Two Japanese companies have said that they will begin work on the world's first ship to have propulsion engines partially powered by solar energy, which will leave a cleaner plume.

According to a report in New Scientist, Japan's biggest shipping line Nippon Yusen KK and Nippon Oil Corp said that solar panels capable of generating 40 kilowatts of electricity each would be placed on top of a 60,000-tonne car carrier to be used by Toyota Motor Corporation.

The solar panels would help conserve up to 6.5 per cent of the fuel used in powering the diesel engines that generate electricity aboard the ships.

"The ship system is expected to help reduce carbon dioxide emissions by 1 to 2%, or about 20 tonnes per year," said Hideyuki Dohi, general manager at Nippon Oil's energy system development department.

Nippon Yusen will invest about 150 million yen (1.4 million US dolars) in the solar panel system to be designed by Nippon Oil.

Solar panels capable of generating several kilowatts of electricity have been used on large vessels before, but their use has been limited to power for the crew's living quarters.

Solar panels for an average home usually generate 3.5 kW of electricity.

Damage to the panels from salt and vibration are hurdles that remain to be overcome. The ship is scheduled to be completed in December.

According to Nippon Oil executive vice president Ikutoshi Matsumura, "If it's possible, we want to aim for the full commercialization of the system in the next three to five years."