The piezoelectric effect has been known since 1880 but it is only since the 1990s that piezoelectric energy harvesting – in which energy is extracted from a mechanical stress – has attracted growing serious interest. However, the efficiencies are generally low and the output is small. While there is a variety of potential applications under investigation, such as embedding piezoelectric materials into roads or pathways to generate energy from the pressure of vehicles moving or people walking, these technologies are still very much in the development stage and some years off commercial application.
But that may be about to change with a new concept from Dutch architect Janjaap Ruijssenaars named ‘gravity energy’. Mr Ruijssenaars' mechanism, which is patent pending in the Netherlands with an option globally, requires perpetually unbalancing a weight to release energy.
"Intuitively, I thought that gravity must have something to offer, given that everything is drawn to earth,” explains Mr Ruijssenaars. “By unbalancing a weight at the top that is only just stable using little force, a large force is created at the bottom at a single point. The idea was that this should yield something."
The gravity-piezo concept
In an interview Mr Ruijssenaars explains the concept as akin to an upside down pendulum, which is unbalanced with an electric impulse and then rebalanced, while also generating a current, with the gravity-driven piezo material. Repetition of the cycle enables the generation of energy with an efficiency estimated as high as 80%, he says, pointing out that as an input energy is required it is not as some people have inferred a perpetual motion device.
At this stage the concept is still on paper but within weeks the all important proof-of-concept model is anticipated, which thereafter will be scaled up – closely watched by the number of companies and investors who have expressed interest in it.
Other participants in the development include the Dutch engineering firm VIRO, which could also be a potential manufacturer of a commercial product line, and environmental consultants Tauw.
“Ruijssenaars literally turned the [piezo] method on its head, as a result of which we, as scientists, have started to look at this method in a new light,” says Theo de Vries, system architect and senior lecturer in the Robotics and Mechatronics group at the University of Twente and a consultant at VIRO. “Everything that is currently offered as mechanical energy will actually be useful, thanks to the invention.”
Mr Ruijssenaars says that at this stage the potential for the invention has yet to be determined, but he believes – and his goal to develop – a domestic level product should be the commercial starting point, whether this is a charger for phones or a generator for lighting.
“Like Tesla’s discovery of the relation between electrical current and magnetism more than 100 years ago but only recently have we had wireless phone chargers, we don’t know what all the outcomes will be and at this stage the principle is more important.”
Nevertheless, he says the development group has “started to look at some numbers” and for example a residential generator should be feasible at a size of less than 1m3 with potential for roof or indoor mounting.
Gravity for energy
The concept of using gravity for energy isn’t new and for example, astronomers have long pondered the idea of tapping energy from black holes. But given the challenges of harnessing and integrating the sun’s power that is very far into the future.
Coming closer to home an example is the UK startup Deciwatt, which is developing the GravityLight that generates light from gravity. The system utilises a 12kg weight, which is lifted and when released covers a 1.8m drop at a rate of about 1mm/s. This drop powers a drive sprocket, which rotates very slowly with high torque. Via a polymer gear-train this input is converted into a high speed, low torque output that drives a DC generator with an output of just under 0.1W to power an onboard LED and ancillary devices. Once the weight reaches the bottom, it is simply lifted to repeat the process.
The GravityLight is intended for households that lack electrification. With the increasing efficiency of LEDs, the light produced is claimed over five times brighter than a typical open-wick kerosene lamp while also mitigating the attendant safety and health hazards.