EXAM QUESTIONS

Question 1

15h

Kreuzen Sie bitte die mechanischen und elektrochemischen Energiespeicher an.
 Supraleitende Spulen
 Schwungräder
 Akkumulatoren mit internem Speicher
 Gasspeicher (Elektrolyseur & Brennstoffzelle/ Turbine)

Answer 1

n Supraleitende Spulen
j Schwungräder
j Akkumulatoren mit internem Speicher
j Gasspeicher (Elektrolyseur & Brennstoffzelle/ Turbine)

Question 2

15h

Welcher der folgenden Energiespeicher verfügt über die höchste spezifische Energiedichte?
 Kondensatoren
 Blei-Säure-Batterien
 Lithium-Ionen-batterien
 Doppelschichtkondensatoren

Answer 2

Lithium-Ionen-batterien

Question 3

15H

Nennen Sie jeweils einen Vor- und Nachteil von Schwungmassenspeichern gegenüber Batteriesystemen bei einem Einsatz in einer unterbrechungsfreien Stromversorgung.

Answer 3

Vorteile gegenüber Batteriesystemen:
 Ideale Eigenschaften
 Längere Lebensdauer
 Geringerer Wartungsaufwand
 Unabhängig von Umgebungstemperatur
 Geringere Umweltbelastung
 Geringerer Platzbedarf
 Hohe Leistung

Nachteile
- hohe Kosten (z.B. 500 kW, 6 kWh -> 200.000 €)
- Platzbedarf: Schwungrad kann nicht aufgeteilt werden
- Selbstentladung: Innerhalb von 2 bis 4 Stunden kann der Schwungradspeicher
50% seiner Energie verlieren
- Sinnvoll typischerweise für Entladedauern bis zu wenigen 10 Sekunden

Question 4

15h

Nennen Sie zwei unterschiedliche Definitionen des Begriffs „Kapazität“! Geben Sie hierzu Formel und Einheit an!

Answer 4

Kapasitat im Sinne der Kondensatorkapasität und wird in Farad an gegeben.

Kapasität im Sinne der Batteriekapasität und wird in Ah angegeben.

Question 5

15h

Von einem Schwungmassenspeicher sind folgende Daten bekannt:
Rotormasse: 200 kg, Rotordurchmesser: 2,0 m (Vollzylinder), Drehzahl n: 60.000 /min.

Berechnen Sie die in der Schwungmasse gespeicherten Energie E.

Begründen Sie ob diese Auslegung technisch sinnvoll ist.

Answer 5

Im Falle eines Vollyzlendrs berechnen wir die
J = 0.5 x m x r^2

Bei einem Hohlzylinder
J = m x r^2

daraufhin nutzen wir die
Erot = 0,5 x J x w^2
um die Rotationsenergie in der Joule zu berechnen. Denn sollen wir durch 3600 teilen um die Wh zu bekommen.

Question 6

15h

Wie wird die thermische Energie bei einem „Sensiblen Wärmespeicher“ gespeichert?

Answer 6

Speicherung thermischer Energie durch die Aufheizung eines Speichermaterials
Speichermaterial: Wasser, Stein, Salz

Question 7

15h

Nennen Sie einen Brennstoffzellentypen und die dafür verwendeten Stoffe für das Elektrolyt, Anodengas und Kathodengas.

Answer 7

PEMFC
Elektrolyt: Polymermembran
Anode: Wasserstoff
Kathode: Sauaerstoff, Luft

AFC
Elektrolyt: Kalilauge
Anode: Wasserstoff
Kathode: Sauaerstoff

Question 8

15f

Nennen Sie zwei unterschiedlichen Typen von Druckluftspeichern

Answer 8

Diabate- und Adiabate Druckluftspeicher, isobare Druckluftspeicher

Question 9

15f

Ein Typ von Druckluftspeichern benötigt keine fossile Zufeuerung beim Entladevorgang.
Wie wird in diesem Fall beim Entladen die komprimierte Luft erhitzt?

Answer 9

Adiabatische
Beim Beladen des Druckluftspeichers wird die Kompressionswärme nicht an die
Umgebung abgegeben, sondern in einem Wärmespeicher zwischengespeichert.
Die komprimierte Luft wird bei der Entladung des Druckluftspeichers über den
Wärmespeicher geführt und dort wieder erhitzt -> Wenige Verluste

Question 10

15f

Bitte geben Sie die Funktion des Elektrolyten an.

Answer 10

Leitet die Ionen

Question 11

15f

Wann wird eine Batterie als „leer“ bezeichnet?

Answer 11

Eine Batterie wird als “leer” bezeichnet, wenn die Batteriespannung unter einen definierten Schwellwert fällt.

Question 12

15f

Name 3 different types of bearings in flywheel mass accumulators .

Answer 12

-mechanical bearings
- Superconducting Bearing
-Electromagnetic bearing

Question 13

15f

Name two typical applications of flywheel mass storage devices

Answer 13

Typical applications:
 Short-term storage for acceleration or braking energy in vehicles
 Short-term or stand-by storage for mains fluctuations and short interruptions, mains filtering, frequency and voltage regulation
 Short-term storage for load balancing of weak or local grids, reduction of the required connected load, temporary network reinforcement
 Provision of energy reserves for short power peaks, switch-on and start-up operations

Question 14

15f

State the difference between primary and secondary batteries.

