Thirty years ago, before wind power was considered a viable alternative to coal, gas, and nuclear, the average turbine measured something in the range of 50 feet in diameter. These days, wind turbines approaching 500 feet are common, and the plan in the next few years is to take the engineering beyond 1,000 feet.
The reason for this expansion is simple: economics. Bigger turbines produce more electricity. And it’s cheaper to build, install, and maintain one big machine than several smaller ones. Moreover, the opening of offshore sites, particularly in Europe, means there is more space for bigger machines, and hence more demand for manufacturers to think big.
General Electric is currently working on a 15 MW turbine with three times the capacity of most large turbines in operation (most are smaller than that). Part funded by the Department of Energy, the design uses superconducting magnets usually seen in MRI systems in hospitals.
Economics may not be the only reason to go big, though. A new study from researchers in Switzerland argues that larger turbines are also more environmentally sound, because you get more electricity for less manufacturing, transportation, and installation effort (and hence fewer carbon emissions).
Reviewing 12 previously published turbine lifecycle assessments, and European power statistics, the paper finds that for every doubling of turbine capacity, "global warming potential per kWh was reduced by 14%."
"You get a scaling factor that’s been known to happen for the financial aspects," says lead author Marloes Caduff, at ETH Zurich. "The less material you have, the less environmental impact you’ve got from producing the steel, the concrete, and so on. And you’ve got less disposal impact as well."
The paper notes that manufacturers are generally able to produce larger turbines more efficiently than before, lowering the environmental impact. "The more turbines that are produced over the years, the better they are produced. There are fewer carbon emissions," Cuduff says.
Before concluding that bigger wind turbines are always greener, though, there are several reasons for caution.
First, the study only looks at on-shore machines, and then only of a certain size--between 12.5 meters and 90 meters (41 to 295 feet).
Second, the researchers’ model uses "generic" distances for the transportation of raw materials to the manufacturing plant (62 miles by truck, and 124 miles by train), and for the finished product to the installation site. In real life, of course, these distances vary greatly. (The study also makes important assumptions about wind shear).
Cuduff says bigger and bigger turbines could, in fact, turn out to be relatively less environmental.
"There may be other factors that make it not so good. For example, maybe you need much larger foundations, because the force working on the turbines is much larger. That may mean you might get less green again, because you need more materials in the foundation, and more structural stability," she says.
"There is probably an environmental optimum, though we didn’t look into that in the study."