While Solar Impulse flew around the world on batteries, it was super light. And it used every ounce of sunlight to recharge these. This is hardly practical for a full-size passenger plane passing through day and night in different time zones. A workable battery powered airplane would need sufficient energy in its storage cells for the entire flight.
Challenges Facing a Commercial Battery Powered Airplane
Specific energy relates to the potential stored in material per unit of mass. Jet fuel and aviation gas score around 47 mega joules per kilogram. The best lithium-ion batteries currently produce a miserly 0.9. This makes them too heavy for the airplane to take off, even if we had space for them.
But there is hope we shall someday extract 41 mega joules per kilogram from lithium-air cells. At that point, the scales will begin to balance. That’s because a battery powered airplane does not have fuel tanks, piping or pumps. And an electric motor weighs far less than a powerful jet engine.
But That is Not the End of this Exciting Story by Far
Internal combustion engines are hugely inefficient, because they waste 65% of energy to produce the other 35%. An electric motor, by comparison only loses around 10% in the process. Thus, the storage cells in a battery powered airplane would only need around 17 mega joules per kilogram to compete.
An Englewood, Colorado company has developed an all-electric lithium-ion two-seat trainer which is a step in the right direction. Moreover a four-seat version is in the pipeline too.
“When you first sit in the cockpit of an electric-powered airplane, you see nothing out of the ordinary,” a spokesperson for the company says.
“However, touch the start button and it strikes you immediately. An eerie silence: There is no roar, no engine vibration, just the hum of electricity, and the soft whoosh of the propeller. You can converse easily with the person in the next seat without headphones. The silence is a boon to both those in the cockpit, and those on the ground below.”
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Preview Image: Solar Impulse