Answer 14

Primary batteries: Process is not rechargeable
Secondary batteries can be recharged

Question 15

15f

Fuel cells are often discussed as an alternative to batteries. Which system components must be present to qualify as a secondary battery?

Answer 15

Secondary batteries :
A fuel cell can only work together with a hydrogen storage and an electrolyzer to replace secondary batteries.

Question 16

14f

Kreuzen Sie bitte die mechanischen und elektrochemischen Energiespeicher an.
 Supraleitende Spulen
 Schwungräder
 Akkumulatoren mit internem Speicher
 Gasspeicher (Elektrolyseur & Brennstoffzelle/ Turbine)

Answer 16

Kreuzen Sie bitte die mechanischen und elektrochemischen Energiespeicher an.
 Supraleitende Spulen / diese sind mit Kondensatoren elektrische Speichern
 Schwungräder
 Akkumulatoren mit internem Speicher
 Gasspeicher (Elektrolyseur & Brennstoffzelle/ Turbine)

Question 17

14f

Which of the following energy storage devices has the highest specific energy density?
 Capacitors
 Lead-acid batteries
 Lithium-ion batteries
 Double-layer capacitors

Answer 17

Which of the following energy storage devices has the highest specific energy density?
 Capacitors
 Lead-acid batteries
 Lithium-ion batteries up to 250wh/kg
 Double-layer capacitors

Question 18

14f

Which of the following statements are correct? Please mark the correct statements with a cross.
 For an autonomous power supply, the battery should be able to cover a capacity of at least
20 times the daily energy demand.
 VFD (Voltage and Frequency Dependent) is considered one of the most promising UPS topologies,
which is characterized by low losses (AC-side connection) and low costs.
low cost.
 Fuel cells can be used as modular stacks as alternative storage technologies for
UPS. However, their typical start-up time of 1 to 30 minutes is one of their disadvantages.
minutes is one of their disadvantages.

Answer 18

 For an autonomous power supply, the battery should be able to cover a capacity of at least
20 times the daily energy demand.
 VFD (Voltage and Frequency Dependent) is considered one of the most promising UPS topologies, which is characterized by low losses (AC-side connection) and low costs.
 Fuel cells can be used as modular stacks as alternative storage technologies for
UPS. However, their typical start-up time of 1 to 30 minutes is one of their disadvantages.

Question 19

14f

Please mark the correct statements with a cross.
 The chemical processes in electrochemical energy storage devices run about twice as fast at a temperature increase by 10 K, the chemical processes in electrochemical energy storage devices run about twice as fast.

 A double-layer capacitor with an internal resistance of 2 mΩ delivers a maximum power of
operating voltage of 2.5 volts delivers a maximum power of 1000 watts.

 Charge balancing systems for lithium-ion batteries and double-layer capacitors
are used to protect against overvoltage and increase their service life.

 As electrochemical and electrical storage devices age, their resistance decreases and their capacity resistance decreases and their capacity increases

Answer 19

In principle, the aging processes in electrochemical energy storage systems
energy storage devices run twice as fast when the temperature increases by 10 K.
 The maximum deliverable power of a double-layer capacitor is calculated as follows.
calculated: In the present example, the maximum power of 781.25 watts.
 Due to different self-discharge rates as well as different available capacities of the individual electrochemical energy storage devices in a system (lithium-ion batteries, double-layer capacitors, etc.), premature aging or a possible overvoltage of the aging or a possible overvoltage of the storage devices in the system can be prevented by charge balancing.
 As the energy storage devices age, their resistance will increase sharply and their
available capacity will decrease at the same time.

Question 20

14f

Please mark the correct statements on the topic “Superconducting coils” with a cross.
 Superconducting coils are suitable for fast power output.
 Superconducting coils require a high system effort for cooling.
 Superconducting coils are designed to prevent fuses in power systems from blowing in the event of a fault
 There is no limit to the current density of superconducting coils.

Answer 20

Superconducting coils are capable of providing very high power in a short time.
It should be noted that these systems also require a high level of cooling.
Superconducting coils can be used as a short-circuit current source, with the help of which fuses can be triggered in the event of faults in networks. With superconducting coils, their
current density is limited, otherwise the superconductivity breaks down.

Question 21

14f

Please mark with a cross the correct statements on the subject of “compressed air accumulators”.

 The diabatic and adiabatic compressed air storage systems typically have a system efficiency of 40% or less.

 One of the disadvantages of compressed air storage power plants is that they cannot afford for providing primary control power.

 Engine, generator, compressor, turbine, as well as heat storage are among the main components of an adiabatic compressed air storage power plant.

 Diabatic compressed air storage power plants generally achieve significantly higher
efficiencies compared to modern pumped storage power plants.

Answer 21

1 and 4

Exp: The diabatic compressed air accumulators have a maximum efficiency of 55 %, while the adiabatic compressed air accumulators can have an efficiency of approx. 70 %. In addition, the adiabatic accumulators do not require any additional fuel and autonomous operation as a pure storage system is possible.
 The disadvantages of compressed air storage power plants include, the low energy density,
the necessary construction of caverns, and the non-primary control capability.

The diabatic pressurized air storage power plants usually achieve a efficiency of approx. 40 %, while a modern pumped-storage power plant has an efficiency of up to 80 %.

