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Energy Storage
One of the more complicated aspects of renewable energy production is working out what to do with the excess heat / water / power when there is a surplus ; how can it be stored for long periods of time , but be ready to use when there is a lack of solar or hydro power ? How can we smooth out those peaks and troughs of energy supply ? The chemical engineer Donald Sadoway ( Professor Emeritus of Materials Chemistry at the Massachusetts Institute of Technology ) has been quoted as saying : " If you want to make a dirt-cheap battery , you have to make it out of dirt ." Polar Night Energy seems to have taken that suggestion literally . I spoke with the company ’ s CTO , Markku Ylönen , about the technology , benefits , and seemingly limitless potential of this energy storage system .
“ Someone else ’ s dirt could be our heat storage medium .”
Polar Night Energy CTO Markku Ylönen ( left ) and CEO Tommi Eronen ( right ). Source : BBC
Simple but effective Polar Night Energy was founded by Markku Ylönen ( CTO ) and Tommi Eronen ( CEO ) in 2018 , but they have been working on the concept of a sand battery for 10 years . Both studied power plant engineering with a keen interest in thermal dynamics , flow dynamics , and heat transfer . The pair turned their knowledge to heat storage , discovering that the electricity market was making changes in the direction of wind and solar , producing cheap and clean energy which would need to be stored during times of low demand for later use . Seeing the limitations of water systems for energy storage , Polar Night Energy had an alternative solution : “ We use really , really hot sand as the storage medium .” The PNE sand battery is capable of providing heat at the extremely high temperatures required by the process industries , unlike water storage systems . With a maximum temperature of 100 degrees , a water storage unit would need to be pressurised to reach higher temperatures , but this is not an option in large-scale applications . The company ’ s website explains the innovative system : “ We convert electricity to heat , and store it for later use . We use sand as the storage medium , which leads to safe operation and a natural balance in the storage cycle . Additionally , sand is a cheap and abundant material , which can be heated up to 1000 ° C and even higher .” The high degree of insulation between the storage and environment ensures a long storing period , up to months , with minimal heat losses .
Current applications One of the sand battery ’ s initial case applications was in the Finnish city of Kankaanpää , where PNE installed the system for energy provider , Vatajankoski . The storage provides 100 kW heating power and 8 MWh capacity . Vatajankoski uses the heat provided by the sand battery to prime the waste heat recovered from its data servers which are intended for high performance computing before feeding the waste heat into the district heating network . Depending on the season , the temperature of the 60-degree waste heat from the servers must be raised to 75 – 100 degrees before it is fed into the district heating network .
A schematic of the components and operating cycle of the Polar Night Energy system . Source : COMSOL
34 Heat Exchanger World September 2022 www . heat-exchanger-world . com