„The first practical solar powered aircraft“ this was the declared goal of the Berblinger competition in 1996 – and exactly this is icaré 2.
The idea seems to be quite simple:
Flying with light!
Solar cells on the wing upper surface produce power which is powering the engine directly or is stored in a battery.
With sun energy alone icaré 2 is able to cruise straight at constant altitude and with the power of the battery take-off is possible with this stored solar energy.
What is sounding that easy and logical means in the reality plenty of optimization, extreme lightweight structures, smart electronics and polished aerodynamics.
As result icaré 2 was built, which is able to fly with electric propulsion alone on a solar radiation of approx. 500 W/m² and to take off under own power of the storage battery with a climb rate of 2 m/s, as was specified in the Berblinger competition rules.
In 1996 he could climb with nickel-cadmium batteries up to 300 m, nowadays the installed lithium-polymere battery allows climbs up to about 1000 m.
An electric engine of the transversal-flux-type on the tip of the vertical tail drives a foldable propeller, allowing operation as sailplane with stopped engine. Due to the low mass of icaré 2 climb even in the smallest updrafts is possible, nevertheless the structural strength is identical to a conventional glider.

Icaré 2 became the winner of the Berblinger prize – and since then it is operated by the University and opens students the possibility for further research work.
Additionally icaré 2 has become a record aircraft – last but not least because of the unfailing efforts of Klaus Ohlmann, the record pilot based at his home airfield in Serres in Southern France.

Here some data of icaré 2:

 wing span 25  m
 wing area 25.7  m²
 length 7.9  m
 height 2.0  m
 empty mass ca. 300  kg
 max. flight mass 390  kg
 typical wing loading 15  kg/m²
 min. flight speed 48  km/h
 max. flight speed 90  km/h
 max. climb rate 2  m/s
 best glide ratio 36  --
 max. solar power 3.6  kW
 efficiency of solar cells 17  %
 battery mass 27  kg
 battery capacity 2.9  kWh
 resulting range ca. 60  km
 mean battery voltage 135  V
 max. engine power 12  kW

The structural design of icaré 2 is a combination of CFRP (carbon) and honeycomb sandwich in all main parts of the structure, where all control surfaces and the wing lower side have been covered with fabric.
This resulted into a motor glider which combines the typical appearance of a modern sailplane with the flying speeds and the fabric surfaces of a classic airplane.
This is coupled with the striking look of the solar cell covered wing upper side and the nearly silent sound of the electric propulsion system.
And yes, this unique aircraft is able to fly only with light!