Off the western coast of Scotland, on the Isle of Islay, science teacher Ray Husthwaite turns on the light in his classroom.

The electricity comes from a power cable that runs to the mainland.

But it also comes from the ocean.

A few miles from the school, wave action compresses and decompresses air in a chamber. The moving air powers a turbine, which generates electricity.

“It is pleasant, on a choppy but sunny day, to sit beside the gray, concrete structure and listen to the rising and falling of the waves, driving air through the turbines like the breath of a great sea monster,” Husthwaite said. “It seems insane to me to be investing in nuclear power stations and gas turbines when there are endless, free energy resources in the rivers, oceans and the wind.”

In a world addicted to fossil fuel, turning waves into watts might seem far-fetched. But as the U.S. and other countries look for alternatives to oil, natural gas and coal and try to curb global warming, ocean power gradually is joining the ranks of wind and solar power as a source of renewable energy.

Pacific Gas & Electric Co. caught the wave last month when it became the first California utility to file for permits to study the promise of sea power, a nonpolluting but expensive and mostly untested way to take energy from the ocean.

PG&E’s proposed projects could provide electricity for tens of thousands of homes, said Keely Wachs, spokesman for the San Francisco-based utility. “More importantly, it’s clean and totally renewable.”

PG&E joins a global list of organizations experimenting with harnessing ocean power. In less than three years, U.S. energy regulators have received nearly five dozen applications for water-related energy projects from South Florida to Washington state.

Islay’s wave-power converter, the Limpet 500, has been operating since 2000. In Hawaii, the Navy has been churning up electrons with the help of a floating buoy. And in Portugal, engineers are installing snakelike tubes designed to convert the sea’s motion into electricity.

“We’re going to decide one way or another to displace the use of fossil fuel by clean fuel,” said Roger Bedard, ocean energy leader at the Electric Power Research Institute, a utility industry think tank in Palo Alto, Calif. “And our grandchildren are going to understand the consequences of that decision.”

Anyone who has ever been slammed to the sand by a wave can attest that the ocean packs tremendous power. Technology can harness that energy in several ways. Some designs, like the Limpet, use waves to push air through a column. Others convert the sea’s up-and-down motion into mechanical energy.

While U.S. regulators categorize wave power as hydropower, it differs from other methods of generating energy from water. Tidal power, for instance, relies on the gravitational force of the sun and the moon to provide energy. Wave power is less predictable than tidal power, but experts consider it more potent.

The California Energy Commission estimates that the state’s 1,100-mile coastline could generate seven to 17 megawatts a mile, enough power per mile to serve as many as 13,000 average homes. One wave-power company executive told a congressional committee last year that several hundred square miles off the California coast could supply the electrical needs of all of the homes in the state.

The allure of wave power is so strong that the number of organizations filing for permits has surged, causing the Federal Energy Regulatory Commission to get tough on applicants.

“We label it as a stricter-scrutiny approach,” commission spokeswoman Celeste Miller said. That means more frequent progress reports and greater consultation with federal, state and local agencies are required.

Although wave power does not create pollution, that doesn’t mean environmentalists and others don’t have concerns. Questions have been raised about potential harm to marine life, the coastline, fishing and boating operations and ocean views.