There are now several measured power curves of the Mariah Windspire publicly available. This is one of the very few contemporary household-size (small) Vertical Axis Wind Turbines (VAWTs) to complete full testing and certification in the US.
Mariah’s Windspire is a non-articulating, straight-blade Darrieus with an extended height to diameter ratio (tall and thin) as its signature design feature, and, thus, the name.
See also Mariah: Another Performance Report on ire VAWT, and NREL Mariah Power’s Windspire Wind Turbine Testing and Results.
Most of the new generation of VAWTs introduced within the past decade have not undergone full testing and certification. Mariah Windspire stood out because early on they were convinced that only with full testing and certification could they honestly inform their customers of what to expect from their turbine.
Unfortunately, Mariah’s design and marketing were fundamentally flawed as indicated by the many very poorly sited Windspire turbines installed in the US. See How Not to Site Vertical Axis Wind Turbines (Mariah Windspire), and Mariah In the Running for Worst Small Turbine Install.
The poor siting led in part to the company’s demise in early 2012. See Some Nevada wind power users say returns lacking.
Nevertheless, there are published power curves for this particular brand. Here’s Windward Engineering’s measured performance at its site in Utah: Power Performance Test Report for the Windspire by Windward Engineering.
Of interest is that Mariah didn’t overhype the performance of their turbine that is so typical of most if not all VAWT promoters. Mariah rated their small turbine at 1.2 kW at 11 m/s. Windward Engineering found that the turbine would deliver 1.3 kW at 11 m/s or more than the manufacturer said the turbine would produce. Further, using the conservative standard power rating of 200 W/m2 the turbine could be rated at 1.5 kW. This is one of the few small turbines in my experience that was rated lower than the standard power rating.
Alas, the turbine, because it was so small—only 7.4 m2–would only produce a few thousand kWh annually. Based on an annual conversion efficiency of 19%, the turbine would generate nearly 2,400 kWh at a site with an average annual wind speed of 5.5 m/s at hub height.
