What is a Supercapacitor – Working and Its Applications

A simple passive element that can store electrical energy, when a voltage source applied is called a capacitor. It has an ability or capacity to store electrical energy by producing potential difference across its plates, and it behaves like a rechargeable battery. The capacitor consists of two parallel conductive plates, which are not connected to each other. The plates are separated by an insulating material called Dielectric, which is waxed paper, ceramic, mica plastic or liquid gel. Due to this insulating material, the DC current cannot flow through the capacitor. It blocks the flow of current and the capacitor charges up to its supply voltage and acts as an insulator. When the capacitor is used in AC circuits, the flow of current is straight through the capacitor with no blocks. The electrical property of the capacitor is capacitance and it is measured in Farads (F).  Depending on the dielectric, the capacitance of the capacitor various. There is one capacitor which has the highest storage capacity. One such is a Super Capacitor. This article discusses an overview of supercapacitor.

What is Supercapacitor?

Definition: A supercapacitor also called as ultracapacitor or a high-capacity capacitor or double-layer electrolytic capacitor that can store large amounts of energy nearly 10 to 100 times more energy when compared to the electrolytic capacitors. It is widely preferred than batteries because of its faster charging capacity and faster delivery of energy. It has more charging and discharging cycles than rechargeable batteries. These are developed in modern times for industrial and economic benefits. The capacitance of this capacitor is also measured in Farad’s (F). The main advantage of this capacitor is its efficiency and high-energy storage capacity.

Supercapacitor Working

Similar to a normal capacitor, the supercapacitor also has two parallel plates with a bigger area. But the difference is, the distance between the plates is small. The plates are made up of metals and soaked in electrolytes. The plates are separated by a thin layer called an insulator.

When opposite charges are formed on both sides of the insulator, an electric double layer is formed and the plates are charged. Hence the supercapacitor is charged and has higher capacitance. These capacitors are used to provide high power and enable high load currents with low resistance. The cost of the supercapacitor is high because of its high charging and discharging capacitance.

An electric-double layer is created when the plates are changed and opposite charges are formed on both sides of the plates. Hence the supercapacitors are also called double-layer capacitors or electric double-layer capacitors (EDLC’S). When the area of the plates increases and the distance between the plates decreases, then the capacitance of the capacitor increases.

When the supercapacitor is not charged, all the charges are distributed randomly within the cell. When the supercapacitor is charged, all the positive charges are attracted to the negative terminal and negative charges are attracted to the positive terminal. Generally, supercapacitors are available with 420F capacitance, charging and discharging current 4-2Amps with a room temperature of -22 degrees centigrade.

How to Charge a Supercapacitor?

The supercapacitor has the self-discharging capacity and unlimited charging-discharging cycles. These types of capacitors can work with low voltages (2-3 volts) and can be connected in series to produce high voltage, which is used in powerful equipment. It can store more energy and releases instantly and more quickly when compared to batteries.

When this capacitor is connected to the circuit or DC voltage source, the plates are charges and opposite charges are formed on both sides of the separator, which forms a double-layer electrolytic capacitor.

To charge a supercapacitor, connect the positive side of the voltage source to the positive terminal of the supercapacitor and the negative side of the voltage source is connected to the negative terminal of the supercapacitor.

If the supercapacitor is connected to 15 volts voltage source, then it charges up to 15 volts. As the voltage is increased beyond the applied voltage source, the supercapacitor may get damaged. So, the resistor is connected in series with the voltage source and capacitor to decrease the amount of current flowing through the capacitor and it doesn’t get damaged.

The constant current supply and limited voltage supply is suitable for the supercapacitor. When the voltage is increased gradually, the amount of current flowing through the capacitor changes. In the fully charged mode, the current drops by default.

Supercapacitor Vs Battery

The batteries are widely used with a specific volume and weight, also have better energy density. Supercapacitors are high-capacity capacitors with high power density. When compared to a battery, the supercapacitor has a fast charging-discharging capacity, can handle low-high temperature, high reliability, and low impedance.

The cost of the battery is low whereas the cost of a supercapacitor is high. Supercapacitors have the self-discharging capacity. In the battery, the operating voltage determines the charging and discharging modes. In a supercapacitor, the allowable voltage depends on the type of dielectric material used between the plates. And also the electrolyte in the capacitor may increase the capacitance.

Batteries are available in lead-acid batteries, Ni-MH, Li-Po, Li-ion, LMP, etc. Supercapacitors are available with organic electrolyte, aqueous electrolyte, ionic liquid, hybrid, and pseudo supercapacitors. Batteries are used to store large amounts of energy and supercapacitors are used to deliver high power density.

Solar Inverter using a Supercapacitor

The solar inverter is helpful for the farmers in irrigation, fencing, etc. The solar inverter uses solar plates and the solar energy obtained from these plates is stored to a battery. The complete solar inverter system has an ON/OFF switched to control the charging of the battery according to the purpose of the farmer.

The block diagram of the solar inverter using supercapacitor contains,

• Solar panel
• Pulse generator
• Step-up transformer
• MOSFET
• ON/OFF switch
• Supercapacitor and
• Rechargeable battery

When the battery leads are connected to the pulse generator and in turn to the MOSFET, it is capable of generating ON/OFF pulses at different frequencies. The pulses are fed to the step-up transformer to obtain low AC voltage. This AC voltage is used for different applications during farming. The supercapacitor is used in the whole process to deliever high power, for fast charging and storing solar energy and to increase battery life.

The output energy of the solar plates can be increased by increasing the dimensions of the solar plates.

Applications

The applications of supercapacitor include the following.

• To deliver high power and bridge power gaps
• Industrial and electronic applications
• Used in wind turbines, electric and hybrid vehicles
• Regenerative braking to release the power in acceleration
• To start power in start-stop systems
• Regulate voltage in the energy grid
• To capture and assist the power in lower loads and lifted loads
• Back-ups the power in a quick discharging state.

FAQs

1). Can supercapacitors replace batteries?

To deliver high power density, and for simple and fastest charging purposes, the supercapacitors can replace batteries.

2). How much energy can a supercapacitor store?

The supercapacitor stores 22.7 joules maximum amount of energy for 5.5 volts supply. It stores 10-100 times more energy per unit mass or volume when compared to electrolytic capacitors

3). What is the difference between a battery and a supercapacitor?

Batteries are used to store high energy and supercapacitors have high power density.
Supercapacitors are used to store and release power quickly whereas batteries stores the energy for longer periods.

4). How long can a supercapacitor hold a charge?

The charging time of the supercapacitor is 1-10 seconds when compared to the 10-60 minutes to reach a fully charged battery. It delivers 10,000W/kg with unlimited charging-discharging cycles.

5). Why not use capacitors instead of batteries?

Capacitors store electrical energy and have thousands of charging-discharging cycles. The battery stays constant when it discharges at a constant current and has constant power output. While the capacitor’s voltage is dropped linearly at a constant current, the power output also drops. So, the capacitor cannot be replaced with a battery. A voltage regulator circuit is used to replace a capacitor with a battery.

Thus, this is all about an overview of a supercapacitor. These are used in electronics as well as industrial applications. Here is a question for you, what is the function of a supercapacitor?