The Antares 20E is equipped with a battery-system utilizing Li-Ion cells of the type SAFT VL41M. The Antares 20E was worldwide the first product to utilize these cells, but meanwhile an impressive array of other users have recognized the advantages of this cell, and its field of application is constantly broadening.
Lithium is the lightest of all metals, and has the highest negative standard potential. The low weight and high voltage level of the system result in a high specific energy density. Compared to other currently available Lithium based cells (Li-Po / Li-Su), SAFT VL41M exhibits very high current capability and very good cycleability. This qualifies SAFT VL41M Li-Ion cells for application as aircraft energy storage before all other available cells.
Performance
Positioned in the leading edges of both inner wings, the two battery packs consist of a total of 72 cells divided into 24 modules containing 3 cells each. Each cell is carefully and redundantly monitored and controlled to ensure that it delivers maximum performance while remaining within its safety limits.
A full charge will deliver the Antares 20E approximately 3000m above its starting point. It is off course possible to divide the available energy into one or more takeoffs and climbs. An extra takeoff costs approximately 100m climb altitude. A full charge takes approximately 9 hours to complete using the built in charger (optional 230 V or 110V AC). Needless to say, this requires the charger to be connected to the power grid. Li-Ion batteries have no memory effect, so partial charges and discharges have no negative effect.
As with all batteries, the performance of Li-ion batteries is affected by the battery temperature. To counter this effect, the battery-packs are equipped with electrical battery heating. If the battery charger is connected to the power grid, then the energy required to heat the batteries can be provided by the battery-charger. In the air, the battery modules use their own energy to maintain optimal battery temperature. This process happens automatically. It is possible to turn the heating off and on in flight in order to conserve energy during very long flights. With the battery heating turned off, the good isolating properties of the wing ensures that it takes a long time for the batteries to cool down to a temperature where the performance of the battery is affected.
Battery life
The life expectancy of the Antares 20E E drive battery is determined by two factors:
- the number of charge/discharge cycles
- the natural chemical aging
Charge / discharge cycles
The capacity of a battery diminishes with the number of charge-discharge cycles it undergoes. According to the latest knowledge, the battery will withstand more than 3000 SAE cycles. One SAE cycle consists of a full charge, and a discharge down to 20% of battery capacity. A partial charge and discharge equals a partial full cycle. After 3000 SAE cycles, the cells will retain at least 80% of their original capacity. For the pilot, this means that the drive battery will yield approximately 4.150.000 m (13.615.000 ft) climb altitude before it should be replaced.
Natural aging
More relevant to the practical application is the natural chemical aging of the battery. If the battery is stored at an average temperature of 20°C (68°F), then it is advised to change the battery after 20 years. At this point the battery will have a remaining capacity of 80% of the original capacity.
Availability
As a user of SAFT VL41M cells, Lange Aviation is in good company. SAFT VL41M are also used in most new European satellites, the RQ-4B Global Hawk UAV, the F35 Joint Strike Fighter, the Airbus A380 and in many other high-tech applications.
Next to being a great vote of confidence to SAFT VL41M cells, the military implementations mean that the cells which are now being built into the Antares 20E will be available at least until 2031.
Antares 20E: Silent Power