Some of London's iconic red telephone boxes are being transformed into free solar-powered mobile phone charging stations painted green.

The first "Solar-box" was unveiled Wednesday on Tottenham Court Road, with support and funding from the Mayor of London, as a pilot before turning more traditional phone boxes green early next year.

The solar paneled phone boxes provide a clean, carbon-neutral source of energy for phones, tablets, cameras and other devices. Costs are covered through in-booth advertising space enabling the public to power-up free of charge.

"It's fantastic to see our young entrepreneurs already up and running with this brilliant idea," said Mayor Boris Johnson. "In our modern world, where hardly any Londoner is complete without a raft of personal electronic gizmos in hand, it's about time our iconic phone boxes were updated for the 21st Century, to be more useful, more sustainable, and just as striking with a marvelous new green makeover."

Co-founder of ‘solarbox' Kirsty Kenney said, "Our idea was born out of our interest in the use of public space and renewable energy and is all about providing a service that people really need… Phone battery life just can't keep up with the pace of our modern lives."

"It's been an amazing journey, from winning in the competition, to now be bringing our first ‘solarbox' to the streets of London, and we can't wait to expand with more green boxes across the capital in the new year."

London's rapidly growing low carbon goods and services sector is worth around £25 billion a year to the UK economy, and employs over 160,000 people. The Mayor's Low Carbon Entrepreneur competition invites student entrepreneurs to generate and pitch their carbon-busting business ideas to a panel of expert judges.

The 2015 competition, once again sponsored by Siemens, will take entries from 20th October this year, closing in mid-February next year ahead of the grand final at the end of March 2015.