Innovation:

Reinventing urban wind power

Innovation is our regular column highlighting emerging technologies and predicting where they may lead

With the environmental movement gathering momentum, many are thinking of installing wind turbines to generate their own electricity. Unfortunately, wind speeds in urban areas are usually too slow and turbulent to make micro wind generation cost-effective.

So while the strict planning regulations that have prevented homeowners from erecting domestic turbines in the UK are expected to be relaxed next month, city-dwellers may find manufacturers reluctant to sell them their turbines for fear that poor performance will reflect badly on a young and vulnerable industry.

However, researchers at Cornell University in Ithaca, New York, believe that the problem is not with the low wind speeds after all, but with the methods used to harvest wind power. Cities have plenty of wind energy we can use, they say, but to harness it requires a different tack. It's time to reinvent the urban wind turbine.

Moving away from traditional electromagnetic generators and turbines may seem like a radical step, but on a small scale and with low wind speeds, piezoelectric generation looks like an attractive option.

Ephrahim Garcia, a mechanical engineer at Cornell, attached a flexible aerofoil to the end of a pole made out of a piezoelectric material. When air passes over the aerofoil it flutters, causing the pole to flex and generate a small alternating current. "The inspiration came from fish tails," Garcia says.

Garcia and colleague Matthew Bryant tested aerofoils that were 13 centimetres long in a wind tunnel, and found that they generated power in the milliwatt range from wind speeds of just 2 metres per second. With many devices operating in parallel, the amount of power generated could quickly add up, they say.