- 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.
The team which developed the autonomous vehicle say it has covered "thousands of kilometres" during the tests.
The team believe the glider - which needs no batteries - could undertake oceanographic surveys for up to six months at a time.
"We are tapping a virtually unlimited energy source for propulsion," said Dave Fratantoni of the Wood's Hole Oceanographic Institute (WHOi).
But Steve McPhail, an expert in autonomous underwater vehicles at the National Oceanography Centre (NOC), Southampton, said the machine would not totally do away with batteries.
"You still need to provide power for the sensors, for the data-logging system and for the satellite communications system to get the data back," he said.
As a result, the vehicle would have to intermittently return to a ship or shore to recharge its batteries.
"It's always a trade-off between the power used for the propulsion system and the power used for the sensors," said Mr McPhail.
Oceanographers are increasingly looking...