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Molten salt storage for rooftop solar? SA invention wins Eureka prize

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The University of South Australia researchers behind a low-cost energy storage solution that uses salt to store excess electricity have been honoured in Australia’s top science awards, winning the ANSTO Eureka Prize for Innovative Use of Technology.

The “phase change” energy storage technology, which has been patented and commercialised by Glaciem, uses surplus electricity – say from rooftop solar panels – to freeze salt compact coils inside a purpose-built storage tank, not unlike the old-style electric hot water heaters many Australians still have installed at their houses.

solar thermal salt

When that stored energy is needed – say, when the sun goes down, or when grid electricity prices go up – the compact coils release it through melting the salt.

Of course, the notion of using salts for energy storage is not a new one. Molten salt batteries are used at a number of large-scale solar thermal farms, including the world’s biggest solar tower and storage plant, the 110MW Crescent Dunes facility in Nevada, US.

And sodium-ion batteries are widely considered to be a contender to compete with, or replace, lithium-ion technology as the great new battery hope.

But the use of salt as a phase-change material for smaller-scale, rapid-discharge batteries for residential and commercial use – and at a cost of up to 10 times cheaper than batteries – is, apparently, unprecedented.

According to UniSA mechanical engineer, Associate Professor Frank Bruno, his team’s salt-based energy storage system has the advantage over other battery technologies currently on the market, because it is cheap, relatively compact for the amount of energy it can store, rapid discharge, and doesn’t eventually go flat.

He says in a demonstration video that the team used a “novel concept” to stabilise their phase-change materials, ensuring long life and improved responsiveness.

Professor Bruno with the team's "phase change" material

Professor Bruno with the team’s “phase change” material

“The key was getting the price down, to try to develop energy storage that is effective and cheap,” Bruno told the Adelaide Advertiser.

“This energy storage technology can be used for refrigeration, or air conditioning for homes, or solar power plants, so, yes, it is a big change,” he said.

A full-scale commercial version of the technology is already being used at a farm in Australia, according to Bruno – not to store excess solar, but to store cheap electricity from the grid overnight, and then use that to power the farm’s cool rooms during the day, he told ABC Radio Nationals’ breakfast program.  

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  • Petra Liverani

    This seems like a wonderful game-changer … so if Port Augusta doesn’t get its CSP+ (Concentrated Solar Thermal Power plus molten salt storage) plant this development may really be better than a consolation prize. PCM (phase change material) technology is so fascinating.

  • Sunbuntu Ltd

    Too bad is is basically illegal in Australia.

    ANY THERMAL plant must meet the same regulations as 1 GW coal plant. Without looking up the regulation each system requires multiple engineers on a 24×7 basis.

    • Chris Drongers

      but it seems that this material is to shift electricity consumption out of peak hours and into offpeak when electricity would be cheaper.
      Glaciem’s technology is not an electricity generator. It is a form of peak demand management by running chillers on cheap power at night and using the stored cold to run refigerators and airconditioners during peak electricity price times – it should make coal generators operation easier by reducing morning and evening peaks and increasing consumption during the nighttime demand trough.
      Unfortunately it will reduce coal generator’s profits as most money is made during the peaks, not on the 24 hour average.

    • JonathanMaddox

      This is not a thermal power station, it’s a cold store.

  • Peter Campbell

    One of the best phase change materials is also readily available: water. Per kilo it is one of the best for the amount of energy it absorbs and releases between liquid and solid. So, perhaps we should be using off-peak surplus renewable electricity to make ice and then that stored ice can passively cool our houses when we might want to run air conditioning during peak demand times.
    The main advantage of other phase change materials seems to be being able to pick a temperature other than zero degrees C.

  • Henry WA

    It would be interesting to know what the full cycle efficiency factor is, ie the amount of electricity used to freeze or convert the salt medium and then the amount of electricity available when the process is reversed.

    • JonathanMaddox

      It does not deliver electricity. This is a way of storing *cold*. The wording is particularly odd, making it sound like electric energy is what’s being stored.

  • George Michaelson

    Lovely technology. If I am not mistaken they are consciously focussed on the consumer side use of electricity in heat/cool related contexts, which suggests either the efficiency model is a CHP one where excess heat or the cool material provides two functional outcomes, or the stored energy in the phase change is used directly at time of consumption as a thermal agent, not as re-gen of electricity.

    Secondly, This is hugely applicable in lots of contexts. It may be a niche, but its a niche which exists everywhere there are large endeavours which need 24/7 thermal control. Shopping centers for instance, have huge AirCon needs during the day which generate heat energy, and then a constant chilling requirement for the co-located supermarket chiller rooms.

    Lastly, it felt like an inherently safe mechanism. Low risk of explosive failure, lower toxicity. Which makes it a good fit for distribution into residential or non-industrial locations.

    Most thermal storage systems gain efficiency from scale, because heat loss or gain to the outside world is a function of surface area/volume. Is this any different?

