Energy Storage for Commercial Hybrid Electric Aircraft

Energy storage options for a hybrid electric commercial single aisle aircraft were investigated. The propulsion system features twin Geared Turbofan™ engines in which each low speed spool is assisted by a 2,500 HP electric motor during takeoff and climb. During cruise, the aircraft is powered solely by the turbine engines which are sized for efficient operation during this mission phase. A survey of state of the art energy storage options was conducted. Battery, super-capacitor, and flywheel metrics were collected from the literature including Specific Energy (Wh/kg), Volumetric Energy Density (Wh/L), Specific Power (W/kg), Cost ($/kWh), and Number of Cycles. Energy storage in fuels was also considered along with various converters sized to produce a targeted quantity of electric power. The fuel and converters include fuel cells (both proton exchange membrane and solid oxide operating on hydrogen or on jet fuel) and a turbogenerator (jet fuel or LNG). The various energy storage options were compared across a range of stored energy on the basis of weight. The selection of a lightweight energy storage technology depends on power and quantity of energy storage. A turbogenerator auxiliary power unit has the best energy and power density for the application. The fuel cells tend to be heavy options due to low specific power. PEM fuel cells operating on compressed or liquid hydrogen are lighter weight than SOFCs, however, PEMFCs are comparable to batteries at the energy storage design point of 1500 kWh. Applications requiring low detectability and long duration favor PEM fuel cells.