Offshore wind power has the potential to overcome some of the biggest limitations of land-based wind power.
Wind speeds are higher, and more consistent. There's more space available. Concerns over noise are nonexistent, and while there have been clashes over visual impact for offshore wind farms (the Cape Wind project being the most prominent example), the issue of NIMBYism ought to be greatly reduced when turbines are built where there literally are no backyards.
But there are challenges too.
A harsh marine environment
As anyone who has ever owned a boat knows, the marine environment can be harsh on any mechanical equipment. The likelihood of extreme weather is increased — and with extreme weather comes the danger not just of damage to the turbines, but also the more frequent need to power down the turbines if they are creating too much power for the grid. Of course installation and maintenance are considerably more complicated when the nearest piece of dry land is more than six miles away!
Enter a new generation of wind turbines. As the United Kingdom continues its massive push for offshore wind with a third extension to the 172-megawatt Gunfleet Sands offshore wind farm, it is testing technology that may significantly improve the cost-benefit equation of producing wind power offshore. Here's how a news release from the Department of Energy and Climate Change announced the new turbine installation:
"Energy Minister Greg Barker today opened a new extension to the Gunfleet Sands offshore wind farm that will see the first demonstration in UK waters of the next generation of offshore wind turbines. The turbines, made by Siemens, and installed by DONG Energy, have been deliberately designed to be used at sea and have the potential to significantly cut the cost of producing renewable energy from offshore wind. Many turbines currently installed off the UK coastline are variations on turbines designed for use onshore. The new generation used at Gunfleet will be more cost-effective and efficient – improving the UK’s energy security and increasing the amount of energy generated from renewables."
With a power output of 6 MW, the turbines generate a lot more power-per-turbine than many onshore machines (like these state-of-the-art energy-storing turbines, for example) and this is, in itself, one of the major advantages for offshore wind.
There aren't many places on land where you can install a 6-MW turbine without a major political backlash!
A simplified wind turbine for lower maintenance
But as much as the power capacity itself, it's the inner workings of the turbine that Siemens hopes are going to drive down costs and make offshore wind more commercially viable. Instead of the usual main shaft, gearbox and high-speed generator, the Siemens 6-MW turbines feature a direct drive, low-speed generator with less than 50% of the moving parts of its geared counterparts. (Think of it like the fixie bike of offshore power.)
Not only should this simplification of the mechanics result in fewer maintenance visits — a big deal out at sea — but according to the manufacturer it also allows for more of the pre-commissioning testing and assembly to happen onshore, further reducing costs.
Responsive monitoring and operation
Of course power capacity, installation and maintenance aren't the only concern for power plant operators; they also want to know how reliable and steady their power supply is going to be. For this, the D6 turbines include sophisticated monitoring capabilities that communicate everything from weather conditions to the status of its mechanical components, and then adjust their operations accordingly. Instead of shutting themselves down when wind speeds and power output are too high, for example, these turbines use Turbine Load Control (TLC) and High Wind Ride Through (HWRT) to regulate their output in cases where the loads exceed normal values.
It's all impressive stuff on paper, but how will it work now the rubber has hit the proverbial (somewhat wet and salty) road?
The turbines have already been tested using accelerated lifetime tests, during which time they are put through a simulated 25 years of operation in a three- to six-month period. But it will be in commercial operation that they'll truly be judged. For this, Henrik Stiesdal, chief technology officer at Siemens Wind Power, told Renewable Energy World that the new UK offshore installation will be a crucial proving ground:
“Gunfleet Sands III is a very important project for us to bring the 6 MW direct drive turbine out to the offshore environment. The two prototypes have been pre-tested under hardest conditions and we have made tremendous progress with the experiences gained by that. Now we will test the turbines under long-term conditions of normal energy production.”
Here's more from Siemens on the development of the direct-drive offshore wind turbines in the video below: