From the outside, Seatrec’s ocean thermal generator doesn’t look like much. The SL1 is about as tall as a person, 6 inches wide, and has a smooth, nearly featureless black and gray exterior. But it’s what’s inside that counts. The bottom of the cylinder is packed with a specially designed wax that changes its phase depending on the temperature. The wax solidifies when the SL1 lowers itself into the frigid depths of the deep ocean. Then, when the tube resurfaces, the relatively warm water causes its waxy innards to liquify. During the phase change from solid to liquid, the wax increases in volume and raises the pressure inside the tube, which forces a fluid through a generator and creates electricity. All the device has to do to recharge is descend into colder water to resolidify the wax; it can do this by releasing a tether or deflating an internal air bladder.
Over the course of three weeks last February, Chao and his team sent two of the company’s generators on several dives to 3,000 feet beneath the surface while attached to a profiling float. It was only the third time that an SL1 had ever been deployed in the ocean, and the submersible generators were going hundreds of feet deeper than they had on previous dives. Yet they still managed to generate enough energy to power many types of research tools deployed by oceanographers. It was an unambiguous success.
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“We were confident it would work, but then we proved it,” says Chao. “Demonstrating the two SL1s is game-changing, because it’s 100 percent energy-neutral. Essentially we solved the energy limitation of the underwater float.”