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Sun power can work, but more is needed

ESPOO, Finland – Nokia’s research project on phone charging using harvested solar energy has now been completed. So can the sun be relied on to charge your phone?

Nokia is continuously searching for improved energy efficiency and more sustainable alternatives for mobile phone users. The solar energy project was designed to assess the viability and ease of solar charging for mobile phones. The idea was also to look at the possibilities for phone charging in conditions where it’s not possible to plug in to recharge the phone, or where the electricity supply is uncertain.

So what did we exactly do? We started with developing a prototype phone for the project featuring a solar charging panel integrated in the back cover for harvesting solar energy. The phone was tested last summer by a team of five people in a range of different environments. Two of the phones were tested up north at the Arctic Circle, one in southern Sweden and one in Kenya, and the fifth member of the test team was sailing in the Baltic Sea.

We wanted to do this project as openly as possible and in real time, and so we set up a blog (Nokia Solar Charging) for it. It enabled readers to follow what the testers were doing and to see the project’s progress and results, as well post comment on the progress. Along with the test reports, around ten technical articles on solar energy and its use were published on the blog. The idea was to boost people’s interest and expand their knowledge of the subject.

The test kit

Amount of charge depends on many factors

The tests showed that charging a mobile phone by simply using a solar charging panel on the back cover is possible but challenging.

When carefully positioned, the prototype phones were able, at best, to harvest enough energy to keep the phone on standby mode but with a very restricted amount of talk time. This means there’s still some way to go before a workable and care-free solution is achieved. The most substantial challenge is the limited size of a phone’s back cover, which restricts the extent to which the battery can be charged. What’s more, to ensure mobility, it is essential that the phone’s weather protection doesn’t cover the solar charging panel.

The amount of charge generated for use by the phone is not solely dependent on the weather conditions and the amount of sunlight. Factors such as lifestyles and the angle of light also have a significant impact on the amount of charge generated.

The greatest amount of charge was generated in Kenya, as there was no shortage of sunlight and the phone tester, Amos, who works as a security guard, was often stationary. From the energy profile of his phone, we could see that he’s an active phone user, listening to the radio and making a lot of calls.

On the Arctic Circle, by contrast, the amount of sunlight depends very much on the time of year. But even during the light summer months, the sun’s angle is relatively low, which means a lot of shadows. If the user is frequently on the move, the phone will receive a fairly low charge. Nevertheless, a test record was achieved at the Arctic Circle, as the tester, Ilkka, was able to move his phone from one side of the house to another to track the summer sun as he got on with his house-building work.

Reasonably good results were also obtained when the tester was able to carry the phone while moving around outdoors, for instance in a holder around his neck. However, this isn’t necessarily the most stylish or convenient arrangement, and another solution is needed.