Electric jumbo jets: How many batteries do you need to get airborne? March 22 2016, 4 Comments
A jumbo jet with its nose cargo door open. It sure would be a nice place to put some... batteries...
Electric airplanes are perhaps the most exciting prospect for the future of aviation.
The record-breaking Solar Impulse II is one of the projects that shows how much things can improve. In a previous article, we covered the tech involved to get the Solar Impulse II airborne.
Last year, the plane was grounded in Hawaii because of batteries overheating. After completing a five-day long, 7,212km journey across the Pacific, the Solar Impulse 2 showed us the feasibility and the opportunities that lithium-ion batteries can bring to the aviation industry.
The decisions required to make those advances are being discussed as we speak.
A window of opportunities, if it opensThe Federal Aviation Administration published on March 9th a proposal to modify its Part 23 rules. This governs the design and alterations of piston-engine airplanes, which applies to small airplanes that can seat up to 19 passengers and have a maximum takeoff weight of 19,000 pounds or less (around 8,600 kg).
This proposal, if approved, would be effective from September 30, 2017.
More about the proposal: why it matters
With rules as they are now, it’s nearly impossible to add technological improvements that modify the mechanics that have kept airplanes working since the 1960’s. This applies for almost every kind of airplane you can imagine, except those that are considered to be used as a hobby. That is, carrying 1 or 2 passengers. This turns out to be frustrating as there is great interest in offering more efficient designs that can reduce oil consumption during flights and reduce the environment footprint that today’s airplanes leave behind.
Yes, the proposal only applies for small airplanes, but the changes that could be done are of such a magnitude that they could open the doors for the whole industry. To get there, it'll take a long time because the improvements made have to be thoroughly tested for them to be safe, because that's the FAA’s highest concern right now.
To give an example, in 2013 Boeing introduced the 787 Dreamliner, an airplane that would add additional electrical systems, complying with the FAA’s requirements, in order to reduce fuel usage and be more eco-friendly. They used certain Li-ion battery from a manufacturer called Yuasa, and because it didn't have a proper short circuit protection built-in, it had a failure within the first few months of operation after its introduction, burning the circuit that goes over the battery in the process.
Here’s the comparison between a brand-new battery and the remains of the one involved in the incident.
This event caused a lot of concerns in specialized media, leading Yuasa to retire said battery from their website’s product listing. Boeing acted quickly and made the necessary modifications to their systems and no new reports of incidents regarding their electrical systems have come up to date.
This kind of circumstance is a headache because companies can’t use their full potential to provide more efficient designs to larger airplanes - a situation that this proposal can change if it provides results relevant enough for the idea to gain traction. An age of sustainable innovation in aviation with fewer roadblocks.
What can be improved today?
Considering the time it could take for such a change to happen in the industry, let's take a look at the feasibility of using electric batteries that are already in our homes and what’s available in the market. Let’s see how many we would need to satisfy the energy requirements of putting a commercial airplane in the skies and maintaining its energy consumption during a normal flight.
We'll take a broad approach to the calculations, to keep them simple and manageable. We’re not aviation experts nor are we considering the weight of the systems involved to keep the batteries connected and safe for travel. Just raw energy density.
For weight considerations, we used the weight capacity that the airplane has for fuel in kilograms.
Airplanes we took into consideration for the calculations
As test subjects, we will be using three widely-used large airplanes that many of has have flown on:
- The cargo-carrying Boeing 747-8F
- The world-famous Boeing 747-8I
- The narrow-body Airbus A320
The specifications of each airplane took into consideration for the calculations will be shown in a table, for practical reasons.
The battery contenders
As there’s such a wide variety of batteries in all types and sizes from each manufacturer, we’ll take two batteries that everyone knows - Blackberry and Samsung smart phone batteries.
Let’s also take two leading-edge batteries developed for more power-consuming applications, the Yuasa battery discussed earlier, and the Tesla Powerwall.
- D-X1 Blackberry (LiPo) battery
- Samsung Galaxy S4 (LiPo) battery
- Boeing 787 Dreamliner Li-ion battery (Manufactured by Yuasa)
- Tesla Powerwall (18650 Li-ion) battery
A typical mobile phone battery
A powerwall next to people for scale, image credit: Gizmodo Australia
Specifications used for calculations are shown in the table below, and the considerations that are taken for each case.
