Variations in sea temperature will power future oceanographic equipment such as marine monitoring systems, says California-based start-up Seatrec. The company, along with defense giant Northrop Grumman has recently been awarded a DARPA (Defense Advanced Research Projects Agency) grant to explore the creation of energy-efficient, deep-sea drones and robots. Hurricane-studying and eco-monitoring are two uses for ocean-obtained IoT data.

Seatrec said early last year, in a press release, that it has already used two energy harvesting modules to propel a data collecting device at a depth of 1,000 meters. The sensors employed, called floats, could ultimately be powered indefinitely with water-temperature energy, the company claims.

“Ocean observation can be 100-percent powered by naturally occurring temperature differences in the ocean, extending life and measurement capabilities,” the company says.

Why do it?

It would save money in the quest for oceanographic discovery, but also have ecological benefits: As it is now, when a traditional float fails (as does over time as the batteries become depleted), the device simply descends to the ocean floor to be discarded, batteries and all—it’s too expensive to retrieve the device.

The new float that the DARPA money is going towards will not only dive to 1,000 meters, but do it at a speed of one meter-per-second, Seatrec said in another press release, last year, announcing the funding. That’s faster than what’s available now: Speed is important in deep-sea sensor sampling because hour-to-hour conditions change—crucial variables in weather forecasting is one time-dependent data-collection example.

Materials science

Temperature responsive materials are behind the tech, the firm explains. They’re called Phase Change Materials (PCMs) and have actually been used in commerce since the beginning of the industrial revolution—steam engines perform liquid-to-gas phase-change, for example—water becomes steam which shifts the piston. Heating pads perform another variant of PCM. That’s a solid-to-liquid change producing energy.

The PCM-based underwater drones work because the ocean’s temperature is stratified—layers of temperature are found within the mass of water and it can become colder as one descends from the warmer surface. In Seatrec’s case, it’s using a change in materials volume, cause by PCM expansion as the temperature changes. That volume change drives a motor:

“During the warming phase the contained substance changes phase from solid to liquid; expands and generates pressure that forces hydraulic oil through a generator to produce electrical energy,” the company explains on its website. “During the cooling phase the working substance freezes and contracts.”

Underwater drones

Oceanic drones and other kinds of Autonomous Underwater Vehicles (AUVs) could use the technology, the company says. Underwater gliders, which are AUVs using buoyancy, rather than propellers, and that move laterally, as well as up and down (through the use of wing-like hydrofoils), could be a use-case.

Future overall deep-sea industry expansion could include aquaculture underwater farming, and mining, if costs and eco-concerns can become mitigated.

Seatrec thinks its solution will do that. “Wherever and whenever there is temperature difference or change, we turn that thermal energy into electricity,” Seatrec says.