By George Harvey
We hear a lot today about power storage because of the increased use of solar and wind for generating electricity. The explanation for this is that solar and wind are intermittent – the sun is not always shining, and the wind does not always blow.
The fact is that all sources for power generation are intermittent; even nuclear needs to go offline periodically to be refueled, a process that usually takes a month or more. Also, baseload plants are inflexible and do not match grid demand well. For both reasons, utilities rely on special “peaking” power plants that are very expensive to run.
Power storage has been around for years, however. One option is pumped storage, that can provide huge amounts of power storage. The Northfield Mountain power station in Northfield Massachusetts, was installed to help match the output of the Vermont Yankee nuclear plant to grid demand. Its peak output was about twice the output of Vermont Yankee.
Other types of storage have been used as well. Recently, there have been attempts, many successful, to work with flywheels, thermal storage, compressed air, hydrogen, synthetic gas (power to gas systems), various kinds of capacitors, and others.
Deep-cycle lead-acid batteries have been the most common choice for household storage, and they see some use even for grid backup. The high-quality batteries from Rolls and Trojan Battery, for instance, use well-established technology. This fact that the characteristics of deep-cycle lead-acid batteries are well known means that knowledge about maintenance is well established. Rolls’ website is www.rollsbattery.com. Trojan’s website is www.trojanbattery.com.
Interestingly, another old design being revived is the iron-nickle battery. These use potassium hydroxide, a powerful alkali, as the electrolyte, with iron negative plates and nickel(III) oxide-hydroxide for positive plates. They are capable of withstanding a fair amount of abuse, including overcharging, over-discharging, and even short-circuiting, and have very long lives even under such circumstances. Iron Edison is a manufacturer, and it may be worth while to check their web site, ironedison.com.
Some of the most interesting recent work has been with newer kinds of batteries. There are many of these, and some of them are very different from what most of us might imagine. We might look at four of these that seem promising.
Surely most of the readers of Green Energy Times have heard of lithium-ion batteries. What many of us have not heard of is sodium-ion batteries. Sodium is much more abundant than lithium, and also does not have some of lithium’s problems. The trouble with sodium is that the atom is rather large, compared to a lithium atom, and this results in the need for a larger battery for a given task. You will not find these helpful with a cell phone, but they can power the grid about as easily as the more expensive lithium-ion batteries. Aquion Energy, of Pittsburgh, Pennsylvania is bringing such batteries to the grid. You can find more information at www.aquionenergy.com.
Diagram of a zinc-cerium redox flow battery. Created by Earth-Rare, posted to Wikimedia Commons
Flow batteries are being developed. In a typical flow battery, two electrolytes are pumped past each other with a membrane between them. Chemically, the action is very similar to the old lead-acid batteries in some ways, but the chemicals remain in solution for the entire process of charging and discharging. There is no reduction of quality over time, and the electrolytes can be discharged 100% on a daily basis for years. There are many kinds of these being developed.
One flow battery comes from Imergy Power Systems, which has offices in Fremont, California and Haryana, India. This battery uses a vanadium-based electrolyte. Vanadium is expensive, but the people at Imergy found a way to recover it from fly-ash in such a way that it requires only slight purification. The result is a rather inexpensive flow battery that can be built in sizes suitable for a household to those supporting a large microgrid. There is more on this at www.imergy.com.
Another flow battery comes from Harvard University. This battery uses a quinone compound that can be found in such natural places as rhubarb plants, in its electrolyte. This makes it much less expensive than those that use metals that may be in limited supply. The technology is very new, but the underlying science has been confirmed, and it is now getting tested in a pilot plant. The originators see the project as possibly transformative. There is no company website we can provide, but a web search, “Harvard quinone battery,” will yield news and articles.
One of the most remarkable solutions comes from Ambri, a company in Cambridge, Massachusetts. In this case, electrodes are made of magnesium and antimony. They are molten, and are separated by an electrolyte of molten salt. The three liquids are not capable of mixing, and so remain stratified with the lightest, magnesium, at the top and the heaviest, antimony, at the bottom. As bizarre as this might sound, the design of the battery is otherwise rather ordinary. You can see more at www.ambri.com.
These are just a few of the many battery designs that are being developed. They show some promise that in the near future, batteries with very different properties will come to market, and are likely to be much less expensive than most current batteries, with much longer lifetimes. And that will help us move to a distributed, entirely renewable, power system.
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