The sand battery is the brainchild of two Finnish engineers, Markku Ylönen and Tommy Erone. It is simplicity itself. Make a really big pile of sand. Heat it up to about 500º C (932º F) with already renewable electricity, then use that heat to heat homes, factories and even swimming pools. They say the sand can stay warm for 3 months or more. Together, they set up their first installation in Kankaanpää – Polar Night Energy, which fills 100 tons of sand inside what looks like a silo.
Americans may have trouble seeing the value of this idea. Hot sand isn’t very good at generating electricity, so what’s the point? But don’t let American Exceptionalism cloud your judgment. There are many places in the world – especially in colder climates – where central heating is common. Instead of separate furnaces in each building, heat is produced in a central location and distributed to homes, factories and businesses through a system of underground pipes and ducts. The first Polar Night Energy system was installed at the Vatajankoski power station, which controls the district’s central heating system.
The sand battery is primarily designed to supplement those central heating systems and significantly reduce the amount of electricity, oil or methane used to heat buildings. Anything that reduces the need for methane and electricity from Russia is welcome news, especially now that the madman in the Kremlin is busy playing “mine is bigger than yours” on the international stage. After Finland decided to join NATO, Moscow stopped supplying gas and electricity to this country.
according to BBC, A sand battery is a simple, cost-effective way to store energy. It uses excess electricity from renewable energy sources to heat the sand, which can remain at around 500ºC for months. “We have already learned that our system has more potential than we originally estimated. It was a positive surprise,” says Ylönen. “When there’s a high growth rate of green electricity available, we want to get it into storage really quickly.”
The first unit has a thermal capacity of 100 kW and an energy capacity of 8 MW/h. “This innovation is part of the transition to smart and green energy. Heat storage can significantly contribute to increasing intermittent renewables in the electricity grid. At the same time, we can bring the waste heat to the required level to heat the city. This is a logical step towards non-combustion heat generation,” he adds.
Vatajankoski uses heat from local data servers as part of its district heating system. Ideally, the waste heat should be between 75 and 100 degrees before it is fed into the central heating system. When the temperature drops too low, the heat from the Polar Night unit can make up the difference. The district heating system also keeps the water in the town’s pool warm during the long Arctic winter. In terms of emissions, Polar Night says that apart from additional emissions from building the sand battery, the system has the same carbon intensity as the energy source that originally provided the electricity to heat the sand.
The sand battery idea was first developed in a former pulp mill in Tampere, where the council donated the workplace and provided funding to get it off the ground. Elina Seppänen, the city’s energy and climate expert, says: “If we have some power plants that run for a few hours in the winter, when it’s coldest, it will be very expensive.” We have this kind of solution that provides flexibility for the use and storage of heat, which helps a lot in terms of cost.”
Other research groups, such as the National Renewable Energy Laboratory, are actively considering sand as a suitable form of battery for green energy. But the Finns are the first with a working trading system. “It’s really simple, but we liked the idea of trying something new to be the first in the world to do something like this,” said Pekka Passi, managing director of the Vatajankoski power plant.
Sand Batteries For Every Need
Polar Night Energy says it can design a sand battery for every need, from a single building to an entire city. Each system is individually tailored to the customer’s requirements and designed using COMSOL Multiphysics software, 3-D transient heat transfer models, and simulations with real-life input and output data. When the surface area of the project is limited, the systems can be buried underground to protect the ground.
Each system is fully automated and has a nominal power rating of up to 100 MW and storage capacity of up to 20 GWH. The projected cost of the system is less than €10 per kWh of storage capacity. The company says, “Production from renewable energy sources such as wind and solar is highly variable and only partially matches consumption over time. As these volatile electricity sources rapidly increase in societies, more energy storage technologies will be needed. Our technology provides a convenient way to turn cheap and clean excess electricity into valuable heat, to be used when it is needed most.”
NREL Silica Sand Battery
Image credit: Patrick Davenport and Al Hicks, NREL
The NREL system differs from the Polar Night system in that it focuses more on using stored heat to generate electricity. In addition to testing a new thermal energy storage technology that uses inexpensive silica sand as a storage medium. Long-term Economical Electricity Storage using Low Cost Thermal Energy Storage and High Efficiency Power Cycle (CYCLE) is a reliable, economical and scalable solution that can be deployed anywhere.
ENDURING uses excess solar or wind electricity to heat silica sand fed through an array of electrical resistance heating elements to heat up to 1200°C. The heated particles are then fed into insulated concrete silos where they are stored by gravity. The system can store up to 26,000 MW/h of thermal energy. With a modular design, storage capacity can be scaled up or down relatively easily, NREL says.
When energy is needed, the hot particles are fed through a heat exchanger, where a gas is heated and pressurized to spin generators that generate electricity for the grid. The system is unloaded during periods of high electricity demand and when limited solar photovoltaic or wind power is available. After discharge, the spent, cold particles are fed back into insulated silos for storage until conditions (and economics) are suitable for refilling.
Silica sand is abundant, durable and inexpensive, with a low environmental impact both in production and during operation. Lithium-ion batteries have exceptional energy storage density, but are expensive. Particle thermal energy storage is a less energy-dense form of storage, but at a 900°C discharge temperature difference, it is very cheap at $2-$4 per kWh of thermal energy.
The energy storage system is safe because inert silica sand is used as the storage medium, making it an ideal candidate for massive, long-term energy storage. CIRCULATION systems have no specific location restrictions and can be placed anywhere in the country. NREL says these systems can also be built using existing infrastructure from old coal and gas-fired power plants.
The Takeaway
Energy storage is key to the renewable energy revolution. There are ways to create an eco-friendly and inexpensive warehouse. Polar Night and NREL are promoting two of them, but there will be others as more people focus on the need for massive, affordable energy storage. Something that was unthinkable 20 years ago will become commonplace in 20 years. Sand batteries may seem strange today, but they will undoubtedly be part of the energy storage mix in the future.
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