Design Engineering

Report suggests global wind resource potential over-blown

Harvard research suggests real-world generating capacity of wind farms at large scales has been overestimated.

February 26, 2013   by Design Engineering Staff

New research conducted by Harvard University applied physicist David Keith and funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) suggest the amount of potential wind power has been significantly overstated.

On the surface, wind power would seem to be inexhaustible, unlike oil or coal reserves, which have a measurable limit. However, according to Keith’s mesoscale atmospheric modeling research (published in the journal Environmental Research Letters) wind power has a number of real-world limiting factors.

First and foremost is the limit on the density of large wind farm installations. Previous estimates of their generating capacity assumed more turbines meant more power, approximately 2 to 7 watts per square meter. In reality, Keith’s research shows that the drag of each turbine blade creates a “wind shadow” that slows the wind.

While most installations balance density against wind shadow, the effects of turbines in larger wind farms begin to interact and the regional-scale wind patterns matter more. According to Keith’s research very large wind power installations (larger than 100 square kilometers) may peak at between 0.5 and 1 watts per square meter.

“If wind power’s going to make a contribution to global energy requirements that’s serious, 10 or 20 percent or more, then it really has to contribute on the scale of terawatts in the next half-century or less,” says Keith.

If we were to cover the entire Earth with wind farms, he notes, “the system could potentially generate enormous amounts of power, well in excess of 100 terawatts, but at that point my guess, based on our climate modeling, is that the effect of that on global winds, and therefore on climate, would be severe—perhaps bigger than the impact of doubling CO2.”

In addition to wind shadow, Keith says other real-world constraints, like geography and economics, further limit the maximum capacity wind power could ultimately contribute to global power needs. For example, wind installations only make sense in locations with a constant wind supply while also being relatively close to where that electricity would be consumed.

In order to stabilize the Earth’s climate, Keith estimates, the world will need to identify sources for several tens of terawatts of carbon-free power within a human lifetime. In the meantime, policymakers must also decide how to allocate resources to develop new technologies to harness that energy.

“It’s worth asking about the scalability of each potential energy source—whether it can supply 3 terawatts, which would be 10 percent of our global energy need, or whether it’s more like 0.3 terawatts and 1 percent,” Keith says.

“Wind power is in a middle ground,” he continues. “It is still one of the most scalable renewables, but our research suggests that we will need to pay attention to its limits and climatic impacts if we try to scale it beyond a few terawatts.”

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