Solar powered hot air balloon

[Sillychris]

Could a well functioning solar powered hot air balloon be built with today's technology?

I am picturing a fan, heating element, and a whole lot of solar panels.

Photoelectric balloon fabric would be the best choice, but I don't think that exists yet?

What do you guys think?

[Genius Evil]

You might want to look at solar Montgolfieres. They're essentially large bags that use sunlight to warm the air inside them. Most of the balloon designs for Mars are these, actually.

[KerbMav]

I think he intends to propell the balloon with a propeller - that he named as a fan?

http://en.wikipedia.org/wiki/Solar_cell_fabric

[Aghanim]

This: http://en.wikipedia.org/wiki/Solar_balloon

Why convert it to electricity first with huge amount of losses while you could just let it become heat and heat the air directly?

[Idobox]

Using photoelectric panels for heating is very inefficient. Just paint the balloon black, and you'll get nearly 100% conversion efficiency, although a big part of that heat will be lost to the outside. A double layer balloon, with a transparent outer shell and a black inner shell would be more efficient.

Then you can put a few PV cells to power your engines.

[Sillychris]

The only problem with a black balloon is you can't control your buoyancy... Kinda hard to get down

[Nibb31]

Just open a flap at the top to let the hot air out and you go down.

[jwenting]

The only problem with a black balloon is you can't control your buoyancy... Kinda hard to get down

[einsteiner]

Any inefficiency in the solar panels just generates heat anyway, so you're not going to lose any potential heat. It may be useful to convert some energy into electricity that you either store or use for propulsion.

[lajoswinkler]

worse, you never generate enough heat to get off the ground...

Not true. I don't even understand why do you think it should be right.

Solar cells are futile for this kind of thing (and lots of other stuff, too), because you can do what Idobox said, paint the thing black.

[einsteiner]

It probably wouldn't be useful, but I'd like to see a balloon covered with LCD material so it can switch between light and dark to control heat absorption.

[Sillychris]

Just open a flap at the top to let the hot air out and you go down.

EXCELLENT idea! I'm sold.

[Idobox]

Any inefficiency in the solar panels just generates heat anyway, so you're not going to lose any potential heat. It may be useful to convert some energy into electricity that you either store or use for propulsion.

Solar cells are heavy. If you can make solar cells that are comparable to black paint, then why not.

[nhnifong]

I'f we're going to include a small solar panel for auxiliary electronics, where will we put it? if it's on top of the balloon, won't the weight collapse it? and if it's on the basket, won't it be shadowed by the balloon? Maybe we need to stick it out on a pole.

[Sillychris]

I'f we're going to include a small solar panel for auxiliary electronics, where will we put it? if it's on top of the balloon, won't the weight collapse it? and if it's on the basket, won't it be shadowed by the balloon? Maybe we need to stick it out on a pole.

You could hang it below the balloon such that it would only be shadowed when the sun is directly overhead.

[Seret]

So when the sun goes behind the clouds you lose control of your buoyancy? That doesn't sound safe.

[Idobox]

So when the sun goes behind the clouds you lose control of your buoyancy? That doesn't sound safe.

Thankfully, balloons have a significant thermal inertia, and are not piloted like flappy bird. It won't crash, but slowly loose altitude, giving you maybe 10 or 20 minutes to react if the sun stays hidden.

And before flying a hot air balloon, you'd better check the weather anyway, because they are highly dependent on wind and don't like storms at all. Getting caught by clouds would mean either terrible luck, or bad preparation.

Finally, the balloon could be unmanned, or fly above the cloud layer, but in the end, you're going to face a big problem when night comes.

[Seret]

I realise that, you've also got the option of using ballast to limit an externally imposed rate of decent. But you've got to admit it would limit the utility of such a balloon somewhat.

[K^2]

It probably wouldn't be useful, but I'd like to see a balloon covered with LCD material so it can switch between light and dark to control heat absorption.

LCD tends to absorb a ton of light even in the "light" mode, which is why LCD screens have such powerful backlights. One not designed to be a screen can do much better, but it's still going to absorb a lot of light.

What would probably work way better is something like e-Ink. That stuff can be designed to switch between extremely reflective and extremely good at absorbing light. Just turn the sun-facing surface coal black, and the shadow side silver, and you have yourself a nice amount of heat buildup in the balloon.

[Sillychris]

So when the sun goes behind the clouds you lose control of your buoyancy? That doesn't sound safe.

Propane backup.

[Nibb31]

I'f we're going to include a small solar panel for auxiliary electronics, where will we put it? if it's on top of the balloon, won't the weight collapse it? and if it's on the basket, won't it be shadowed by the balloon? Maybe we need to stick it out on a pole.

Solar panel technology is improving. Companies are working on ultra-thin, flexible, and transparent solar panels. I've seen prototypes of cell-phone screens that include a transparent solar film, and there are plans to make car paint that acts as a solar cell to recharge your batteries.

It is quite probable that we will see ultralight solar film pretty soon.

[Seret]

Propane backup.

If you're talking about carrying people, you'd certainly want to have some other way of adding buoyancy.