Over the past decade, we have seen multiple industries looking to transition to renewable fuel sources, and while we have been making huge strides in the production of renewable energy, the technology required to allow every industry to use it has not kept pace. We do not have such efficient technology to store the widely available renewable energy around us. electric planes
This energy storage dilemma is slowing our adoption of renewable energy, and one of the most apparent is the aerospace industry. You can just calculate the vital role played by this industry as, Elon Musk is running around pushing electric vehicles and solar-powered homes. But do you know every time a Falcon 9 spacecraft launches, it burns 147 tonnes of fossil fuel.
Boeing and Airbus the two big giants companies of this industry are in a constant battle to create the most fuel-efficient plane, allowing their customers to save on ever-increasing fuel costs and increase their bottom line, yet they are still using kerosene, when energy from the grid is cheaper.
The aerospace industry has one massive hurdle to overcome before it can successfully adopt renewable energy. The energy density of our storage methods. Energy density is a measure of the energy we can harness from 1 kilogram of an energy source. For kerosene, (the fuel jet airliners use) energy density is about 43 MJ/kg.
But at present, even our best lithium-ion batteries have an energy density of around 1 MJ/kg. The energy obtained from the battery is over 40 times heavier than jet fuel.
A plane flies when the lift equals the weight of the plane. so when we increase the weight (due to battries), we have to increase the lift, which requires more power. The requirement of more power means we need more batteries, which increases the weight again.
Let’s explore little dipper to understand why it is such a big issue. Now take the example of two different planes, the Airbus A320 and a small personal aircraft like a Cessna, to battery power. Ultimately, we want to know the power requirements of flight and how it will draw on the energy supply of the battery.
Work = F ×Δx,
where Δx is the distance over which a force acts.
Power is work per unit time, so
Inserting our equation of work we get,
Here delta-V is the velocity of whatever is getting worked on, in this case, it’s the air.
When a plane is flying at a constant height, we know that the force of lift and the force of gravity are balanced. That means the upward force of lift (Flight) has to be equal in magnitude to the downward pull of gravity, which equals the mass of the plane multiplied by gravity So, the power required for lift equals the mass of the plane multiplied by gravity and delta-V.
(After having some mathematical calculation related to this equation, the result we need is…)
Now from the equation, you can see a real picture of why increasing the mass of a plane is such a huge issue. The mass component of this equation is not only squared, but also doubled. Doubling the mass will increase our power requirements by 8 times.
let’s see some real-world calculations and consequences of converting a giant Airbus A320 To an electric plane.
we can take the battery weight to be the usual mass fraction that’s devoted to fuel, about 20% of the plane’s mass for both. We also need to take into account the fact that at the cruising altitude, the atmosphere is much thinner than at ground level. For the Cessna (a small electric plane), the density falls by a factor of 2, and for the Airbus, by factor of 3.
Now take the specific power of leading-edge Lithium-ion systems, at about 0.340 kilowatts per kilogram kW/kg. To meet the power demand, the Airbus and would need 31 tonnes of batteries.
10,500 kW / 0.340 kW/kg ≅ 31 000 kg
while the Cessna would need just 100 kilograms:
35 kW / 0.340 kW/kg ≅100 kg
For the Cessna, this compares very favorably with the typical weight of fuel it would carry otherwise, and it isn’t terrible for the Airbus, but this is just the power the plane needs at any one moment in time.
What we are really interested in is the weight of batteries we would need to match the typical range of these planes. For the Airbus, that have a 7 hr flight from JFK to LHR and for a Cessna, that might be a four-hour flight from New York to South Carolina. The energy capacity required for
a trip is given by the equation,
Power required per hour multiplying the duration of the flight.
Again if we use leading-edge figures for Lithium-ion battery capacity, we can store about 278
watt-hours per kilogram. For the Cessna, the equivalent battery weight is around 500 kg or just less than two thirds the weight of the plane without fuel. For the A320, the required battery weight is around 260,000 250 000 kilograms or about 4 times the weight of the empty airplane!
If you compare it to the typical 20% that’s allocated to fuel, this is devastating a huge. Now, we have a base figure for how heavy the batteries are going to be, we can re-calculate the actual range taking the added weight of the batteries into account.
Let’s assume that at the very least, we’re not going to accept a reduction in flight speed or increases in total energy used per flight. How much is the range diminished for flights of similar
speed and total energy?
As expected, this downgrades the Cessna’s ( a small electric plane) flight time from 4 hr to about 2 hr. Not negligible, but livable. A two-seater Cessna usually holds about 150 kg fuel and another 100 kg for passengers and luggage. It is easy to imagine fly the Cessna with the required battery capacity through a combination of lowering the carrying capacity, lowering speed, increasing wingspan, with lighter parts and more efficient electric engines. In fact, this is exactly what we are seeing with small electric aircraft coming to market in the past few years, like the Alpha Electro.
However, the downgrade is substantial for the A320, taking us from 7 hours down to just 20 min, less than one-twentieth of the way across the Atlantic. If we plot the flight duration as a function of battery mass for both planes as in the figure. electric planes
you can see that the Cessna is already sitting around the optimum and could actually increase its
battery capacity and improve its flight range. But for the airbus, it’s a different story, where we overshot our optimum battery capacity significantly. Reducing our battery weight to 60 tonnes will
increase our flight duration by only about 15 minutes. So we could last a little bit longer before
crashing into the ocean, assuming we could find a place to fit those 60 tonnes of batteries in the first place.
you might have noticed that many short-range small aircraft are coming to the market, and if we fly very slowly with low drag wings we can even build a solar-powered drone that never has to land.
We won’t be seeing airliners using electric engines any time soon, unless we can find a more energy-dense medium for storing that energy. if you have read till here, means you liked our work. so plz share this article with your friends and comment to motivate us, if you want more such content, because it takes a lot of hard work to make such content. you may be interested in my other article on Enlil turbine.