Question 22

14f

Please mark with a cross the correct statements on the subject of “flywheel”.

 In principle, flywheels are divided into two classes: Flywheels with mechanical coupling and flywheels with electrical coupling.

 Modern high-speed flywheels can reach rotational speeds of up to 5,000 min-1.

 In the power supply network, flywheels can be used for short-term storage of energy during grid fluctuations and can be used for voltage regulation.

 Flywheels have a very short lifetime compared to the electrochemical energy storage systems (e.g. lead-acid batteries).

Answer 22

2,3 and 4
Exp:
There are two classes of flywheel accumulators. Flywheels with mechanical coupling and
flywheels with electrical coupling.
The fast rotating flywheels reach a rotation of approx. 100000 min-1. Their energy content is mainly stored by these high rotational speeds.
At the same time, the slowly rotating flywheels achieve a rotation of approx. 5000 min-1.
Typical applications of flywheels include:
1. short-term storage for acceleration or braking energy in vehicles.
2. short-term or stand-by storage for grid fluctuations and short interruptions, frequency and voltage regulation.
3. provision of energy reserves for short power peaks, switch-on and start-up processes.
start-up processes.

One of the advantages of the flywheels is their fairly long service life. Their service life in continuous operation is approx. 20 years. This corresponds to a number of about 5 million full load cycles. At the same time, the lead-acid batteries reach about 1000 full cycles during their whole lifetime.

Question 23

14f

Please tick the correct statements on the topic “Thermal energy storage”.

 Gravel-water storage tanks, aquifer heat storage tanks and geothermal probe storage tanks are suitable for long-term heat storage.
 Resistance to high temperatures and the lowest possible heat thermal conductivity are among the requirements of storage media for high-temperature storage.
 Thermo-chemical storage systems have an energy density of less than 100 and are more expensive compared to sensible and latent storage.
 The thermal energy of a sensible heat accumulator is calculated with the help of
delta Q = m x c x delta T
calculated. To heat 5 liters of water from 20 °C to 80 °C, 1257 kWh of heat would be required. Note: The specific heat capacity of water is c= 4190 J. kg-1K-1

Answer 23

1 and 2
Exp:
Storage media for high-temperature storage must meet a variety of requirements:
 resistant to high temperatures
 sufficiently dimensionally stable or inherently strong
 low thermal expansion
 good heat storage properties
 have the lowest possible thermal conductivity
Thermochemical storage units utilize the heat turnover of reversible chemical reactions.
These have a storage capacity of approximately 1000 MJ/m3.
The sensible heat accumulators have a storage capacity of about 100MJ/m3

5 liters of water are to be heated from 20 °C to 80 °C.

delta Q = m x c x delta T
.

Question 24

14f

Please mark the correct statements with a cross.
 In a modern pumped storage power plant, the storage efficiency is 85 % and the energy recovery efficiency 85 %. The overall efficiency
of the power plant is therefore 85 %.

 The output of pumped storage power plants is available on demand within minutes (secondary control power, minute reserve) and can be flexibly controlled over a wide range.

 Capital costs, efficiency during charging, storage and discharging, and the self-discharge rate are a selection of input parameters that are used in the calculation of the cost per kWh returned to the grid must be considered.

 The following is a schematic of the daily output of a pumped storage power plant. The areas marked in green (negative power) illustrate the
power output to the grid by the turbine.

Answer 24

2 and 3
Exp: The overall efficiency of a pumped storage power plant can be calculated as follows:
ETAspeicer + ETAruckgewinngung
In this example, the overall efficiency of the pumped storage power plant would be 0.72
The following are the parameters for calculating the cost of energy throughput for the reservoirs
are listed below.

Question 25

14f

Which of the following different materials can generally be used for lithium-ion batteries at the anode?

 LiCoO2, LiMn2O4, Li4Ti5O12 und Li22Si6
 Li22Si6, Li4Ti5O12 und LiC6
 LiFePO4, LiCo1/3Ni1/3Mn1/3° und LiNiO2
 LiC6, Li4Ti5O12, LiFePO4 und Li22Si6

Answer 25

 LiCoO2, LiMn2O4, Li4Ti5O12 und Li22Si6
 Li22Si6, Li4Ti5O12 und LiC6
 LiFePO4, LiCo1/3Ni1/3Mn1/3° und LiNiO2
 LiC6, Li4Ti5O12, LiFePO4 und Li22Si6

siehe in der 14F Losung dazu das Bild

Question 26

14f

Please tick the correct answers.
 One of the disadvantages of battery storage systems for use in stationary systems is, that they are not capable of primary and secondary regulation.

 Compared to short-term storage systems, medium-term energy storage systems must be able to be capable of providing energy in the range of one to ten hours with one or at most two cycles per day.

 The economic viability of stationary storage depends very much on the power plant mix (share of fluctuating renewable energy and non-fluctuating renewable energy) and the costs
of the storage technologies.

 A peak load on the power grid is accompanied by a very strong increase in the demanded power, so that in order to balance supply and demand, rapidly controllable and demand, fast regulating peak load power plants have to be deployed.

