When I saw Marvel’s Black Panther, the fictitious vibranium—a material that harvests energy—caught my attention. Was there an existing material with similar properties?
In my research, I came across piezoelectric crystals, which create electricity when vibrated or put under pressure. They’ve been used for some time in the medical field, but the California Energy Commission is now testing a system whereby piezoelectric crystals are embedded in roadways to harvest the energy of passing cars. A similar effort in Israel a decade ago fizzled amidst reports of fraud, but in the US, it’s full steam ahead. The commission has awarded $2.3 million in grants for two projects—one with University of California, Merced, and the other with a private advanced energy firm.
I spoke with Dr. Rizaldo Aldas, program manager for the California Energy Commission’s Research and Development Division’s Energy Generation Research Office, to find out more.
How does this research on piezoelectric crystals fit into your remit?
As we lead the push into renewable energy sources, one of the things we’re looking at is to generate cost-effective energy solutions for California.
We know that piezoelectric materials such as crystals and certain ceramics, when pressure is applied, produce energy, which can be stored in nearby batteries. This could be a useful future source of renewable electricity and so what we would like to do is investigate the feasibility for future deployment. We need to prove the technology behind it [and] ensure reliability and durability—as any solution will need to last for a significant period—and know that cost savings can be passed to the California consumer.
California has plenty of roads to test this tech on. According to the California Department of Transportion, 200.7 billion vehicle miles were traveled on state highways in 2017.
Right. Our larger vision is, once we have a better understanding of how this technology works when embedded beneath the roadway, we would work closely with the DOT as they embark on construction and repair of our state highways.
When did piezoelectric crystals first hit your radar?
Of course it’s not a new technology; in medicine it’s been used for a while. But this would be a new use case and a compelling one. We first considered it as a feasible pilot back in 2012 when a bill from the California State legislature [passed]. That was the original motivation that led us to initially investigate the viability of the technology and now the pilots are underway.
It’s important to clarify that there’s no clear [prior peer-reviewed] science on the feasibility of piezoelectric crystals as yet. We don’t have the answers so we’re not duplicating a research study that exists.
Through the grant process you received many proposals, and chose two; we’ll focus on the academic collaboration with UC Merced today. What was it about their grant application that made their bid a success?
Based on technical merit and approach, UC Merced clearly defined an innovative concept that has high potential for meeting the technical targets that we specified. Dr. Jian-Qiao Sun, engineering professor at UC Merced, is leading the project from their end and we awarded his team a grant of $1.2 million. We have laid out some of the potentials but the goal is to see their empirical research, the rigorous scientific methodologies and results.
Can you clarify the potentials you’re looking for in this pilot to make it a feasible investment for the California Energy Commission?
Here’s the hypothesis we’re looking to prove: So, with 600 vehicles per hour passing each lane, an average weight (vehicle plus load) of a five-axle vehicle of 33,000 pounds, with an average force in the vertical direction on each tire of 3,300 pounds, at a speed, per vehicle, of 60mph, the resulting power estimate (based on the road deformation ≤ 2 mm) is electrical power density of 333 watts per square foot.
What are the cost estimates for this hypothesis?
We estimate—which is what we’re looking to prove—$9,010 per kW gained of power from the piezoelectric crystals with a lifetime (for the piezoelectric crystal install) of up to 20 years.
What will that power be used for?
It could power signal control boxes on the highways, and streetlights, we could work to comprehensively integrate it with the electric system on our state highways and possibly in the future integrate with energy storage to support the grid.
How will Californians benefit directly?
The project will help the ratepayers in the state by lowering electricity bills, reducing pollution from power plants, and creating new jobs in the renewable energy sector. This innovative under-pavement piezoelectric energy harvesting system would be a new distributed generation source providing reliable and green electricity from the highways and streets.
How do you feel about the pilot so far?
It’s still in the very early days. So far at the UC Merced lab, they’ve focused on the material itself, looking at when you apply force and how that generates energy. But we need to go further. We need to understand how you package that into a system that can go into our road system—the actual techniques to put the system together.
At UC Merced they’ve set aside a 60-meter (200-foot) stretch of roadway near the campus, and will “salt the pavement” with 2-centimeter-wide piezoelectric generators in layers. They have the piezoelectric crystals materials in the lab now, and are testing it. Next they need to complete the control systems or power electronics to manage the generated electricity prior to the actual field testing part of the pilot.
When can we come and see it in action?
In December 2018, I’ll be going to the lab for early trials but we welcome you to visit when we do the actual road testing in spring 2019.