A sea-going robotic glider that harvests heat energy from the ocean has been tested by US scientists.
The yellow, torpedo-shaped machine has been combing the depths of seas around the Caribbean since December 2007.
It generates its energy for propulsion from the differences in temperature between warm surface waters and colder, deeper layers of the ocean.
Wax-filled tubes inside the craft expand when it is gliding through warmer water. This heat is used to push oil from a bladder inside the hull to one outside, changing its buoyancy.
Cooling of the wax at depth reverses the cycle.
"Gliders can be put to work on tasks that humans wouldn't want to do or cannot do because of time and cost concerns," said Dr Fratantoni. "They can work around the clock in all weather conditions."
The team which developed the autonomous vehicle say it has covered "thousands of kilometres" during the tests.
clipped from: news.bbc.co.uk 