But for now, G24's factory in Cardiff, not a city known for its sunshine, remains powered by a wind turbine.

ECONOMIST: A new type of cell may bring ��solar�� energy indoors

G24 confirmed it had been instructed to cancel the parking charge.

BBC: Toys R Us parking firm G24 cancels heart patient's charge

Barrie James, from Torquay, who has had two heart attacks, was charged by G24, a private parking company that runs the Toys R Us car park in Plymouth.

BBC: Toys R Us parking firm G24 cancels heart patient's charge

Despite explaining his circumstances in writing, G24 refused his appeal.

BBC: Toys R Us parking firm G24 cancels heart patient's charge

By changing the composition of the dye, G24's engineers ensure that the maximum sensitivity of the cell coincides with whatever frequency mix is appropriate for the artificial light concerned.

ECONOMIST: A new type of cell may bring ��solar�� energy indoors

Steven Burt, G24's chief financial officer, talks of light-bulb-powered TV remote controls, smoke detectors and computer keyboards. (A non-removable internal battery would store charge for use when the lights are off.) The company already offers prototypes of bags and jackets with photosensitive panels woven in, designed to charge digital cameras and mobile phones, and a hotel in Las Vegas is using G24's products to run its electric window-blinds.

ECONOMIST: A new type of cell may bring ��solar�� energy indoors