Lecture 5 – High-Power Energy Storage Flashcards
Where are high energy storage technologies commonly used?
The high energy storage technologies are used in applications where high power is required for shorter durations and with high frequency.
What kind of a storage technology is used in a SuperCaps
Electrostatical Field: Electrical Storage Technolgy
Batteries vs SuperCaps
limited Power vs. High Power
for long time vs. for short time
more Energy vs. Low Energy
- SuperCapasitor can deliver at very high rate and has very low limitaitions on cycle Numbers
Which types of SuperCaps is there available?
- Double layer Capacitor
- Pseudo Capacitor
- Hybrid Capacitor
Explain the physical principle behind DoublelayerCap.
- DLC is internally series of two capacitors, also in name plate you get the total cap. of these 2 capacitors
- Both electrodes are attached to aliminium current collector
In what order of magnitude do DLC have their stored energy? and what is the difference between an electric capacitor and a film capacitor? capacitor,film capacitor
the DSK have a stored energy quantity of Wh while the normal capacitor has some Ws and film capacitor some mWs
Explain SuperCap electrodes and its characteristics?
Special, electrochemical carbon powder with a specific surface area of about 2000 m²/g. The carbon powder is applied together with auxiliary materials as a paste onto the aluminum foil.
- As active material in the electrodes we have carbon with very large surface area per gram, 2000m2 per gram.
- Carbon with very high internal surface area, but poor electronic conductivity.
- Additives to improve conductivity (“ conductive carbon black as electron emitter “) and stability (“ Teflon as binder “),
- The more expensive electrode material largely determines the price of the supercaps
- Very small distance between ions and carbon
- Order of magnitude in nm.
What is the resting potential of a SuperCap?
The supercaps do not have a rest potential, which is created by the electrochemical reactions. The reason for this is that in the supercaps the energy is not stored by electrochemical storage but by an electrostatic storage mechanism. So when the SOC drops to 0%, a potential of 0V is present between the electrodes.
the fact of not having a chemical reaction also leads a longer lifetime
How is the structure of a DLC?
The DLC has two Caps connected in series. So the Total Capacity is half of the one Capacitor.
When can the DLCs be installed as an option?
In the UseCases when there is a need for a high performance for a small amount of a time and that is really often in the lifetime. If these circumstances are given, then a DLC is a consirablke option to install.
Real use cases are for example the pitch system of wind turbines, assistance in starting lights or motors, braking systems.
The SuperCaps are an option when high power or very high cycle counts are needed.
Although there is no aging limitation, it does not go to voltages as low as 0V and DOD at 100% because,
Because if i take all the capacity out with a const. Power Discharge then after a curtain point of time the voltage will drop significantly and for the purpose of still provding a const. Power the current will rise exponentially. This may lead a problem with othe electrical devices may require to set them at a higher current rate which will increase the costs. Besides than that it also causes higer loses due the I^2 * R which than followed by a higher Tempertatuers and eventuelly a less life time.
The 75% of the Energy stored can be used even with a Max Voltage use of Umax = Un/2 , because the Energy stored formule indicates that E = 1/2 C* ((Umax)^2-(Un/2)^2) = 3/4Emax
Discharge with the constant power
How does the voltage and current waveforms look?
we have a overlinear voltage drop because we have a constant discharge and as the voltage drops the current must increase to provide constant power and as current increases the voltage drops faster
Explain impedance spectra for supercaps
45° angle at the frequency increase due to the pore structures of pores and has to do with the porosity.
At the very low frequencies we have then an almost capacitive behavior by 1 /jwC
With decreasing temperature, we have a decreasing resistance around the frequency values of 70 to 100 Hz, this phenomenon is reversed and with increasing frequency, the resistance increases at lower temps.
How is the Aging Phoenmenon in the DLC?
- Aging is significantly due to the **decompostion of the electrolyte **
- As a thumb rule we can say that the aging processes run twice as fast with
* Temperature increase around 10K
* Voltage increase around 100mV
Properties of SuperCaps
High performance
….. Stored energy, therefore charges and discharges with high powers are short (order of magnitude a few seconds), very …… volumetric and gravimetric energy density
….. Cycle life (order of magnitude ….. ) at 100% depth of discharge
….. Voltage drop at constant current ( 𝑈=1/𝐶∙ int( 𝐼) 𝑑𝑡 = Q/C) and thus in ….. Charge states at constant power demand very …. currents. So the electrochemishce discharge voltage, which is fairly constant, we do not have here.
High performance even at very low temperatures
Relatively easy state determination with respect to …. and ….., therefore interesting in safety-critical applications due to high achievable reliability
Strong …. Aging ( halving of lifetime with ….., see analyses in this lecture)
High …. per kWh storable energy
High performance
* Little stored energy, therefore high power charges and discharges are short (order of magnitude a few seconds), very low volumetric and gravimetric energy density
- High cycle life (order of magnitude 10 5 to 10 6 ) at 100% depth of discharge
- Linaer Voltage drop at constant current ( 𝑈=1/𝐶∙ int( 𝐼) 𝑑𝑡 = Q/C) and thus in low charge states at constant power demand very high currents. So the electrochemishce discharge voltage, which is fairly constant, we do not have here.
- High performance even at very low temperatures
- Relatively easy state determination in terms of power and energy, therefore interesting in safety-critical applications due to high achievable reliability
Strong temperature-induced aging ( lifetime halved with** 7K temperature rise**,)
High cost per kWh of storable energy
