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LEED Leads to Bad Wind Installations

September 26, 2008
Paul Gipe

Aerovironment's AVX 1000 Rooftop Turbines at Logan Airport


AeroVironment has installed 20 units of its AVX 1000 rooftop turbines on a building at Boston's Logan International Airport. The 20 kW installation, part of what AeroViron[ment calls its "architectural wind system" contributed to the building's obtaining a LEED Gold certification.

By mounting the turbines on the building's parapet, AeroVironment claims that the turbines will experience 15% higher wind speeds that result in 50% more energy capture than comparable tower mounted wind turbines. This is a claim based on aerodynamic modeling, a specialty of AeroVironment, famous for its stunning achievements in human- and solar-powered aircraft.

Unlike other wind turbine manufacturers that advertise the rotor diameter of their products, AeroVironment does not give the diameter of the AVX 1000 directly. Instead AV gives the turbines dimensions in height and width, information that's suitable for architects, the product's targeted audience.

 

The diameter of the rotor on the AVX 1000 is inferred from a "width" of 72 inches, or 1.83 meters. The AVX 1000 sweeps about 2.6 square meters of the wind stream. Other wind turbines of this size are rated at 500 watts. AeroVironment rates the AVX 1000 at 1,000 watts.

AeroVironment asserts that the 20 turbines will generate 60,000 kWh per year at this installation.

Massport, the Massachussetts Port Authority, claims in a September 17, 2008 USA Today article that the turbines will instead produce 100,000 kWh/year.

The projected yields from the turbines are 1,900 kWh/m²/yr according to the Massport estimates, and 1,100 kWh/m²/yr according to AeroVironment's original estimates.

For comparison, manufacturer's of small wind turbines typically estimate that their turbines will produce no more than 600 kWh/m²/yr at a windy site with an average wind speed of 7 m/s. Southwest Windpower estimates that its Skystream 3.7 will deliver 650 kWh/m²/yr.

AeroVironment's estimates appear to be twice that what other turbines can produce under similar conditions. Massport's estimates appear to be three times what other small wind turbines can produce under comparable conditions.

There is no publicly available data on the actual field performance of the AVX 1000 turbines at Logan airport or at any other site.

Can AeroVironment's AVX 1000 turbines generate the amount of electricity advertised? Unlikely.

Architects should ask for field performance verification of AeroVironment's claims before using what appears are inflated estimates of generation in LEED applications.


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