Milena Ristovic, a secondary school teacher in the Serbian capital of Belgrade, suffers from a complaint common to millions around the world. “My battery-hungry devices run out so quickly,” she laments. Sitting on a bench in a busy square in front of a business school in the Zvezdara district, she is plugged in to a solution, however. As she attends to her work emails, her smartphone and laptop are charging, courtesy of an innovative, solar-powered device known as a Strawberry Tree.
The charging station, which resembles a quirky arts installation, made its debut in 2010. A dozen Strawberry Trees are now installed in parks, streets and squares throughout Serbia and the Balkans region. And by the end of the year the concept will have spread to California due to a collaboration with 3fficient, a US company that supports renewable energy products and services. Winner of an EU sustainable energy award, the charging station features WiFi, USB sockets and 16 chargers for various types of mobile phone and other digital portable devices. The energy comes from two photovoltaic solar panels.
The service is free to use at all times of the day and night. Rechargeable batteries in the “trunk” can even allow the tree to function for up to a month without direct sunlight. The first of its kind in the world, the device was developed by a team of young graduates at Strawberry Energy, a Belgrade start-up.
“We had to think about how to make the tree vandal-proof,” says Milos Milisavljevic, Strawberry Energy chief executive. “We decided not to use fragile or thin materials like glass or plastic which could easily be damaged.” The sensitive digital equipment is protected by the trunk, while the solar panels are high enough to be out of the reach of vandals. It is also possible to upgrade the charging stations to reflect technological advances and changing urban needs: “We had to make sure that the tree is not a dead-end product.”
With advances in technology rapidly bringing down the cost of manufacturing photovoltaic cells, solar energy is becoming more cost-effective. In Serbia, the €17,000 cost of each Strawberry Tree has been funded by city authorities, green funds or by corporate donation. Mike Sapien, an analyst at market researcher Ovum, predicts that demand will rise for products such as the Strawberry Tree and the “Soofa”, a type of public solar bench recently installed in the Boston area. Mr Sapien says it might take time for these green innovations to catch on, adding that their growth could be limited in regions where the weather tends to be gloomy. But he adds: “California, on the other hand, is known for its sunshine and love of the outdoors and it is very likely that parks and municipalities will accept this as a great way to provide this public service and limit its cost of supplying power.”
With her phone and laptop charged, Ms Ristovic unplugs her devices and sets off for her next appointment, declaring that it is “exciting to see the benefits of solar power, first hand”.