Islands in the sun

Could man-made iskands, floating in the sea or hovering above the desert sands, be the key to plentiful, low-cost solar energy?

Shimmering and revolving beneath the relentless desert sun, the giant disc will look, from the air, like a visitor from another galaxy.

But though it may look like something from another world, the 80m diameter structure being assembled in the desert of Ras Al Khaimah (the northernmost of the United Arab Emirates) has a more down-to-earth purpose. It is, in fact, the first step in an audacious plan to bring low-cost solar power to the masses by placing giant, rotating ‘solar islands’ in the vast open spaces of the world’s oceans and deserts.

They are the brainchild of Dr Thomas Hinderling, chief executive of Swiss R&D company the Centre for Electronics and Microtechnology (CSEM) — the facility, being constructed with $5m of UAE funding. This should be finished later this summer, when it will begin generating an expected 1GWh/year.

The device is based on the well understood concept of concentrating solar power (CSP) which uses mirrors or lenses to concentrate solar radiation on to pipes containing water which boils and can be used to spin turbines.

But although there are a number of ongoing efforts to build CSP power plants, Hinderling claimed that the solar island concept has considerable advantages over existing approaches.

The system under construction in Ras Al Khaimah consists of a doughnut-shaped ring floating in a concrete water-filled channel. This enables the entire structure to be turned throughout the day to face the sun’s rays and focus them on to its surface.

Over this structure are stretched two membranes; an upper membrane that supports the solar collectors and mirrors and a lower one that creates a sealed off air space. Electric pumps are used to create a pressure between the two which is used to bear the weight of collectors.

Hinderling said by using air pressure to support the structure, the system gets around the high cost of the civil infrastructure required for conventional solar power plants. ‘The prime idea is to provide a lower cost solution,’ said Hinderling. ‘people seem to forget that if you have a large field of solar panels a big part of the cost is the civil engineering needed — in our case you don’t have to do that because you don’t have to work on the surface below the panels.’

He explained that during operation the sun’s rays will fall on mirrored slabs on the top membrane. These will concentrate the radiation density of the sunlight by a factor of around 20 and reflect the sun on to a central pipe containing water stored under high pressure. The water will evaporate at 270°C, and the vapour will be conducted to the centre of the island to a steam generator where it will drive a turbine, and generate electricity.

The claims for the prototype are modest. Hinderling said he expects mean power to be about 100kW and maximum to be around 1200kW. This will be used to power air conditioning and create fresh drinking water at the adjacent visitor centre. He also estimates the cost of the energy generated to be around 15 US cents kW/h, a figure which compares favourably with existing solar power systems and would be expected to drop as the solar island is scaled up in size.

While the UAE prototype will use solar collector technology, Hinderling explained that the system could be used to support a lower cost approach to photovoltaics. In this case, mirrored slates on the platform would focus the flight on to the photovoltaic panels, concentrating the sun’s rays by a factor of five and, he claimed, would significantly reduce the cost of solar power.

One of the most challenging civil aspects of the prototype is the development of the concrete trench in which the system will float. This is why, while it is being constructed on dry land, Hinderling’s longer-term goal is to put the solar islands in the ocean.

Hinderling envisages gigantic structures, a mile across, using a GPS-enabled propulsion system to graze on the huge amounts of solar energy otherwise lost to the surface of the world’s seas.

He said that the systems could either operate close to shore and generate electricity which could be sent back to land along a cable, or they could operate further out to sea where they would most likely use solar power to extract hydrogen from seawater which would then be shipped back to land.

Clearly the development of such platforms presents some pretty steep engineering challenges, and Hinderling confessed that while he is confident that waves won’t create too much of a problem he is not sure how the solar islands will respond to some of the more extreme weather conditions the oceans will throw at his system. ‘Wind is very difficult to emulate because you don’t know how it will behave. Linear winds up to about 43mph (70kph) are not a problem, but the effect of turbulence and sudden gusts are not well understood.’

Hinderling said that he hopes to put a 1,500ft diameter platform into the water by 2010, but before he can begin to realise what he acknowledges may be an ambitious dream, his energies are firmly focused on the prototype. After that, he hopes to build a 500m diameter version expected to cost around €40m (£31m).

He said there is plenty of interest in his concept. At the moment this is mostly from governments, but he hopes that this summer’s switch-on of the Ras Al Khaimah island will drum up some industrial interest.

Three countries are particularly interested — India, Pakistan and South Africa. ‘They are not talking about a coming energy crisis, they are already deep in one, and have to switch off large factories because they don’t have sufficient power. South Africa recently had to force its citizens to use 10 per cent less energy because it didn’t have enough for industry.’

As the rest of the world looks like following suit, the attractions of Hinderling’s bizarre looking system might just catch on.