Monday, March 11, 2013
Send a text message to charge your cellphone
New Scientist reports: [edited]
AT THE Konokoyi coffee cooperative on the edge of Uganda's Mount Elgon national park, Juliet Nandutu is trying out a new toy: a solar-powered cellphone charging station that is activated by text message. She is offering the service to her village. "I charge 18 phones a day, sometimes 20," she says.
How many phones she charges depends on the local electricity supply. When it's there, people can charge their phones at home, but that's not very often. "It's not so reliable," she says. "It's on and off."
A patchy or absent power grid poses a conundrum for rural areas in the developing world, particularly in Africa and Asia, where the use of cellphones is rapidly rising. Farmers, for instance, use cellphones to get up-to-date pricing information for nearby and distant markets, allowing them to better manage the sales of their crops.
In Kenya, people without access to banking services exchange money using their phones. Still, an estimated 500 to 650 million cellphone users are off-grid. Now London-based company Buffalo Grid and its portable charging station is hoping to step into the gap.
The lack of access to grid power means that people have to trek for kilometres to a nearby town to find a charging station, powered by diesel generators or solar panels. More importantly, it's not cheap. In Uganda, charging a cellphone can cost 500 Ugandan shillings, or about $0.20. That's a huge burden for those who earn less than a dollar a day, especially when you have to charge the phone two or three times a week.
Rural areas need stronger signals from cellphones because there are fewer cellphone towers nearby, a further drain on power. "In rural economies, about 50 per cent of the money spent on mobile phones is actually spent on charging them," says Buffalo Grid's Damon Millar. "That is some of the most expensive electricity in the world."
Buffalo Grid's basic technology, which was recently trialled in Uganda, should help cut those costs. A 60-watt solar panel charges a battery that is taken to the village on the back of a bicycle. The battery extracts power from the solar panel using a technique called maximum power point tracking (MPPT). A solar panel's power output is dictated by environmental conditions, such as temperature and the amount of sunlight, as well as the resistance of the circuits connected to it. MPPT monitors the conditions and changes the resistance to ensure the maximum possible power output at any given time.
The innovation lies in how the stored power is released to charge a phone. A customer sends a text message, which in Uganda costs 110 shillings, to the device. Once it receives the message, an LED above a socket on the battery lights up, indicating that it is ready to charge a phone.
At the Konokoyi coffee cooperative, each text message allows a phone to be charged for 1.5 hours. A fully charged Buffalo Grid unit can last for three days, has up to 10 charging points and charges 30 to 50 phones a day.
To bring the cost down further, Buffalo Grid hopes to co-opt the cellphone network operators into subsidising power for charging the phones, or even making it free. What's in it for the network operators? "When you bring power to phones that don't have any, people will use them more," says Buffalo Grid's Daniel Becerra. "Instead of paying for the charge, people will spend more on airtime."