Answer 26

2 and 3 and 4

The advantages of battery storage systems include primary and secondary controllability as well as the short amortization periods and thus lower economic risk.
The so-called daily or medium-term energy storage systems are capable of providing energy in the range of one to ten hours. These are typically used for balancing within one day. In contrast, short-term storage units are suitable for rapid provision of power.
The economically operable capacity of storages, depends very sensitively on
 power plant mix (share of fluctuating renewable energy, non-fluctuating renewable energy).
 grid expansion, especially transnational grid expansion
 Cost of storage technologies
 Amount of storage with dual use
Peak load refers to short-term high demand for power in the electricity grid or in other
supply networks. Peak demand is often characterized by a sharp increase in the amount of power demand, so that quickly controllable peak power plants have to be used for the power supply.

Question 27

14f

Please mark the correct answers with a cross.

 Vertical network load is the sum of all feed-ins and outputs of the transmission network via directly connected transformers and lines to
connected distribution networks and end users.

 Decentralization of power generators in the transmission grid results in an additional load on the transmission grid.

 Energy storage systems with short lifetimes and low efficiencies are attractive because of
their low costs, are advantageous for use in the power grid.

 In solar thermal power plants, mirrors are used to concentrate solar radiation and thus a high temperature is generated in a heat transfer medium, which is then used to used to evaporate water and drive steam turbines

Answer 27

1 and 4
Solution:
Dropping unneeded loads when there is too little power available. Vertical network load corresponds to the sum of all inputs and outputs of the transmission network via directly connected transformers and transmission lines to connected distribution networks and
end users. After a detailed analysis of the cost calculation for the energy storage systems, it turns out that only the storage technologies with short lifetimes or low efficiencies will result in high lead to high costs during their system lifetime.

Question 28

14f

Let there be a coreless coil with only 1000 turns, radius 0.25 m and 50 cm length. (μr=1 and μ0=4 π *10-7 Vs/Am) Please tick the correct answers.

 The storable energy in a coil and its power loss decrease quadratically with the current.
with the current.

 The self-inductance of this coil is 0.49 H. The magnetic conductance can be assumed to be 4.9*10-7
Vs/Am can be assumed.

 An energy of 450 Wh can be stored in this coil. At the same time
a constant current of 40 A and an inductance of 0.5 H can be calculated.
can be calculated.

 If the ohmic resistance of this coil would be 50 Ohm and a constant current of
current of 40 A, the power dissipation would be 65 kW.

Answer 28

2 and 3

Question 29

14f

Please mark with a cross the correct answers to the question “Hydrogen and gas storage systems”.

 A total of approx. 500 billion m3 of hydrogen is produced worldwide coal gasification or from the partial oxidation of heavy oil

 Renewable energy sources for hydrogen production include crude oil, natural gas and coal.

 In a PEM fuel cell, hydrogen is generally fed to the anode and oxygen to the cathode.
oxygen is supplied to the cathode.

 The theoretically achievable voltage in a fuel cell is higher than that of a lithium-ion battery (3.3 V).

Answer 29

1 and 3

Question 30

14h

Was sind die wesentlichen Nachteile von supraleitenden Spulen?

Answer 30

Geringe Energiedichte
Hoher systemischer Aufwand wegen Kühlung

Question 31

14h

What are the main characteristics of high-speed flywheels?

The rotational speed is in the range of 100,000 revolutions per minute.

Steel isotropic flywheels are used

The strength of the rotating body used depends on the load direction depending on the direction of load

Bearing in a vacuum completely eliminates frictional losses, so that self friction losses, so that self-discharge is excluded

Answer 31

The rotational speed is in the range of 100,000 revolutions per minute.

The strength of the rotating body used depends on the load direction depending on the direction of load

Question 32

14h

What are typical applications for flywheels?

Use as long-term storage
Short-term storage for acceleration or braking energy in vehicles
Use in solar home systems in remote regions
Stand-by storage for grid fluctuations and short interruptions

Answer 32

Short-term storage for acceleration or braking energy in vehicles

Stand-by storage for grid fluctuations and short interruptions

Question 33

14h

Mark the correct statements about the main technologies of the Compressed air power plants.

Adiabatic compressed air storage units require additional fuel

Diabatic compressed air storage units achieve efficiencies of approx. 70%.

 Adiabatic compressed air storage systems require an additional heat accumulator

 The efficiency of the adiabatic compressed air storage system is higher than that of the diabatic compressed air storage system.
compressed air storage

Answer 33

 Adiabatic compressed air storage systems require an additional heat accumulator

 The efficiency of the adiabatic compressed air storage system is higher than that of the diabatic compressed air storage system.
compressed air storage

Question 34

14h

Which of the following options can be considered for compressed air storage?
 Salt cavern
 Aquifer storage
 Submariner compressed air storage facility
 Mine

Answer 34

 Salt cavern
 Aquifer storage
 Submariner compressed air storage facility
 Mine

Question 35

14h

Please mark the appropriate characteristics of the Francis turbine

It is used at heads of 2 - 30 meters
It achieves turbine power up to 1 GW
It enables pumping operation
It achieves efficiencies of up to 90%.

Answer 35

It achieves turbine power up to 1 GW
It enables pumping operation
It achieves efficiencies of up to 90%.

Question 36

14h

Please mark the correct statements regarding phase shifter operation

In phase-shifting mode, active power is supplied to the grid or absorbed from the grid.

In phase-shifting operation, reactive power is fed into the grid or absorbed by the grid.

