Of course these aren’t the only drains on a battery. Modern smartphones pack everything from small accelerometers to energy hungry global positioning systems. And then there is the display - the whole selling point of the smart phone is the interface that lets you access the world wherever you are. Until researchers can develop electronic-inks similar to these used in the Kindle e-book or other pixelated passive systems that refresh as fast as lit screens, simply viewing the phone comes at a substantial cost.
The obvious solution would be to pack in a bigger battery, but of all the components in your handset, the battery is the one that represents seriously mature technology. Most of the electrochemistry was laid down a hundred years ago and, as one battery manufacturer confessed to me, there's little they can do about. The introduction of the rechargeable lithium-ion battery in the 1990s was something of a step change. But since then … well, while virtually every other phone parameter doubles in a year or two, it takes a decade to double battery performance.
There are ongoing efforts to improve battery technology (See: Charging Tomorrow’s smartphones) but there may also be another route: harvesting energy from the environment.
Solar power is long-established, and has been tried many times with mobile phones, but has failed largely because of inconvenience. As the front of phones is crowded out with buttons, photovoltaic cells have largely been put on the back – but that has required turning a phone upside down to keep the battery charged.
But the form of the modern smart phone, freeing up the top face, has changed all that. And one potential solution is on display at this week’s Mobile World Congress in Barcelona this.
WYSIPS (“What You See is the Photovoltaic Surface”), as it is known, is a joke, according to Francis Robcis, sales director for the new product. “Because you can’t see it,” he explains.
And it needs to be like that, because WYSIPS has silicon solar cells embedded within the large smartphone display.
“Go into the office, and most people will leave their phones lying around with the face up,” says Robcis. So that when the set is idle, the tiny silicon strips (too small to see) are busy recharging the battery.
The challenge has been to integrate the photovoltaics into the display without dimming the image by more than 10 per cent – a reduction users should find acceptable. And to allow it to sit alongside the touchscreen function. If the system takes off, the future mobile screen could become a busy place.
The company hopes to have a pilot line producing screens by the end of the year, to prove the technology is viable.
Powering by sunlight, of course, is conventional, even if unfamiliar in mobile phones. At the University of Washington Seattle, ex-Intel researcher Joshua Smith is planning something much more radical: powering mobile phones - with gratifying circularity - by radio waves.
His lab, funded by tech giants Intel and Google, has already made great strides. “The largest TV towers in the US put out around a megawatt of energy,” Smith explains. “We’re able to operate our energy harvester as much as 30 km from one and get small but usable amounts of energy.”
In essence, harvesting radio energy requires rewiring the phone antenna to extract not the signal but the power of the carrier wave. And it’s not only powerful TV transmissions that you can tap into. Recently, Smith’s lab has been able to harvest energy from mobile phone masts.
The quantities available are down in the microwatt range, so not enough to power voice transmissions. But enough energy can be accumulated, Smith says, to send short texts, or just to stretch the battery life.
“It would be enough to have perpetual standby. My favourite example is driving along in my car. My son is playing Angry Birds on the cell phone, and completely drains the battery. And then I get a flat tyre. It would be nice if I could send an emergency SMS using this ambient energy. And of course, compared to solar power, you could even do it at night.”
All of which means that the daily ritual of recharging your phone could soon be a thing of the past.