Can man-made islands designed to store energy solve renewable power problems?
Architects at Copenhagen-based Gottlieb Paludan have long known how to design power stations. For decades the architecture firm has created coal-fired power plants, gas-fired stations and combined heat and power plants.A few years ago though, they wanted to diversify.
'We have a history of designing coal plants since the 1950s,' says Sten Södring, company architect and senior project manager. 'But we couldn't keep designing coal-fired plants, they are not a thing of the future.'
The architect's first idea for adjusting the company's future plans was fusion; why not design fusion power plants, the energy fix that everyone is waiting for? Södring approached academics at the nearby Technical University of Denmark (DTU) and was quickly informed that an operational fusion power plant would be decades away, so any designs would remain on paper for some time yet.
As an alternative, Dr Allan Pederson and colleagues from DTU's Risoe National Laboratory for Sustainable Energy pointed 'unanimously' at energy storage.
Wind and solar power, they explained, are forces of nature that cannot be regulated to match demand. For a nation like Denmark, which relies heavily on wind generation, safely integrating this varying electricity supply to the grid is crucial. Fast-responding gas-fired power plants, demand-side management and increasing interconnection capacity all help, but energy storage, on a multi-megawatt scale, would be a real result.
In response to this, Södring and Pederson developed the 'Green Power Island'.
The Green Power Island is an artificial island that incorporates pumped hydro storage to store energy in seawater. The island encloses a lagoon-like reservoir, which can be emptied using pumps driven by excess power from a nearby wind farm. As power demand rises the seawater is allowed back into the reservoir, driving turbines that generate power.
Pederson calculates that up to 80 per cent of the energy that goes into pumping the reservoir empty can be regenerated. He says: '[Energy Islands] are not rocket science, they are easy to understand and a simple idea that everyone can relate to.'
Clearly, the concept of pumped hydro storage isn't new – in mountainous regions around the world, pumped hydro is used to balance power systems – but Gottlieb Paludan's ambitious designs are unique. Taking Pederson's artificial island, designed specifically for hydro pumped-storage, the architects designed six islands in locations around the world, varying in size up to 65km2 with capacities ranging from 2GWh to 50GWh.
Each location was selected first based on its geographical topography. Many low-lying coastal regions are suited for land and offshore wind farms but lack methods for storing large quantities of electricity. The architects then looked at political and environmental agenda, and selected locations in the process of building a 'strong, green profile'.
'We could see that Bahrain, for example, would make a good location. Renewable industries are moving in and the nation has a modern tradition of building artificial islands in the Gulf, so why not make something useful out of these millionaires' playgrounds?' says Södring.
'Likewise, the Jiangsu province in China is spear-heading the green movement and already building deep-sea coast facilities [on man-made islands]. It seemed obvious to extend what is there.'
But what about cost? Firm figures are not forthcoming, but Södring likens the cost of construction to that of the Öresund Bridge, which joins Denmark to Sweden, and the Great Belt Bridge connecting the Danish Islands of Zealand and Funen. Both are nudging 8km in length and cost £3bn to build.
Despite hefty financial implications, Södring and Pederson are not alone. Wouter de Boer of energy consultancy, KEMA, The Netherlands, and colleagues at marine engineering company Lievense, have also designed an 'Energy Island' specifically for large-scale energy storage off the Dutch Coast in the North Sea.
The 8km by 4km island will comprise a 40m-deep dredged open pit – dug into clay and lined with cement to prevent seawater ingress – that will be enclosed by a ring of dykes. Up to 500MW of wind turbines could line the island perimeter, as well as other renewable energy sources, and the storage capacity of the lake will top 20GWh.
In a similar vein to the Green Power Islands, when the wind turbines generate energy that exceeds demand, seawater will be pumped out of the lake into the sea. When demand exceeds supply, seawater flows back into the lake to drive a generator.
Based on proven technology, de Boer claims that using sand from the dredged pit will make building the island a 'piece of cake' and estimates construction costs of £2bn. But he is clear on the technical and financial risks.
Would the necessary clay layer prove unstable, and could pump turbine generators be built into clay? Are investment figures underestimated and might social pressures lead to lengthy planning processes? Likewise, Södring points to the need for thorough marine investigations to assess impact on marine life and seabed conditions, as well as detailed cost-benefit analyses.
By 2010, de Boer and colleagues had joined forces with the team at Risoe National Laboratory and Gottlieb Paludan to submit a proposal to the European Commission, based on the two energy island concepts, to work towards a 'pilot' island.
Both teams set out with enthusiastic visions of large-scale energy storage but were left disappointed. Just a few weeks ago, the EC said no funding will be forthcoming.
Pederson and de Boer now plan to wait, with Pederson saying: 'maybe in a few years, when the issue of storage becomes more urgent.'
Södring, however, disagrees and is now in talks with local energy companies to realise his storage designs on a smaller scale in Denmark.
'From my experience, [storage] is like 'the elephant in the corner of the room'. It's a difficult issue to grasp, it's difficult to see the solution and people are very hesitant to take it on,' he says. 'But we architects are a bit more impatient than the researchers. We have to keep moving.' *