A NEW CONTENDER FOR ENERGY STORAGE XX A NEW CONTENDER FOR ENERGY STORAGE Energy storage has long been a challenge for those in the renewable energy field – what happens to unused energy generated by solar or wind power for example? A new system of storing it as liquid air could provide answers. Dominic Joyeux discussed how the system works with Highview Power’s Dr Javier Cavada, CEO and President, and Gareth Brett, Chief Technology Officer, as well as Professor Yulong Ding, Director of the Birmingham Centre for Energy Storage.

In years to come, 2018 may storage plant’, Ingenia 76). be seen as the year renewable The plant has a capacity of energy came of age. At the five megawatts and can store beginning of the year, UK 15 megawatt hours (MWh) of government data showed that, electricity, which is enough to for the first time, the 29% of power about 5,000 homes for electricity produced by wind and around three hours. solar was more than the total produced by nuclear (21%). The increase means that low carbon STORAGE energy sources now account CONTENDERS for over half of all electricity The main energy storage generated. providers are pumped However, a long-running hydroelectric – 95% of global challenge has been how to capacity – and lithium-ion store energy at times when batteries, which have been the there could be shortfalls caused fastest growing and account for by the wind not blowing or most of the rest of the world’s the sun not shining. UK energy energy storage. However, storage enterprise, Highview although pumped hydro has a Power, is going some way to long lifecycle of between 40 and solve this problem. In 2018, it 50 years and very large storage opened the world’s first grid- capacity, its main drawback scale cryogenic (liquid air) is geographical, requiring the energy storage plant in Bury correct topography and two The 15MWh cryogenic energy storage demonstration plant at Bury commissioned in 2018 © Highview Power (‘World’s first liquid air energy large reservoirs, the building of

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UTILISING THE CLAUDE CYCLE Invented in 1902, the Claude Cycle has enabled production of industrial quantities of liquid nitrogen, oxygen and argon. It developed and improved the Hampson-Linde cycle, patented seven years before, which had introduced regenerative cooling and enabled the low temperatures required to liquefy gases. The main drawback with the Linde method had been the loss of temperature at the end of the expansion process. Georges Claude developed a cycle that used a turbo-expander to expand gas to lower temperatures for more efficient cooling. A turbo-expander operates in the same way as a turbine, expanding high-pressure gas so that it becomes lower in pressure and temperature and power can be recovered. Turbo-expander is used when its primary purpose is to cool gas, while turbine is used when the purpose is to recover power. Highview Power’s system has adapted both the Claude and Linde cycles. Its charging process involves the compressing of air to ~12 bar, before it is cleaned and compressed further to about ~60 bar. The air is then fed into the top of the heat exchanger in the system’s ‘cold box’, where it is cooled to around -100°C. At this energy store where the liquid that gathers the compression point, some of the air is then bled off and expanded through a air is held in an insulated tank heat generated during air turbo-expander to cool it down further. at low pressure, and a power- liquefaction and is used for The remaining air that was not bled off continues through recovery unit where re-gasified increasing air temperature prior the heat exchanger. When it gets to about -180°C, it is expanded liquid air is used to drive a to expansion in the turbine. A process diagram showing the three stages of the producing, storing and recovering liquid air for generating power turbine and generate electricity. The second is a propriety cold © Highview Power through a Joules-Thompson (JT) valve. It is at saturation point after it has finished expanding and a large portion of it condenses into Ambient air is taken from the store that captures waste cold which can impact heavily on the responder when needed, Dearman and power researcher The company partnered with its liquid phase. The remainder is a very cold gas. surrounding environment then from the regasification of liquid environment. batteries have relatively short Toby Peters founded Highview Professor Yulong Ding, who The liquid and the gas enter a phase separator, which reduces using electricity it is cleaned, air while power is recovered In 2017, the potential of lifecycles (between five and ten and tested the concept at the in 2014 was appointed as the the pressure, along with the air from the turbo-expander. Here, dried and refrigerated through and later delivers the cold into lithium-ion batteries captured the years), they degrade and they University of Leeds. In 2011, Highview Power/Royal Academy the liquid drops out and is sent to tanks, while the gas returns a series of compression and the liquefier to reduce power headlines when Elon Musk made have a realistic economic limit of the engine part of the business of Engineering Research through the heat exchanger to the top of the system, cooling expansion stages until the air consumption – these measures a $50 million bet on Twitter that about four hours for harnessing subsequently branched off Chair in energy storage at the the incoming air along the way. Once it emerges from the heat liquefies – this process is based close the thermal loop for Tesla could build a 120 MWh large amounts of power. to form the Dearman Engine