transporting

An international study led by researchers from Austria has developed a novel way to store energy by transporting sand into abandoned underground mines. The technique is called Underground Gravity Energy Storage or UGES.

As the world deploys growing amounts of wind and solar energy, it is increasingly important to find ways to accessibly and efficiently store that energy to eliminate the inherent variability of the generation. There are many ways to store energy on a short-term basis – most commonly in batteries – but cost-effective long-term storage is still in its early stages.

The UGES technique generates electricity by lowering sand into an underground mine thereby converting the potential energy of the sand into electricity by the same regenerative braking effect used in hybrid and electric cars. The lowering sand operates a generator. Storing energy is accomplished by lifting the sand from the mine with electric motors to an upper reservoir where it is ready for the next cycle. By its nature, this storage technique has an indefinite duration, unlike batteries, for example, which lose energy to self-discharge.

The main components of UGES are the mineshaft, motor/generator, sand storage sites, and mining equipment. The deeper and broader the mineshaft, the more power can be extracted from the plant, and the larger the mine, the more energy can be stored. Mines generally already have the basic infrastructure needed and are connected to the power grid. The researchers estimate that there is global potential of 7 to 70 TWh of storage. Total global generating capacity is currently at the lower end of that range.

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Turning abandoned mines into batteries

Photo, posted October 21, 2020, courtesy of Christine Warner-Morin via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Many power plants in Europe and elsewhere are replacing coal with wood. For example, the Drax Power Station in Britain was its largest coal-burning plant and is now using wood pellets shipped from the southern U.S. in its boilers. According to the carbon accounting rules at the EU and elsewhere, the process is considered to be “carbon neutral.” But is it?

The idea is that new trees are being planted in the forests where the trees are cut to be burned in power plants. So, there is carbon neutrality. In principle.

European countries have embarked on a massive effort to switch to generating power from renewable energy. While there has indeed been major growth in wind and solar power in the 28 countries of the European Union, much of the new “green” power has come from burning wood in converted coal power stations.

A group of 200 scientists wrote to the EU last September insisting that bioenergy from forest biomass is not carbon neutral and that there must be tighter rules to protect forests and their carbon. Wood burning has become a loophole in controlling carbon emissions.

There are problems with the claims of carbon neutrality. There is no way to know whether enough new trees are actually being planted to replace those being burned. And then there is the time lag for tree replacement. Trees don’t grow overnight. There are also the carbon emissions associated with harvesting, processing and transporting wood.

There are most certainly ways in which burning biomass can be carbon neutral and can represent real progress over the use of fossil fuels. But caution must be taken to avoid exploiting loopholes in current climate rules that might actually result in increased carbon emissions.

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Carbon Loophole: Why Is Wood Burning Counted as Green Energy?

Photo, posted April 26, 2014, courtesy of Flickr.

‘A Carbon Loophole’ from Earth Wise is a production of WAMC Northeast Public Radio.