For each type of battery, we’ll determine:
- How many batteries required to power up the engines to reach takeoff speed (assuming that it takes a minute to do so)
- How many would be in the airplane if we swapped fuel with batteries (assuming no volume restrictions)
- How much energy would said amount of batteries represent
- How many would be needed to cover energy consumed in a normal flight
Results for D-X1 Blackberry batteries (LiPo)
If we compare the amount of batteries we can carry compared to the amount needed to feed the enormous energy consumption rates that commercial airplanes have, we can see that there's a lot of work to do.
Looking at the data, we'll see that:
- We need 337 to 504 times the number of batteries to be able to reach takeoff speed.
- We need 3 to 5 times the amount of batteries to cover energy consumption in-flight per hour.
- Fuel has 162 times more energy density than the batteries for the same capacity (in kg).
The Blackberry D-X1 battery doesn’t look very good for these results, but that’s expected considering that fuel’s energy density surpasses greatly the one available to be used from the batteries by the airplane.
A custom lithium-ion pack would be an alternative to getting more energy density, providing at least three times the amount of energy these batteries provide with an improved configuration.
Results for Samsung Galaxy S4 batteries (LiPo)
Taking a look to the data we have, we can conclude that:
- We’d need 132 to 197 times more batteries for the airplane to reach takeoff speed.
- We’d need 1.22 to 1.82* times more batteries to cover energy consumption in-flight per hour.
- Fuel has 63.08 times more energy density in the same capacity (in kg).
Results for Boeing 787 batteries (Li-ion)
After considering the virtues of household batteries, let’s take a look at the bigger contenders on the block. Looking at our calculations, we can see that:
- We’d need 452 to 644 times more batteries for the airplane to reach takeoff speed.
- We’d need 4.18 to 5.96 times more batteries to cover energy consumption in-flight per hour.
- Fuel has 206.8 times more energy density in the same capacity (in kg).
The energy stored rate for these batteries is the lowest of the batteries tested, but that’s likely due to:
- Using old cell chemistry so it doesn't have to be recertified
- Added bulkiness of the protection system
- Cell chemistry used favors safety rather than performance
Results for Tesla Powerwall (18650)
At last, but not least, we have a Tesla Powerwall. If you don’t know what it is, it’s a big box full of lithium-ion 18650 batteries that can power your house (optimally in conjunction with solar panels).
What would happen if you stuffed jumbo-jet fuel tanks full of Tesla Powerwalls?
In this case, we can see that:
- We’d need 295 to 440 times more batteries for the airplane to reach takeoff speed
- We’d need 2.66 to 4 times more batteries to cover energy consumption in-flight per hour
- Fuel has 138.27 times more energy density in the same capacity (in kg)
Compared to previous batteries, this battery is just below the Galaxy S4 battery in terms of stored energy. However, these batteries bring with them the idea of being constantly recharged via solar panels. If we manage to also borrow a few of the ideas used in the Solar Impulse II we could be looking towards a self-sustained airplane, at least for its in-flight energy consumption needs, as the batteries have more time to recharge themselves during flight.
After giving a look at the strengths and weaknesses of various battery systems we can come to the conclusion that there’s a long way to go in order to improve both energy density and weight of batteries if we wanted to use them as the airplane’s only energy source, but we can see there’s a lot of motivation and interest to bring the technological improvements needed to do so as soon as possible. With innovating designs regarding engines, batteries, and even aircraft designs, the approval of Rule 23 modifications proposal could be a golden opportunity to show off the improvements that alternative energy sources can provide to the aviation industry, and the much-desired pollution reduction in order to have a more sustainable future.
This NASA jumbo-jet breaks expectations and shows us that the future of aviation can be interesting.
Some possible further questions to ask:
- What is the minimal viable electric commercial aircraft (rather than a jumbo jet)? What are the most efficient?
- What would it take to bring the energy consumption in-flight per hour to equal current planes?
- If we need a lot of power in the beginning, could we use a rocket engine to save on fuel?
- What are better battery options - how about doing calculations with leading drone and RC batteries?
What other advantages do lithium-ion powered planes have over traditional engines? Could they perhaps go faster than traditional planes without a loss in efficiency?Note: if somebody wanted to improve the calculations made, it would be a good idea to calculate the amount of energy needed to keep the batteries at an optimal temperature, efficiency between charges, and the weight of the equipment needed to build a large, safe custom battery pack.