OK, this is more fun than useful - but it IS fun: a dance club with a floor that converts some of the dance energy into electricity!
From the Daily Mail:
"... The brainchild of 35-year-old property developer Andrew Charalambous, aka Dr Earth, Surya has its own wind turbine and solar energy system....
The dancefloor uses the concept of piezoelectricity, where crystals and ceramics create a charge to generate electricity.
'We estimate that if you had loads of clubbers dancing vigorously it would provide 60 percent of the club's energy needs,' said Mr Charalambous." ..."
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