Liquid batteries also offer other advantages. Prudent Energy's Vanadium Redox Flow Battery stores energy in ionic forms of vanadium and pumps it across a proton exchange membrane. By doing so, the battery produces a reaction that's reversible, enabling it to be easily charged and discharged.
Hennessy compares the technology to a car's engine and fuel tank. In a car, increasing the size of the engine produces more power, while a bigger fuel tank offers greater range. The same goes for the flow battery, he said. Greater size means more power, while adding more liquid results in longer application times. "With lithium-ion, it's all power and energy wrapped in one box," Hennessy told us. "You can't add hours separately from megawatts. With ours, if you want extra hours, you just add extra liquid."
He said the Redox battery's energy density is about one-seventh that of lithium-ion (20Wh/kg versus 140Wh/kg for lithium), but contends that it can be cycled almost indefinitely. He also adds that its initial costs and operating costs are far lower than that of lithium-ion. The technology has been used in applications in Ireland, Japan, Denmark, Germany, South Africa, and Alaska, among other places.
Prudent Energy's Vanadium Redox Flow Battery: Greater size means more power, while adding more liquid results in longer application times.
Flywheels: Power versus energy
As demand for grid storage batteries rises, some experts expect flywheel solutions to find a niche, as well. Vycon Inc., for example, is employing fast-spinning flywheels in uninterruptible power supply (UPS) applications. Using 200-pound flywheels rotating at 37,000rpm, the company says its technology can bridge the 15 seconds between when utility power is lost and backup generators kick in. Up to now, server farms and other users of such systems have typically used batteries to bridge that gap.
"The flywheel provides enough run time to get the gen-set started," said Frank DeLattre, president of Vycon. "And we know with good confidence it will be available when we have a power outage."
Vycon's technical twist is that it trades larger flywheel size for rotational speed. Because energy varies with the square of the velocity, the company says it can get more energy by spinning the flywheel faster. "If you double the mass, then you've doubled the storage energy," DeLattre said. "But if you double the speed, then you get the benefit of the square. That's why we use a smaller mass rotating at a higher speed."
The key to doing that is the company's application of magnetic bearings instead of conventional mechanical units. Conventional bearings can't handle the speeds of Vycon's flywheel, DeLattre said. With their magnetic bearings, Vycon's flywheels can provide high power for a short period of time (20 seconds), instead of the higher energy that a battery-based unit would supply over a 10-minute duration. "Flywheels are focused on power density rather than energy density," DeLattre added. "So when the application calls for high power over a short run time, the flywheel hits the sweet spot."
Thanks for a fantastically detailed and comprehensive article, Chuck! It stands to reason that the electricity grid will be wildly more efficient and economical when we have on-line storage within the distribution system. Just imagine how wasteful things would be if we did not have warehouses, stockrooms, and distribution centers for material goods, or reservoirs and tanks for water and petroleum storage. Even the use of capacitors within electronic circuits permit amazing systems to be designed.
This of course is not a new observation, but the technology required to realize efficient, large-scale electricity storage is new. Let's hope the promise of a new market with huge demand is enough to spur further development...
We are on the brink of a cataclysmic change as the whole world shifts from Petroleum to Electricity. There is a great abundance of opportunities, and needs, for new energy technologies. It feels like an overfilled water-balloon ready to burst. Efficient and dense energy storage is way overdue. At the pace we are transitioning to Electrical Energy I believe our motivation will evolve from convenience to survival. Then many solutions will quickly surface.
William, I want to second that. Actually, Chuck stole my thunder. Just last night at an IEEE Committee meeting we were discussing this as a topic for a future meeting.
I have implemented flywheels as a backup for a data center. They are smaller and more environmentally friendly (and safer) than standard batteries.
The biggest issues, beyond cost, are two fold. One is the conservative nature of the utility industry. The other is the investment model.
The utility industry makes their money by providing a reliable source. It is highly regulated and therefore conservative in its approach. Based on their incentives, that makes sense. That is why you have states having to pass laws requiring target percentages of renewables and, now, batteries.
The investment model has served us very well. Most utitilities are funded through long term bonds. The government role is to provide regulation, and sometimes support, but generally the investor owned utility is privately funded and provides a steady profit. Thus, there is a disincentive to take risks, since most infrastructure has to last a couple of decades to justify the investment.
The upshot is that battery technology, like renewables, has to be "proven" in long term operations before utilities will routinely install them. Since the technology is so new, this might make sense. Let's hope the investors in these technologies have a long term view as well.
Well stated, naperlou. I find it interesting that our heated discussions about solar, wind, hydro, biofuels, and fossil fuels are actually an argument over energy storage. Either collect the solar energy immediately, extract the energy from wind created by evaporating water, from condensed water, from short-term storage in living organisms, or extremely long-term storage in fossilized organisms in the form of petroleum and coal. So I guess our current debates have always been over our preferred energy capacitors...
The current technologies available for massive energy storage are not much better than a lake on a hill. With the growing needs for electricity, the limited capacities of these energy storage technologies are probably more suited for supplementing individual home alternative power systems. We need a major breakthrough in high density energy storage or an extremely efficient source of uninterrupted power. I don't think much will change until then.
While we may be hitting a wall on energy storage, the lake on the hill looks better and better. it's dependable, and once you've bought the land (which is a one-time expense), it's inexpensive.
Charles, renewal energy sources are common in universe and storage is a major concern, even from cell phones to smart grid technology. Most of the storage mechanisms can hold power for a shorter duration and forced us for a recharge. So there should be some new technologies which can hold more power and can sustain for a longer duration.
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