- How to find a device to store electric charge that can be charged to full capacity so that the time taken to provide a full charge is comparable to the time taken to full a tank with petrol.
- How to find a device to store electric charge that can deliver energy rapidly enough to the motors of our hypothetical car so that the car can accelerate as well, and haul loads as well, as cars powered by internal combustion engines.
- How to find a device to store electric charge that has an energy density and longevity similar to that of the same mass and volume of petrol.
As far as getting energy in and out of an ECSD is concerned the most obvious choice is the ultracapacitor. Capacitors are basically two sheets of conducting material held a short distance away from each other, with a layer of insulator between them. The two conducting sheets are attached to a circuit, connected to a potential difference.
The electrons flow into one of the sheets, so that each plate has an equal and opposite charge. The magnitude of the charge grows until the capacitor reaches a critical threshold and a current forces its way between the two plates.
Ultracapacitors (AKA: hypercapacitors, or supercapacitors) are simply capacitors capable of storing a very, very large charge in a small volume (compared to traditional capacitors). As there is no chemical reaction involved, as in cells, the discharge and charge times can be very short (so capacitor-based cars would be very powerful and very quick to charge).
Capacitors are the basis of the company EEstor's project to produce a low-cost, high energy-density, rapid-recharging, and rapid-delivery capacitor.
Meanwhile elsewhere, lead-acid batteries are being given a new lease on life by a company called Firefly Energy. Their idea is to take the 19th century technology and use 21st century manufacturing and processing methods to make the surface area of the lead electrode greater, whilst also making it more stable (traditional lead-acid batteries tend to crystallise over time, particularly if they are not being used). Firefly have replaced the lead plates found in traditional lead-acid batteries with a carbon graphite foam that contains the lead.
The company boasts that the greater surface area afforded by the lead-impregnated graphite foam means recharge times are smaller, energy delivery times are smaller, and the whole shebang is more stable.
The soon-to-be-more-famous Tesla Roadster uses lithium-ion batteries, the kind (I assume, wait... yes, hang on... yeah) used in my laptop and many other portable electronic devices.
Li-ion batteries also have problems, as they sometimes catch fire.
So there are three different technologies competing for the title of automobile ECSD:
- Lithium ion batteries.
- Improved lead-acid batteries.
"Among EEStor's claims is that its "electrical energy storage unit" could pack nearly 10 times the energy punch of a lead-acid battery of similar weight and, under mass production, would cost half as much.
It also says its technology more than doubles the energy density of lithium-ion batteries in most portable computer and mobile gadgets today, but could be produced at one-eighth the cost.
If that's not impressive enough, EEStor says its energy storage technology is "not explosive, corrosive, or hazardous" like lead-acid and most lithium-ion systems, and will outlast the life of any commercial product it powers. It can also absorb energy quickly, meaning a small electric car containing a 17-kilowatt-hour system could be fully charged in four to six minutes versus hours for other battery technologies, the company claims."
EEstor seem to be very secretive (if they can back up their promises they have every reason to be suspicious of someone stealing a march on them), but I am attracted to the elegance of the ultracapacitor. It is the hydrogen-fuel-cell problem writ on a smaller scale: why go to all the trouble of juggling chemicals (hydrogen for fuel cells and lead-acid and lithium for electrochemical batteries) when you can store the charge directly?
"The first commercial application of the EESU is intended to be used in electric vehicles under a technology agreement with ZENN Motors Company. EEStor, Inc. remains on track to begin shipping production 15 kilowatt-hour Electrical Energy Storage Units (EESU) to ZENN Motor Company in 2007 for use in their electric vehicles. The production EESU for ZENN Motor Company will function to specification in operating environments as sever as negative 20 to plus 65 degrees Celsius, will weigh less than 100 pounds, and will have ability to be recharged in a matter of minutes."
Neat. At the moment, if I'm asked to place a bet - I'd say the inheritor to the internal combustion engine automobile will be hybrid-electric/electric cars, rather than vehicles based on hydrogen, bio-ethanol, or other biological sources. And I'll also wager that the successful technology out of the ECSD set will be the super/ultra/hyper-capacitor.
Ultracapacitor-based electric cars strike me as much more elegant, and much more sensible. I suspect that when people turn to bio-diesel and bio-ethanol, they're thinking about what fluid they could use to replace petrol in their tanks - rather than what is the most effective way of storing energy.
But the best technology isn't always the most marketable technology. I look forward to finding out how things pan out.