Researchers at the U.S. Naval Research Laboratory are exploring technology that allows unmanned aerial vehicles to fly for more than 12 hours using thermal and solar energy.

Solar-soaring technology uses both thermal energy in the atmosphere and solar energy to power UAVs. Dan Edwards, senior aerospace engineer in NRL’s Tactical Electronic Warfare Division, described in a press release how UAVs can use sensing and guidance algorithms to detect a thermal updraft, when air close to the Earth is warmed by the sun and starts to rise, to soar.

Solar-soaring technology also uses solar energy to power solar cells that convert light to electricity. New solar cell technologies are now small enough to justify the weight they add to UAVs.

“For a long time, even though there has been solar aircraft since the 1990s, the efficiency of the solar cells wasn’t high enough to pay the mass penalty,” said Phil Jenkins, head of the photovoltaics section in NRL’s Electronics Science and Technology Division. “But over the last 10 years, that has really changed. The cells have gotten more efficient and lighter.”

Solar-soaring technology combines thermal energy and solar energy technology to better power UAVs.

“Between the two, you have the most robust energy-harvesting platform,” Jenkins said n a release.

Using solar and wind energy, UAVs can have higher endurance, which can be useful for both military and civilian applications. Tasks like information gathering, surveillance, communication and pollution monitoring require long-term observation, which UAVs can do.

“In these cases, you just want eyes up there for hours and hours, and solar-soaring makes that possible,” Jenkins said.

Although solar cells are now more efficient, UAVs still carry batteries, which can now be smaller because the UAVs can more effectively use solar energy.

One of the challenges that researchers still face is the UAVs’ ability to fly through the night, when solar-soaring technology cannot be used.

“We still can’t fly through the night because the batteries are just too heavy, but we currently get dawn-to-dusk enhanced endurance,” Jenkins said.

The next step to making UAVs more efficient is replacing the batteries with fuel cells, which are more efficient than batteries, Edwards said.

“Fuel cells have much more energy per unit mass than a battery, so we’re marrying the fuel cells, which are great for getting through the night, and the solar-soaring, which is great in the daytime for getting energy directly from the sun and wind,” Edwards said.

Maddy is a senior at George Washington University studying economics.

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