University of Birmingham to exchanger, a compressor recycles it and returns it to ~60 bar on a modified version of the cryogenic energy storage [see battery storage in South Australia Highview Power’s cryogenic Company and has since found further develop the cryogenic before it rejoins the input air and forms a semi-closed loop. Claude Cycle and can convert Cold storage technology and in under 100 days – if not, then storage solution ticks many applications with transport energy storage technology, Some of Highview’s patents cover the capturing of high- 700 litres of ambient air into one materials]. the company would charge boxes including sustainability, refrigeration units and other alongside other thermally based grade cold and recycling it into the liquefier, an important litre of liquid air [see Utilising the The separation of the nothing for its construction. cost, effectiveness and the fact cool-power projects. concepts). He had worked with step that doubles the efficiency of the liquefier and makes it Claude Cycle]. power, storage and recovery The state had been crippled by that it has a small footprint and In 2006, Gareth Brett, an Highview since 2005 and had economically viable. The liquefied air – air turns components provides flexibility power shortages and took him can be sited anywhere. The only electrical engineer with a seen the potential for energy to liquid when refrigerated to in the system’s design. up on his wager. Tesla delivered box it had not marked until now background in utilities and storage at very large scale. From a sufficiently low temperature Because power and energy are in 60 days and the result is the was usedemonstration at large banking, joined Highview and 2006 to 2007, Professor Ding (~-196°C at atmospheric independent of each other, largest battery storage facility scale. Now, with plans to begin fundraised for a pilot plant. worked with Highview to invent pressure) – is kept in insulated requirements can be tailored in the world, which supports building two large cryogenic In 2009 he became CEO. By and file patents for cryogenic tanks (acting as giant thermoses) so that clients can decide how and stabilises existing electricity energy storage plants in 2019, 2011, the world’s first liquid air energy storage and generation. at low pressure, which function much of a tank they want to fill, supplies in the state. that is set to be ticked too. pilot installation was installed Professor Ding’s work help as energy stores. When how much energy to store and However, although lithium- in Slough and connected to develop the world’s first research power is required, liquid air then how quickly it needs to be ion batteries seem to be the the grid with the help of a £1.1 centre for cryogenic energy is withdrawn from the tanks, emptied. This modularisation main contender for solving CLEAN COLD million grant from the then storage at the University of pumped to high pressure, of the process enables different the renewable energy storage BEGINNINGS Department for Energy and Birmingham. reheated and then expanded. configurations and solutions to conundrum, they do have Highview Power has created a Climate Change. The plant had The resulting high-pressure gas suit each customer. drawbacks. Lithium is relatively whole new industry – clean cold. a 350-kilowatt charge with two is then used to drive expansion rare and its supply is controlled, Co-founder Peter Dearman had and a half megawatt hours of HOW IT WORKS turbine generators to generate in effect, by a handful of mining an idea to build a reciprocating storage. Now the technical fine- The cryogenic energy storage electricity. No fuel is burnt in DEMONSTRATION companies. Cobalt, which is engine that was effectively tuning of the cryogenic storage system consists of three main the process, which results in the PLANT Diagram showing how Highview’s pilot plant uses the Claude Cycle. In needed for the cathode, is both driven by liquid nitrogen project could be done, ensuring components: a charging device addition, the system uses recycled cold (shown in blue) input from its cold exhaust producing clean dry air. In June 2018, these elements toxic and rarer still. Although and could be used to power that an actual plant would that uses off-peak or excess store. (MAC is the main air compressor, RAC the circulating air compressor Operating efficiency is were brought together in the and booster, the compressor for compressing the main stream air into the battery prices have dropped transport [‘Delivering clean cold perform in the same way as the electricity to power an industrial cold box (heat-exchanger) © Professor Yulong Ding enhanced by adding two stores. cryogenic energy storage plant recently and they are a quick- and power’, Ingenia 48). In 2005, process model of the system. liquefier to produce liquid air; an The first is a thermal store in Bury. The 5MW/15MWh