Phase-shifting operation is used to reduce transmission losses

Phase shifting is achieved when the power plant is neither in pumping nor in generator mode.

Answer 36

In phase-shifting operation, reactive power is fed into the grid or absorbed by the grid.

Phase-shifting operation is used to reduce transmission losses

Phase shifting is achieved when the power plant is neither in pumping nor in generator mode.

Question 37

14h

Tick the correct characteristics of heat storages.

The specific storage capacity of sensible heat accumulators is higher than the Storage capacity of latent heat storages

The specific storage capacity of sensible heat storages is higher than the Storage capacity of thermo-chemical heat storages.

Sensitive heat stores store thermal energy by heating a storage material

Common storage media for latent heat stores are salt hydrates and kerosenes

Answer 37

3 and 4

Question 38

14h

Which storage systems use an electrochemical conversion process in the energy storage?

Lead-acid batteries
Compressed air storage
Lithium ion batteries
Double layer capacitors

Answer 38

1 and 3

Question 39

14h

correct definition of coulombic efficiency

Question 40

14h

Which of the following energy storage devices has the highest specific energy density?

Capacitors
Lead-acid batteries
Lithium-ion batteries
Double-layer capacitors

Answer 40

Lithium-ion batteries

Question 41

14h

Mark the correct characteristics of lead-acid batteries?

Lead sulfate is formed at both electrodes during discharge
Sulfuric acid is consumed during discharge
The negative electrode consists of lead dioxide mass
Dendrites can be formed during charging at low temperatures,
which in the worst case can lead to internal short circuits

Answer 41

1 und 2

Question 42

14h

Wobei handelt es sich um Alterungsprozesse in Bleibatterien?

Answer 42

 Korrosion
 Sulfatierung
 Verlust von aktivem Material
NICHT Ausbildung des Solid Elektrolyte Interface (SEI)

Question 43

14h

Mark the correct characteristics of lithium batteries.

At the start of discharging an ideally fully charged battery, there is a clear voltage sag

For lithium batteries the constant current - constant voltage - charging method is suitable.
constant current charging method

Polymer electrolytes have comparatively poor conductivity at 25°C

The lithium iron phosphate technology shows the flattest discharge curve.

Answer 43

3 and 4

Question 44

14h

Wobei handelt es sich um mögliches Kathodenmaterial für Lithium-Ionen-Zellen
mit organischem Elektrolyt?
LiFePO4
LiCoO2
LiMn2O4
LiC6

Answer 44

1 2 and 3

Question 45

14h

Mark the disadvantages of a nickel cadmium battery

Poor performance at low temperatures
Efficiency is lower compared to lead acid batteries.
High self-discharge at high temperatures
Low cell voltage

Answer 45

2 3 and 4

Question 46

14h

Highlight the characteristics of a NiMH battery

Good cycle strength even at high depths of discharge.

Memory effect leads to capacity loss if operated incorrectly

Heavy metal use poses an environmental risk

During hydrogen storage, grid expansion leads to mechanical stress

Answer 46

1 und 4

Question 47

14h

What typical tasks does a battery management system perform?

Protection against overcharging or deep discharge
Protection against overtemperature
Equalization of the state of charge of individual cells
Increased crash safety

Answer 47

1 2 3

Question 48

14h

Mark the characteristics of a hydrogen fuel cell?

The reaction converts hydrogen and oxygen to water.

The membranes are susceptible to CO impurities.

The specific energy content of hydrogen is comparable to the energy content of natural gas

Die Spannung einer einzelnen Brennstoffzelle liegt im Bereich von 2,5 bis 2,7 Volt.

Answer 48

1 and 2

Question 49

16f

What is the maximum gravimetric energy density that can be achieved with an electrochemical storage system can theoretically be achieved with an electrochemical storage, if both active materials are taken into account?

Answer 49

5 kWh/kg

Question 50

16f

In practice, the energy density achieved by an electrochemical storage system typically
typically lags behind the theoretically achievable energy density of the respective technology by a factor of of the respective technology. Name one reason for this

Answer 50

Since, in addition to the energy-storing materials, current conductors, electrolytes, separators, housings and additional materials have to be used.

Question 51

16f

The following basic design of a PEM fuel cell is given. Please complete
the missing labels for the marked elements, 1, 2, 3 and 4.

Question 52

16f

If no more energy is supplied to a flywheel, its rotational speed decreases as a result of
rotation speed decreases as a result of friction losses. In which these losses can be largely neglected when considering the system as a whole?

Answer 52

For frequent charge and discharge cycles (e.g. every minute).

Question 53

16f

In a flywheel mass accumulator, energy is stored in kinetic form.
a) How is the energy content in slow and fast rotating flywheels mainly achieved?
b) For which of the mentioned flywheels are anisotropic materials used? to the

Answer 53

a)
Slow: Energy content is mainly achieved by large
moment of inertia
Fast: Energy content is mainly achieved by high
rotational speeds

b)
Fast rotating flywheels

Question 54

16f

How is the thermal energy stored in a “latent heat storage” system

Answer 54

Through phase change (solid → liquid, liquid → gaseous)

Question 55

16f

Compressed air storage
a) Name the three technology lines of compressed air storage systems.

b) State the main difference between diabatic and adiabatic compressed air srorage.

