MASSACHUSETTS: Museum of Science Analyzes Rooftop Turbines
by Marian Tomusiak, Wind Turbine Lab Analyst, Museum of Science
Two years ago, the Museum of Science in Boston expanded its commitment to reducing its environmental footprint by exploring and embracing wind energy. With several site challenges, and considering the lack of available field data on small-scale wind turbines in the built environment, the project evolved into a rooftop Wind Turbine Lab showcasing five different types of small-scale turbines.
The Windspire, Skystream, Swift, AVX100s and Proven turbines add a dynamic aspect to the Museum’s otherwise mundane roof-scape. They contribute clean power to the facility as well as provide its renewable energy exhibit with an interesting experiential aspect. In addition, as an independent rooftop consumer test lab — the first of its kind — the Museum serves as a community resource for both professionals and the general public.
Since October 2009, wind and power data and statistics have been collected and the results analyzed. To compare performance equitably, each turbine system’s data is measured at the wall, after passing through inverters and a step-up transformer. Live and historical data is fed to the Catching the Wind exhibit, where visitors learn about wind turbines and energy technology. Behind the scenes, turbine performance is analyzed in detail, providing solid data and project experience for professionals, universities, government, and consumers.
Initial assessment of the site, structure and wind profile showed it was impractical to scale wind turbines for the Museum’s electrical load (9GWh/year). Therefore, the installed rooftop turbines do not power a significant fraction of the Museum’s electrical load. Nonetheless, they are grid-connected and the Museum does use their energy. In 2010, the turbines provided 4,409 kWh of clean electricity – that’s 60% of the electricity needs of an average Massachusetts home (2009). The Museum’s Wind Turbine Lab has experienced no issues with noise, vibration, ice throw, flickering shadows, bats, or other environmental problems, and recorded just one bird-strike in its two-year history. The neighbors seem to like them, too.
Project implementation began in 2006 with a yearlong site and wind assessment, funded by the Kresge Foundation for the Museum of Science. The Museum is a complex site, composed of several buildings constructed over decades, resulting in structural engineering challenges. The largest and highest building on a dam across the Charles River, it has no access to land for ground installation, so roof mounting was the only option. The city line between Boston and Cambridge, Massachusetts, runs right through the lobby. Though Boston had previously processed the wind turbine installations, the Museum of Science broke new ground to obtain the required variances in Cambridge. (Two turbines are in Cambridge. The others are in Boston.) One and a half million visitors come through the doors each year and the street in front is heavily traveled and often congested, so public safety is paramount.
Neighboring residential high-rises were approached early in the planning process, to allay concerns about their views and noise. Feedback indicates that the turbines are actually seen as an improvement – many say they are entertaining to observe. Noise has proven not to be an issue from neighbors, staff or visitors. A range of other concerns were also addressed successfully, with considerable time and effort: the Museum lies in city and state historical districts, over wetlands, in the flyover zone for military and medical flights, and is just a few miles from Boston’s busy Logan Airport.
The core data for the wind assessment came from five anemometers recording wind direction and speeds for a full year. Correlated with historical data, this narrowed down potential locations. In spite of the human perception that this is a windy area, the data showed an average speed of just under 5 meters/second in the best location. The precise location of the turbines required consideration of not only wind resources, but structural and safety concerns. Current data shows the average wind speed for the turbines as installed are all under 4 meters/sec.
Meanwhile, candidate wind turbines were evaluated. Each turbine was required to be commercially available, scaled for residential use, operational in the local wind regime, and within budget. (Massachusetts Renewable Energy Trust, now Massachusetts Clean Energy Center, provided a grant of $300,000 for purchase and installation.) The manufacturer had to be willing to allow a roof installation and open dissemination of performance data. And they all had to be different from each other.
The wind turbines installed at the Museum, from left to right in the photo are:
Windspire, rated 1.2 kW at 11m/s, the only vertical axis model, 10 meters high, including the 6-meter-tall rotor;
Skystream 3.7, rated 2.4 kW at 13 m/s, downwind passive yaw, 10-meter tower;
Swift, rated 1.0 at 11m/s, upwind passive yaw, 3-meter tower;
Five AVX1000s, each rated 1 kW at 13 m/s, upwind passive yaw, hub height 2 meters above the edge of the central building;
Proven 6, rated 6 kW at 12m/s, downwind passive yaw, 9-meter tower.
The data acquisition system has been accessing and storing data since October 2009. Each turbine has its own anemometer; a single wind vane near the Skystream provides wind direction. The computer samples wind and power data every 2-3 seconds, after inverters and transformers, to measure all systems similarly. Data is aggregated into 10-minute intervals, and includes wind speed and power averages, minimums and maximums. Select information, both live and historical, is displayed in Catching the Wind, part of an expanding exhibit on renewable energy.
Detailed data is used to study power curves, energy production and wind distribution. In the future, this data should be available via the internet; until then, Museum personnel are the primary conduit for data and analyses. Over the past year and a half, the Wind Turbine Lab has provided data and project information for industry professionals, including National Renewable Energy Lab’s National Wind Technology Center; facilities managers; potential owners; researchers, notably MIT’s Wind Group and CS/AI Lab; students, Museum staff and volunteers, and the general public. Presentations from their May 2010 conference: Lessons Learned from the Museum of Science Wind Turbine Lab, are accessible at www.mos.org/WindTurbineLab. Included there also is contact information for the many professionals who contributed their expertise throughout the project. More detailed questions can be answered by the staff of the Wind Turbine Lab.
While performance details are outside the scope of this article, Museum staff highlight several lessons learned so far.
The turbines are not scaled to the Museum’s electrical load. And though tall buildings may access higher winds, the electric load would also increase, so it is unlikely that small-scale wind turbines on large buildings could be a primary power source. The available data shows that some of these turbines could provide significant power for a residential-scale building, given similar wind profiles.
Roof mounting is expensive. The project’s single largest cost was for structural steel – more than the capital cost of all of the turbines, and almost a quarter of the entire $350K project budget. The support structures were conservatively designed, and the larger turbines are not really intended for roof installation, which increased material requirements. Recall that the Museum used the roof because it has no access to ground.
Analyze the wind profile to estimate energy production. Record a range of wind speeds as close to hub height as possible, especially in a built environment. Wind flow around buildings makes wind shear adjustments difficult. In the Lab data, 80% of the wind is under 10 mph; 80% of the energy is generated over 10 mph. A single wind speed average masks this imbalance and we have some evidence that roof top wind distribution does not follow a Rayleigh curve.
Maintenance is not expensive. After the initial installation, the regular Museum facilities staff can handle most of the operations, by themselves or coordinating with vendors. The turbines are a small fraction of building maintenance efforts.
The primary arguments against installing wind turbines were not borne out for the Museum Wind Turbine Lab. There have been no complaints about noise or views, the top concerns expressed before the project. In fact, many people report that they enjoy watching the turbines. There has been no evidence of ice throw nor vibration issues, and no complaints about shadow flicker. The turbines caused just one bird death in two years of operation, and there were no other wildlife or environmental problems.
As a visible expression of sustainable energy at the Museum, the lab is a beacon for strong public interest in wind turbines. Its history demonstrates the importance of measuring the wind regime on site, understanding what each turbine can produce over time, and weighing the engineering retro-fit costs of roof mounting against simpler ground installation. Wind power can be considered among other sustainable energy options, including conservation measures and use of other renewables. The Museum of Science Wind Turbine Lab continues to generate clean electricity and contribute valuable real-world data from wind turbines in a built environment.