NASA Jet Propulsion Laboratory (JPL) researchers who developed a new way to power robotic underwater vehicles believe a spin-off technology could help convert ocean energy into electrical energy on a much larger scale. The researchers hope that clean, renewable energy produced from the motion of the ocean and rivers could potentially meet an important part of the world’s demand for electricity.

Other technologies have been developed to turn the energy of ocean currents, tides, and flowing rivers into another kind of power, called hydrokinetic energy. Many of these systems use underwater turbines, similar to those in wind farms. Ocean currents or tides turn the turbines, which generate electricity that can be transferred by cable to shore.

In the proposed hydrokinetic energy transfer system, the flow of water current causes turbine blades to rotate. The rotor’s rotational speed is increased through a gearbox, which drives a high-pressure fluid pump. The high-pressure fluid would be transported though flexible tubes to a larger pipe, and then to an efficient, onshore hydroelectric power plant.
Jack Jones, a JPL engineer, and Yi Chao, a JPL scientist, designed a new kind of underwater hydrokinetic energy system that uses water motion to generate a high-pressure liquid rather than electricity. That liquid is then transported to shore and used to produce electricity on land. The system is a spinoff from a research project to find a new way to power robotic underwater vehicles. “I saw we could extend the lives of these vehicles significantly by harvesting energy from the ocean environment,” Chao said.

In the original project, ocean tides and waves, as well as river flows, would provide the energy source to create a high-pressure liquid. “The trick was to find a special substance known as a phase change material that changes from a solid to a liquid as the temperature in the environment changes from cold to warm,” said Chao. “When the material melts, it expands, compressing a central tube in which another liquid is stored. This liquid, now under high pressure, is used to generate electricity to charge the battery underwater.”

While they were working on this project, the researchers realized that they could employ the same concept — using an environmental pump to generate a high-pressure liquid — to produce electricity from the world’s oceans. In the new system, the high-pressure fluid would be transported though flexible tubes to a larger pipe, and then to an onshore hydroelectric power plant. The stored hydraulic energy can be used to generate electricity when it is needed to respond to energy demand. Most environmentally friendly energy systems produce power intermittently.

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