EXAM QUESTIONS Flashcards
15h
Kreuzen Sie bitte die mechanischen und elektrochemischen Energiespeicher an.
Supraleitende Spulen
Schwungräder
Akkumulatoren mit internem Speicher
Gasspeicher (Elektrolyseur & Brennstoffzelle/ Turbine)
n Supraleitende Spulen
j Schwungräder
j Akkumulatoren mit internem Speicher
j Gasspeicher (Elektrolyseur & Brennstoffzelle/ Turbine)
15h
Welcher der folgenden Energiespeicher verfügt über die höchste spezifische Energiedichte?
Kondensatoren
Blei-Säure-Batterien
Lithium-Ionen-batterien
Doppelschichtkondensatoren
Lithium-Ionen-batterien
15H
Nennen Sie jeweils einen Vor- und Nachteil von Schwungmassenspeichern gegenüber Batteriesystemen bei einem Einsatz in einer unterbrechungsfreien Stromversorgung.
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
15h
Nennen Sie zwei unterschiedliche Definitionen des Begriffs „Kapazität“! Geben Sie hierzu Formel und Einheit an!
Kapasitat im Sinne der Kondensatorkapasität und wird in Farad an gegeben.
Kapasität im Sinne der Batteriekapasität und wird in Ah angegeben.
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.
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.
15h
Wie wird die thermische Energie bei einem „Sensiblen Wärmespeicher“ gespeichert?
Speicherung thermischer Energie durch die Aufheizung eines Speichermaterials
Speichermaterial: Wasser, Stein, Salz
15h
Nennen Sie einen Brennstoffzellentypen und die dafür verwendeten Stoffe für das Elektrolyt, Anodengas und Kathodengas.
PEMFC
Elektrolyt: Polymermembran
Anode: Wasserstoff
Kathode: Sauaerstoff, Luft
AFC
Elektrolyt: Kalilauge
Anode: Wasserstoff
Kathode: Sauaerstoff
15f
Nennen Sie zwei unterschiedlichen Typen von Druckluftspeichern
Diabate- und Adiabate Druckluftspeicher, isobare Druckluftspeicher
15f
Ein Typ von Druckluftspeichern benötigt keine fossile Zufeuerung beim Entladevorgang.
Wie wird in diesem Fall beim Entladen die komprimierte Luft erhitzt?
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
15f
Bitte geben Sie die Funktion des Elektrolyten an.
Leitet die Ionen
15f
Wann wird eine Batterie als „leer“ bezeichnet?
Eine Batterie wird als “leer” bezeichnet, wenn die Batteriespannung unter einen definierten Schwellwert fällt.
15f
Name 3 different types of bearings in flywheel mass accumulators .
-mechanical bearings
- Superconducting Bearing
-Electromagnetic bearing
15f
Name two typical applications of flywheel mass storage devices
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
15f
State the difference between primary and secondary batteries.
Primary batteries: Process is not rechargeable
Secondary batteries can be recharged
15f
Fuel cells are often discussed as an alternative to batteries. Which system components must be present to qualify as a secondary battery?
Secondary batteries :
A fuel cell can only work together with a hydrogen storage and an electrolyzer to replace secondary batteries.
14f
Kreuzen Sie bitte die mechanischen und elektrochemischen Energiespeicher an.
Supraleitende Spulen
Schwungräder
Akkumulatoren mit internem Speicher
Gasspeicher (Elektrolyseur & Brennstoffzelle/ Turbine)
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)
14f
Which of the following energy storage devices has the highest specific energy density?
Capacitors
Lead-acid batteries
Lithium-ion batteries
Double-layer capacitors
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
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.
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.
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
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.
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.
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.
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.
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 %.
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).
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.
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
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
.
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.
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.
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
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
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.
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.
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
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.
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.
2 and 3
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).
1 and 3
14h
Was sind die wesentlichen Nachteile von supraleitenden Spulen?
Geringe Energiedichte
Hoher systemischer Aufwand wegen Kühlung
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
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
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
Short-term storage for acceleration or braking energy in vehicles
Stand-by storage for grid fluctuations and short interruptions
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
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
14h
Which of the following options can be considered for compressed air storage?
Salt cavern
Aquifer storage
Submariner compressed air storage facility
Mine
Salt cavern
Aquifer storage
Submariner compressed air storage facility
Mine
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%.
It achieves turbine power up to 1 GW
It enables pumping operation
It achieves efficiencies of up to 90%.
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.
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.
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
3 and 4
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
1 and 3
14h
Which of the following energy storage devices has the highest specific energy density?
Capacitors
Lead-acid batteries
Lithium-ion batteries
Double-layer capacitors
Lithium-ion batteries
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
1 und 2
14h
Wobei handelt es sich um Alterungsprozesse in Bleibatterien?
Korrosion
Sulfatierung
Verlust von aktivem Material
NICHT Ausbildung des Solid Elektrolyte Interface (SEI)
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.
