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Aarhus University to demonstrate technology that can store green energy in giant underground ‘water balloons’

With a grant of almost DKK 5 million from the Energy Technology Development and Demonstration Programme, EUDP, under Danish Energy Agency, work is about to begin on building a 100 sqm test facility to demonstrate new technology that stores green surplus energy in giant underground water balloons.

In collaboration with the entrepreneurial company AquaNamic, Aarhus University will now start construction of a 100 sqm demonstration facility for new energy storage technology that can store green energy in water.

Basically, the technology uses surplus energy to pump water from a reservoir into a giant, specially designed membrane buried under massive amounts of soil.

The project has received DKK 4.9 million in funding from the EUDP, and the aim of the project is to ready the technology for implementation.

"The plan is to build a test facility of minimum 10x10 metres in order to best simulate a full-scale system. There is a huge need for storage technologies as we move into a future with more and more renewable energy. We are already experiencing having to give away energy because we can't store it optimally yet," says Kenny Sørensen, professor (Docent), who is heading the project from the Department of Engineering at Aarhus University.

Negative energy prices

The Danish Energy Agency's latest baseline projections show that the Danish electricity network will not be 100% based on renewable energy until 2028 at the earliest. Even though we are far from reaching our target at the moment, there are already paradoxical situations in which energy production exceeds consumption and generates negative energy prices because the energy cannot be stored and used later.

It then costs money to get rid of electricity, and without better storage options, this trend will just accelerate in the future.

Today, there are only a few energy storage technologies that function on a large scale, and the most dominant and mature technology is the so-called PHS systems, Pumped Hydro Storage, where excess electricity is used to pump water from lower-lying areas to a higher-lying reservoir.

A gigantic 'hill-battery'

There aren’t many mountain lakes in Denmark, and the plan is therefore to pump water into a membrane lying beneath a large mound of soil. Water is pumped in using excess electricity, and once the energy needs to be used again, the valve is opened and, under the tremendous pressure of the soil, the water is pushed out of the balloon through an electricity-generating turbine.

It’s a kind of gigantic topographical hill-battery, and we're not talking small numbers. The final project aims at creating a balloon of 330 x 330 metres buried under a maximum of 25 metres of soil that will be raised by up to 14 metres when the balloon is filled up. This will store 230 MWh.

"We’re about to begin analysing, designing and testing selected critical technologies related to the membrane and to the construction of the 'movable hill ' that will form the terrain part of the battery. Naturally, we’ll have a strong focus on abrasion testing for the membrane, and we’ll need to develop a specially designed test rig to carry out lifetime tests for representative membrane solutions," says Kenny Sørensen.

The project is being developed in collaboration between AquaNamic, Solmax, PlanEnergi, Vestas, European Energy, AquaEnergy andAarhus University. The technology has been developed by AquaNamic and, since 2018, Aarhus University has contributed with verification and further development.

The exact location of the demonstration facility is still uncertain, but it will be somewhere with local support for the project.

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