Answer 55

Isobaric (submarine) compressed air storage, diabatic compressed air storage, and
adiabatic compressed air storage

The difference is that in the case of adiabatic compressed air accumulators, the heat generated during the compression of the air is temporarily stored and used in the used in the further course of the process, which results in better efficiency.

Question 56

16f

Name one advantage and disadvantage of this topology each in comparison to other UPS topologies.

Answer 56

+ No switching necessary
- Complex design
- Energy runs completely through the inverters

Question 57

16h

Sort the given energy stores according to their specific energy density.
Start with the smallest.
1 Lead-acid batteries 2 Lithium-ion high energy
3 Double layer capacitors 4 Sodium nickel chloride

Answer 57

3 4 1 2

Question 58

16h

Label the structure shown below (Figure 4) of a PEM fuel cell by adding the following designations:
Electrolyte, Separator,
H2, O2, Pb2+, H2O, H+, anode, cathode, lead grid. It is not necessary to use all be used.

Question 59

16h

Nennen Sie 3 Alterungsprozesse in Bleibatterien

Answer 59

Corrosion
Sulfation
Loss of active material

Question 60

16h

Sketch a UPS topology and name one advantage and disadvantage of each.

Question 61

16h

Are pumped storage power plants capable of primary regulation? Brief justification

Answer 61

No, Due to the long response times (up to 195 s to generator from 0 MW to full load).

Question 62

16h

For a run-of-river power plant, a turbine is to be used which is suitable for fluctuating flow rates.
fluctuating flow rates. Which turbine type would you use? Specify 2 further characteristic properties of the turbine type

Answer 62

Kaplan turbine
1. efficiency 80 - 95%.
2. head 2 -30 meters (rivers with natural gradient)
3. base load power plant (the higher the flow, the higher the achievable power)
4. No energy storage

Question 63

16h

Which storage medium would you use for a UPS, if within second and over a period of 2 hours the full capacity is to be available?
be available? Give two reasons for your choice.

Answer 63

Lead acid battery
- Low price
- Robust
- High state of charge (high SOC)
- Low number of cycles
- High reliability
Other battery technologies possible if detailed and logically justified for
Flywheel and Li-ion battery

Question 64

16h

Nennen Sie je einen Vor- und Nachteil von bidirektionaler Netzanbindung von Fahrzeugen

Answer 64

Advantage:
- Provision of positive control power
Disadvantages:
- Additional cyclic load
- Additional costs for charger

Question 65

16h

Name 3 types of reactions of thermochemical storages

Answer 65

1. catalytic
2. thermal dissociation
3. adsorption

Question 66

16h

Name one main difference between sensible and latent heat storage in terms of phase change

Answer 66

Sensible heat: no change of state or phase
Phase change (solid, liquid, gas)

Question 67

17f

Name, in bullet form, three technologies that provide short-term flexibility for grid stabilization

Answer 67

1. flexible generators
2. battery storage
3. demand-side management in households
4. peak shaving
5. flywheel storage
6. disconnectable loads,

Question 68

17f

In bullet point form, list three options for the use of generation surpluses?

Answer 68

1. storage
2. electric heat generation
3. generation of materials and gases for use outside the
   Electricity sector
   Alternative: derating, power to heat, power to gas, power to power (e to e),
   Compressed air storage, electrical, thermal, mechanical

Question 69

17f

Name one impurity to which the membrane of a fuel cell in particular is sensitive?

Answer 69

CO contamination

Question 70

17f

In order to achieve technically usable voltages when using fuel cells these are connected together. Which circuit topology is useful here to increase the voltage?

Answer 70

Series

Question 71

17f

Complete the sentences by filling in the gaps with less than “<” or greater than “>”.

The energy density of a mechanical accumulator is generally ____ as that of a chemical storage device. The cyclic lifetime of a lithium Ion cell is generally ____ than that of a lead cell. The effort
for safety management of lithium ion cell is generally ____ than that of lead cells. The operating temperatures of Flywheel batteries are generally ____ than those of NaNiCl batteries.

Answer 71

<
>
>
<

Question 72

17f

Are pumped storage power plants capable of primary regulation? Brief justification

Answer 72

No;
Due to the long response times (up to 195 s to generator from 0 MW to
full load

Question 73

17f

For a pumped storage power plant, a turbine is to be used which is suitable suitable for low-pressure and high-pressure applications. In addition, it should be suitable for pumping operation. Which turbine type would you
use? Specify 2 other turbine types.

Answer 73

Francis turbine,

Turbine power 1 GW, efficiency 90 %, runners up to 150t weight,
destruction by cavitation possible

Question 74

17f

Explain what quantity is meant by the following formulas and
indicate the units in each case.
a) ? = ∫ |Ibatt|dt

b) ? =𝜀𝑟∙𝜀0∙𝐴 / 𝑑

Answer 74

The amount of charge carriers that can be taken from a battery storage unit.
can be taken. Unit: Ah or As.

Measure of the capacity of a capacitor for electrical charge,
related to the value of the applied voltage. Unit: As/V or F.

Question 75

17f

Explain the difference between adiabatic and diabatic compressed air accumulators. Indicate in which case a higher efficiency can be achieved.

Answer 75

Diabat: Heat energy dissipated to the environment via heat exchanger.
Efficiency 49 %.

