The organization said the 14 metre-boat produced 2,000 kilowatt hours of solar energy during its voyage thanks to a roof of photovoltaic panels mounted above the twin-hulled design.
The solar energy was used to power the boat's electric motors and any surplus was stored in batteries, allowing it to travel at a constant speed of five to six knots (10 to 12 kilometres an hour) day or night, the group's website said.
The group said this shows the crossing can be made entirely without fuel, a claim which could not be independently verified.
"This proves that in our modern society it is indeed possible to travel the world efficiently and still safeguard the environment," said the boat's skipper, Michael Thonney.