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Week of November 16
Submitted by Dan Sweeney on Tue, 2008-11-25 22:04.
Super-capacitors and mini nukes
I have been relatively inactive in my coverage of the alt fuels business of late because I have been engaged in performing due diligence for a company seeking to develop a new type of mass electrical storage system, a kind of super-capacitor.
I can reveal few details of the specific technology in question, but I can provide some background and can discuss the possible implications of the new technology in question, which actually isn't new at all, merely forgotten.
Super-capacitors, also known as ultra-capacitors, are devices for storing a large electrical charge. The energy storage capacity of existing commercial super-capacitors is roughly a tenth of that of a lead acid battery, the worst performer among common battery chemistries. So why even use the devices? What super-caps have going for them is high power density, that is, the ability to release the stored charge quickly. A super-capacitor can be fully discharged in a matter of seconds and can be just as quickly recharged. It provides massive surge power when you need it.
Super-capacitors were patented back in 1958, but they are based on concepts going back to the late nineteenth century. They've been on the market since 1978, but they've never been big sellers. The devices are expensive, and there aren't that many applications where the cost appears to be justified.
One very obvious application which has never really materialized is augmenting the battery banks in electric vehicles. Batteries tend to be taxed during hard acceleration, and repeated high current draws on batteries shorten their operating lives. Super-caps suffer no such liability. The obvious solution is to mate a super-capacitor with a battery and use the super-capacitor to provide high instantaneous power while relying on the battery to provide most of the electrical power consumed by the motor. A sophisticated energy management system will generally be required to select between the two devices according to the varying electrical load imposed by the motor.
Such a pairing results in a synergy that is truly more than the sum of its parts. But it also results in a big cost increment for the auto maker. A better solution at present appears to be the new UltraBattery technology being marketed by Furukawa and described in earlier articles in this journal. This combines a super-capacitor and a battery in a single module, and dispenses with the energy management system. While it doesn't quite equal the performance of discrete batteries and super-capacitors operating in tandem, it's fairly close.
In the past many research efforts have been devoted to producing a super-capacitor that would exceed the energy density of a battery. One company calling itself EEStor has managed to secure tens of millions of dollars of investment capital to further such aims without demonstrably succeeding.
The company I've been assisting is taking a somewhat similar approach to that of EEStor, but one with a better chance of success in my view.
This takes a bit of explaining.
Capacitors of whatever sort store electrical energy based upon a simple formula. Energy measured in joules is a function of capacitance times dielectric number times electrical field strength. So what's this mean? Capacitance is basically a function of the surface area of the electrodes, the positively and negatively charged elements. That's an oversimplification, but it's not too far off the mark. Dielectric number is difficult to define in a few words but essentially it refers to the ability of the insulating material to store charge and to permit ionic migration between the electrodes while keeping the circuit between them open. Electrical field strength is a function of the voltage impressed upon the electrodes and is inversely related to the distance between the electrodes. In both cases the relationship is exponential. Charge strength increases by the square of the voltage and decreases by the square of the distance separating the electrodes.
Commercially available super-capacitors have tremendous capacitance, fairly high dielectric numbers, and very low operating voltages. They also have very closely spaced electrodes. In most cases the electrodes are made of activated carbon granules which present extremely large surface areas. The insulating material, known as the electrolyte, is a fluid which seeps into the electrodes establishing an intimate bond.
We seem to be approaching a point of diminishing returns regarding the electrodes. There appears to be an optimum pore size for the material, and further reductions in pore dimensions will produce a larger surface area but not one that is capable of storing more charge. Improvements can be had by resorting to porous precious metals and arguably by use of certain very expensive carbon nano-tube structures, but enormous augmentations of capacitance by such means do not appear to be in the offing. So that leaves dielectric number, also known as dielectric constant, also known as permittivity, as well as voltage to examine.
With charge equaling the square of the voltage, much higher voltages would appear to be desirable. The problem there is that the high permittivity liquid electrolytes almost always have very low voltage breakdowns.
Now there are a number of solid electrolytes that have both high dielectric numbers and high voltage breakdowns. One such electrolyte, which the company in question has been employing, has a dielectric number as high as 4,000 and is capable of sustaining voltages as high as 80,000. In contrast, the electrolytes used in commercial super-caps have dielectric constants of less than 100 and maximum voltage points of less than five.
The problem is mating the hard, solid electrolyte to an intricately convoluted electrode so that ions can pass freely from the electrolyte to the electrode and vice versa. If that problem is solved then the way is clear to a super-capacitor of unprecedented performance. If it is not solved, then lithium ion batteries in one form or another will remain the preferred electrical storage technology.
A company named Hyperion Power Generation has been publicizing itself very effectively to the investment community of late. Made up of ex-Los Alamos scientists, Hyperion supposedly has developed a "nuclear battery" a zero maintenance nuclear generator the size of a bath tub which will provide decades of power for small communities.
How do they do it? Their Website doesn't say but purportedly the technology is based on a patent from the nineteen seventies.
One of my investor friends rang me up and asked for my take. If it is worth something to him, maybe it's worth something to you.
First of all, micro and mini nukes aren't a new idea. Rice University published a book length paper on the subject several years ago, and there's plenty of other literature in the public domain. There are also plenty of competing technologies, the best known of which is the pebble bed reactor developed in Germany back in 1968 and marketed today by a firm in South Africa. Toshiba also claims to have a micro nuke which is ready to go.
Nuclear energy is a polarizing topic. Most environmentalists abhor it and I've had people tell me that it is inherently immoral. Self styled "energy realists" embrace it, on the other hand, believing it to be an inexhaustible source of low cost electrical power and essentially benign.
While I do not believe that nuclear is immoral, I see it as a finite resource posing a lot of waste disposal problems. Whether it's micro or macro isn't going to change that. It's also a technology that is seemingly on the way out. Nuclear plants are getting decommissioned faster than they are being built, and unless that trend is reversed, nuclear could all but disappear by the middle of this century.
In all developed countries of the world nuclear power generators are rigorously regulated and that militates against micros and minis. What community coop is going to be able to afford compliance? Of course, the manufacturers claims there's no need for oversight, but they won't be making that determination, governments will. And that doesn’t bode well for the future of the minis.