Storage Energy
How does a Supercapacitor Work?
The supercapacitor, also known as ultracapacitor or double-layer capacitor, differs from a regular capacitor in that it has very high capacitance. There are three types of capacitors and the most basic is the electrostatic capacitor with a dry separator. This classic capacitor has very low capacitance and is mainly used to tune radio frequencies and filtering. The size ranges from a few pico-farads (pf) to low microfarad (ΞF).
The electrolytic capacitor provides higher capacitance than the electrostatic capacitor and is rated in microfarads (ΞF). These capacitors deploy a moist separator and are used for filtering, buffering and signal coupling. Similar to a battery, the electrostatic capacity has a positive and negative that must be observed.
The third type is the supercapacitor, rated in farads, which is thousands of times higher than the electrolytic capacitor. The supercapacitor is used for energy storage undergoing frequent charge and discharge cycles at high current and short duration.
The supercapacitor has evolved and crosses into battery technology by using special electrodes and electrolyte. All capacitors have voltage limits. While the electrostatic capacitor can be made to withstand high volts, the supercapacitor is confined to 2.5â2.7V. Voltages of 2.8V and higher are possible, but at a reduce service life. To get higher voltages, several supercapacitors are connected in series.
Function | Supercapacitor | Lithium-ion (general) |
Charge time Cycle life Cell voltage Specific energy (Wh/kg) Specific power (W/kg) Cost per kWh Service life (industrial) Charge temperature Discharge temperature | 1â10 seconds 1 million or 30,000h 2.3 to 2.75V 5 (typical) Up to 10,000 $10,000 (typical) 10-15 years â40 to 65°C (â40 to 149°F) â40 to 65°C (â40 to 149°F) | 10â60 minutes 500 and higher 3.6V nominal 120â240 1,000â3,000 $250â$1,000 (large system) 5 to 10 years 0 to 45°C (32°to 113°F) â20 to 60°C (â4 to 140°F) |
Applications
Supercapacitors are ideal when a quick charge is needed to fill a short-term power need; whereas batteries are chosen to provide long-term energy. Combining the two into a hybrid battery satisfies both needs and reduces battery stress, which reflects in a longer service life.
Supercapacitors are most effective to bridge power gaps lasting from a few seconds to a few minutes and can be recharged quickly. A flywheel offers similar qualities, and an application where the supercapacitor competes against the flywheel is the Long Island Rail Road (LIRR) trial in New York. LIRR is one of the busiest railroads in North America.
Japan also employs large supercapacitors. The 4MW systems are installed in commercial buildings to reduce grid consumption at peak demand times and ease loading. Other applications are to start backup generators during power outages and provide power until the switch-over is stabilized.
Supercapacitors have also made critical inroads into electric powertrains. The virtue of ultra-rapid charging during regenerative braking and delivery of high current on acceleration makes the supercapacitor ideal as a peak-load enhancer for hybrid vehicles as well as for fuel cell applications. Its broad temperature range and long life offers an advantage over the battery.
Supercapacitors have low specific energy and are expensive in terms of cost per watt.