A project to create electricity using gravity has generated power for the first time at a demonstrator site in Edinburgh.

The 15m (49ft) high demonstrator is housed in a tower on the quayside at Leith docks.

The Gravitricity system works by using excess power to raise heavy weights which keep that energy "stored" until it is needed - electricity is generated when the weights are dropped.

It has been designed to be housed in old mine shafts rather than towers and in the UK could go to depths of 750m (2,461ft) - twice the height of the Eiffel Tower in Paris.

But in African countries, where it could be placed in holes specifically built for the job, the depth could exceed 2km (1.2 miles).