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Stop putting wind turbines on buildings!

A recent article in the San Francisco Chronicle outlined why the new Public Utilities Commission headquarters at 525 Golden Gate Avenue isn’t quite as green as planned.  The LEED Platinum building was “touted as the most energy-efficient building on the continent.” The building has some great features. For example, the natural ventilation design allows the building to operate without air conditioning on mild days, which are numerous in San Francisco. It may sound simple, but most windows in office buildings are locked shut, requiring energy intensive air conditioning all day, every day. The building also houses one of the first blackwater treatment systems in the US. The system recycles wastewater for non-potable uses throughout the facility. While Australia has been doing kind of thing for 15 years, getting the system through intensive US regulations was quite a feat!

The article’s focus is on the fact that the wind turbines integrated with the building facade simply don’t work. This is not a new problem. For years, newer green building designers have tried to SUS blog picintegrate the technology on our buildings. I am asked at least once a quarter whether we should consider wind turbines for a green building project. Council House 2 in Melbourne Australia was one of the greenest buildings constructed in 2006. The bright yellow turbines on the roof signify the government’s dedication to sustainability.  But they are only a motionless symbol, and have collected negligible amounts of energy over the past decade. At Arizona State University’s Global institute for Sustainability, you can get an up close look at facility’s six roof-mounted turbines standing perfectly still. Finally, we have the turbines sitting on top of the home stadium of my beloved Philadelphia Eagles. In the only video I could find with them spinning, they spin too slowly to produce measurable power. In most videos, they are as stationary as Andy Reid’s fourth quarter offense.

The reason that these systems fail is simple physics. As the wind blows, friction from the ground produces turbulence which slows down the flow of air. This is especially true in cities, where the varying heights of buildings, cars, and roads produce windshadows that impede laminar flow. Every wind turbine has a minimum wind speed required to produce even a drop of power. We call this the “cut-in speed,” which typically hovers around 6 mph for most high output turbines. Vertical Axis Wind Turbines, like the ones on Lincoln Financial Field, boast a lower cut-in speed, but still need laminar flow to produce consistent power. Next, we must look at the power curve of a wind turbine. It may start to produce power at 6 mph, but it doesn’t meet its rated power until 31 mph!

The need for high speeds is why we tend to make wind turbines as tall as possible. The higher you get off the ground, the faster the air. The typical hub height of a utility-scale turbine is 260 ft. We also want the blades to be big. The power potential of a turbine is based on the “swept area” of its blades. This means that if you double the length of the blades, you can get four times as much energy! (It’s a pie-r-squared thing.)  These tiny building-mounted systems never stood a chance.

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Does this all mean the Public Utilities Commission got it wrong? Those wind turbines might not work, but they sure got a lot of press when the building opened. I can also guarantee they inspired more than one college student or young professional to join the green building industry. An engineer can make a lot more money designing bombs at Northrup Grumman or helping drill for oil in Texas. In order to make the transition to a fossil fuel free world, we need the smartest people to be inspired enough work for something they believe in. With enough of these bright, young minds we might just beat climate change after all. So, kudos to 525 Golden Gate Avenue for helping inspire the next generation. But next time, if you don’t mind, invest the wind turbine money into more solar panels. The rooftop panels only produce 7% of the energy the building uses, which isn’t even close to the Zero Net Energy future we need.

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