Organic solar panels : a smarter way to a truly brighter future:- Research

IT COULD herald a great leap forward in the way we live our lives. The internet of things, 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 in your fridge. It will mean a trillion new "smart sensors" being installed across the world by 2020. But what’s going to power these devices?

In some cases, the energy source is obvious: sensors in fridges or traffic lights can tap into mains electricity. But it’s trickier to power something that detects water quality in remote reservoirs, cracks in railway lines, or whether a farmer’s cows are happy and healthy.

Organic solar panels might be the answer. They’re cheap, and are flexible enough to power minuscule sensors, whatever their shape. The cells can be just two micrometres thick — about a 50th the width of a human hair — but they are able to absorb a huge amount of light for such a thin surface.
These organic photovoltaics differ from silicon solar cells as they can be made entirely from synthesised organic materials, which are deposited on to cheap substrates such as PET, a form of polyester used in soft drink bottles and crisp packets. This material is lighter, more flexible and can be tuned to provide different colours — who said solar cells have to be black?
Critically, it takes just one day for organic photovoltaics to earn back the energy invested in their manufacture, known as "energy payback time", which compares to about one to two years for regular silicon solar cells.

Organic photovoltaics can also be moulded on to 3-D surfaces such as roof tiling or even clothing. In our latest research, colleagues and I demonstrated that this makes them more effective at capturing diffuse or slanting light. This wouldn’t make much difference for a regular solar farm in a sunny country, but cloudier places at higher latitudes would get benefits.
For the internet of things, however, these improvements are a game-changer. Few of those trillion sensors will be placed in the sunshine, facing upwards; far more will be in unusual locations where light falls indirectly. Tiny organic solar cells will enable energy to be captured throughout the day, even indoors or when attached to clothes.
There’s no denying the huge need for such technology. The "trillion sensors" figure at first seems outlandish, but consider the fact that a typical smartphone possesses about 10 smart sensors that measure light, temperature, sound, touch, movement, position, humidity and more. More than a billion smartphones will be sold this year, so that’s 10-billion new sensors just in phones. And not all smart sensors are confined to smartphones; they are already used in personal care, environmental monitoring, security and transport.

Whatever the exact numbers, we can assume that many more sensors will be deployed in future and their complexity and usefulness is growing. My colleagues and I at Bangor 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 "sleep" when not needed, even ultra-low power sensors still consume about 3.5mW (milliWatts) per measurement. Poorer quality sensors might use much more.
Now, assuming the "average" 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 22kW/h (kilowatt-hours) in a calendar year. On its 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 21,900GW/h per year. That’s a big 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.
Low-power electronics will be developed that should reduce the amount of energy the sensors need. But, for long-term operation, many sensors can’t rely upon an internal battery — a finite energy store.
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 — and it’s here that organic solar technology will find its niche.

• Jeff Kettle lectures in Electronic Engineering at Bangor University, Wales. He is funded by the Wales Ireland Network for Innovative Photovoltaic Technologies. This article first appeared in The Conversation