If you think about all of the unlikely places in which to mount wind turbines — on top of skyscrapers, over freeways, affixed to the Eiffel Tower, at Alec Baldwin’s house in the Hamptons, etc. — nestling one (or two or three or more) under a bridge doesn’t seem at all that far-fetched. After all, why erect massive wind farms, on or offshore, when you can simply incorporate them into the dead space below existing infrastructure?
That’s the question being posed by a team of Spanish and British researchers who recently zeroed in on one particular vehicular bridge — the 206-foot-tall Juncal Viaduct on Spain’s perpetually pleasant Canary Islands — to study the feasibility of spans that produce clean energy while also carrying traffic.
The team’s findings were recently published in the journal Renewable and Sustainable Energy Reviews.
Using computer simulations, the team, headed by Oscar Soto of Kingston University in London, sought to answer two crucial questions about the potential pairing of wind turbines and bridges: how many and how big? Using Juncal Viaduct as a theoretical guinea pig, Soto and co. found that two identical turbines of medium-size installed between the bridge’s existing pillars would be the most practical in terms of cost and logistics to mount under existing bridges. However, for optimum power generation, two turbines of different sizes would be more effective while also maximizing the amount of available space — that or an entire matrix of up to 24 small wind turbines.
If matrix-style under-bridge wind turbine arrangements sound at all familiar, that’s because it’s been proposed before in an earlier concept out of Italy, a renewables-embracing nation known for having turbines in somewhat unexpected places. As part of a 2011 design competition, designers Francesco Colarossi, Giovanna Saracino and Luisa Saracino proposed installing a network of 26 small wind turbines under a decommissioned bridge near Calabria in lieu of demolishing it. The adaptive reuse-minded concept, dubbed Solar Wind, also involved re-opening a section of the bridge’s original roadway and covering it with a grid of solar cells. The bridge, which would also boast a new park and roadside kiosks in the form of greenhouses hawking super-fresh veggies to motorists, could produce up to 40 million kilowatt-hours of electricity annually.
Back in Spain, researchers found that going the two-turbine route would offer promising potential results, with each generating enough juice (.25 megawatts each) to power several hundreds homes on the island of Gran Canaria, home to upwards of 800,000 people.
"This would be the equivalent to 450-500 homes average consumption,” Soto explains. “This kind of installation would avoid the emission of 140 tons of CO2 per year, an amount that represents the depuration effect of about 7,200 trees”.
There are, of course, the not-so-small issues of load weight and vibrations inherent with adding such an installation to existing structures. From an engineering standpoint, would wind turbines be better suited for newly built spans specifically designed to accommodate them from the get-go? The answer is most likely yes.
Although the Juncal Viaduct won’t be retrofitted to include wind turbines at any point soon, such a project, in concept, makes sense for the Canary Islands. In 2014, the vacationer-heavy archipelago’s smallest and most isolated island, El Hierro, became the first island in the world to be completely powered by wind — with a not-so-little assist from hydropower. Previously, the off-grid island, home to 10,000 residents, ran completely off of diesel-powered electric generators. The Canary Islands are also already home to a few spectacular (and a touch terrifying) bridges including Los Tilos Bridge on La Palma, a ravine-spanning feat of engineering that's one of the longest arch bridges in the world.
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