Converting pedestrian footsteps into energy  

Anthill magazine has a look at an ambient energy collection device being trialled in the UK - Switched-on innovation converts pedestrian footsteps into energy.

There’s an interesting post over on Springwise about Pavegen slabs, an eco innovation by UK-based Pavegen Systems, which harvest the kinetic energy from pedestrian footsteps and converts it into electricity.

They look a little bit like floodlights embedded in an astroturf tennis court, but they are designed to be prominent in order to encourage pedestrians to step on them. As Volkswagen demonstrated last year, simple environmental incentives can dramatically alter pedestrian behaviour. Five percent of the energy Pavegen harvests from each step is expended on lighting up its LED — affirmation for the pedestrian that the energy transfer was successful.

The energy can be used to power traffic lights, safety signs and other outdoor ambient items that require electricity. Pavegen slabs have already been trialed in East London, with the developers now seeking investment.

Technology Review also has a look at harvesting energy from motion, in their case via a piezoelectric material called PZT - Flexible Sheets Capture Energy from Movement.

Researchers at Princeton University have created a flexible material that harvests record amounts of energy when stressed. The researchers say the material could be incorporated into the soles of shoes to power portable electronics, or even placed on a heart patient's lungs to recharge a pacemaker as he breathes.

The energy-harvesting rubber sandwiches ribbons of a piezoelectric material called PZT between pieces of silicone. When mechanically stressed, a piezoelectric material generates a voltage that can be used to produce electrical current; a current can also be converted back into mechanical movement.

The rubber material can harness 80 percent of the energy applied when it is flexed--four times more than existing flexible piezoelectric materials.

Flexibility could prove vital if energy-harvesting technology is to take off. For example, the military tested stiff-soled piezoelectric shoes as a power source, but soldiers complained of foot pain. And previous flexible energy harvesters--based on piezoelectric polymers, nanowires, or other types of crystal--put out little electrical current.

PZT is the most efficient piezoelectric material known, but its crystalline structure means that it must be grown at high temperatures, which normally melt a flexible substrate. The Princeton researchers, led by mechanical engineering professor Michael McAlpine, got around this by making PZT at high temperatures and then transferring thin ribbons of the material onto silicone. ...

Proof-of-concept tests described this week in the journal Nano Letters show that the rubber-encased PZT ribbons maintain their high power-conversion efficiency. McAlpine says the simple printing process should readily scale up to make larger sheets; he has filed a patent on the process.

Vibration related energy harvesting also appears prominently in an article about unusual energy technology at Cleantech.com - Renewable energies you don't hear about every day.

Mechanical energy from piezoelectric generators

Israel-based Innowattech has developed a new alternative energy system that harvests mechanical energy imparted to roadways, railways and runways from passing vehicles, trains and pedestrian traffic and converts it into electricity by installing generators beneath a road's asphalt layer.

The company says it ran a successful trial along a ten metre stretch of road and plans to expand the trial to several one-kilometre stretches of road in Israel.

It's not alone. Washington D.C.-based New Energy Technologies claims it's developed something similar (see New device for capturing kinetic energy from vehicles).

Piezoelectrics that recoup energy from spinning auto tires are also being investigated by Silicon Valley-based EoPlex (see Printing up cleantech, towards the end of the story). ...

Motion energy harvesting

Researchers are working to harness energy from movement — such as from walking and natural vibrations in the environment — by using “tunable” devices.

While some devices already exist for converting kinetic energy to electrical energy, they’re limited to a narrow range of motions, or frequencies. But what about technology that could convert a range of vibrations instead of just a narrow band?

Research in this area is going on at Duke university in North Carolina.

Their technology is basically a small cantilever that releases power when strained. It is several inches long and a quarter inch wide, with a magnet on one end that interacts with nearby movable magnets. By changing the distance of the movable magnets, the researchers were able to “tune” the interactions of the system with its environment, and thus produce electricity over a broader spectrum of frequencies.

Motion is also harnessed by M2E Power of Idaho, which is pursuing a batteries for the military that charge themselves by the movement of troops' bodies (see M2E captures $8M with kinetic energy). The objective: Generate power throughout the day so soldiers don't have to carry as many heavy batteries.