IDG News Service — Charging a mobile phone by simply using a solar charging panel on the back cover is possible but challenging, Nokia has concluded after ending a research project on the subject.

There's still some way to go before a workable and care-free solution can be achieved, according to Nokia. When carefully positioned, prototype phones developed by the company and tested as part of the project were able, at best, to harvest enough energy to keep the phone on standby mode but with a very restricted amount of talk time, Nokia wrote in a blog post on Tuesday.

The biggest challenge is the limited size of a phone's back cover, which restricts the size of the panel and the extent to which the battery can be charged, according to Nokia.

Reasonably good results were obtained when carrying the phone while moving around outdoors, for instance in a holder around the neck. However, that isn't "the most stylish or convenient arrangement, and another solution is needed," Nokia said, without proposing what that could be.

The best test results were achieved in Kenya. Nokia's prototype was also tested in southern Sweden, at the Arctic circle and on the Baltic Sea.

Charging mobile phones using sun rays isn't a new concept. For example, Nokia launched what the company contends was the first solar-powered phone back in 1997.

More recently, vendors such as Samsung Electronics and LG Electronics introduced smartphones with a solar panel on the back cover. The Samsung S7550 Blue Earth and LG GD510 Pop were both announced in 2009.

The vendors thought they would be able to capitalize on public interest for environmentally friendly products, according to Francisco Jeronimo, research manager at IDC. But consumers were not willing to pay more for the addition of a solar panel, and the technology was and still isn't mature enough to go mainstream, he said.

Still, in parts of the world where electricity is a scarce resource it makes sense to use solar power, even though the technology is far from perfect, according to Jeronimo.

American inventor Charles Fritt is credited with creating the first working solar panel back in 1883, according to Nokia. Fritt coated the semiconductor material selenium with an extremely thin layer of gold, creating a panel with just 1 percent efficiency, it wrote in a blog post last year.

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