MELBOURNE, Australia — Off the coast of Western Australia, three big buoys floating beneath the ocean’s surface look like giant jellyfish tethered to the seafloor. The steel machines, 36 feet wide, are buffeted by the powerful waves of the Indian Ocean. By harnessing the constant motion of the waves, the buoys generate about 5 percent of the electricity used at a nearby military base on Garden Island.

The buoys are a pilot project of Carnegie Wave Energy, a company based in Perth and listed on the Australian Securities Exchange. In late February, the buoys started supplying 240 kilowatts each to the electricity grid at HMAS Stirling, Australia’s largest naval base. They also help run a desalination plant that transforms seawater into about one-third of the base’s fresh water supply.

Renewable energy is not an urgent matter in Australia, given the country’s plentiful supplies of fossil fuels, particularly coal. But Carnegie’s demonstration project is ultimately aimed at island nations that must import expensive fuel for electricity, as well as military bases looking to bolster energy and water security.

“Island nations are all looking to be sustainable,” said Michael E. Ottaviano, chief executive of Carnegie. Wave energy could be a good fit, especially for islands where tropical clouds impede solar power or where wind turbines disturb the aesthetics of tourist destinations.