In the waters off the coast of Hawaii, a tall buoy bobs and sways in the water, using the rise and fall of the waves to generate electricity.

The current travels through an undersea cable for a mile to a military base, where it is fed into Oahu's power grid - the first wave-produced electricity to go online in the US.

By some estimates, the ocean's endless motion packs enough power to meet a quarter of America's energy needs and dramatically reduce the nation's reliance on oil, gas and coal. But wave energy technology lags well behind wind and solar power, with important technical hurdles still to be overcome.

To that end, the US Navy has established a test site in Hawaii, with hopes the technology can someday be used to produce clean, renewable power for offshore fueling stations for the fleet and provide electricity to coastal communities in fuel-starved places around the world.

"More power from more places translates to a more agile, more flexible, more capable force," Joseph Bryan, deputy assistant secretary of the Navy, said during an event at the site. "So we're always looking for new ways to power the mission."

Hawaii would seem a natural site for such technology. As any surfer can tell you, it is blessed with powerful waves. The island state also has the highest electricity costs in the nation - largely because of its heavy reliance on oil delivered by sea - and has a legislative mandate to get 100 percent of its energy from renewables by 2045.

Still, it could be five to 10 years before wave energy technology can provide an affordable alternative to fossil fuels, experts say.

For one thing, developers are still working to come up with the best design. Some buoys capture the up-and-down motion of the waves, while others exploit the side-to-side movement. Industry experts say a machine that uses all the ocean's movements is most likely to succeed.

Also, the machinery has to be able to withstand powerful storms, the constant pounding of the seas and the corrosive effects of saltwater.

"The ocean is a really hard place to work," said Patrick Cross, specialist at the Hawaii Natural Energy Institute at the University of Hawaii at Manoa, which helps run the Hawaii test site. "You've got to design something that can stay in the water for a long time but be able to survive."

The US has set a goal of reducing carbon emissions by one-third from 2005 levels by 2030, and many states are seeking to develop more renewable energy in the coming decades.

Jose Zayas, a director of the Wind and Water Power Technologies Office at the US Department of Energy, which helps fund the Hawaii site, said the US could get 20 to 28 percent of its energy needs from waves off the US coasts.