Traditionally, when we think of storing energy we automatically look to batteries. Due to their chemical characteristics, batteries take time to charge up, and this is particular the case with Lithium Polymer batteries. Therefore, Lithium-Ion batteries are better suited for the EV market, with their high-power density and lack of memory effect, which is when batteries become harder to charge over time. However, despite these features, batteries are not always suited for some vehicles such as hybrids. This is where capacitors can be applied with great effect. As we already know from using capacitors in electrical circuits, they have the ability to rapidly charge and discharge as required. This is why they are best suited for hybrid vehicles that require a large amount of energy in the shortest time, and why this gap is being more commonly filled by supercapacitors.
What are supercapacitors?
Supercapacitors (or ultracapacitors) are broadly different from traditional capacitors in two ways: they have a bigger plate area as well as a tighter gap between these plates because the separator behaves slightly differently from a standard dielectric.
In an ordinary capacitor, there are two plates coated with a metal porous material to give a larger area for storing charge, separated using a thick plastic film or ceramic dielectric. As the capacitor is charged, the electric field is created from the positive charge forming on one plate and the negative on the other. This then polarises the dielectric and aligns the molecules in the opposite direction to the field, reducing its strength and allowing the plates to store more charge.
In a supercapacitor, there is no dielectric in the traditional way. Instead, there are two plates soaked in an electrolyte and separated by a much thinner inductor (usually plastic or paper). When the plates in a supercapacitor are charged, the opposite charge forms on both sides of the inductor. This has been referred to as an ‘electric double layer’, and for this reason you may also see supercapacitors referred to as double layered capacitors. The combination of the following features allows supercapacitors to achieve a much greater capacitance level:
- Plates with a bigger and more effective surface area
- Reduced distanced between the plates
Battery vs supercapacitor
Supercapacitors also have characteristics that are common to both batteries and traditional capacitors. The key difference between the two is that batteries have a higher density (storing more energy per mass) whilst capacitors have a higher power density (releasing and store energy more quickly).
Supercapacitors have the highest available capacitance values per volume and greatest energy density of all capacitors. The power density of a supercapacitor is generally 10 times greater than a conventional battery, which means that they are capable of much quicker charge/discharge cycles, simplified charging circuitry, significantly longer cycle life, wider operating temperature range, and a high peak discharge rate for loads that require high power for a short duration.
The technology is increasingly coming more in line with the properties of a traditional rechargeable battery and is forming a hybrid in the space between the standard capacitor and battery. This means they are also well suited to parallel connection with batteries to take the best features of both.
If you need to store a reasonable amount of energy for a relatively short period of time (from a few seconds to a few minutes), you’ve got too much energy to store in a capacitor and you’ve not got time to charge a battery, a supercapacitor may be just what you need.
Current use and future
Supercapacitors are becoming ever present in general consumer devices as the cost has started to come more in-line with batteries. They provide everything from back-up power for mobile phones to battery life extensions for devices that sometimes need quick bursts of power like a digital camera’s zoom feature.
They are also becoming commonly used in more demanding applications for power and energy requirements such as:
- Memory backup in electronic equipment to help manage low power input
- Electric Vehicle applications that often need short, high current power
- Recovery of braking energy for vehicles such as buses and train
- Energy harvesting in wind and solar to help smooth out intermittent power supplies
However, their uses can go far beyond this and they are increasingly being seen as a genuine replacement for batteries as part of the Green Energy Drive in energy harvesting and electric vehicles.
SPSCAP are the forefront of this technology with their module series of capacitors. Already this technology is being widely used in hybrid buses, plug-in hybrid buses, dual-source trolley buses, fuel cell buses, school buses and other commercial vehicles. The ultracapacitor modules can be used as efficient, highly reliable, safe, and intelligent energy storage units for starting, acceleration and braking energy recovery. These principles are also now being trialled in trams and trains to further fuel this conversion.
Furthermore, as the IoT continues to accelerate, devices that are a part of the network will most probably rely on some form of energy harvesting for their continuous use and power management. It is likely that supercapacitors, with their small form but powerful storage capabilities, will be integral to this. The development of a ‘flexible’ supercapacitor (with no loss of features) is also currently ongoing, promising endless applications. This could be crucial for the future of not only the IoT but wearables, portable consumer goods and medical tracking systems and devices.
Featured products
Eaton Hybrid Supercapacitors
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Vishay 196 HVC Series Energy Storage Capacitors
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KEMET FT Series Supercapacitors
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