Adiabatic: The heat of compression is not released to the environment,
but is temporarily stored in a heat accumulator. Higher efficiency 70 %

Question 76

17f

In practice, the energy density achieved by an electrochemical storage unit typically falls short of the theoretically achievable energy density of the respective energy density of the respective technology. Name three reasons for this

Answer 76

In addition to the energy-storing materials, current conductors, electrolytes, separators, casings and additional materials.

For lithium batteries, 40% more lithium must be used for cathode stability.

Question 77

17f

Explain the difference between latent and sensible heat storage. Give the physically correct formulas for the calculation of the stored heat

Answer 77

Latent: Storage of thermal energy by phase transition of a storage material.
Q = c ∙ m ∙ ΔT + q ∙ m

Sensitive: no change in state or phase.
Q = c ∙ m ∙ ΔT

Question 78

17h

a) According to which storage principle do super caps work?
b) Are storage hydropower plants used for the provision of positive and negative negative control power?
c) How does the temperature behave in ideal sensible heat storages cover the stored heat.
d) Which of the two storage technologies typically has lower energy density, mechanical or chemical storage?
e) Evaluate qualitatively the energy density of a superconducting coil versus a lead-acid battery.
compared to a lead-acid battery.
f) In which temperature range is the optimal operating point of a NaNiCl2 battery?
of a NaNiCl2 battery?

Answer 78

a) On electrostatic effects.
b) No.
c) It is linear.
d) Mechanical storage
e) It is lower.
f) Everything between 220°C and 300°C is evaluated.

Question 79

17h

Draw an equivalent electrical circuit of a supercap. Name and explain the individual components.

Question 80

17h

Which two processes are accelerated when a supercap is overcharged?

Answer 80

aging
Decomposition of the electrolyte
Cover layer formation

Question 81

17h

What causes the charge imbalance in series-connected lithium-ion cells? Name two factors

Answer 81

Different self-discharge, Different capacities, Aging, different internal resistances,

Question 82

17h

Explain in short sentences how superconducting coils work

Answer 82

Superconducting magnetic energy storage (SMES) systems exploit the properties of the resistive current conduction of some metals
and ceramic oxides at low and very low temperatures (below the material-specific
(below the material-specific transition temperature).

Classical superconductors have a transition temperature in the range of of a few K, high temperature superconductors in the range of 30 to 70 K.

Question 83

17h

The efficiency of an H2 storage system, taking into account the hydrogen generation efficiency, is generally ____ better than that of a lead-acid battery. The power density of a supercap is generally ____ than that that of a lead-acid cell. The cycle stability (full cycles) of lithium cells is
generally ____ than that of supercaps. The ability to recycle of a lead acid battery is generally ____ than that of a LIB battery.

Answer 83

< ; > ; < ; >

Question 84

17h

What are the chemical equations at the anode and cathode for a PEM electrolyzer.

Answer 84

Anode: 2H2 → 4H+ 4e-
Kathode: O2 + 4e- + 4H+ → 2H2O

Question 85

17h

Name two mechanical and two electrical storage
(a) Mechanical:
(b) Electrical:

Answer 85

a) Compressed air, pumped storage, flywheel
b) Superconducting coil, capacitors, supercaps, DSK

Question 86

What is the mathematical formula for calculating the efficiency of a of a diabatic CAES memory? Please name the quantities.

Answer 86

ETAcaec = Wturb / (W komp + Qbr)

WTurb: Power of the turbine
WKomp: Power of the heat of compression
QBr: Power of natural gas

Question 87

WS2020

What is the approximate utilization rate (i.e. efficiency from source to wheel) of battery electric vehicles starting with electric energy as input?

Question 88

What is the approximate utilization rate (i.e. efficiency from source to wheel) of fuel cell vehicles starting with electric energy as input?

Question 89

WS2020

Please mark the correct statements about the phase shifter operation. (Multiple-Choice)

In a synchronous machine, reactive power is transferred into the grid or absorbed from the grid

In a synchronous machine, active power is transferred to the grid or absorbed from the grid

Reactive power generation is used to cover the inductive reactive power demands of transformers and asynchronous machines

Phase shifter operation is used to improve the load angle and to reduce transmission losses

Answer 89

In a synchronous machine, reactive power is transferred into the grid or absorbed from the grid

In a synchronous machine, active power is transferred to the grid or absorbed from the grid

Reactive power generation is used to cover the inductive reactive power demands of transformers and asynchronous machines
**
Phase shifter operation is used to improve the load angle and to reduce transmission losses**

Question 90

The capital cost per kWh for typical heat storages is

compared to the capital cost per kWh for typical electricity storages.
The efficiency of a typical adiabatic compressed air storage system is

compared to the efficiency of a typical diabatic compressed air storage system.
The typical discharge time of flywheels is

compared to the typical discharge time of compressed air storages.
The OCV-voltage of a typical fully charged sodium-sulfur cell is

compared to the OCV-voltage of a typical fully charged lithium-ion cell

Answer 90

<,>,<,<

Question 91

WS2020

In which thermal energy storage system is thermal energy stored by phase transition of storage medium? Also select the one corresponding, adequate storage medium.

Latent

Sensible

Thermo-chemical storage

Answer 91

Latent

Question 92

WS2020

Typically used storage medium for phase transformation

Answer 92

Paraffin oil

Question 93

WS2020

What is the approximate utilization rate (i.e. efficiency from source to wheel) of battery electric vehicles starting with electric energy as input?

