Having said all that, if this is true it may just be the silver bullet I've long denied existed. Apparently (and there's very little information out there to substantiate this, so HUGE grains of salt are warranted) a Texas company called EEStor has designed and is near production of an ultracapacitor with incredibly high energy and power densities, and very low cost. From Clean Break:
EEStor's technology could be used in more than low-speed electric vehicles. The company envisions using it for full-speed pure electric vehicles, hybrid-electrics (including plug-ins), military applications, backup power and even large-scale utility storage for intermittent renewable power sources such as wind and solar.It's that last one that is most promising, I think. The biggest problem with electricity to date has been the difficulty in storage. With a cheap, clean, long-lived way to store energy, these ultracapacitors may very well be the key to making solar and wind a critical part of the grid.
For those who don't know, ultracapacitors are analogous to batteries in that they store electricity. Probably every piece of electronics you own has capacitors in them, so this isn't some far-out technology. Where capacitors differ from batteries is that they are a solid-state electronic component as opposed to an electrochemical reaction. This means that capacitors can charge and discharge very quickly, relative to batteries.
(For a simple analogy, capacitors are to batteries, as the transistor is to the vacuum tube.)
However, until recently the amount of energy a capacitor could hold was far less than the best batteries. If EEStor is legit, than that's about to change. How big a change? According to the Energy Blog, the "product" that EEStor is producing weighs 400 lbs and holds 56kwh. 56kwh is enough - even with some pessimistic estimates - to power an electric car for more than 150 miles. More importantly for electric vehicle purposes, the power the product can deliver is astonishing - something like 400 horsepower, according to one estimate. The limiting technology for electric cars thus far has been the batteries. After EEStor, it might be the motors. My mother and her lead foot might even enjoy driving a car with one of these in it.
Now, 150 miles is still a bit short for a standard car, so the first application is liable to be plug-in hybrids. But even this 56kwh module could serve another purpose - install it in homes, and consumers would never have to pay peak electricity rates again. The module could charge at night, in offpeak hours, and run the home during the day without drawing off the grid. Alternately, a green-minded homeowner could combine this module with a solar rooftop and live entirely off the grid, as far as electricity is concerned. Even with an early cost of $3,000 that would be a minor expense compared to the solar panels, or with the home itself.
If homeowners don't go wild for these (and there's no reason to expect them to) the utility operators should consider a program of building decentralized "water towers" for electricity. By charging them at night, and draining during the day, utility generators could level out the load, allowing them to sell more electricity overall without building new capacity. These kinds of structures would have been impossible with even the best batteries - the life cycles are too short. Capacitors regularly perform for hundreds of thousands of charge-discharge cycles.
A little math. Assume a capacitor is charged at off peak prices - say, $0.04-$0.06/kwh here in Ontario. The peak price for a kilowatt-hour has been anywhere between $0.10 in the winter to $0.24 during the summmer, when we had to import electricity. (Thank you Manitoba - you kept our AC running!) These capacitors hold 56kwh. So if they fill up at the highest off-peak time (0.06) and sell the energy back during the lowest peak prices (0.10), we get this:
(56 * 0.1) - (56 * 0.06) = 2.24, or $2.24 profit per cycle.
If we pessimistically assume that these ultracapacitors are only good for 100,000 cycles (not the conventional meaning of "hundreds of thousands") then each $3,000 module could repay its investment almost 75 times. There's real potential here, technologically and economically.
Note that I actually suspect the profit potential here is overstated - the whole point is to allow a market to arbitrage the peak price of electricity down, by consuming more during off-peak hours. A cheap, long-lasting ultracapacitor makes this much more than a fantasy.
I should note that, thus far, EEStor doesn't have so much as a webpage. This isn't necessarily a bad thing - a lot of investors are still gun-shy from the dot-coms. And serious people are investing in EEStor, but that's actually beside the point. EEStor isn't the only company investing in ultracapacitors - some companies already have similar (though not as impressive, yet) products on the market.
I wasn't aware that ultracapacitors had come so far. It's nice to be surprised by good news these days.