Salt, silicon or graphite: energy storage goes beyond lithium ion batteries

Technologies that use gels, liquids, and molten silicon or salt could all claim a slice of the growing renewable energy storage market

Between the political bickering following a spate of blackouts in South Australia and the billionaire entrepreneur Elon Musk tweeting that he had a fix, and then the South Australian government announcing that it will build a grid-connected battery storage facility, interest in renewable energy storage has never been higher.

While lithium ion batteries sold by Tesla and others are perhaps the most widely known storage technology, several other energy storage options are either already on the market, or are fast making their way there.

All are hoping to claim a slice of what, by all indications, will be a very large pie. The Australian Energy Market Operator forecasts that more than 1.1m new battery storage systems will be installed in Australian households by 2035. And, according to a 2015 report by the Climate Council, battery storage capacity is expected to grow 50-fold in under a decade.

“The market for storage is huge,” says Kevin Moriarty, the executive chairman of 1414 Degrees, an Adelaide-based thermal storage company hoping to win South Australia’s 100MW storage system tender. The South Australian system will be the largest in Australia so far but Moriarty describes it as “a drop in the ocean” compared with what will be needed as Australia transitions away from carbon-dioxide emitting fossil fuels.

The need for energy storage solutions is the natural consequence of an energy grid that has an increasing amount of renewable energy sources. Solar power plants don’t produce energy when the sun doesn’t shine and windfarms grind to a halt when the wind doesn’t blow.

At the grid level, the resulting fluctuations in supply, combined with demand that can rapidly spike during hot weather, for example, can play havoc with the steady 50Hz electricity supply needed to power everything from microwaves to factory production lines.

Traditionally, fossil fuel-powered turbines are used to rapidly respond to load changes. If switched on when needed, electricity output ramps up or down so that there is enough electricity, at the right frequency, to supply demand.

Renewable energy storage systems, which include batteries and thermal storage systems, run from small household units to power plant and grid-scale technologies. What they aim to do is enable electricity to be released into the system when it is needed – so-called load shifting – rather than only when solar collectors or wind turbines are operating.

“Storage allows you to spread out the load and, if you can do that, you no longer need the big so-called base-load generators,” Moriarty says.

In thermal storage systems, renewable electricity or electricity purchased from the grid at off-peak rates is used to heat a material to a high temperature. 1414 Degrees uses molten silicon – an abundant and cheap element that is the main component of sand – that is heated to its melting point of 1414 degrees. The stored heat can then be used at a later time to generate electricity – using turbines – that is fed back into the grid. It can also release heat to be used in district heating systems for hot water or space heating.

The company has developed 10MW or 200MW systems, which can store heat for up to two weeks, although they are designed to be able to constantly charge and discharge according to demand. Unlike batteries, which have a finite number of charge/discharge cycles, the molten silicon can be used indefinitely and can be recycled when the units reach the end of their 20-year service life.

Other thermal storage systems take heat directly from the sun to heat storage materials. In these systems, concentrating solar collectors – rather than photovoltaic cells – are used to heat a liquid that can then heat a storage medium. Pilot scale facilities in Jemalong and Lake Cargelligo, both in central west NSW, use molten salt or graphite, respectively, to store heat.

According to Prof Frank Bruno, leader of the Thermal Energy Storage Group at the University of South Australia, one of the advantages of thermal storage is the ability to operate at high temperatures, unlike batteries, whose components suffer once temperatures go above about 50 degrees.

The other advantage is price. “Storing energy as thermal energy is much cheaper that battery storage,” says Bruno, although photovoltaic power plants currently out compete concentrated solar collectors.

The Australian Solar Thermal Research Initiative, of which Bruno is a member, is trying to bring the cost of concentrated solar collectors down, which would make integrated solar thermal storage systems more price competitive overall.

Battery makers are concentrating on trying to solve some of the key limitations of lithium ion batteries. One of those is the scant supply of raw materials required to make them, a supply that is unlikely to meet future energy storage demands, according to Prof Thomas Maschmeyer, co-founder of the University of Sydney spin-off company Gelion.

Gelion batteries use zinc and bromide, elements with more stable and abundant supplies than the lithium and cobalt of lithium ion batteries. Unlike lithium ion batteries, which will become more costly as demand for raw materials outstrips supply, the price of Gelion’s batteries will only decrease with increased production scales.

Gelion’s technology is based on a tweak of zinc/bromide chemistry – which is already used in Redflow batteries – that means the battery operates with a gel rather than a liquid. The resulting batteries look and work much like a lithium ion battery, but with greater heat tolerance. Gelion is currently raising funds to get their prototype into commercial production.

While there’s currently no front-runner to replace lithium ion batteries, according to those working across the range of storage devices available, there will be plenty of options ranging from household electricity storage, to grid-level systems like that proposed for South Australia.

“The market’s big enough and the needs are varied,” says Moriarty, so “there’s a place for all of them.”


Dyani Lewis

The GuardianTramp

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