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All About Energy Density in Aviation

We have electric cars, electric scooters, and electric bikes — what about electric aircrafts? Is battery technology ready for electric applications in aerospace? The issue lies in energy density, as flying requires a lot of energy that traditional batteries can’t yet provide.

However, that doesn’t mean that battery technology will never get there. Aviation and aerospace companies are working on aircrafts that do not require fossil fuels. Common estimates for a viable electric commercial aircraft suggest that it is going to happen sooner than most people think.

What is energy density?

In simple terms, energy density is the amount of energy that can be stored in a system or material. Energy is released in four different reactions — nuclear, chemical, electrochemical, and electrical. Let’s explore the applicability of energy density in aerospace applications.

How is it used in electric-vehicle technology?

Electric vehicles (EVs) are powered by lithium-ion batteries. This battery technology has been improving year after year with energy density being one of those improvements. Increasing the energy density of an electric vehicle battery has many applications and benefits.

Practically speaking, it means using less materials to provide more energy. In this case, that means increasing the range of a vehicle. You could also think of it as using the same number of batteries but getting a greater range from the material.

Today, some of the best battery technologies only produce about 260 watt hours per kilogram, and results in a heavy EV battery. Compared to their combustion counterparts, electric cars are heavy! This affects collision safety, road wear, tire noise and more.

In aviation, more weight means more energy required, leading to more batteries, resulting in a vicious cycle. Thus, scientists have been working toward creating lighter and more sustainable technologies.

Why is energy density important in aerospace engineering?

The problem with energy density, electric flight, and aerospace engineering is that batteries are very heavy with a low energy density when compared to traditional aircraft fuel. Gasoline or jet fuel is far more energy dense than even the best batteries available.

To compare some statistics, the battery in a Tesla Model 3 comes in at 260 watt hours per kilogram. Jet fuel, calculated pound for pound with that battery, is almost 50 times more energy dense.

What role does energy density play in aircraft performance?

When looking at a high-energy density alternative fuels like sustainable aviation fuels (SAF), aircraft performance is actually improved. Many SAFs contain fewer aromatic components, which in simple terms means that they burn more cleanly in aircraft engines. There are fewer local emissions, fewer contrails, and improved aircraft performance.

If battery technology comes to fruition allowing fully electric or electric hybrid aircrafts, engineers predict performance improvements as well. That includes more efficiency, lower emissions, low noise levels and better take-off and landing capabilities, including vertically.

What are the challenges with achieving high energy densities in aerospace?

Unlike electric cars and other electric vehicles, electric aircrafts need to meet a large range of operating conditions. Examples include extremely high and low operating temperatures, reserve power for emergency landing and maneuvering (further reducing operating range), safety requirements, as well as many others.

To meet these challenges, battery technology is continuously improving to address the needs of aircraft electrification, with aviation companies looking beyond the use of sustainable aviation fuels to manage greenhouse gas emissions.

What about moving away from fuel entirely?

When considering the potential use of future battery technology, range is a key issue for using batteries to power aircrafts. It might seem like a simple and logical solution to add more batteries to fly further, but as noted previously, this causes a vicious cycle of energy increase followed by weight increase.

Another concern with existing battery technology is retaining energy as the battery ages. This is already an issue with EVs as older cars lose some of their range. While this is more of a nuisance for EVs (cars are still drivable with 20% range loss), an aircraft losing range is much more concerning, particularly since range loss tends to accelerate after 20%.

What is the future of energy dense materials in aerospace engineering?

What technology is currently being developed?

Hybrid electric aircraft is one solution to the current limitations of battery technology. Similar to hybrid electric vehicles, the idea is that these airplanes can fly with power from renewable resources in combination with energy generated by fossil fuels.

Companies are also making strides in battery technology itself. Advancements in silicon based battery solutions and the potential of solid state batteries provide a clear path towards full electrification of the aerospace and aviation industries.

With the only commercially available 100% silicon anode 1 lithium-ion batteries in the industry, Amprius’ energy density batteries, currently at up to 450Wh/kg, can substantially improve the performance of aircrafts and drones. When compared to competing technologies commercially available today, Amprius’ batteries can nearly double the flight times of Unmanned Aircraft Systems (UAS).

Another application of Amprius’ technology is the use of silicon anode lithium-ion battery cells to improve performance, communications and high-resolution imaging in High-Altitude Pseudo Satellites (HAPS).

How far are we from electric aviation?

There are already existing electric aircrafts, although nothing that is being used widely or for widespread commercial purposes. The first two-seat electric aircraft was the Taurus Electro, with the production version introduced in 2011.

The Alice, a plane developed by Eviation, is one of the latest endeavors showing what is possible. This is the worlds first all electric passenger aircraft, which went through engine testing in January 2022. It is a nine-passenger plane that can fly for about an hour, with a range of about 440 nautical miles and a max cruise speed of 287 miles per hour.  We’d note that as of June, 2022, The Alice has not yet been test flown.

The company hopes that electric planes fitting 20 to 40 passengers will be a reality in the coming years. There are three Alice prototypes. The commuter variant, mentioned above, accommodates nine passengers and two pilots plus 850 pounds of cargo. The executive prototype offers six passenger seats. The cargo prototype holds 450 cubic feet of volume.

Shipping company DHL Express has 12 Alices on order, anticipated for delivery in 2024. The company intends to use them to make short-distance, cargo carrying trips, reducing their carbon footprint.

Although we may still be a few years away from commercially available electric-powered jets or international flights, the pace of battery technology development shows it will become a reality sooner than many people realize.

As the CEO of Aero Consulting Experts predicts, an electric airplane from a big-name company capable of passenger jet travel could be as little as a decade away. High energy battery development is a key component of making this a reality.

 

1 Actual percentage of silicon is 99.5%-99.9% which is in the range of acceptable purity levels for materials that are considered 100%.