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storage plants around the 5 world supplying and storing 10 gigawatt-hours of energy. Long-duration storage 3 has always been critical to 2 enable the wider deployment of renewable energy and overcome the intermittent nature of solar and wind energy. It seems that cryogenic energy 4 storage can provide that and will soon be smoothing out the peaks and troughs of renewable demand in the UK and wherever incorporates is already globally it is needed. used for the bulk storage of liquid nitrogen, oxygen and BIOGRAPHIES LNG – such as heat exchangers, A diagram showing the energy storage options available with their respective storage options – in terms of time and Dr Javier Cavada, is CEO 1. Liquid air storage 2. Cryo pumps 3. Containerised power turbine and generator (2 x 10 MWh ) 4. Heat exchanger packed-bed storage units and capacity © Highview Power and President of Highview containers 5. High grade cold stores © Highview Power cryogenic insulation. This way Power. He joined the it can confidently state the company in 2018 after 17 COLD STORAGE TECHNOLOGY storage unit was sited at lifespan and efficacy of each years in leadership positions AND MATERIALS Viridor’s Pilsworth Landfill Gas plant’s hardware – Highview at Wärtsilä Corporation, Generation site to convert its will guarantee a 30-year lifetime High-grade cold storage plays a key role in reducing the power including executive roles in waste heat to power, thereby for its systems. The end-of-life consumption of the air liquefaction process and hence improving China, Italy, the Netherlands, increasing the system’s recycling characteristics of the the round-trip efficiency of cryogenic energy storage. The first Spain, and Finland. efficiency (‘efficiency’ measures system are also favourable consideration to make when compiling the liquid air system’s Gareth Brett is Chief the percentage of electrical as most of the tanks and components was the selection of appropriate cold storage Technology Officer at energy discharged compared equipment are made of technology. Packed-bed (a hollow tube, pipe or other vessel that Highview Power. He joined to the amount used to charge stainless steel with some is filled with a packing material) was chosen because it serves as the company in 2006 and the storage system). Cryogenic copper in the generators; apart both a cold storage device and a heat-exchanger. This selection storage systems could also from lubricating oil, Highview helped lead it in taking was based on the technology’s maturity, cost, performance use industrial waste heat and states that the process uses cryogenic energy storage and scalability. cold from applications such as nothing toxic. from concept to market- The other major selection considerations were to do with the thermal generation plants, steel The last piece of the jigsaw ready technology. From cold storage materials. The density and specific heat capacity of mills and liquefied natural gas to be fitted before the first 2009, he served as CEO, cold storage materials need to be as high as possible to increase (LNG) terminals to improve the big sale was to improve the before being appointed Vice the energy density of the store and reduce the physical size – and standalone efficiency. response times when supplying Chairman in 2018 and Chief therefore cost – of the containment structure. Building the demonstration energy to the grid. For this Technology Officer in 2018. The material’s thermal conductivity should be sufficiently high plant allowed Highview Power purpose, supercapacitors This chart shows the cost of cryogenic energy storage(LAES) provided by Highview Power’s system over 30 years Professor Yulong Ding is to ensure that the charge and discharge speeds can be achieved compared to other forms of energy storage © Highview Power to test the best economies and flywheels have been quickly. It should also be able to minimise the temperature gradient Director of the Birmingham of scale and figure out where added to the Pilsworth plant inside the individual particles to ensure efficient heat transfer. The company can scale-up and the air in it boils off and then Centre for Energy Storage. In economic efficiencies could be and response times are now The material’s mechanical properties needed to be strong incorporate three or four extra WHY NOW? must be topped up with liquid 2014, he was appointed as made. One of the company’s measured in seconds. In September 2018, Dr Javier enough to withstand thermal stresses due to the system’s repeated tanks of stored energy for this air; usually, the system cycles the Highview Power/Royal guiding principles when Highview Power sees Cavada was appointed as thermal cycling. It was also required to cope with the hydrostatic purpose. Effectively, balancing is daily and never reaches this Academy of Engineering developing the energy storage cryogenic energy storage as CEO and he sees the future stress due to packing. After much testing, gravel was chosen about moving energy from one point. He also feels that the Research Chair in energy system has been to use proven being most useful in supplying storage capacity of liquid air as the cold storage material. The gravels picked had a thermal time slot to another. Regulation 50-megawatt size will, thanks to storage at the University of components from mature the electricity grid via reserve, increasing from five hours to conductivity of ~ 1.8W/m.K, specific heat capacity of 0.71kJ/kg.K entails keeping the frequency the modularity of the system, Birmingham. He also holds industries that are tried, tested regulation and balancing. The perhaps 20 hours and then and a density of 2600kg/m3. The added advantages of the gravel constant so that the plant is increase to 100 megawatt. the founding Chamberlain and available. idea of reserve is to keep spare a couple of days or even were its low cost and the fact that it could cope with both ambient matching in real time, second by In five years’ time, he thinks Chair of Chemical The energy storage capacity in the system and weeks. Liquid air can be kept and cryogenic temperatures. second, supply with demand – that there will be around 20 Engineering at the university. equipment that the company keep a cache of stored energy. stabilising frequency. for months until eventually Highview cryogenic energy

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