What Are ‘Supercapacitors’ And What Are They Doing In Lamborghini’s New Sián Supercar?
Bill Roberson
But there won’t be a battery hiding inside the rumored $3.6 million Sián, of which only 63 units will be made available (oops, spoke too soon, they’re all sold). Instead, the car will use a 34-horsepower electric motor that gets fed electrons from something called a “supercapacitor.”
Okay, a little science 101 (or maybe 201) first. What makes a capacitor “regular” or “super?” And what does a capacitor do? Basically, it’s an electrical component that stores energy, but not really in the same way as a battery. And it’s not rare: You’re surrounded by regular capacitors right now. They’re in almost everything: Smartphones, computers, stereo equipment, microwave ovens, pretty much anything with a circuit board. Capacitors are great at storing and releasing energy at a rapid pace - as in thousands of times per second, and they can do it millions of times without degrading like a battery typically does. You can go more in depth here, but the bottom line is that they’re crucial for the proper operation of complicated electrical equipment - and they’ve been around since the dawn of electricity itself: 1745. So they’ve had some time to develop as it were.
But back to the Sián and those “supercapacitors.” It’s pretty much what is sounds like: Really BIG capacitors that store a lot of energy and are then able to dump it quickly into something like an electric motor, or the amplifier section of your stereo. In the case of the Sián, the supercapacitors power a small electric motor that’s connected to the engine . . .
But why just 34 measly horsepower? And how are those supercaps charged up if there’s no battery? Here’s where capacitors and batteries sort of part company (despite the fact they both store energy). While big batteries take many minutes or even hours to charge, big capacitors take mere seconds, and they can dump all their power in seconds as well. But, capacitors (at present) don’t hold a charge over time very well. A big supercapacitor array like that in the Sián will likely bleed off all of its stored energy in just a few days while parked. Also, capacitors don’t have the energy storage density of batteries, so they don’t store nearly as much power as a battery of the same physical size. At least, they don’t right now.
The Sián’s trick to charge up its supercapacitors is to use regenerative braking. When the driver slows, the Sián’s brakes work like generators, and quickly fill the capacitors with electricity. When the driver then accelerates, that energy is dumped into the small electric motor, which helps accelerate the Sián more quickly: Lamborghini is claiming it can hit 60 miles an hour in about 2.8 seconds. The reason the motor is so small is two-fold: The overall electrical energy system is small, likely to save weight (batteries are far heavier than capacitors) and it's more like an assist system than a full-on hybrid power plant. The Sián will not be able to move under electrical power alone.
Physics tells us that an object at rest requires a lot of energy just to get moving, but once underway, not nearly as much power is required to maintain a cruising speed (that’s why you get such good gas mileage on the highway). The small electric motor in the Sián, with its supply of essentially free energy from the car’s brakes stored in the capacitor system, helps get the car moving in tandem with the V12. It gives it a sort of free energy boost, either from a stop or from a lower speed when acceleration is called upon (like coming out of a corner). If this sounds like the KERS (Kinetic Energy Recovery System) device in race cars, it is indeed very similar in principle. Lamborghini says the system will also be used to smooth gearshits in the Sián.
So why doesn’t every car use this “supercapacitor” system to improve power and efficiency? Likely because it’s expensive and complicated to make and integrate, but now that it’s appeared in a (barely) civilian production car, the tech will likely be refined and start to trickle down to more affordable vehicles if economies of scale can be brought to bear.
Additionally, capacitors continue to be developed, with the hope that someday, perhaps some sort of battery/capacitor hybrid can be developed that will give the benefits of both systems: The ability to store large amounts of power long-term, quickly, and the ability to dump the power into motors for extreme performance. It could be a step on the road towards the ultimate battery technology: High-capacity solid state batteries that hold enormous power, charge quickly and last far longer than current “wet” batteries.
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