What's super about supercapacitors?
Supercapacitors are an alternative to using a battery or indeed the more common-or-garden variety of capacitor in many energy storage applications, perhaps as backup power or for high-surge demand applications. Avnet Abacus' Adam Chidley explains.
Also known as ultracapacitors or electric double-layer capacitors (EDLCs), these devices come with many advantages over batteries including, very importantly, a maintenance-free long life. And of course the environmental impact of products is becoming increasingly important, which makes the supercapacitor highly attractive for use in designs rather than batteries as they do not contain lead or other potentially harmful substances, making them compliant to EU directives such as RoHS.
The range of applications these devices can address is extremely diverse ranging from long-life replacements for coin-cell batteries that back up real time clocks, up to high capacity units that power servo-motors in industrial control. In terms of energy storage, supercapacitors fit nicely into the gap between aluminium electrolytic capacitors and batteries: offering significantly greater capacitances and energy densities than conventional capacitors, but still only a fraction of the energy density offered by batteries.
What is really super about supercapacitors is their ability to deliver a much greater power density – delivering energy to the load. They are suitable devices where there is a requirement for high capacitance and also rapid charge and discharge, so they bring significant benefits in both peak- and power-assist applications. Talking of this specific ability, there was a rather good blog published a couple of years ago by the Berkeley Energy & Resources Collaborative (BERC) that made a metaphor of the well-known Aesop fable of the Tortoise and the Hare (although strangely featuring a turtle instead of the tortoise).
Supercapacitor energy density & power density vs. batteries, fuel cells and other capacitors
In this re-imagining of the tale, the ‘rather-slow-moving-creature-that-lives-in-a-shell’ (in North Atlantic détente speak) is the battery, which delivers a slow and steady supply of energy. Whereas the pleasingly consistent hare (recognised on both sides of the pond) is the supercapacitor, which offers quick charging and discharging in lower energy applications. But unlike the moral tale, where it seems somehow important to have a winner, the point is to view these competing technologies as offering complementary qualities, combining to meet a desired goal, especially in next-generation vehicle applications such as electric and/or hybrid cars or buses. For example, supercapacitors are used for acceleration and deceleration and decreasing the weight of the batteries, which of course are required to provide the bulk of the energy required to power these vehicles. So, in many applications, at the system level, the combination can be much more than the sum of the parts.
The pleasingly consistent hare is the supercapacitor
Of course, possible applications for the super capacitor go well beyond electrically powered equipment and regenerative power systems in automotive hybrid and electric vehicles, although there is much excitement for the technology in this area. But in fact the list of applications is extremely diverse: in energy storage applications, they can make a significant contribution to power saving in equipment that uses energy storage devices for standby power such as TVs or set-top boxes or other consumer equipment; or as short-term power backup in power utilities; or in power supplies used in life-support equipment, meaning there is no need to change batteries and thereby achieving a virtually maintenance-free environment; or as power supplies used in conjunction with solar batteries for example, such as outside or street lighting or flashing ‘cat’s eye’ road-safety markers perhaps. The other side is their use in high input or output load levelling for the protection of equipment such as control systems or potentially assisting in energy saving in power generation such as solar or wind-power generation systems.
In this area, Avnet Abacus offers a wide range from world-leading suppliers such as AVX, Cooper Bussmann ), Murata (DMG series), Nichicon, Panasonic and now KEMET. The Avnet Abacus KEMET product line has recently been extended to include a range of new devices including small-cell variants that target a wide variety of board-mounted applications such as RAM backup and small motor assist. Finally, Avnet Abacus can now offer the Vishay 196HVC series hybrid energy storage capacitors.
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