Powering the Internet of Stuff – by sucking electricity from TREES
Where are my generating wellies?
The Sun has got his (old) hat on
By harvesting standards, Solar energy is old hat. Photovoltaic cells turn sunlight into electricity with limited efficiency but are perfectly adequate if the power required is minimal and the light source consistent. The best example is solar-powered calculators, which have the added advantage of being able to rely on a human to take them out of the shade.
Energy harvesting versus device power consumption. Source: Kamal Shah, Intel
In the Internet of Things solar power is less interesting, as shade can pop up from anywhere and the intermittent supply from light means that harvesting has to charge a battery (or capacitor) to provide a consistent supply.
The other traditional form of renewable energy, wind, is equally useless, as it doesn't scale well. The nature of a circle means that adding 20cm to a 2m turbine blade increases the catchable wind by almost half (4.52sq m compared to 3.14), while removing 1cm reduces the harvested wind by half a square metre*, meaning that tiny turbines are no more than novelties, despite the enormous amount of backing they keep getting on Kickstarter.
Practical energy harvesting needs an alternative supply, but fortunately there are a handful of techniques being developed.
The alternative to alternative energy
First up is piezoelectricity: a flow of electrons generated by squeezing a crystal, turning vibration or other mechanical energy into electricity. The most popular use of piezoelectricity is in sensors, such as a pickup on an acoustic guitar – the vibrations generate electricity which is amplified – but anyone who's used a barbecue lighter (or a posh cigarette lighter) will have pressed a button to generate an electrical spark which comes from a compressed crystal.
Piezoelectricity is also used by the latest generation of light switches, which use power generated from the pressure applied to send a radio signal to the computerised lighting system. Systems such as the Philips Hue lights – multicoloured bulbs controlled from a central hub – can now be wirelessly connected to an energy-harvesting switch.
The Philips switch is really four switches, allowing the user to pre-program four mood settings which can be activated without booting up a smartphone, but the power comes from the action of pressing the switch.
Philips Hue Tap: She'll have to hold it tight, as it's easier to press when on a wall
In use, the control is a little strange. We're used to switches being mechanical, or sensitive to the slightest touch, but the Hue switch clearly needs to be pressed and the firmness with which it needs to be pushed can catch out those unfamiliar with it. If the switch fails to work, the correct behaviour is to push it again – slightly slower and with more pressure – but that is a learnt behaviour and far from intuitive.
It might be a novelty in wireless light switches, where a battery would generally work equally well, but there are other areas where piezoelectricity is the perfect solution, such as monitoring the performance of heavy machinery.