Testing Urban Turbines

Renewable energy in the form of wind farms with large wind turbines are becoming increasingly prevalent nationwide. But over the past few years, the market for small wind turbines also has grown--by 15 percent in 2009, an increase of about 10,000 new units, according to the American Wind Energy Association. States and the federal government helped fuel their sale by offering renewable energy incentives, including a 30 percent federal tax credit for alternative energy investments.

Small-scale turbines provide 100 kilowatts of energy or less (enough to power, on average, 12-volt appliances), are pointed by a simple wind vane, and can be mounted on a rooftop much like a satellite TV dish. But unlike solar energy, wind can be fickle, making it difficult to predict exactly how much power a given turbine will generate.

This is especially true in cities, where buildings and trees cause wind turbulence. So to help people navigate the complexities of urban wind, Reno, Nev., recently partnered with the U.S. Department of Energy (DOE) in a study focused on local wind patterns. The project, funded by $550,000 in DOE wind and stimulus grants, will install nine small turbines in various locations around the city. Project staff will collect data on wind speed, wind direction and electrical output, and then create a 3-D map showing citizens what kind of wind energy to expect for their residence or business.

"We're trying to help the average person understand what that turbine is doing and if that wind resource is good or bad," says Andy Solberg, a mechanical engineer with CH2M Hill, an engineering and consulting firm that's using computational fluid dynamics software to help develop the 3-D map.

Although most turbine manufacturers provide estimates of electricity generation for a given product, Solberg says those estimates are based on steady wind speeds. When those speeds dissipate--which often happens in the real world--the turbine generates only a "tiny fraction of what it's rated," Solberg says.

A study commissioned by the Massachusetts Renewable Energy Trust showed just how fickle wind energy can be. The analysis, which reviewed electricity output from 21 small wind turbines placed throughout the state, showed that the manufacturers' estimate of power generation was about three times higher than the turbines' actual performance.

Known for its afternoon "zephyr" winds coming from the Sierras, Reno provides robust consumer incentives for wind installation, including streamlined permitting and $3- and $4-per-watt rebates from the local utility, NV Energy, depending on whether the customer is in the public or private sector. With the help of the 3-D map, which will be available online, residents and business owners will soon see if those incentives are worth the upfront investment. By simply plugging in an address, they'll receive guidelines on likely wind speed and ideal turbine height and placement.

In 2007, CH2M Hill helped develop a similar mapping program for solar energy in San Francisco--a project that will soon include a wind power component. Such tools are becoming invaluable as cities weigh the relative benefits of different green energy sources. "Everyone thinks wind is a good resource here," says Jason Geddes, Reno's environmental services coordinator. "But we don't have the data to prove it."