As solar and wind power grow, another renewable energy source with vast potential — the power of tides and waves — continues to lag far behind. But progress is now being made as governments and the private sector step up efforts to bring marine energy into the mainstream.

After years of fitful starts, the Pacific island nation of Kiribati this month banned all commercial fishing inside its huge marine reserve. New satellite transponder technology is now helping ensure that the ban succeeds in keeping out the big fishing fleets.

Despite daunting challenges, technology to harness the power of the waves and tides is now being deployed around the world from Portugal to South Korea to New York’s East River. These projects, just beginning to produce electricity, are on the cutting edge of renewable energy’s latest frontier: hydrodynamic power.