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PERSPECTIVES

Turbines in the city


Renewable energy production is no longer considered alternative or optional. When more sustainable energy is produced in Texas than in California, you know renewable energy has become mainstream. It’s now time to begin looking at sustainable energy 2.0—urban generation facilities.

 

QUICK TAKES

  • More than 4.3 billion people or 55% of the world’s population live in urban settings, and the number is expected to rise to 80% by 2050. (World Economic Forum)

  • Approximately 80% of the U.S. population lives in urban areas. (US Census Bureau)

  • Wind is the largest source of renewable electricity generation in the United States, providing 10.2% of the country's electricity and growing. (cleanpower.org)

 

When you think of wind turbines, you undoubtedly picture massive windmill-type structures occupying large plots of land along ridge lines, amid farm fields or in ocean waters. These have worked well to lay the foundation for sustainable wind energy generation, but their size has limited where wind energy can reasonably be accessed. Now, innovative engineering has reduced the size of the “wind catchers,” as well as improved their ability to work in low-wind conditions, allowing electricity to be generated by wind within urban environments, where the majority of people live. Moving generation closer to the end-user helps to decentralize the energy production, which reduces the need for long-distance transmission lines and can increase the reliability and resilience of the grid.


The key to miniaturizing the turbines has been changing the direction of the axis and rotor. Traditional wind turbines use a horizontal axis. Urban turbines, however, use an axis positioned on a vertical plane, which results in slim towers rather than windmills. Vertical axis wind turbines are better adapted to urban requirements because:

  • They do not need a great deal of height or the large areas that horizontal turbines do.

  • They do not need to face the wind and they are not greatly affected by changes of direction—a distinct advantage in areas where wind might swirl between tall buildings.

  • They can be placed closer to the ground and use the natural or artificial physical features of the land that favor the flow.

  • Their environmental impact is lower, particularly in terms of birds.

Two projects now underway in France are good examples of how urban turbines can be integrated into cities.


The Paris-based company New World Wind has developed a “wind tree” in an attempt to do away with the disadvantages associated with turbines. (See photo at the beginning of this blog.) These artificial trees are designed with three steel trunks and other smaller branches that house miniature wind turbines in the shape of leaves. The wind tree only requires an 11-meter radius of land to be installed. New World Wind claims a single wind tree can generate 83% of a French household’s annual electricity consumption.


The micro technology is based on a cone-shaped “aeroleaf” that catches wind energy at 360°, and only requires a wind speed of 2.5 meters per second to initiate energy generation.


Another project is the EU-funded Horizon 2020 EOLI FPS project. Engineers developed a 4-ft. tall, rooftop vertical axis wind turbine specifically designed to work under low windspeed conditions found in the urban environment. “Its internal rotor design facilitates the creation of vortexes out of the wind turbulence that drastically increases the driving force of the laminar wind,” says project coordinator Sergio Pedrosa. “Furthermore, it is safe, noiseless, does not vibrate and fits into the urban landscape.” The wind turbine offers the customer energy at a cost of EUR 0.05 per kilowatt hour (kWh) produced, compared with the current European average cost of EUR 0.21 per kWh for the electricity network.


We are still in the early stages of moving sustainable energy production closer to consumers. The technology is still quite new and, in general, developers have not invested a significant amount in the technology. While there are several ongoing projects in Europe, urban turbines are not commercially available in any substantial numbers yet. And there are still questions to be answered, particularly in the areas of upkeep, upgrades, replacement and ownership. But as consumers become more comfortable with generating their own electricity — rooftop solar panels are already ubiquitous — it makes sense that urban wind turbines will receive more attention. And, as the size of the turbines continues to shrink, it seems only a matter of time before wind trees and small rooftop towers begin sprouting in the US urban core.

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