Citrus Clock by Anna Gram
Citrus clock created by Anna Gram runs on the energy of a lemon, which powers it for a week or longer. The somewhat magical dimension of the operation is in fact simple electrolysis, like a conventional electric battery. Technically, it’s almost the same principle than Mr Volta used to invented the battery in 1799: an electrolysis of zinc and coper (the plug under the lemon) in an salted or acid liquid (the lemon). The oxidation phenomenon create the electricity. Anna Gram call that a pedagogic project because the aim is obviously not to replace our actual clocks, but at least to help people think (or remember) about nature and energy.
Source: Anna Gram