lunes, 23 de septiembre de 2013

(Energy) Harvest Festival

ORIGINAL: Traffic Technology International
August/September 2013

Illustration courtesy of Patrick George
The energy produced by vehicles driving on our roadways is a potentially huge source of untapped electricity. Louise Smyth meets the people who will have cause to celebrate if the concept sparks into life

Although the ideas of piezoelectric generation and embedding functionality into roads are not new, the notion of merging the two is novel. We've long embedded technologies in roadways, a case in point being the much-maligned loop detector Meanwhile, we've used piezoelectric materials for numerous applications over the years. So when considering a marriage between the two, a simple question to ask is, can any of the power created by vehicles driving over our roads be harnessed? Answering how this could be achieved is rather more complicated.

Simple thingsA piezoelectric energy harvesting system for roads is relatively straightforward. Vehicles drive over the surface, their tires place pressure on piezoelectric crystals embedded in the road, wíuch subsequently produce a small amount of energy. Multiply that scenario over a stretch of road with many vehicles traveling over the top and thousands of embedded crystals and you can almost envision a day when the lights of the Golden Gate Bridge could be powered by the vehicles driving over it We're not there yet We're at the academic and research stages, although some commercial outfits are taking the tentative steps to forming a compelling business case, as well as selling energy-harvesting equipment designed for roads. The potential would seem to be enormous, but fulfilling it is not without major challenges - something that anyone who's worked in the área can testify. John Gambatese, professor in the School of Civil and Construction Engineering at Oregon State University, is festival one of those researchers. Hot on the heels of Oregon’s successful solar highway deployment, he submitted his Research Problem Statement on energy harvesting for roadways to Oregon DOT at the end of 2012. 
We leave a lot of energy on the road in different ways,” he says. “Whether it’s the vibration on a bridge or roadway, or the wind produced by the traffic, there’s energy there that can be harvested. It might only be a small amount at each location but when you add it up, it could help to power our traffic infrastructure, our streetlighting, or other electrical requirements we may have.
So if that goes according to plan, what about selling the surplus back into the grid? 
For now we’re just trying to develop the technology so we can start collecting energy,” Gambatese says. “Once we do that, we can monitor how much we obtain and then there’s a chance we can optimize the technologies with the goal being to feed electricity back into the grid. Whether or not we’ll have that capability in the next five to 10 years, though, I’m not so sure.

From research to reality?
The FHWA is funding work on energy harvesting for roads, indicating that it sees some future potential in the concept. The Administration’s Eric Weaver reveals how the testing is being conducted and what the initial results have shown

The Virginia in Tech Transportation Institute (VTTI) presence is a notable in the testing of piezoelectric energy harvesting for roads and is currently involved in a US$1M FHWA-funded project.  The stated aim isn’t to assess commercially available systems but to put a VTTI-developed system through its paces. The research is being overseen by Eric Weaver, a research civil engineer in the FHWA’s Office of Infrastructure, R&D, and an expert in this sector. “We are currently exploring the potential," says a cautiously optimistic Weaver about the technology. “Our initial research indicates that the amount of energy harvested might be modest but could theoretically offset some utility costs or provide power in areas that  are currently inaccessible to the grid.

Like many people in the field, Weaver foresees any power generated being used only where it is harvested, for th short term at least. "It's meant to provide energy within the energy right-of-way to be used for transportation infrastructure demands,” he continues. “However, depending on the application and the infrastructure demand, excess energy could potentially be transferred back to the grid, provided that the electric grid infrastructure is updated to enable this.
 “Our work has involved a significant amount of analytical modeling, as well as laboratory trial and error with different  geometric configurations of piezoelectric generators and the materials that encase them. Virginia Tech researchers have installed some sensors at two locations in the state, one of which is at a truck weigh station and the other at a full-scale test road called the VA Smart Road."

Interestingly, for comparison purposes, researchers also installed sensors from the Israeli company Innowattech in at least one of those locations.

Although Weaver reveals that the results so far are perhaps not as encouraging as vendors or proponents of the technology might hope, the work is helping to identify teething problems that likey be overcome. “So far in our research, low power output is observed with each axle load application. Part of the reason for this is that the wheel load doesn’t always pass directly over the generator, because they’re centered in the wheel path, where the wheels don’t onsistently track. To mitigate this problem, researchers are exploring other generator geometries that provide more spatial coverage.

The sensors have been rugged enough so far to hold up to the traffic loading they have received,” Weaver continues. “A further benefit is that the data from this project has been used to support another study performed for the California Energy Commission to evaluate the feasibility of all piezoelectric generation technologies currently on the market.

Complete Text: Traffic Technology International August/September 2013 

"Depending on the application and the infrastructure demand, excess energy could potentially be transferred back to the grid"

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