A stocking-like balloon

Storing surplus wind energy in a nylon stocking is not an idea that would ever spring to mind. Yet, a Canadian start-up currently has a pilot project to store unused gusts of air in enormous underwater balloons, which, just like a stocking, are made of nylon.

Back and forth: when the wind is strong, compressors force air into the underwater balloon, when the wind dies down, these balloons release this stored air to a turbine – et voilà: electricity / Source: Hydrostor

Back and forth: when the wind is strong, compressors force air into the underwater balloon, when the wind dies down, these balloons release this stored air to a turbine – et voilà: electricity / Source: Hydrostor

A wind turbine produces green electricity – a wind farm with hundreds of wind turbines produces a rather large amount of green electricity, particularly at times when a strong wind blows through the rotor blades for an extended period of time. Due to the fact that this wind-generated green electricity would, in effect, overload the network, network operators sometimes have to take whole wind farm offline to avoid a blackout. The problem is that short-term storage of surplus wind energy is almost impossible using conventional means of storage – and so it is lost.

This is what the Canadian company, Hydrostor, is currently looking to change by fixing its gaze on the bottom of Lake Ontario near Toronto, where, since the end of last year, six, enormous, underwater balloons have been swimming, firmly fixed to the bottom at a depth of 55 metres, three kilometres from the coast. They are similar to those giant balloons used to raise shipwrecks. However, they have not come to lift, but to stay in place, at least for the next two years. The idea is that, peacefully co-existing with Canadian fish in their location close to the shore, they demonstrate whether they have the capability to provide a storage solution for offshore wind farms. For this application, the fact that the balloons consist of robust nylon fabric is an advantage.

Polyamide 6.6: sexy, but questionable linguistically

Made from the same material as stockings but not as sexy: Hydrostor's nylon balloons on their way to the bottom of Lake Ontario. // Source: Hydrostor

Made from the same material as stockings but not as sexy: Hydrostor’s nylon balloons on their way to the bottom of Lake Ontario. / Source: Hydrostor

“Nylon is a reasonably robust fibre with high tear strength. For such underwater applications it has the advantages of minimal gas permeability and reduced water absorption capacity”, explains Dr. Frank Gähr, head of textile chemistry research at the Denkendorf Institute of Textile Chemistry and Chemical Fibers (Institut für Textilchemie und Chemiefasern). Back in 1935 it was developed in the laboratories of DuPont, the US chemical company, as the first fully synthetic fibre to be made from polyamide 6.6. Whilst it was originally intended for use in toothbrushes, its career really took off on 15 May 1940: it was on this day we now know as ‘N-day’ that within a few hours in cities of the United States of America millions of synthetic fibre stockings were sold to women, who previously had known only woollen or cotton stockings. And since “darling, I’m wearing polyamide 6.6. stockings today” does not have particularly attractive ring to it, a new linguistic term was also coined, namely the ‘nylon stocking’.

But let us get back to the nylon balloons in Lake Ontario. They are connected to an onshore compressor station by means of a compressed air line. When the wind turbines produce surplus green energy in the power lines, compressors force air into the underwater balloons. The pressure of the water ensures that the air that is forced into the balloons is highly compressed without damaging the balloons themselves. This enables more energy to be stored. Now, when the wind dies down and energy is needed, the air flows out of the balloons and drives a turbine which produces electricity. According to the company’s own figures the six nylon balloons could supply around 330 homes with electricity. The idea is that in future they will help to stabilise the power supply to coastal cities and even make whole islands self-sufficient in energy.

Watch the video about how Hydrostor works and about the progress of the project.

Ronny Eckert

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