Finally, boffins have found something useful to do with sprouts at Christmas: they've turned the evil vegetables that are only willingly eaten by those who really shouldn't into a power source for Christmas lights to promote a popular kids science-and-technology fair.

Shown off on the South Bank in London today, the stunt sees a tree with 100 high-efficiency LED bulbs attached to the sprout-filled battery (above). The battery is filled with 1,000 sprouts across five 'cells', with copper and zinc electrodes stuck through each spout. This generates a current beween the electrodes – providing a total of 63 volts to a capacitor that feeds the tree, according to the organisers.

A display at the top of the battery shows how much power has been produced.

The lights have been turned on by children from the City of London Academy in Islington (below).

The stunt is to promote the Big Bang Fair, which aims to inspire children and teenagers about science and engineering. It takes place from March 13-16 2014.