The newest types of unmanned aerial vehicles powered by solar energy are being developed in Russia that can stay in the air for several days. Dean of the Department of Aviation Technology of the Russian International Aviation Institute, Alexei Yefremov notes that the unmanned device will not exceed 25 kg and will have about 5 meters long wings. According to Yepremov, the first working model has already been tested in June, 2018, but without the use of solar panels. Now developers are studying the minimum and maximum speeds, as well as the stability and control characteristics. This unmanned aerial vehicle will be launching its first ever flight  from August, 2018.

Source: Here.