Britain is a pioneer in offshore wind energy, with more turbines placed out at sea than any other nation. However, constructing such offshore wind farms is far tougher and more expensive than land-based wind energy.
In the dockyards at Belfast in Northern Ireland, where the Titanic was built, there are blades longer than the entire wingspan of a jumbo jet at 61.5 meters and weighing 22 tons. The blades are made of fibreglass and become thicker toward their point of attachment where they are fixed by 128 massive bolts in a ring to the rotor hub of the machine. Once the three blades are fitted, an extraordinarily delicate crane operation ensues with cutting-edge technology to raise the turbine and ferry it onto the barge which takes it out to sea.
But how reliable is the technology? The turbines are intended to run for 20 years but in some cases they have had to be pulled in after only eight years. It remains to be seen whether this is a particular feature of the North Sea conditions or a more general aspect and if the latter, it must seriously jeopardise the future of offshore wind energy.
One wind farm subsided on its foundations which have to be sunk 14 meters into the ocean floor. Transportation costs are high both for taking the turbine out to sea in the first place and for subsequent maintenance operations. Curbing carbon emissions using wind power is an expensive option and one such farm in the Irish Sea is costed at £500 million ($774 million). The sea-jack is raised on four legs, looking rather like an oil platform and the tower is assembled. The lower section is first attached and the giant tube is rotated into section and finally guided by hand into place, being monitored from the deck by remote control.
Next the nacelle is raised into place which contains the gearbox, the generator and control systems that will be located at the top of the turbine tower. The final stage of the work is lifting the giant set of blades up to the top of the tower. Again guided by hand to prevent damage to the tip of a blade, the hub is finally put into place, and fixed there. The barge then returns to Belfast for another load of components. Each turbine has a rated capacity of 5 MW and it is claimed that 200 of them are needed to match the output of a conventional power station. However, the capacity factor (efficiency) is probably only 20 -30%, and so a mean output from 200 turbines will be nearer 300 MW, far short of the 1,000 MW power output of a typical fossil-fuel fired or nuclear power station.
It is claimed that the wind farm in the Irish Sea will supply enough electricity for 100,000 homes when the wind spins all of its 30 turbines. Of course, this is not a consistent situation, due to the variable nature of wind-force. The U.K. plans to get one quarter of its electricity from offshore wind by 2020. However, to place this in perspective, at around 11 GW of generating power, at least 7,000 turbines will need to be installed (ignoring for a moment the inconsistency of supply) and it being the start of 2012, this must be done at a rate of 2-3 per day which is an acutely challenging undertaking. Germany, Denmark and Holland also have serious plans for wind farms at sea.
At present there is no real indication for a global offshore wind farm effort. While good locations exist across the globe where wind farms might be placed offshore, prevailing weather conditions must also be taken into consideration. In Asia, storms and typhoons can cause severe damage and there is the issue of cost. In Europe, such projects are supported by generous subsidies. In principle, wind farms produce electricity without generating greenhouse gases and the level of imported energy is reduced. Oil and gas prices are expected to increase over the next decade which makes a case to pursue home-grown electricity. However, is this a halcyon vision of green energy in a zero-carbon world or a gamble with uncertain technology in an already overstretched economy?
Indeed, there are plans for wind farms on a scale far greater than anything existing now, and it has been mooted that these along with solar energy might best feed into a European super-grid, including the import of electricity from North Africa into Southern Europe. In the U.K., my fear is we are placing all our energy eggs in one basket and should the technology not prove as robust as has been thought, or be far more lengthy and expensive to implement, we will be in serious trouble both economically and in meeting our green energy targets as promised to the European Commission.
Forbes, 11 January 2011