While researchers have been working on ways to harvest small amounts of energy to power wearables, LEDs, and other devices, vibrational energy could provide much more power. Mechanical engineering professor Lei Zuo has been researching methods of harvesting vibrational energy and in August 2015 he got some more attention when Virginia Tech published an article about his research. He has been working on shock absorbers that could help cars and heavier vehicles reduce their fuel consumption.
Some vehicles already use energy-harvesting devices; regenerative brakes appear on hybrid vehicles and some electric bikes. They help hybrid vehicles get better city mileage since the car gains some energy when it stops at an intersection. Regenerative shock absorbers could complement regenerative brakes, making the vehicle even better at recapturing power. Researchers are working on heat recapture systems for vehicles as well.
Lei Zuo is an expert in energy recapture systems and he released two presentations in 2011 that provide some additional details about using shock absorbers to capture vibrational energy. The most striking thing I learned was that only about 10%-16% of the fuel a car uses actually pushes it forward. So cars could become much more efficient and there are opportunities to recapture energy at multiple points in the system.
A 2011 presentation describes the energy-harvesting shock absorber as a retrofit device. So it looks like the device could be sold as an aftermarket upgrade and it would not be necessary to redesign the entire vehicle to capture vibrational energy. As for the payback period, it looks like 3-4 years for cars and 1-2 years for trucks and big rigs, possibly even less time for very heavy vehicles. With oil prices below $50 in August 2015, the current payback period might be longer depending on how long the price of gasoline remains depressed. However, in certain places gasoline prices are still relatively high. California has relatively expensive gas, with a gallon near $4 right now while it costs about $2 in other states, and gas also remains relatively costly in Europe at around $7 per gallon. So the energy-harvesting shock absorber might sell better abroad.
It also appears that the energy-harvesting shock absorber could replace standard shock absorbers. This could potentially result in a smoother ride, especially on roads that are not well maintained. So drivers might buy these devices for reasons besides energy efficiency. Low quality roads can also damage vehicles, resulting in higher repair and maintenance costs, and the energy-harvesting shock absorber might be able to help here as well. So using a payback period alone here might not capture the full value of the device. The energy-harvesting shock absorber captures more energy on low-quality roads; at freeway speed, a car could capture 1600 watts on a bad road and 100 watts on a good one, or 400 watts on an average quality road. Fuel efficiency could increase by 1%-5%, depending on typical road quality. This may not only save consumers money, it could help auto manufacturers as well, since their fleets have to meet minimum gas mileage standards which are growing tougher over time. Other fuel efficiency solutions have involved expensive lightweight materials, and energy-harvesting shock absorbers could provide a cost-effective alternative to materials like carbon fiber; on the other hand, a car with a carbon fiber body and energy-harvesting shock absorbers might use even less fuel. Energy-harvesting devices might even work for airplanes as well because of turbulence. Exotic auto body materials can also pose challenges for auto repair shops.
Vibrational energy-harvesting devices don’t necessarily have to be attached to vehicles, either. Stationary devices could harvest energy from train tracks and speed bumps. Lei Zuo tested a vibrational energy-harvesting speed bump device and got much better results than piezoelectric devices and other alternatives, with the device capturing 200 watts at one point. The prototype device used springs and a metal speed bump cover, resulting in a relatively durable device. As with the train track energy-harvesting device, the speed bump energy-harvesting device could help road designers get around the limitations of the grid. To set up a traffic signal far away from cities and power plants, electricity would need to be transmitted over a long distance, which would not be efficient; energy-harvesting devices could be used to power traffic signals in remote locations, increasing safety while keeping costs and electricity use down.
Energy-harvesting shock absorbers look like a subject to watch. Even if the payback period is 3-4 years for a standard size car, many cars on the road are much older than that with a domestic average of around 11 years. Auto loans often last for longer than 3-4 years as well. The device could be even more attractive for big rigs and trucks because of the shorter payback period, and fleet owners may be able to buy multiple devices at bulk prices. With benefits for both auto manufacturers and consumers, adoption of energy-harvesting shock absorbers could be relatively fast as well.