To store energy for a high demand situation.
The efficiency of this cycle is around 80%
The main problem in building new PSPs, is the high investment costs and the use of a lot of energy.
A suggestion to overcome this is to use a renewable energy.

Question 15

What is the difference between impulse turbines and reaction turbines?

Answer 15

While the impulse turbine gets the kinetic energy and the momentum transferred by the water mass of a high-pressure jet, a reaction turbine is subjected to the pressure or potential energy generated by the weight of water at the bottom of the head working on one side of its blades called pressure side
Impulse turbines have better controllability but lower efficiency.

Question 16

Graphs of dynamic and static pressure along the stream path through the turbine.

Answer 16

Slide 34 aula 1

Question 17

Which turbine type is used in which head range?

Answer 17

High head (with low to medium flow) we use pelton.
Medium to high head (with low to high flow) we use francis.
Low to medium head (with medium to high flow) we use kaplan.

Question 18

What are the main elements of pelton turbines? Which elements serve for the
control?

Answer 18

They have a rotor disk, a bucket, a nozzle, and a jet deflector.
Nozzles serve for the control.

Question 19

For francis turbines how does the runner shape change from high to lower head?

Answer 19

The blade canals get shorter and their difference between the inlet and outlet diameter increases

Question 20

Which three types of Kaplan turbines need to be distinguished?

Answer 20

Propeller, Kaplan-Bulb, and Straflo

Question 21

Can you distinguish the efficiency characteristic of Pelton, Francis and Kaplan turbines?

Answer 21

Kaplan has the highest efficiency, then it is Pelton and finally Francis

Question 22

Which are the two basic possibilities of harvesting tidal energy? Can you describe how they work?

Answer 22

Using the potential energy in the difference in height below high and low tides.

Question 23

Can you describe how the tides are produced? Which movements and forces are responsible for the creation of the tides?

Answer 23

Tidal forces are periodically variations in gravitational attraction from the moon and the sun.

Question 24

Can you describe why the real electricity production of a tidal barrage plant is significantly lower than the theoretical one calculated from the potential energy stored in the reservoir?

Answer 24

Thanks to the limited sluice gate capacity as the reservoir are not completely filled, limited turbine capacity as the reservoir not completely emptied, and limited turbine efficiency

Question 25

Can you sketch the operating diagram (reservoir and sea level vs. time) of a single-acting and a double-acting tidal barrage? Can you name the different operating phases?

Answer 25

Slide 24 aula 2

Question 26

Do you know a possibility of producing a continuous output from a barrage tidal power plant? Can you sketch the layout of such a plant?

Answer 26

A two basins design, slide 24 aula 2

Question 27

Which type of tidal power plant can utilize tidal power without needing a barrage? What do these plants consist of, how do they work?

Answer 27

Tidal stream power plants. It uses the kinetic energy of the moving water with stream turbines.

Question 28

Which important criterion must a site for a tidal power plant fulfill in order to make it economically feasible? Where are such places normally found?

Answer 28

The places must have high tidal amplitudes and/or found where bays can be blocked with a relatively short dam

Question 29

Can you name three types of tidal stream generators (hydrokinetic turbines)? Which one is the most useful one

Answer 29

Marinized wind turbines with 2/3 blades, Darrieus (Vertical axis turbine),
Oscillating blades.
The mot useful one is the 2/3 bladed marinized wind turbines

Question 30

How are ocean waves created?

Answer 30

Ocean waves are created by the gravitational forces and most importantly wind. The sun heats up the air that passes over the surface of the sea. Due to friction energy transferred from the wind to the water. Furthermore, the pressure difference caused by the air turbulences causes additional forces that move the water up. Eventually, waves are built up which increases friction even more, which leads to higher pressure differences and so on.

Question 31

Where do we find the highest wave energy potentials in Europe and why?

Answer 31

Coast of UK, France, and Spain.
The highest tidal ranges are found where the tidal wave meets local structural changes such as bays or obstructions. In this case, the likelihood of resonance phenomena is higher.

Question 32

Which quantity is used to quantify a local wave energy potential?
How big is this figure approximately in the sea in the West of the UK?

Answer 32

Hs. Is the significant wave height, which is defined as the mean wave height of the highest third of the waves.
In UK this figure is about 150cm

Question 33

Which four categories of wave energy converters do you know? Can you sketch them and name their main elements?

Answer 33

Floating body converters, oscillating water column converters, hydrokinetic converters, and overtopping converters.
Slide 26, aula 2

Question 34

Oscillating water column converters: Can you describe how they work?

Answer 34

We have a container that is submersed in water, it’s open on one side. The movement of the water level on the outside causes a higher movement on the container inside and therefore a change of pressure in the air that goes trough a turbine generates electricity.

Question 35

Can you describe what an overtopping converter is?

Answer 35

It has a ramp where the wave transports water up the ramp into a reservoir, from there we use the potential energy in the reservoir compared to the lower water level to produce electricity in a hydro turbine.