mardi 17 novembre 2015

Cool New Batteries for Solar Impulse

SolarImpulse - Around the World patch.

November 17, 2015

After several months of designing and testing, it’s now time to get Solar Impulse back on its feet! And to avoid the batteries overheating again, our engineers have upgraded the whole battery system and integrated a cooling system. Take a look at how and when the repair work will take place to get the plane ready for part 2 of the round the world tour.

As you may have heard, Solar Impulse has been hangared in Hawaii since July – not the worst place to be stranded we reckon – because its batteries overheated during the 5-day and night record breaking flight from Nagoya, Japan. Since the plane had been exposed to harsh weather conditions from Nanjing to Nagoya, we decided to do a test flight before leaving for Hawaii. Having to perform a test flight followed by a mission flight had not been taken into account in the design process of the battery system, which did not allow the batteries to cool down in between the two.

Technicians carrying out maintenance work on the batteries in Hawaii in July

But the show must go on, and for the plane to be back in the air by April 2016, our technical team still has a lot on its plate. Why wait until spring? Because the days are longer, which means more daylight hours to recharge the batteries during flight periods.

Let’s remember that we are at the limits of technology: each morning the charge goes down to 10% of battery capacity.

Imagine how you feel when you realize that the battery level of your cell phone is red and that you only have a few minutes left before it shuts down! The first batch of upgraded elements, five in total (four to replace the plane’s damaged ones, and one for testing), is currently under construction. The second one, the four spare parts, will be hatched beginning of 2016.

Let’s take a look at the planning concerning the first round. The three types of elements are designed separately and then mounted together before being integrated into the aircraft.

1. The key components, the batteries, have been produced by our supplier Kokam, and are now on their way to Germany to be tested, assembled, and placed in their boxes. They are similar to the former ones.

Battery dummy cells made out of aluminum sheet metal for thermal tests

2. In parallel, the battery containers, are being built and undergoing shock testing in Dübendorf, Switzerland. They will be ready at the end of November, and the batteries will thus be encapsulated in December. Like the previous ones, they contain silver (a good electrical conductor), but the novelty lies in a fail-safe system which should safeguard us from anymore temperature-related glitches in case we have to follow a different mission profile than the one foreseen. It can be controlled from the cockpit and includes a cooling and backup system. In case the cooling system breaks down, the backup one steps in and allows the pilot to control the opening so that it doesn’t stay completely open, which would cause freezing, or closed, leading to another overheating scenario. Indeed, this could "Jeopardise" the continuation of the flight which would be critical if the airplane was flying over an ocean.

Structural load test of the new battery box: 1000 kg towards the ground, 370 kg to the side

3. The last level is the engine housing (or gondola), which shelters both battery and engine, seeing as the former powers the latter at night. A few adjustments concerning the electronics have been made and an air vent has been added to let air flow into the battery’s cooling system. The gondolas are also currently being pieced together in Dübendorf, by our hard working engineers and technicians.

Air inlet on gondola front part for the new battery cooling system

And for now, you can give the world leaders a hand by voting here for the solutions to tackle climate change you think most efficient. We will take the most popular ones to the UN climate conference COP21:

For more information about Solar Impulse Around the World, visit:

Images, Text, Credit: SolarImpulse.


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