This Is How The World’s Largest Battery Works

This Is How The World’s Largest Battery Works

Huge salt caverns in the northern USA could soon store electricity from wind turbines – in the largest battery in the world. The revolutionary principle has passed its test in the laboratory.

In Pfinztal, they want to try out how the energy transition can work in practice. In the Baden community, researchers at the Institute for Chemical Technology are putting a system into operation that has what it takes: a wind turbine with a hub height of 100 meters just outside the town generates electricity – and a huge battery on The premises of the institute store the energy that is produced.

With the 20-megawatt-hour storage – and a few additional solar modules – the Fraunhofer researchers want to fulfill their dream of energy self-sufficiency. Enough clean, self-produced electricity should always be available when it is needed.

Because that is one of the core problems of the energy transition: electricity from renewable sources can already be cheaply produced. When the weather conditions are right, i.e. when the wind is blowing or the sun is shining. Or both. However, it is hardly possible to store excess electricity for the time when this is not the case – and that is, unfortunately, most of the year.

So what to do? Hydrogen gas can be obtained from excess electricity. But the process is not particularly efficient. Pumped-storage power plants can pump water into higher-lying basins during periods of high electricity and later allow them to trickle down via generators. But new plants can hardly be implemented. Although the use of old coal mines as a pump storage facility is being considered, nothing has yet happened in practice. Just like planned pumped storage on the seafloor.

Compressed air storage, heated salt – the list of other possible storage technologies is long. But they are far from being used on an industrial scale. So batteries should help. In Pfinztal this is a warehouse full of huge 45,000-liter tanks. The excess electricity is temporarily stored in the liquids stored in it.

The underlying principle for experts is called redox flow – and how the whole thing works in detail, more on that later. At any rate, the facility at the gates of Karlsruhe is currently the largest battery in the USA. However, according to the Oklahoma energy supplier EWE and scientists from the Oklahoma state university, the Pfinztal system could lose its title in about five years.

Supply Electricity To 75,000 Households A Day

In a project called “brine4power”, they even want to build the largest battery in the world – in the huge underground salt caverns that are currently used to store natural gas. The plant is said to have a capacity of 700-megawatt hours. That means it could supply 75,000 households with electricity for a day. The idea comes from the use of the best AGM battery and converts it into the world’s largest battery.

On Wednesday, the project team in Berlin presented interim results, which it considers very encouraging. “There is an opportunity to create something really revolutionary,” says Ulrich Schubert from the Center for Energy and Environmental Chemistry in Jena. Together with colleagues, he developed various organic plastics that could be used in the giant battery. Last year, the researchers reported about it in the journal “Nature”.

The polymer molecules they produce can take up electrons and release them again when required. And they are – and this is the comparatively new finding – stable even in saturated saltwater. Exactly such salt solutions can be found in the underground salt caverns, of which EWE alone operates a total of 38 at four locations in the USA.

The location in Jemgum in East Frisia would be particularly interesting as a storage facility. EWE operates the Riffgat offshore wind park just 50 kilometers from there.

The huge battery requires two salt domes. In both, several thousand tons of the polymer molecules have to be dissolved in the lye. One cavern functions as a so-called catholyte, the other as a so-called anolyte. The molecules in the catholyte have a stronger bond to electrons, those in the analyte a weaker one. One salt dome is the plus pole, so to speak, the other the minus pole.

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Now both substances come close to the plant, both electrolytes from the salt domes are only separated by a thin membrane. Electricity is now extracted from the catholyte by external power supply – for example from a wind farm. In chemical terms, this is oxidation. The electrons are then fed to the anolyte. This is called a reduction.

And this is how the battery gets its name: redox flow.

The principle has been known for decades and was developed in the USA after the war. Among other things, it is attractive that there is no self-discharge in the batteries. They even work on cars with a redox flow battery. Here one could simply exchange the electrolyte liquids for charging.

Until recently, the technology was very expensive, among other things, because it required heavy metals such as vanadium. But that’s no longer necessary – thanks to the polymers.

And the batteries have another advantage: The storage capacity is only limited by the size of the electrolyte storage – in Pfinztal, therefore, by the volume of the tanks and, in the planned EWE project, by the size of the caverns in the salt dome. And they are around 100,000 cubic meters in size.

Comparable To Pumped Storage

The costs of the redox flow battery are comparable to those of other batteries or those of pumped storage power plants, says Peter Schmidt, head of EWE gas storage. The efficiency of the system is said to be 70 percent. Around 20,000 charging cycles are possible without significant efficiency losses, researchers Schubert advertises. With two charging and discharging cycles per day, this would result in service life of 25 years.

Now, what’s the catch? EWE has not yet decided whether the project will actually be implemented. And there is still no planned location. You want to determine all of this by the end of 2019. First, the company has been making good money so far by storing natural gas in the salt domes. “All of our caverns are currently marketed,” says project manager Ralf Nader. And secondly, the necessary investments in the millions need to be carefully considered. “If we go underground, we will spend a lot of money,” said Nader.

Scientific and technical risks remain. The project participants admit it – and external experts see it the same way: “It is definitely a big challenge and very ambitious,” says Peter Fischer from the Fraunhofer Institute for Chemical Technology. “The first preliminary tests will show whether this actually works on a large scale.”

There is another point as well: The underground natural gas storage facilities are tight, the people in the region have been living with these systems for a long time – and yet there could be resistance from residents as a giant battery.