Storage of Electric Power
by Ron Kurtus (revised 31 May 2018)
Besides being able to create electricity, it would be nice to be able to store electric power and use it at a later time. There are several methods to do that.
Static electricity can be stored in a Leyden jar, which allows you to release the electric charges when you want to do that. Direct current (DC) electricity can be stored in a capacitor and a rechargeable battery. Batteries can also e used to create DC electricity.
Unfortunately, there is no way to store alternating current (AC) electricity, although it can be obtained from stored DC power.
Questions you may have include:
- How is static electricity stored?
- How is DC electricity stored?
- How can AC be obtained from DC?
This lesson will answer those questions. Useful tool: Units Conversion
A common way to store static electric charges, such that they can be discharged at will, is with a Leyden jar. This simple device consists of a glass jar with metal foil wrapped both inside and outside of the jar. A metal rod—often with a metal chain on its end—is located from an insulating stopped at the top of the jar.
Drawing of Leyden jar
from 1914 book Wireless Telegraphy - Wikimedia Commons
The way the Leyden jar works is that you put a static electric charge on the metal ball, which then is carried to the inside metal foil. The electric charges on the inside metal foil induce opposite electric charges on the outside foil. The glass insulates the charges and allows for a potential difference buildup, thus "storing" the static electricity.
Touching the metal ball will cause a discharge of the electric power.
Direct current electricity
Direct current (DC) electricity can be stored in a capacitor—which is similar to a Leyden Jar—or in a rechargeable battery.
A capacitor—also called a condenser—consists of two terminals attached to metal plates, separated by a thin dielectric material. Although any insulating material can be used as a separator, certain materials are more suitable in capacitors. Mica, ceramic, cellulose, Mylar, and even air are some of the non-conductive materials used in capacitors.
When DC electricity is applied to the positive (+) and negative (−) terminals, they collect and build up charges, which can be released when connecting the terminals to an electric circuit.
DC circuit with capacitor
A light bulb in a DC circuit will glow until the capacitor is completely charged. At that time, no current passes through the circuit. Taking the battery out of the circuit will allow the capacitor to discharge and light up the bulb again for a short time.
A regular battery creates DC electricity through a chemical reaction of metal plates and an acidic solution. In a rechargeable battery, the process can be reversed, such that a spent battery can become charged again. Thus, a rechargeable battery can store DC electric power.
Alternating current electricity
Because the direction of the current changes in AC electricity, you cannot directly store the power. Placing a capacitor in an AC circuit has no effect on the alternating flow of the electricity.
The only way it can e stored is indirectly, by storing DC and then using a power inverter to convert the DC to AC. But this really isn't storing AC.
It is desirable to store electric power and use it at a later time.
Static electricity can be stored in a Leyden jar, Direct current (DC) electricity can be stored in a capacitor and a rechargeable battery. Unfortunately, there is no way to store alternating current (AC) electricity, although it can be obtained from stored DC power.
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Resources and references
Leyden Jar - How Stuff Works
Leyden jar - Wikipedia
How Capacitors Work - How Stuff Works
Capacitor - Wikipedia
Can Supercapacitors Surpass Batteries for Energy Storage? - ElectronicDesign.com
Rechargeable battery - Wikipedia
How DC/AC Power Inverters Work - How Stuff Works
Electricity Storage - List of methods from epa.gov
Questions and comments
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Storage of Electric Power