What is the approximate utilization rate (i.e. efficiency from source to wheel) of fuel cell vehicles starting with electric energy as input?

Answer 93

70

25

Question 94

What is the round-trip energy efficiency of a lithium-ion battery?

What is the coulombic efficiency of a lithium-ion battery battery?

What is the round-trip energy efficiency of a Lead acid battery?

NiMH?

Answer 94

[90,97]

[99,100]

80-90%

65-75%

Question 95

WS2020

Assume that two systems of identical battery cells are used to provide the same power output, one with 20 cells in parallel called 20p1s and one with 20 cells in series called 1p20s
. Select the true statement and the correct explanation(s)

The losses inside the battery cells are higher for 20p1s

The losses inside the battery cells are higher for 1p20s

The losses inside the battery cells are the same

The current in each cell is higher in 20p1s

The current in each cell is higher in 1p20s

The current in each cell is unaffected

Answer 95

The losses inside the battery cells are the same

The current in each cell is unaffected

The voltage drop across each cell is unaffected

Question 96

WS2020

Which charging modes would typically be acceptable in an electric vehicle? Select the correct option(s) (Multiple-Choice, more than 1 answer is correct!)

Constant Power - Constant Current

Constant Voltage - Constant Current

Constant Power - Constant Voltage

Constant Current - Constant Voltage

Answer 96

Constant Power - Constant Voltage

Constant Current - Constant Voltage

Constant voltage as second phase helps to fill a battery while not exceeding the batteries voltage bounds. Constant current in the second phase would either result in low charging speeds if the current is set low or alternatively in a too early termination of the charging process if voltage limits are exceeded.

Question 97

2021SS

c) Tick the correct statements on large scale centralised energy storage systems.

Diabatic compressed air energy storages store the compression heat to release it for the decompression.

Sensitive heat storages are operated below ambient pressure.

Pumped hydro energy storage systems usually have a higher efficiency than compressed air energy storages.

Adiabatic compressed air enegry storages have a lower energy efficiency than diabatic compressed air energy storages.

Answer 97

Pumped hydro energy storage systems usually have a higher efficiency than compressed air energy storages.

Question 98

2021SS

Which of the following statements are true? Check the right boxes

Voltage limits can be defined as discharge end criterion to ensure the operation voltage window of electronics downstream is within specifications.

The battery terminal voltage is lower during charging than during discharging.

Thicker active material coatings lead to a lower ohmic resistance of a battery cell.

Thicker active material coatings lead to a higher energy density of a battery cell.

Answer 98

Voltage limits can be defined as discharge end criterion to ensure the operation voltage window of electronics downstream is within specifications.

Thicker active material coatings lead to a higher energy density of a battery cell.

Question 99

SS2021

Choose if the following ageing processes belong to the main ageing processes in VRLA (valve-regulated lead acid) batteries. Check the boxes where this is true.

Electrolyte degradation

Sulfation

Corrosion

Lithiation

Answer 99

Sulfation

Corrosion

Question 100

SS2021

Fill in percentage values for the battery technologies listed in the table below.
NiMh:
Lithium-Ion:
Lead-acid:

Answer 100

70,
90,
80

Question 101

b) Select the correct answer and the correct explanation(s). If heat from the sun generated in the summer should be used to heat a household in winter, what temperature range would be most suitable? (Combi-Choice)

A low temperature (<100°C)

A high temperature (>100°C)

Explanation(s)

Losses are lower with the same level of insulation

Investment costs for insulation are lower for the same amount of losses

Answer 101

A low temperature (<100°C)

Losses are lower with the same level of insulation

Investment costs for insulation are lower for the same amount of losses

Question 102

SS2021

A conventional lithium NMC battery cell is, all else being equal, more energy efficient if … (Multiple-Choice)

… the cell voltage is higher

… the capacity in Ah is higher

… the energy density is higher

… the internal resistance is lower

Answer 102

… the cell voltage is higher

… the internal resistance is lower

Question 103

SS2021

b) Why is a battery typically charged in a constant voltage (CV) mode when reaching high states of charge? (Multiple-Choice)

CV allows for roughly the same power flow when charging the last ~20% of the battery

Using a CV mode reduces the risk of overcharging

CV charging is considered more grid friendly due to the more constant current

The CV mode helps to use the full battery capacity and avoids early termination of charging

CV charging reduces the internal resistance during end of chargeUsing a CV mode reduces the risk of overcharging

Answer 103

Using a CV mode reduces the risk of overcharging

The CV mode helps to use the full battery capacity and avoids early termination of charging

Question 104

SS2021

d) Tick the correct statements on superconducting coils. (Multiple-Choice)

Strong magnetic fields are proven to have no effects on biological organisms

Superconducting coils have a low power density compared to batteries

Cryogenic cooling is needed for the high efficiency of superconducting coils

Superconducting coils have a low energy density compared to batteries

Answer 104

Cryogenic cooling is needed for the high efficiency of superconducting coils

Superconducting coils have a low energy density compared to batteries

Question 105

Gravimetric Calorific value (in MJ/kg)
Volumetric Calorific value (in MJ/m³)

h2 ch4

Answer 105

50.0 120.0
35.9 10.8