Solar Impulse Grounded Until 2016

An anonymous reader writes: The Solar Impulse 2 has been grounded in Hawaii for at least nine months because of battery damage sustained during its record 118-hour trans-Pacific flight from Japan. The project team says the aircraft is not expected to take off on the next leg of its journey until late April or early May 2016. The BBC reports: "...[the] plane experienced damaging overheating in its lithium-ion battery system. Although the battery units performed as expected, they had too much insulation around them, making temperature management very difficult. Engineers on the project have not been able to make the quick repairs that might allow Solar Impulse to have a crack at completing the round-the-world journey this year."

Comments

I admire

[phantomfive]

I admire their persistence. It's a cool project.

9 months in Hawaii

[Anonymous Coward]

What a *terrible* thing to happen.

Re:9 months in Hawaii

[Rei]

"Yes, André, I finally finished replacing the batteries. But, wait a minute, what's this?..." (BAM! BAM!) "Oh damn it, I just noticed that there's some serious cracks in the fuselage! I'm going to need several more months to get her flightworthy..."

Hey Elon!

[xeno]

Hey Mr. Tesla! Surely the Solar Impulse team would be happy to slap a very thin sponsor sticker on a prominent spot, in exchange for Tesla waking up some of its lithium-Ion gods out in the desert. Can't think of a better entity to say "let me look into that" and return 48 hours later with a station wagon full of the latest Li-polymer batteries formed in precisely the right shape with precisely the right chemistry.

Maybe? I know Elon's other team needs a bit of a moral boost at this moment; why not get that boost from the team that's NOT fully occupied doing fault analysis at the moment, and totally qualified to solve this specific energy problem?

Re:Hey Elon!

[Rei]

Or maybe he meant "morel boost". I mean, they're based out of California so some trendy hipster food with wild mushrooms and the word "boost" in the name might be what's needed to get the job done.

I've seen this up close

[cerberusss]

I've seen this up close. I'm a software engineer and I've worked for a scientific institute in the past. One of the project involved putting a camera on a helium-filled balloon. The electronics and PC equipment (a PC104-sized Linux box) were powered from a big pack of lithium batteries.

The problem is basically that lithium batteries perform best in a certain temperature range, say from 10 to 25 degrees Celsius (50 to 65 F). But that's rather difficult.When you lift off, it might be cold and you want the batteries to have a decent temperature. Otherwise they can't deliver enough power. So you insulate them and they stay warm by themselves, because when you draw power, they get warm.

But then the higher you lift off into the air, the thinner the air gets. Thus convection will be less and less. You can shed heat via radiation (into the infrared spectrum) but that's only half of the heat or so. And then the insulation can overheat the battery packs.

There's all sorts of tricks, for example copper-strapping the packs to a large piece of black metal so you increase the heat radiation. But if you automate that (or the insulation), you also get additional possible failures.

What it comes down to, is some calculation but also some experience.

Re:I've seen this up close

[Rei]

What's wrong with, you know, a simple thermostat-controlled fan, like most large battery packs use? Or if you want it to be passive, a greenhouse window opener to open up the insulation when it gets hot?

I'm not faulting them for their oversight - bad decisions happen in every engineering project. But this doesn't strike me as any sort of unusual nor unexpected situation. News flash, temperature-sensitive batteries need proper temperature regulation rather than just being slathered in foam, details at 11....

Re: I've seen this up close

[Rei]

Potassium nitrate foliar spray!

Re:I've seen this up close

[Mr D from 63]

They could simply run some air duct tubes through the insulation near the batteries, then open/close dampers as needed. Very little energy used or added weight required.

Re:I've seen this up close

[amalcolm]

Wheras you are an anonymous fuckwit

Re:I've seen this up close

[Rei]

The main problem with this solution is the amount of power the fan would draw.

Solar Impulse is a 30kW airplane. Cooling fans are nothing compared to that. Furthermore, I also wrote: "Or if you want it to be passive, a greenhouse window opener to open up the insulation when it gets hot".

This isn't rocket science here. Everyone who works with large format battery packs knows that you can't just cover them in foam insulation and pretend that's good enough. You don't have to go to the sort of extremes Tesla and GM go to - Nissan's Leaf doesn't even use cooling fans. But it does use cooling channels with passive forced air coming from the car's motion, as well as pad heaters to warm them up when it's too cold. Because they're not so daft as to think that you can just pack them in insulation and call that good.

They probably know more about batteries than you will ever learn.

You know nothing about me, let's leave it at that.

They are attempting something very difficult that hasn't been done before, There will be problems.

As I said - "I'm not faulting them for their oversight - bad decisions happen in every engineering project."

But as I also said: "But this doesn't strike me as any sort of unusual nor unexpected situation. News flash, temperature-sensitive batteries need proper temperature regulation rather than just being slathered in foam, details at 11...."

Building a manned solar powered airplane to make such long runs is very much a new and challenging thing. Designing large format battery packs, not so much.

Re:I've seen this up close

[tomhath]

Power and weight. The plane could barely fly with what it had, they shaved every ounce of weight to get where they are.

Re:I've seen this up close

[cerberusss]

Our first flight didn't end well due to another reason. The next balloon flight, the electronics engineer just removed enough insulation to keep it cosy at the height where the balloon would mostly stay. He then added a small additional battery pack connected to a heating element. A colleague coded a PID algorithm to keep the big pack warm at the start of the flight.