  • JohnRD

    I hate to mention it but the use of phase change materials to store heat or cold has been around for a long time (See: http://reneweconomy.com.au/2012/the-case-for-moving-air-conditioners-off-peak-82794 and http://www.climateplus.info/2014/05/19/energy-storage-using-phase-change-materials/) It is not clear why the system described in the article would be better.
    One of the advantages of using phase change materials is that less power is needed if the heating or cooling of the phase change material can be done when the outside temp is closer to the target temp. For example, in some locations taking advantage of cooler night temp may allow the house to be kept cool during the day without needeing a heat pump at all.

  • Peter Thomson

    ‘Battery’ is not the right term for this technology, as it is not storing and returning electricity, but return thermal energy. Good to see some innovation in the domestic HVAC area though.

    • Ice Czar

      Incorrect
      A phase change electrical battery system
      Molten salt batteries powering an ICBM near you

      • Peter Thomson

        There are ICBM’s near Melbourne? Wow! And I never knew!!

        But seriously, molten salt batteries only use solid-phase to extend storage life, up to 10’s of years. You need to pump significant amounts of energy into a molten salt battery just to heat the electrolyte salt back to liquid-phase (+100’s C) and activate the battery. The solid-liquid phase change itself does not store or return electrical energy.

        This article talks about doing the exact opposite – solar or cheap off-peak energy is used to *freeze* salts, not heat them, then the frozen salts are used to provide cooling for cold rooms or HVAC. If you listen to AProf. Bruno’s ABC interview (starts at 2:17:20 on the link in the article) this is exactly how he describes it. So this system is not a molten salt battery – it is a thermal storage system that returns thermal (cooling) energy, not electricity.

        Phase change material is also used in lithium-ion batteries, but only for thermal control. It helps keep the battery temperature in its safe operating area at high charge/discharge rates; again it does not generate electricity from the phase change.

        I don’t personally know of any system that uses a phase-change material to store and return electricity. Please do post a link of you do know of one, I would be very interested to read about it!

  • Warwick Johnston

    What is the released heat used for?

    • Ice Czar

      A molten salt battery can discharge almost like a capacitor or charge at nearly the same rate when molten

      When frozen they are inactive but will not slowly discharge

    • Peter Thomson

      It is a heat absorber rather than a heat releaser. When electrical energy is available (from solar or off-peak low-rate grid electricity), it is used to drive a cooling system that removes heat from the salt storage system, freezing the salt.

      When the frozen salt warms up it absorbs heat from the environment, cooling air or chilling water for air conditioning or keeping cold stores cold. The point about phase change is that a lot of latent heat is needs to be removed (freezing) or added (melting) to change phase from liquid to solid and vice versa, so more heat (or cold) can be stored in a smaller volume.

      Two use cases:
      1. The one described in the article, where a commercial cold store uses cheap off-peak electricity to store cold during the night (freeze the salt), then use the stored cold to keep its cold rooms cold during the peak day period when electricity is expensive.
      2. A suggested domestic use to convert solar energy to cold during the day, then use the stored cold to run the air conditioning during the evening and night time when the sun ain’t shining (the solar system can directly drive the air conditioning during the day as per normal).

      This is the technology the article and the radio broadcast both describe – it does not appear to be a molten salt battery, as Ice Czar suggests.

  • eddierothmanisatool

    yeh this is phase change not battery. and honestly as elon musk says “lithium density increases 8-10%/annum and costs are falling around 20%/annum so by the time these “breakthroughs” make it out of the lab in 5 years its sort of like………who cares?

    • Ice Czar

      Incorrect an electrical battery that phase changes

  • Ian

    I have to say that I find this article, and all the rest of the information I can find on the internet on this topic, a little confusing. To charge these batteries they freeze the salts- lowering their energy, and visa versa when they discharge. Where is that energy going? Freezing a salt is not storing thermal energy, it’s extracting thermal energy. How is energy being stored? Also, the beginning and end form of the energy seems to be electricity. If this is some kind of thermal battery, how are they converting between thermal and electric power? Some very key aspect of this technology seems to be missing from this report. I’d love to know what it is.

    • Joe Chip

      With the systems I’ve read about, thermal is converted to electricity via steam turbine.

    • A Wall

      I know I’m pretty late here, but…

      The source of your confusion is that it is not actually “energy” that we use to do work, but an “energy gradient”. For example, a heat engine allows energy to move from a hot place to a (relatively) cool place and extract work from it.

      Cold phase-change materials, such as this, create the energy gradient. However, I don’t think this is a method of storing electricity, but then a big demand for energy storage is for thermal energy anyway…

  • Lawrence Winder

    Nahhh… can’t be true.Crow-Eaters can’t even make canoes!

  • Audrey

    I had no idea that was possible. I love how people keep inventing different sources of power or way to keep it. I was surprised to learn they’ve invented completely see-through solar panels, basically new type of windows! I’ve read it here http://www.readwave.com/invisible-solar-cells-will-make-our-windows-a-power-source_s94507

  • Geoff

    so does that mean we’re going to see CST’s on peoples roof tops?

  • Jasku

    Sorry, this is such a low quality clickbait article. Sophie needs review the definition of Energy. The device in question does not store energy. It has great potential for refrigeration and cooling applications. Thank you to those in the comments who could actually explain what the technology is.

    Sophie Vorrath go back to school.