US: Researchers at the U.S. Naval Research Laboratory, Vehicle Research Section and Photovoltaic Section have investigated the presence of solar photovoltaics to the cooperative autonomous soaring techniques to enable long endurance flights of unmanned sailplanes that use solar power.
The Solar Photovoltaic and Autonomous Soaring Base Program and the U.S. Marine Corps’ Expeditionary Energy Office have begun to improve UAV’s so they can support a round-the-clock information, surveillance and reconnaissance mission, which would be able to benefit warfighters because it will reduce the amount of batteries or fuel needed to carry into battle and improve the availability of continuous coverage of ISR assets.
“NRL has twice flown our solar UAV [based on the SBXC sailplane] over 10 hours using a combination of solar photovoltaics and autonomous soaring as part of the ‘solar-soaring’ research program,” Dan Edwards, Ph.D., an aerospace engineer, said in a statement. “This research is investigating the value of combining autonomous soaring algorithms and solar photovoltaics for capturing energy from the environment to extend flight endurance and mission operations of an aircraft.”
A custom built photovoltaic array is integrated into the center wing panel of the PV-SBXC aircraft as a drop-in replacement to the original wing, while a power management and distribution system converts the power from the solar arrays into direct current voltage, which the electric motor can use for propulsion or to recharge a smart battery.
The UAV with solar arrays was able to fly for 10 hours and 50 minutes last October without using the entire charge on the battery. Another UAV took off in April and flew for 11 hours and two minutes while using significantly less battery power.
“The experiments confirm significant endurance gains are possible by leveraging thermal updrafts and incident solar radiation, rather than ignoring these free sources of energy,” Edwards said. “Future testing will focus on quantifying the trade space between improvements in solar cell efficiency and combining with autonomous soaring for improved solar-recharging.”