Have you ever taken a supercapacitor bus that " charges for 30 seconds and travels 5 kilometers "?
It is not difficult to understand that the supercapacitor bus is powered by supercapacitors. Capacitors are one of the common circuit components, mostly used for filtering, decoupling, etc. But now a capacitor can actually drive a car? ! It simply subverts everyone's perception!
Indeed, ordinary capacitors are difficult to do, but super capacitors can! With the advantages of fast charging and large capacity, super capacitors have created a precedent for capacitor-driven cars. It is reported that the bottom of each supercapacitor bus is equipped with supercapacitors, and the platform is transformed into a charging station with charging piles . Since the charging time only takes 30 seconds, the bus can keep running for 5 kilometers by charging the bus every time it stops and picks up passengers.
So the question is, why is the capacity of supercapacitors so large compared to ordinary capacitors?
1. The king of capacity - super capacitor
A supercapacitor is an electrochemical component that stores energy by polarizing an electrolyte, also known as an electrochemical capacitor or an electric double layer capacitor. Compared with other capacitors of the same size, the capacity of supercapacitors is much larger. The capacity of ordinary capacitors is at the microfarad level, while the capacity of supercapacitors reaches the farad level. Therefore, supercapacitors are known as "capacity kings" and "golden capacitors".
2. Why can the capacity of supercapacitor be so large?
First of all, what determines the capacitance of the capacitor? The electric energy stored in the capacitor comes from the charge accumulated on the two plates, and the capacity of the capacitor is related to the facing area and distance of the two plates.
The formula for calculating the capacitance capacity is:
C=εS/4πkd
ε is the dielectric constant, S is the facing area of the two plates of the capacitor, and d is the distance between the two plates of the capacitor (that is, the thickness of the medium).
It can be seen from the above formula that the larger the facing area of the two plates, the greater the capacitance; the smaller the distance between the two plates, the greater the capacitance . Therefore, if you want to obtain a larger capacitance and store more energy, you must increase the area S or reduce the distance d between the plates, but for ordinary capacitors, the space is very limited, and the general volume is not large, so the ordinary capacitor Power storage is limited.
Ordinary capacitor structure
But the supercapacitor is different. The supercapacitor belongs to the electric double layer capacitor. It uses activated carbon material to make porous electrodes, and at the same time fills the electrolyte solution between the opposite carbon porous electrodes to obtain a large capacity.
When a voltage is applied across the supercapacitor, positive and negative electrons are gathered on the opposite porous electrodes, and the positive and negative ions in the electrolyte solution will be gathered on the interface opposite to the positive and negative plates due to the action of the electric field, thus forming two collectors. The electrical layer is equivalent to two capacitors connected in series. Since the activated carbon material has a super high specific surface area of ≥1200m2/g (that is, a large electrode area S is obtained), and the interface distance between the electrolyte and the porous electrode is less than 1nm ( An extremely small medium thickness d) is achieved!
Super capacitor charging process
According to the previous calculation formula, it can be seen that the capacitance of this electric double layer capacitor is much larger than that of traditional physical capacitors. The huge surface area and the extremely small distance between charges make the super capacitor have a large capacity, specific capacity It can be increased by more than 100 times, so that the capacitance per unit weight can reach 100F/g. The capacity of a single supercapacitor can range from 1 farad to several thousand farads.
Three, the prospect is bright! Four application scenarios of supercapacitors
In addition to large capacity, supercapacitors also have various advantages, including the ability to turn on instantaneously, fast charging, etc., and do not require too complicated charging circuits, etc., so they are used in many fields.
1. Public transport/electric vehicles
Due to the special process, the equivalent resistance of the supercapacitor is very low, the capacitance is large and the internal resistance is small. The supercapacitor can have a very high peak current, so it has a high specific power, which is 50 to 100 times that of the battery, and can reach about 10kW/kg. This feature makes the supercapacitor very suitable for short-term high-power applications. Like electric cars.
The composite power system composed of supercapacitors and other energy storage components takes into account the advantages of high specific energy of other energy storage components and high specific power of supercapacitors, which can better meet the requirements of starting and accelerating performance of electric vehicles, and can improve the performance of electric vehicles. Recovery efficiency of vehicle braking energy. Increase driving mileage. At present, supercapacitors can form a composite power supply system with batteries, fuel cells, and flywheel batteries. The use of a supercapacitor-battery composite power supply system on pure electric vehicles and hybrid electric vehicles will be one of the important directions for the future development of the electric vehicle field.
2. Wind power generation
Wind power is currently the fastest growing renewable energy generation technology. However, wind energy is a randomly changing energy source, and changes in wind speed will cause fluctuations in the output power of wind turbines, which will affect the power quality of the grid. Therefore, it is an important issue in wind power technology to study the output power regulation of grid-connected wind farms. The additional energy storage equipment can not only adjust the reactive power, stabilize the bus voltage of the wind farm, but also adjust the active power in a wide range, which is a current research hotspot.
With the development of manufacturing technology, the energy density of supercapacitor has been greatly improved, and it has entered the stage of commercial application in some short-term power storage occasions. Using supercapacitors to store energy and smoothing wind power fluctuations in important frequency bands of wind farm output power has a good application prospect.
3. Microgrid/grid
In the grid operation, when the total power generation capacity is less than the total load demand and enters the island operation due to external faults, the secondary load must be removed in order to protect important loads. Reconnect to the main network due to the disappearance of the instantaneous fault, and restart the secondary load. From the perspective of power supply stability and economy, it is not good for secondary loads. Therefore, after external faults, supercapacitors can be used to provide short-term power shortages to island-run microgrids, maintain all loads and wait for fault repairs.
4. Building/elevator energy saving
The energy consumption of buildings in my country accounts for about 28% of the total energy consumption in the country. Among them, the electricity consumption of elevators is only second to that of air conditioners, and is much higher than that of lighting and water supply. The energy consumption of elevators has attracted great attention in the industry, so the energy saving of elevators has very important practical significance.
Therefore, the research and development of high-efficiency motor drive system is the key to energy saving of elevators. Energy feedback type energy-saving elevators have a relatively mature technology, but due to price factors and impact on the power grid, it is still difficult to promote. The supercapacitor is directly connected to the DC bus to absorb the feedback energy. The supercapacitor is directly connected to the DC bus of the inverter. Supercapacitors have good application effects and advantages in high-power electrical and electronic products, especially elevator products, and their application prospects are unlimited.
epilogue
In recent years, the technology of supercapacitors has developed rapidly, and its electrode materials have been continuously updated and iterated from activated carbon to new carbon nanomaterial systems such as carbon nanotubes and graphene; the structure of the device has been shifting from the original symmetric type to the asymmetric and battery type. Multi-system development such as , capacitor hybrid type, etc.; the shape of the device is also developing from rigid and opaque to flexible and transparent. Technology changes the future. I believe that the emergence and development of supercapacitors will continue to innovate modern industrial technology and change the world we live in.