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Tina Casey headshot

Want Renewable Energy? Just Go with the Flow

By Tina Casey

Earlier this week we described how Boulder, Colorado has been striving to establish its own municipal electric utility, with the goal of getting more renewable energy than provided by its utility company, Xcel Energy. Some time in the not too distant future, though, Xcel and other utility companies may be able to integrate far greater amounts of renewable energy into their mix, thanks to researchers at Stanford University and the Department of Energy (DOE) National Accelerator Laboratory.

The research team has been developing a low cost, improved version of an energy storage system called a flow battery, which could be scaled up to enable utility companies to store significant amounts of solar and wind power during peak generating periods, and then draw on them to smooth out supply valleys brought on by nightfall, cloud cover or a drop in wind conditions. While cities like Boulder may still have good reasons to strike out on their own, flow batteries could be a solution for many other utility customers.

The unrealized potential of flow batteries

Flow batteries literally flow. They are based on the chemical interaction between two liquids flowing through a chamber, separated by a membrane.

Flow batteries have some potentially significant advantages over other battery technologies. It is relatively easy to scale them up to utility size, simply by building larger pumps and tanks. They also have a long lifespan, and they charge and discharge quickly.

Another potential advantage is that flow batteries can be idled for long periods of time without losing their charge, making them a perfect match for storing energy from intermittent sources like wind and solar.

However, there are still significant obstacles to overcome. Flow batteries are expensive, partly because they rely on expensive, somewhat toxic substances that have been experiencing unpredictable price swings in the global market. They also have tricky and expensive maintenance issues, primarily involving the membrane, and in their current configuration they are too bulky for large-scale storage.

How to build a better flow battery

Under the guidance of Stanford associate professor Yi Cui, the research team came up with a simplified design that requires no membrane. Instead of two streams of liquid it uses only one, a lithium polysulfide solution. Consisting mainly of lithium and sulfur, it is relatively inexpensive compared to conventional flow battery solutions.

Instead of the interaction taking place between a membrane, it occurs when the lithium polysulfide solution comes into contact with a piece of lithium metal. Normally the metal would degrade under these conditions, but a special coating enables it to remain intact.

If the word lithium raises a bit of a red flag, it should. Though lithium is not rare, currently the U.S. imports most of the lithium it uses, which could provoke supply issues over the long run. However, the Obama Administration has been nudging the U.S. lithium production industry forward. Last year, for example, the company Rockwood Lithium (formerly Chemetall) expanded production at its Kings Mountain lithium facility in North Carolina, under a Recovery Act grant.

In addition, a significant lithium deposit has just been confirmed in Wyoming, which should help matters along.

A long wait for flow batteries

So far, the team has demonstrated a hand-sized version of the concept. The next step is to scale it up to laboratory size before it even gets to the pilot project stage, and to work on a more compact, cost-effective system.

In other words, if Boulder is serious about getting more renewable energy sooner rather than later, it should probably just go ahead with its plans to set up its own utility (alternatively, as of this writing the city is still in talks with Xcel to increase the renewables in its mix).

Flow batteries and green businesses

On the other hand, the Obama Administration has gone full court press on utility-scale energy storage, so Stanford's  flow battery research will probably not remain in the laboratory for long.

The Stanford project is just part of a broader Administration research initiative under the recently established Joint Center for Energy Storage Research, which also aims at improving electric vehicle batteries.

Once flow batteries are ready for widespread commercial use, the impact on businesses could be significant, leading to far greater access to renewable energy.

On a small scale, one immediate result is that on site or hyper local energy storage would become more practical and affordable. For individual property owners and business parks with wind turbines or solar arrays, that provides a means for keeping more renewable energy on site rather than selling it back to the grid.

Assuming Boulder pushes ahead with its utility plan, large scale flow batteries would enable it to achieve an even greater use of renewable energy than previously planned. Under the current circumstances, Boulder will still rely partly on the grid mix, but flow battery storage will enable it to set aside more renewable energy for peak use.

Similarly, flow batteries would enable utility companies to buy up more solar and wind power during peak generating periods, enabling them to provide a more favorable gird mix during peak periods (currently, utilities have to limit their use of renewable energy to ensure supply stability throughout usage periods).

Once flow batteries are mainstreamed into the utility sector, it's fair to ask whether switching to a city-owned utility is worth the trouble and expense.

That most likely depends on the circumstances of individual cities, but there are several factors that could work in favor of the city-owned model, including the potential to take greater advantage of low cost renewable energy sources, the capability to micro-adjust rates to benefit local economic development and civic goals, and the potential to improve quality of service including emergency response.

[Image (cropped): Courtesy of Stanford University]

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Tina Casey headshotTina Casey

Tina writes frequently for TriplePundit and other websites, with a focus on military, government and corporate sustainability, clean tech research and emerging energy technologies. She is a former Deputy Director of Public Affairs of the New York City Department of Environmental Protection, and author of books and articles on recycling and other conservation themes.

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