Flywheel Energy Storage: Steel Yourself For Carbon

Red Leader. writes: "Hey. Here's an interesting article on flywheels and the future of batteries from Wired Magazine (8.05). Nothing super-promising yet (as always; vapourware) -- but down the road, these could make your laptop 'spin' a little longer." I'm a big fan of simple machines, and flywheels are one of my favorites. The mention of carbon nanotubes is especially interesting -- it'd be neat to see that technology enter the mainstream.

Comments

Flywheel Cars

[kornack]

I've long loved the idea of flywheel cars but have always worried about the gyroscopic effects.

Consider a car with a flywheel in it. If the flywheel lies in the horizontal plane, its axis of rotation (and, thus, its moment of inertia) is vertical. If such a car were to turn on a flat road, nothing would happen. But if this car were to drive onto a ramp, the flywheel acts like a gyroscope and would cause the car to violently turn to the left or right.

Likewise, if the flywheel is oriented so that the axis is horizontal, any turn to the left or right would cause the car's nose or rear to pluge into the ground. The exact direction would depend on the direction of rotation.

What am I missing in this account? Am I simply wrong to think that the precessional force would be so strong? I haven't checked any numbers for myself, so it could be that the effect is sufficiently weak. Indeed, the bus that was described in the article didn't seem to flip over. Of course, it was just using the flywheels as temporary storage for acceleration in combination with hybrid power (right?). So perhaps its flywheels are smaller than the ones I'm envisioning as replacements for the batteries in modern purely electric cars.

The solution that I see is to place two counter-rotating flywheels right next to each other so that the total moment of inertia is zero. There would be tremendous stresses on the support structure for the flywheels, but the sum moment of inertia is zero.

Tom Kornack

Carbon Nanotubes

[WombatControl]

Carbon nanotubes could be the energy source of the future. Not only are they useful for flywheels as the article mentions but they also are being tapped for use in hydrogen fuel cells. The nanotubes can trap hydrogen and make it safe for storage and use as fuel. The nanotubes need to be able to carry 6.5% of their weight in hydrogen. Some researchers have claimed that they have formulated nanotubes which can hold up to 65% of their weight in hydrogen but those results have not been revealed because of "commercial reasons." (Don't these people ever learn? You're not going to make a cent unless your process stands up to scientific review!) Still, carbon nanotubes are an exciting new prospect in the quest for a cleaner burning engine system. Between hydrogen fuel cells and flywheel power, the prospects of these structures are enormous.

Re:Carbon Nanotubes

[Anonymous Coward]

The research has gone pretty far in the last few years. I worked on producing carbon nanotubes for my undergraduate thesis in physics in 1994-1995, when metal doping of the carbon electrodes was first described for generating single-wall nanotubes (SWNT's). Since then, fullerene research has pretty much continued at a feverish rate, with numerous papers published each year describing improved methodology, fullerene properties, and new practical applications. These have for the most part born out the incredible theoretical predictions about their unique properties, including astronomical length to width ratio, superb tensile strength and geometry-dependent conductivity. Like the laser, fullerenes hold the promise of being a solution looking for a problem.

In answer to the question specifically on carbon nanotubes, there has been a lot of experimentation done on them. Carbon nanotubes come in a variety of geometries that can be thought of conceptually as rolling chicken wire (a hexagonal array) up with varying amounts of stagger or offset. They can range in conductivity from metallic to semiconducting, depending on this geometry (Science, 288(5465):494-7). They have been used as tips for atomic force microscopes (PNAS, 97(8):3809-13). Tensile strength studies have found individual nanotubes with a Young's modulus E of nearly 1 TPa, or 1000 GPa (Science, 287(5453):637-40). Various other electromechanical applications like field emission effect (Science, 283(5401):512-4) have been dreamed up.

Not being in the field any longer, I can't make any predictions about timescales of the integration of carbon nanotubes into new technologies. However, you can usually tell that a material is no longer just a laboratory curiosity when the major chemical distributors start selling it, like Sigma-Aldrich. The fact is that carbon nanotube production is incredibly cheap and easy (doable by a fresh undergrad student, yours truly...). It is the purification of the desired nanotube type from the mishmash of soot you obtain from the arc that is the real challenge.

Ryan.

Flywheel problems (and solutions thereunto...)

[trims]

Pardon the silly title.

yes, even the smallest flywheel has gyroscopic precession problems. Yes there is a danger that they might shatter and shoot out lots of nasty fragments. Then again, your typical battery can spontaneously burst into flames, spew acid all over the place, and generally trash your surroundings at the drop of the hat. I don't see too many peole complaining about those problems.

The precession problem with flywheels can be almost completely negated by using two counter-rotating flywheels. yes, I am aware that there will be some problems with movement along the Z-axis, but this is managable in instances where there is little Z-movement (such as cars).

Furthermore, the heat problem is significantly reduces (in fact, almost eliminated) if the flywheel is contained in a sealed vacuum shell. For safety's sake, making this shell from something like kevlar would reduce the small risk associated with flywheel failures at high speed.

The biggest problem with using flywheels is that there has to be some sort of electric motor - that is, something that can change mechanical movement to electrical energy. In items like cars and UPSes, this isn't much of a problem. In your laptop (and similar compact places) this is definately a stumbling block. I wouldn't look for flywheels in laptops anytime soon.

I expect to see flywheels in electric cars in the near future, since they offer alot of advantages over a most batteries: lighter weight, a very high energy capacity, ability to deliver large amounts of current quickly (something most non-lead-acid batteries can't do), and virtually no maintenance.

Honestly, I can't wait for the hybrid car to come along: small, constant RPM gasoline engine, electric generator, and flywheel. You have a lead-acid to start the whole thing, and store any excess energy in the flywheel. Cool!

-Erik

You know you're a geek if...

[httptech]

this comment from the article: The wheels are then derated to - that is, run at - 50 percent of maximum speed made you think: "Ooh! I could
overclock that puppy!"

More on this topic

[phandel]

Another page here proposes to use this same technology in a next-generation UPS. They make some pretty bold claims:

Conventional UPS is mainly a combination of high-maintenance diesel-generators and lead-acid batteries. Other flywheel batteries offer only short-term (most "tens of seconds") ride-through power, during utility line outages; and while the utility or on-site generator supplies power, they constantly consume typically kilowatts while idling. That's over 1000x more losses than RPM's Flywheel Battery; which runs far cooler, will have far longer service life, negligible self-discharge, far higher reliability, far lower life-cycle cost, no wear-out, and no maintenance!

There are quite a few additional links at the bottom of that page.