Islands in the sun

Work is nearly complete on the 100 m prototype of a remarkable new solar power concept – a floating artificial solar island that promises electricity and hydrogen production at one fifth of the current cost.

Ras al Khaimah, one of the smaller states within the United Arab Emirates, is set to deploy the first example of it. The project, designed by Neuchâtel's Swiss Centre for Electronics and Microtechnology, will if all goes well eventually see a kilometre-wide solar panel put out to sea, where it will convert sunlight to electricity (via steam production) either for direct export to land or to be used in the electrolysis of water to produce hydrogen. The solar island will then store the gas for transportation back to the mainland, eliminating the need for a network of gas pipes and freeing the island from the constraint of a fixed position at sea. One of the advantages of the concept is that the island is self-propelling, using its own electricity production to run motors that rotate the structure during the day for the most efficient aspect, and for propulsion as a way of avoiding bad weather.

The first prototype, the unit shown in the illustrations currently being built at a ‘solar field’ in the UAE, is a circular structure 100 m across. After testing the next phase will be to construct an industrial version 500 m in diameter, ultimately leading to the 1 km diameter fully realised structures for commercial deployment.

Design aspects

Ras al Khaimah initially contracted CSEM to design this power plant as a solution to the problem of lack of space on land, and is paying $US5 million toward the construction costs. The aim of the first testing stage is to validate the concept and prepare the construction of large islands. Testing will take place not at sea but in protected inland waterways.

The island will float on an inflated ring, inflatable-raft style. To save money, the array does not use photovoltaic panels but concentrators that heat water running through pipes; the steam generated is what produces electricity. The 1 km version will be 20m in height and consist essentially of a steel torus, which is the steam storage, carrying the thermosolar panels placed on a membrane. Electric pumps maintain an overpressure of 0.1 bar to sustain the membrane 20 m above the water level. The whole platform adjusts its position to the course of the sun. To provide mobility, electric hydrodynamic motors will be fixed every 10 m along the circumference. Ultimately the platform could be situated on the high seas, on remote cost lines and even onshore.

Low cost energy

It is generally agreed that solar energy will be needed in very large quantities even if accompanied by other forms of energy (geothermal, wind, nuclear).The World Energy Council sees three different scenarios for the deployment of energy sources. All of them count on a huge amount of solar energy. But although the energy coming from the sun is immense – the potential is at least 100 times larger than any other renewable energy source – the specific surface energy density is relatively low (maximum 6.5 kWh/m2/day). This, and the implication for cost, is the main limitation on the large scale deployment of solar power plants.

At today’s energy costs and the sun’s energy delivery, assuming a conversion efficiency of 15% and approximately 310 days of sunshine, a solar energy solution generates 3 to 30 USD/m2/year, at about 6.5 kWh/m2/day.

So the maximum allowable cost per m2 (at 10 y amortisation time, 33% of revenues going to amortisation) is 10 to 100 USD/m2 active area. Current solutions cost 10 times that figure or more.

Advantages of the concept

These island structures are expected to produce power at an expected cost 5 times lower per kWh than competing systems, because:

• Extremely simple low-cost panels can be used

• Alignment to the sun is achieved without the need for precision mechanics •

•The active area of panels can be more than 95% of the available area

• Floating platforms in international waters (a prime location open to all) can be very large

• The thermal principle allows the storage of heat, so energy can also be supplied at night.

In addition there are certain natural advantages.

Typically they would be placed near the equator where the solar irradiation is very intense, the water needed to generate hydrogen and cooling is available in abundance, and combination with water desalination is a realistic prospect through collection and passive evaporation.