3 and 4
14h
Wobei handelt es sich um mögliches Kathodenmaterial für Lithium-Ionen-Zellen
mit organischem Elektrolyt?
LiFePO4
LiCoO2
LiMn2O4
LiC6
1 2 and 3
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
2 3 and 4
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
1 und 4
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
1 2 3
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.
1 and 2
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?
5 kWh/kg
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
Since, in addition to the energy-storing materials, current conductors, electrolytes, separators, housings and additional materials have to be used.
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.
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?
For frequent charge and discharge cycles (e.g. every minute).
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
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
16f
How is the thermal energy stored in a “latent heat storage” system
Through phase change (solid → liquid, liquid → gaseous)
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.
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.
16f
Name one advantage and disadvantage of this topology each in comparison to other UPS topologies.
+ No switching necessary
- Complex design
- Energy runs completely through the inverters
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
3 4 1 2
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.
16h
Nennen Sie 3 Alterungsprozesse in Bleibatterien
Corrosion
Sulfation
Loss of active material
16h
Sketch a UPS topology and name one advantage and disadvantage of each.
16h
Are pumped storage power plants capable of primary regulation? Brief justification
No, Due to the long response times (up to 195 s to generator from 0 MW to full load).
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
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
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.
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
16h
Nennen Sie je einen Vor- und Nachteil von bidirektionaler Netzanbindung von Fahrzeugen
Advantage:
- Provision of positive control power
Disadvantages:
- Additional cyclic load
- Additional costs for charger
16h
Name 3 types of reactions of thermochemical storages
- catalytic
- thermal dissociation
- adsorption
16h
Name one main difference between sensible and latent heat storage in terms of phase change
Sensible heat: no change of state or phase
Phase change (solid, liquid, gas)
17f
Name, in bullet form, three technologies that provide short-term flexibility for grid stabilization
- flexible generators
- battery storage
- demand-side management in households
- peak shaving
- flywheel storage
- disconnectable loads,
17f
In bullet point form, list three options for the use of generation surpluses?
- storage
- electric heat generation
- 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
17f
Name one impurity to which the membrane of a fuel cell in particular is sensitive?
CO contamination
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?
Series
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.
<
>
>
<
17f
Are pumped storage power plants capable of primary regulation? Brief justification
No;
Due to the long response times (up to 195 s to generator from 0 MW to
full load
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.
Francis turbine,
Turbine power 1 GW, efficiency 90 %, runners up to 150t weight,
destruction by cavitation possible
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
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.
17f
Explain the difference between adiabatic and diabatic compressed air accumulators. Indicate in which case a higher efficiency can be achieved.
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 %
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
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.
17f
Explain the difference between latent and sensible heat storage. Give the physically correct formulas for the calculation of the stored heat
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
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?
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.
17h
Draw an equivalent electrical circuit of a supercap. Name and explain the individual components.
17h
Which two processes are accelerated when a supercap is overcharged?
aging
Decomposition of the electrolyte
Cover layer formation
17h
What causes the charge imbalance in series-connected lithium-ion cells? Name two factors
Different self-discharge, Different capacities, Aging, different internal resistances,
17h
Explain in short sentences how superconducting coils work
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.
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.
< ; > ; < ; >
17h
What are the chemical equations at the anode and cathode for a PEM electrolyzer.
Anode: 2H2 → 4H+ 4e-
Kathode: O2 + 4e- + 4H+ → 2H2O
17h
Name two mechanical and two electrical storage
(a) Mechanical:
(b) Electrical:
a) Compressed air, pumped storage, flywheel
b) Superconducting coil, capacitors, supercaps, DSK
What is the mathematical formula for calculating the efficiency of a of a diabatic CAES memory? Please name the quantities.
ETAcaec = Wturb / (W komp + Qbr)
WTurb: Power of the turbine
WKomp: Power of the heat of compression
QBr: Power of natural gas
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?
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
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**
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
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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
Latent
WS2020
Typically used storage medium for phase transformation
Paraffin oil
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?
70
25
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?
[90,97]
[99,100]
80-90%
65-75%
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
The losses inside the battery cells are the same
The current in each cell is unaffected
The voltage drop across each cell is unaffected
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
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.
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.
Pumped hydro energy storage systems usually have a higher efficiency than compressed air energy storages.
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.
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.
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
Sulfation
Corrosion
SS2021
Fill in percentage values for the battery technologies listed in the table below.
NiMh:
Lithium-Ion:
Lead-acid:
70,
90,
80
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
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
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
… the cell voltage is higher
… the internal resistance is lower
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
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
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
Cryogenic cooling is needed for the high efficiency of superconducting coils
Superconducting coils have a low energy density compared to batteries
Gravimetric Calorific value (in MJ/kg)
Volumetric Calorific value (in MJ/m³)
h2 ch4
50.0 120.0
35.9 10.8
