BOSTON--When it comes to distributed energy in suburban or urban areas, solar panels do a better job of fitting in than small wind turbines.
Small wind turbines, which are increasingly being marketed to homeowners, can provide power for both grid-tied and off-grid applications, typically require a strong steady wind to meet their generating capacity, and meet estimates for annual production. To tap into a good wind resource, turbines need to be placed high and clear of obstructions, such as trees and buildings, according to experts.
By contrast, solar photovoltaic (PV) panels are less fussy about placement. To make the investment worth considering, they need several hours of sunlight a day but, compared to small wind, that means a wider set of potential locations.
"Small wind is a viable distributed generation option, but it has a lot more siting constraints than PV. Part of it is the complexity and the analysis to determining if you have a good site," said Peter McPhee, a project manager at the Massachusetts Clean Energy Center where he manages the state's microwind program. McPhee was a speaker on a wind energy panel at the Building Energy conference here earlier this month, where there were fewer displays of small wind turbines compared to earlier years.
In the past few years, small turbines of various designs with a generating capacity under 100 kilowatts have been introduced in the U.S., leading to rapid growth and about 10,000 installed units by the end of 2009. Manufacturers often recommend that consumers or businesses should only consider small wind turbines if there is a minimum average wind speed of 10 miles per hour.
There are national wind maps, such as a free one offered by 3Tier, that rate the wind resources for different zones in the U.S. But determining wind dynamics at a specific location can be tricky.
For example, a review of one small wind turbine in Massachusetts found that obstructions from nearby buildings created a high degree of wind turbulence, resulting in a far lower performance than online tools had predicted, said Charles McClelland, an associate at the consulting company the Cadmus Group, which does wind project feasibility testing and monitoring. Similarly, a study of roof-mounted wind turbines in the U.K. found that turbulence diminished wind speed, one reason for disappointing performance.
To get around turbulence from trees and buildings, wind installers should have turbine towers at a minimum of 100 feet, McClelland said. But those high tower heights can often run afoul of local ordinances, making permitting complicated and limiting the available space.
In 2008, Massachusetts did a review of all its small wind installations and found that some of the turbines did not perform as well as expected. That led to a new microwind program in 2009 that sought to stiffen the siting requirements. It also developed a software tool to better assess the wind resource at a specific location, which is a requirement to receive rebates.
As a result of the changes, the state is focusing homeowners and installers on the best wind locations, which are typically near the water or in fields without obstructions. That makes small wind "not as applicable in scope as PV is," said McPhee.
In a survey with small wind manufacturers, the American Wind Energy Association noted that falling prices in solar PV have put more pressure on small wind installers and technology developers. The industry is pushing for equipment certification to provide more certainty on how small wind turbines will perform.
"Increasing publicity, public incentives, and competition from falling prices of solar PV technologies place greater pressure, survey respondents say, on small wind turbines to perform well in the field," AWEA said in its 2009 report on small wind.
Wind turbines can generate more energy per dollar than solar photovoltaics with the right conditions of a good turbine, site, people, as well as proper installation and maintenance, said Gary Harcourt, the founder and manager of installer Great Rock Windpower, who has commissioned more than 30 small wind turbines.
"Proper installation takes knowledge and experience. Short towers don't work--you need to get up there where the wind resource is," he said. "Most really good sites are pretty empty spaces--there's great wind out there."