A race is under way to unlock one of the world’s biggest untapped sources of clean energy—the ocean—with China emerging as an important testing ground. That could heighten competition with Western companies, especially if Chinese businesses begin using technologies developed with joint-venture partners to expand rapidly. The European Union so far has led efforts to harness the sea to make electricity, for which there are three principal techniques: underwater turbines that draw power from the ebb and flow of tides, surface-based floats that rely on wave motion and systems that exploit differences in water temperature. The world’s first commercial, grid-connected tidal-flow generator was installed in Northern Ireland in 2008. Germany’s AG , a big investor in wave and tidal power, predicts that tidal currents alone could someday power 250 million households world-wide. France’s SA also is developing the technology. But with 11,000 miles of coastline rich with energy […]