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Context: Finnish researchers have installed the world's first fully working "sand battery" which can store green power for months at a time.

Details:

• The developers say this could solve the problem of year-round supply, a major issue for green energy.
• Using low-grade sand, the device is charged up with heat made from cheap electricity from solar or wind.
• The sand stores the heat at around 500C, which can then warm homes in winter when energy is more expensive.

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• Concerns over sources of heat and light, especially with the long, cold Finnish winter on the horizon are preoccupying politicians and citizens alike.
• But in a corner of a small power plant in western Finland stands a new piece of technology that has the potential to ease some of these worries.
• The key element in this device? Around 100 tonnes of builder's sand, piled high inside a dull grey silo.
• These rough and ready grains may well represent a simple, cost-effective way of storing power for when it's needed most.
• Because of climate change and the rapidly rising price of fossil fuels, there's a surge of investment in new renewable energy production. But while new solar panels and wind turbines can be quickly added to national grids, these extra sources also present huge challenges.
• The toughest question is about intermittency - how do you keep the lights on when the sun doesn't shine and the wind doesn't blow?
• Adding more renewables to the electricity grid also means you need to boost other energy sources to balance the network, as too much or too little power can cause it to collapse.
• The most obvious answer to these problems is large scale batteries which can store and balance energy demands as the grid becomes greener.
• Right now, most batteries are made with lithium and are expensive with a large, physical footprint, and can only cope with a limited amount of excess power.
• The device has been installed in the Vatajankoski power plant which runs the district heating system for the area.
• Sand is a very effective medium for storing heat and loses little over time.
• So when energy prices are higher, the battery discharges the hot air which warms water for the district heating system which is then pumped around homes, offices and even the local swimming pool.
• The idea for the sand battery was first developed at a former pulp mill in the city of Tampere, with the council donating the work space and providing funding to get it off the ground.
• The sand battery helps to warm homes, offices and the local swimming pool
• One of the big challenges now is whether the technology can be scaled up to really make a difference - and will the developers be able to use it to get electricity out as well as heat?
• The efficiency falls dramatically when the sand is used to just return power to the electricity grid.
• But storing green energy as heat for the longer term is also a huge opportunity for industry, where most of the process heat that's used in food and drink, textiles or pharmaceuticals comes from the burning of fossil fuels.
• Other research groups, such as the US National Renewable Energy Laboratory are actively looking at sand as a viable form of battery for green power.

https://www.bbc.com/news/science-environment-61996520

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