Brine cells offer new method for energy storage

Date: 30/06/2017

Energy stored in brine cells means that the cooling systems at Bergen airport in Norway can run for several days without any mains electricity. The new storage method could change the cooling industry, says civil engineer Rune Teigland of COWI. ​

The future will need energy – lots of energy. This raises issues, including how we can use energy better than we do today.
Now a new answer has been found to that very question: storage in brine cells.

The solution has already been installed at Bergen airport, which basically needed a cooling system with a maximum output of 5 megawatts.
However, the installed cooling system now operates with a maximum output of just 2.5 megawatts, while the last 2.5 megawatts are taken from energy storage tanks consisting of plastic cells filled with salt water, for when extra cooling is needed in the summer months.
“The obvious advantage is that the cooling plant does not need to be big enough to handle the maximum cooling requirement. This offers some clear benefits, in terms of price, energy consumption and maintenance,” explains civil engineer Rune Teigland, who designed the system.

Energy stored in 44,000 small plastic cells
Teigland works for COWI, which was part of the project design group for Terminal T3 at Bergen Airport, looking after fire safety, acoustics and energy among other areas.

But how can energy be stored in salt water? In a few words: The energy is stored with a capacity of 11,000 kilowatt-hours in 44,000 small plastic cells filled with a modified salt water mixture. The cells are 50x25x3 centimetres in size and are stacked on top of each other in four water-filled tanks, each 13 metres long and three metres in diameter.
When water at a temperature below the freezing point is passed through the tanks and on into the salt water mixture, the mixture freezes and energy is stored in the cells. If the water is fed in at a temperature above freezing, the mixture will then melt and produce a cooling effect.

Technology known from vineyards ​
This process – the transition of a substance between a solid and a liquid state – is called a phase change, and it is not a new and unfamiliar technology: for centuries, European wine growers have been placing containers of water between the grapevines when the frost threatens. When the water starts to freeze, it releases heat into the surroundings, which saves the grapes.

But it is unusual to see the technology used in a modern cooling plant, as at Bergen airport. According to Teigland the method can also be applied to cooling systems in warmer parts of the world.
“The method provides for big savings in energy and running costs, and we see great potential for buildings, data centres and production halls, for example, which need to keep both temperatures and CO₂ emissions down. This method could change the whole cooling industry,” says Teigland.

About the cooling plant at Bergen airport

  • The system can run for two hours at full capacity just on the energy stored in the brine cells.
  • Full capacity is rarely needed in Bergen – typically just for a few hours in the middle of the day in the summer months.
  • In practice, the cooling plant can therefore run for several days with no mechanical cooling.
  • The cost to the airport of the cooling system is around NOK 20 million.
  • The system gives annual savings of around 5,000 megawatt-hours, or about NOK 5 million compared to a conventional system.