Electricity storage offers considerable added value for the energy sector, particularly when combined with wind power generating capacity on a large scale

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Storage increases the technical reliability of the power supply, stabilizes the cost of electricity and helps to reduce greenhouse gas emissions.

Large-scale energy storage is already applied in many countries worldwide. Good results have been achieved with pumped storage facilities in countries like Germany, Austria, Norway, the UK and the USA. In the Netherlands, electricity storage is also attracting increasing attention.

Energy Island harnesses offshore wind, pumped hydro storage
DNV, in partnership with civil engineering firm Bureau Lievense and technology illustrators Rudolph and Robert Das, has developed an “Energy Island” concept to store power generated from an offshore wind farm - located in the North Sea off the Dutch coast.

The innovative concept design is the initial result of an on-going feasibility study being conducted for Dutch energy companies. The Energy Island incorporates a new concept in pumped hydro storage – an inverse offshore pump accumulation station (IOPAC) located on an artificially created island.

On the Energy Island when there is a surplus of wind energy, the excess energy is used to pump sea water out of the interior ‘subsurface-lake’ into the surrounding sea. When there is a shortage of wind power, sea water is allowed to flow back into the interior ‘lake’ through commercially available generators to produce energy. The IOPAC is unique from conventional pumped hydro storage systems in that it would be stationed on an artificial island off the Dutch coast in the North Sea and comprised of a ring of dikes surrounding a 50 meter deep reservoir. The island itself would be built from materials dredged to deepen the interior reservoir.

Energy Island technical and environmental performance
The Energy Island would essentially consist of a ring dike, sealed with bentonite and enclosing an area approximately 10 kilometers long and 6 kilometers wide. The water level in the ‘inner lake’ would be between 32 and 40 meters below that of the surrounding North Sea.

Next to the energy storage facility the Energy Island could provide other functionalities like wind turbines on surrounding dike, aquatic biomass (e.g. seaweed), harbors and port facilities (e.g. maintenance centre for offshore wind farms), nature, et cetera.

From the feasibility study, it is clear that a large-scale storage facility in the form of an Energy Island is technically realizable. Key factors in this regard are the presence of a layer of clay tens of meters thick beneath the bed of the North Sea and the fact that the technical feasibility of the engineering work involved has already been demonstrated in practice. Suitable pump generators are already available.

From an economic viewpoint, a 1,500 MW / 20 GWh facility is the most attractive size for the 2020+ situation in The Netherlands. The annual cost saving attainable by storing power produced overnight and returning electricity to the grid by day would be significant. Assuming a storage facility life expectancy of forty years, the saving is likely to be between EUR 1.3 and EUR 1.6 billion. The Energy Island is therefore one of the three attractive large scale electricity storage options.

We are continuing work with our present partners on the Energy Island concept. A detailed location study is planned and the technical capabilities and economic and ecological values of the other functions will be investigated.

The DNV guidebook on assessing wide-scale utility application of storage
Volume two of DNV’s Utility of the Future series, “The promise of energy storage,” explores the issues and questions surrounding the rapidly advancing energy storage technology. The guidebook provides a broad assessment of the electricity storage field and the latest thinking about storage applications.

For more information, please contact us or download our brochure.