Battery selection is the most critical issue for an autonomous solar powered aircraft because it represents the most important part of the total weight. After having compared all energy storage technologies available today, Lithium-Ion-Polymer batteries have been selected for Sky-Sailor project, because it represents currently the best energy/mass ratio that is commercially available.
The batteries are mainly used during the night flight, when the solar power is below the power requirement for a leveled flight.
The actual Li-Po has a capacity of 7200mAh with a nominal voltage of 28,8 V. The total weight is 1,2 kilogram which represents the half of the total weight of the airplane. Improvements in this field are thus very important and new technologies are also investigated. This is the case of fuel cells that are very promising for the future.