Helios Horizon just made aviation history. 

The Florida nonprofit completed what it says is the first piloted flight of an electric aircraft powered by solid-state batteries on Friday. Founder and chief test pilot Miguel Iturmendi carried out a series of short test flights at Zephyrhills Municipal Airport in central Florida on June 5, taking to the skies in a modified Pipistrel Taurus motor glider that the team has simply called the Helios Horizon. 

The aircraft was originally powered by lithium-ion batteries rated at 260 Wh/kg, but has been reconfigured so that the single motor runs on solid-state batteries that deliver 410 Wh/kg. The company says that new batteries are smaller than the lithium-ion batteries in most modern EVs but offer 60 to 80 percent greater energy density. Iturmendi expects that energy density to increase by another 40 percent within two years, too.  The batteries can also be charged from almost empty to 80 percent in less than 15 minutes.

“For the first time, we have a battery technology that yields the range and charging times necessary to make commercial electric aviation viable, while providing the safety the flying public will demand,” Iturmendi said in a statement.

Solid-state cells replace the flammable liquid electrolyte in lithium-ion batteries with a solid material, making them more stable at high temperatures and more sturdy against punctures, according to Helios Horizon. The company says the batteries can be charged using almost any AC electrical source, without any special infrastructure. The aircraft can also recharge in flight via built-in solar panels and by using the propeller as a wind turbine when it isn’t needed for thrust.

“Regenerative flying, in which we glide and windmill the propeller during descents, can significantly increase the range of the airplane,” Iturmendi said.

Friday’s test flights validated the weight and balance of the Helios Horizon following the battery swap, with the new setup performing better than expected over hours of sustained operation. The exact range and top speed have not been shared, though. 

The team previously flew the aircraft at a record 24,000 feet—the highest altitude of any vessel in its class—but hopes to take it higher into the stratosphere, targeting over 40,000 feet. That is higher than most passenger airliners cruise. Iturmendi expects the aircraft to easily complete these stratospheric flights on a single charge thanks to the new solid-state batteries. The tests are planned for later in the year. The Helios Horizon is just a concept demonstrator at this stage, showing what is possible in terms of range and endurance.