Energy scavenging: Cros srail leads the way

The potential of waste energy is particularly significant in urban areas, where other sustainable energy sources such as wind power are not viable on a large scale. London-based start-up Moya Power is tapping into this potential by creating piezoelectric textiles capable of scavenging waste energy from their surroundings. 

Moya’s approach is one of the first energy scavenging technologies to be used in London where it is being incorporated into Crossrail, a massive railway network that will span the city. If successful, it’s hoped that the technology can be rolled out in a number of places, including under bridges and on skyscrapers.

Moya Power’s piezoelectric textile technology was developed by Charlotte Slingsby during her two-year PhD at the Royal College of Art and Imperial College London, but she says the original inspiration came from South Africa.

“I am from South Africa and the needs for energy are very evident and those needs come in many different shapes and forms,” says Slingsby. “Through that I started to explore alternative sources of energy that maybe are overlooked, and how we would need to adapt and change the designs to make sure we actually harness them.”

The piezoelectric effect is the ability of certain materials to create a charge when under pressure or bent. It was first discovered in 1880 by Pierre and Paul-Jacques Curie and is used in a host of applications, for example pickups on guitars.

“Piezoelectric films are used in lots of different applications like robotics,” says Slingsby, “but more as a sensor of movement because when you bend it, it generates an electric impulse”.

 Due to the low energy yield, however, piezoelectricity isn’t used to generate grid-scale power. But by combining thousands of strips of these filaments, Slingsby discovered that they can be used as an effective way to gather wasted energy. Inspired, she developed lamellae-covered plastic sheeting covered in thousands of strips of film that can be blown and bent in the wind to harvest the expended energy.

“Embedded in the filaments is flexible piezoelectric film, which converts strain or bending energy into electricity,” says Slingsby. “That's a direct process, and then of course the additional work that needs to be done to actually gather all these little bits of energy efficiently and be able to use it and store it.”

The technology is specifically designed to easily fit into small or difficult spaces to capture wind energy. “It looks a little bit like a furry sheet of plastic or like blades of grass,” explains Slingsby. “You can take those flexible sheets and stick them on an existing surface and then when the wind hits it, it makes it kind of vibrate and flutter, and that directly generates electricity.”

 Piezoelectric sheets generate a relatively low amount of energy, at about 10% per square metre less than a solar panel. But Slingsby is clear that they’re not intended to compete with solar panels or wind turbines, but to work with them.

“It has great potential, especially looking at city spaces, because we have so much wasted surface area,” says Slingsby. “Even if I don't have the most efficient product, it's making use of space that is not actually used, that compensates for any inefficiencies or the fact that it can't directly compete with other types of products. We're a very different type of product that is looking at the potential of being able to capture energy right where you need it, when you need it.”

With greater numbers of people drawn to cities and urban areas themselves expanding to cope with the influx, predictions indicate that by 2050, 66% of the world's population will live in cities. This poses a problem for energy companies, which will have to keep up with the increased demand.

Currently, most cities rely on large-scale energy sources such as coal-fired power plants, which lie outside of city limits. But to meet future needs and also decarbonise, new, distributed networks of energy sources will need to be found.

 “Sustainable, environmentally benign energy can be derived from nuclear fission or captured from ambient sources,” says the Institute of Physics on its website. “Large-scale ambient energy (e.g. solar, wind and tide) is widely available and large-scale technologies are being developed to efficiently capture it.

“At the other end of the scale, there are small amounts of ‘wasted’ energy that could be useful if captured,” it continues. “Recovering even a fraction of this energy would have a significant economic and environmental impact. This is where energy harvesting comes in.”

As such, energy harvesting, also called scavenging, is expected to become increasingly important as every small bit of energy is needed to support the development of sustainable cities.

In 2017, Moya Power began a pilot project with Crossrail, covering the walls of train tunnels with the furry piezoelectric sheeting. “The example of the tunnel is really exciting because you have so much surface area even if you just looking at the stopping distance of the train,” says Slingsby.

If the project is successful, there is scope for it to be rolled out across the London Underground network. “It’s a really small gap between the train and the tunnel, you can't fit much in and you've got existing tunnels that have already been built, so you need something that can be retrofitted into existing situations,” Slingsby explains.

“So with the fabric, which is really thin and flexible, you can start looking at the space; a space that didn't need to consider it while it was being built, and look at reinforcing it now with an energy harvester.”

Further development and research is currently underway to help refine the solar scavenging technology. “It really is about taking the time and process to find these exact scenarios where all the research and development can be directed so we have a final product that really takes advantage of one scenario instead of trying to adapt to everything, to all the temperamental weather conditions,” says Slingsby.

“The most important thing is that you keep in mind that the product can be really easy and cost-effective to produce so that you really can apply it in scale. It's always about efficiency while keeping in mind development for mass manufacture.”