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January 23, 2012

Sun kissed or missed: Why’s it so tough to make a solar powered mobile?

The sun has been used to power gadgets since 1834 when British astronomer Sir John Herschel invented a solar thermal collector box to cook food. It’s hardly surprising solar power has such a long history when you discover how much energy that great ball of fire produces. In one second, enough to meet the needs of the entire planet for 500 000 years! Why, then, are we still waiting for a truly solar powered mobile device? To find out, we spoke to Technology Manager and Nokia solar power guru, Matti Naskali.

Mobiles are hungry for power

First off, to understand the challenges we need to get a clearer idea of how much power a mobile phone needs to work and how much the current solar panels can produce.  “Think about a solar powered watch,” Matti says. “It consumes about 1 microwatt (µW) of power. A mobile phone needs ten thousand times more energy just to stay on with a blackened display. Yet, when you leave your solar watch indoors, it still stops running. So, to have any chance of a functioning mobile phone, you have to make sure it’s constantly kept in the sun and that it’s incredibly efficient at catching the sun’s rays.

The price isn’t right

Which brings us to the next challenge. The cost of solar panels. To have the same charging speed as a solar watch, we need 10000 times more power just to be on par with standby power consumption. “ With the solar panel area available on a device,” Matti says, “we can generate just enough power to charge a simple mobile phone like the Nokia C1-02. As long as it’s not used much and it’s kept mostly in the sunshine. This would be an ideal commercial option for sun-kissed developing countries, where people currently use less sophisticated mobiles. The problem is, even a small solar panel still costs much more than other kinds of chargers.”

Back to basics  

Will we never see a truly solar powered mobile, then? To answer that question, Matti recently led a research project to find out in what part of the world and in what circumstances, a solar powered mobile might be viable. With a prototype called Lokki, Matti and his team were able to measure how well a Lithium-ion battery was charged by the sun. And the results? “A basic phone can operate with solar power if the consumption is low and if it is exposed to sun for extended periods,” Matti says. “After a good harvesting day, an hour of talk or radio play was possible. However, this did require a full day’s exposure to the sun.”

Sundown for smartphones

However, when it comes to power consumption, there’s a massive difference between a power guzzling smartphone and a basic mobile, such as Nokia X1-01. Even a super efficient smartphone like the Nokia Lumia 800 will drain in a couple of days, while the Nokia X1-01 lasts over a month on standby. “With Lokki’s 30 cm² area, and a high solar panel efficiency of 20%, the available peak power would be still just 600mW.” Matti says. “In the study, the best we harvested was about 50% of the theoretical maximum.” Unfortunately, it would take days to charge a typical smartphone battery like this.

So, if you’re waiting for a solar powered Nokia Lumia, don’t hold your breath. Currently, the only realistic solar charging solution for a smartphone is a large external solar panel that would work like a wall charger. However, if you’re lucky enough to live in a part of the world with constant sunshine and can’t always plug in and load up on electricity, the future could look brighter thanks to solar power.