BOSTON--If you like the idea of greening your home or office by installing a small wind turbine, it may be best to picture the device on the ground and not the roof.
That's one of the pearls of wisdom shared here Tuesday by the city's Museum of Science, during a conference on small-scale urban wind turbines. The museum was reporting data from an experiment involving the installation last year of five such turbines on the institution's roof.
Dozens of young companies have developed microwind turbines designed for residential or commercial customers, leading to rapid growth in sales over the past three years. These turbines can offset a significant portion of a home's or business's monthly electricity bill when placed in the right conditions. But the Museum of Science wind lab highlights some of the challenges the industry and potential customers face.
The museum sits on a dam at the mouth of the Charles River, and the initial goal was to take advantage of river winds to reduce the museum's power use and environmental footprint. Within a few months, though, focus shifted to gathering useful information on small wind, and to using the turbine setup for educational purposes, said David Rabkin. Rabkin is the museum's director of current science and technology, and the mastermind of the project, which is now a museum exhibit and ongoing lab.
At the conference, project participants presented several months' worth of data that showed there's no viable return on investment (ROI) for the five turbines, even the ones that have performed close to expectations. Tests showed that the wind was moderate and putting turbines on the roof means they don't benefit from all the available wind energy, since the building causes changes in the wind flow.
"This is not an economic way to generate power or reduce greenhouse gas emissions. This is not about ROI--it's about education," said Rabkin. "I wouldn't necessarily recommend rooftop-mounted turbines, because it's pricey. But it's a great opportunity for public education. It's a fantastic landmark."
Even with poor economics, the project--estimated to cost a minimum of $350,000--has been revealing in many ways to the dozens of people involved, who had to navigate an immature industry of suppliers and a murky permitting process.
Getting good data
Three of the five turbines installed at the museum came close to matching the power output indicated by their manufacturers. The turbines have also proved reliable in shutting off at high speeds, and there haven't been any deaths of birds or bats, or any problems with noise, since the devices were placed.
But the total power production of a small turbine ultimately relies on the available energy in the wind, which is a function of the wind speed. Wind resource tests at the Museum of Science show that the average wind speed is about five meters per second (11 miles per hour) at a height of 34 meters, said Bob Shatten, principal at Boreal Renewable Energy Development, which helped develop the project.
That wind speed would now fall below the threshold required to receive a rebate from the state of Massachusetts' small-wind program. Massachusetts, which has had 73 small wind turbines installed since 2005, is in the process of raising the requirements for projects, in an effort to focus development in areas with the best wind.
Compared with large, utility-scale turbines, small wind turbines are limited in their ability to capture available energy, Shatten said. Also, it's very hard to know the actual wind conditions of a specific site without gathering data with an anemometer, particularly on roof-mounted turbines where buildings can affect wind flow.
"Your site's going to have to be really windy for you to get good results in your wind study," Shatten said during a presentation. " That's not to say that the technology won't change in the future, but from where we're sitting, the more wind, the more mass, the more energy you're getting."
One of the five turbines, a Swift turbine, which has a ring around a fan to lower noise and vibration, did not come close to performing as expected. But a study--done too late, in retrospect--with computational fluid dynamics software found that the location chosen was the worst possible spot on the museum roof, said Valerio Viti, senior fluids specialist at simulation software company Ansys.
In some cases, organizations are eager to install small wind turbines because they are a visible way to "go green," even though actual wind resources may be marginal or poor. A bank in Boston, for example, wanted to install a wind turbine half way up an office building, even though the turbine would have performed far better on the tower's roof. Alex Weck, an analyst at Boreal Renewable Energy Development, recommended against that project because the return on investment would have taken 130 years.
"There was a lot of passion, but as a wind consultant, I have to say 'no,'" he said. Instead, he said, solar panels can be a better way to produce clean electricity--a fact the Museum of Science has discovered with its own solar array. Weck agreed corporations would do well to perform a wind resource test, but consumers can rely on software to get a wind estimate.
The importance of wind speed is just one of the lessons project participants--some of whom worked pro bono--have discovered.
Installation on top of an existing building is complicated significantly by structural and other concerns. In the museum's case, one relatively large turbine, from Proven in Scotland, is mounted above a domed Imax movie theatre, so were concerns about vibrations and noise. So far, though, there haven't been any problems. Putting small turbines on the ground, or including them in plans for a new building, can avoid many structural challenges, said Shatten.
The metal for turbine mounting, and engineering work for the project, accounted for about one fifth of the project's total costs, or about the same as the actual wind equipment, said Marie Tomusiak, an analyst at the Museum of Science's wind lab. The bulk of the project's costs were paid by state grants.
Permitting was a complex and lengthy process, a problem homeowners and businesses may face as well, particularly in cities and towns that haven't written bylaws specifically for small wind turbines. In the museum's case, people at the state agency for managing public parks and land, which is the institution's landlord, were reluctant to approve the project, since nothing like it had been done before.
Working with the providers of small wind turbines proved to be a challenge as well, reflecting how immature the industry as a whole is. In some cases, providers didn't call back or couldn't provide relevant data, making it difficult to determine if a product, or manufacturer, was economically viable. The Museum of Science's Rabkin expects turbines to become more like appliances in the coming years, making them easier to install and operate.
Despite the travails in getting the lab online, Rabkin said the turbine installation will be useful as a source of data to academics, the general public, and professionals.
The machines, which did not face any opposition from neighbors, also serve as a statement about sustainable practices. They're harder to miss than the museum's other, less visible, eco-minded efforts, such as the solar panels, or carpets made from recycled materials.
"Most people who want us to be a green organization don't notice those things because they can't see them," he said. "The turbines are a very powerful symbol that, yeah, this museum cares."