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How trillions of tiny solar panels could power the internet of things
This article by , βLecturer in was originally published on . Read the .
It could herald a great leap forward in the way we live our lives. The , the idea that objects can be interconnected via a global network, will run your home, keep you healthy and even check how much food is . It will mean being installed around the world by 2020. But whatβs going to power these devices?
In some cases, the energy source is obvious: sensors in fridges or traffic lights can simply tap into mains electricity. But itβs much trickier to power something that detects water quality in remote reservoirs, cracks in railway lines, or whether a farmerβs .
Organic Solar cells: image courtesy of Iwan Saunders Jones.Organic solar panels might be the answer. Theyβre cheap, and are flexible enough to power minuscule sensors whatever their shape. The cells can be just β around a 50th the width of a human hair β but they are able to absorb a huge amount of light for such a thin surface.
These (OPVs) differ from silicon solar cells as they can be made entirely from specially-synthesised organic materials, which are deposited onto cheap substrates such as , a form of polyester also used in soft drink bottles and crisp packets. This material is lighter, more flexible and can even be tuned to provide different colours β who said solar cells have to be plain black?
Critically, it takes for OPVs to earn back the energy invested in their manufacture, known as the βenergy payback timeβ, which compares to for regular silicon solar cells.
Organic photovoltaics can also be moulded onto 3-D surfaces such as roof tiling or even clothing. In our , colleagues and I demonstrated that this makes them more effective at capturing diffuse or slanting light. This wouldnβt make much difference for a regular solar farm in a sunny country, but cloudier places at higher latitudes would see benefits.
For the internet of things, however, these improvements are a game-changer. Few of those trillion sensors will be placed conveniently in the sunshine, facing upwards; far more will be in unusual locations where light only falls indirectly. Tiny organic solar cells will enable energy to be captured throughout the day, even indoors or when attached to clothes.
From billions to a trillion
Thereβs no denying the huge need for such a technology. The βtrillion sensorsβ figure at first seems outlandish, but consider the fact that a typical smartphone, for example, possesses that measure light, temperature, sound, touch, movement, position, humidity and more. More than will be sold this year, so thatβs 10 billion new sensors just in phones. And not all smart sensors are confined to smartphones, of course; they are already routinely used in personal care, environmental monitoring, security and transport.
Whatever the exact numbers, we can assume that many, many more sensors will be deployed in future and their complexity and usefulness is growing exponentially. My colleagues and I at ΒιΆΉΝψ are interested in how we could power them all, which is what led us to organic solar.
Though engineers will always try to reduce energy consumption through better design and putting sensors to βsleepβ when they are not required, even ultra-low power sensors still . Poorer quality sensors might use considerably more.
Now assuming the βaverageβ sensor actually consumes 5mW per measurement, and assuming one measurement is made every minute and takes 30 seconds to complete, this average smart sensor will need 22 Wh (watt-hours) in a calendar year. On itβs own, this is not a substantial value and equivalent to running your TV for about five minutes.
But it all adds up. Based on this simple analysis, 1 trillion sensors will use 21,900 Gigawatt hours (GWh) per year. Thatβs an incredible demand on electricity grids, equivalent to the combined output from a few typical nuclear power plants. This is all before considering the extra demand needed by data centres to handle and store such large sums of information.
Yes, low-power electronics will be developed that should reduce the amount of energy that the sensors need. But, for long term operation, many sensors canβt rely upon an internal battery, as a battery has a finite energy store. This is particularly pertinent as many smart sensors may be placed in remote locations, often far from the electricity grid or without a power connection.
Therefore we must create smart sensors that can harvest their own energy from the local environment β and itβs here that organic solar technology will find its niche.
Publication date: 9 November 2015