MIT NEWS OFFICE Offshore wind turbines cool the marine atmosphere Monday, August 1, 2011

Nadya Anscombe

If wind power is going to meet 20% of our predicted energy needs in 2100, millions of wind turbines must be installed around the globe. Modelling performed by researchers at Massachusetts Institute of Technology, US, has shown that these vast wind farms, if installed in offshore regions, could reduce the temperature of the lower atmosphere above the site by 1 °C.

This is in contrast to earlier work that found that a land-based deployment of wind turbines large enough to meet one-fifth of predicted world energy needs in 2100 could lead to a significant temperature increase in the lower atmosphere over the installed regions.

Chien Wang and Ronald Prinn say their findings show how important it is that rigorous scientific assessments are made before deployment of large-scale wind farms. "We were surprised by our findings at first but we soon realized that the cooling we predicted is due principally to the enhanced latent heat flux from the sea surface to the lower atmosphere," Wang told environmentalresearchweb.

Wang and Prinn found that the effect varied depending on the location of the wind farm. In tropical and mid-latitude sites, the temperature of the lower atmosphere was reduced by up to 1 °C, whereas even greater reductions were seen in the high-latitude sites.

The consequences of such a temperature change are not clear but the researchers believe that it will have an effect on temperatures, clouds, precipitation and large-scale circulation beyond the installed regions. "However, these non-local impacts or teleconnections are much less significant than we saw in the land cases," said Wang. "This is likely due to the much lower response of the ocean to the imposed surface-drag changes relative to the response of the land to the imposed changes in both surface roughness and displacement height."

Wang and Prinn also examined the issues of intermittency and hence reliability, of large-scale deployment of wind-driven electrical power generation by seasonally averaging the available wind power in various regions of the world. They found that intermittency would be a major issue for a power generation and distribution system that relies on the harvest of wind power from large-scale offshore wind farms.

"Intermittency presents a major challenge for power management, requiring solutions such as on-site energy storage, back-up generation and very long-distance power transmission for any electrical system dominated by offshore wind power," said Wang.

Wang is also keen to point out that the method he and Prinn used to simulate the offshore wind-turbine effect on the lower atmosphere involved simply increasing the ocean surface drag. "While this method is consistent with several detailed fine-scale simulations of wind turbines, it still needs further study to ensure its validity," he said.

Wang and Prinn published their work in Environmental Research Letters (ERL).
The report is available here.