As it completed its round-the-world journey, Solar Impulse 2 is still amazing us with its achievements. But this journey has only been possible thanks to the advanced lightweight materials and solutions onboard.
When Solvay signed-up to be part of the Solar Impulse project in 2004 we understood that it was about advanced materials and solutions. We immediately launched 50 projects involving our researchers and the Solar Impulse design team. Each project was designed to find lightweight solutions which would enable Solar Impulse to complete its round-the-world journey without fossil fuels. Around 25 of those projects resulted in products or solutions which have found their way onboard. These include our composite materials which are a key contributor to the aircraft’s light weight.
Letting the sunlight through
I want to look at energy generation first, because that’s where everything starts. Solar Impulse 2 has over 17,000 photovoltaic (PV) cells which line the top of the wings, fuselage, and tail. Covering almost 270 square meters of surface, these cells gather the sun’s energy and transform it into electricity.
Protecting those PV cells is vital if they are to continue harvesting energy during flight. For this application, Solvay proposed our special Halar® ECTFE film. The thin Halar® film (less than 20 microns thick) allows most of the available sunlight to reach the PV cells. This maximizes the energy generation capabilities of the PV system. Halar® film is also flexible and adheres well to the PV cells, creating an original encapsulation system which is energy efficient, flexible, and ultra light. Halar® is also perfect for conventional ground-based PV installations, making them lighter than ever. Take a look at the video to find out more about Halar®.
We also developed a very special product called Solstick® to complete the encapsulation system. Solstick® allows minor movement of the rigid PV cells to cope with deformations in the large flexible Solar Impulse wings and ensures they are weatherproof.
Maximizing battery storage
Energy storage is another area that is critical for Solar Impulse. Solvay has contributed a number of new technologies including Solef®, a polyvinylidene fluoride (PVDF) which is used as a binder in the electrodes of the lithium-ion battery. Thanks to the improved performance of Solef® PVDF, we can use less of it. That allows us to include more electro-active components in the electrodes which improve the energy density of the battery.
We’ve also included Solvay’s F1EC as an additive for the electrolyte in the batteries for Solar Impulse 2. F1EC improves the flow of electricity in the battery, making it more stable and reliable. The combination of these solutions improved the density of the battery from 180 to 260 Watt-hours per kilogram of battery weight. This is the highest level ever achieved. You can read more about Solvay’s latest energy storage technologies in the Asking More article ‘Taking charge’.
Proven technologies lead to cleaner future
Another area of focus for the Solar Impulse team has been energy savings. The goal here has been to minimize energy losses from the aircraft’s systems. Friction is a major problem on board as it wastes energy and wears parts, making lubrication critical. To solve this problem we developed a solution based on Torlon®, a polymer which self-lubricates. It provides exceptional wear resistance in both dry and lubricated environments, and retains its toughness, high strength, and high stiffness at temperatures up to 275°C.
Solvay has also developed the Fomblin® liquid lubricant. The lubricant contains special proprietary additives which enhance the anti-wear and anti-rust properties of the lubricant and increases its lifespan. This reduces maintenance significantly.
The important thing to note about Solar Impulse is that it is a project, not a race. By trialing the products in a highly demanding real-world application such as Solar Impulse 2, we are proving that clean technologies have the power to transform our world.