Battery of the Future?

Even if you get get 100% efficiency (and you can't) the MAXIMUM power you can get from 1 square meter of sunlight is ~100 watts. That's a lot of covering to get that kind of power. Take into account real world efficiencies and so on and you are looking at a pretty crappy power system for a sport RC plane, even if just to charge a flight pack. The real grand idea is to cover as many surfaces as possible with this stuff and add all of that power together to make a dent in the amount of fossil/imported energy we use. Flexible, cuttable, now make it efficient and cheap to manufacture..........

Jim

On Tue, 14 Aug 2007 11:11:48 -0400, I said, "Pick a card, any card" and James Beck instead replied:

You didn't miss the word 'future' in my subject line?

You're correct on all points. However, the technology is very young. Remember when the only storage for electricity was a Leyden jar? Before our time, certainly, but look at the leaps in battery technology over the past 100 years. Just the past 10 years of advances have been phenomenal.

A friend of mine and I played around with amorphous solar cells back in the early '90s, sputtering them on the top of a panel mounted on a VW Bug. They weren't pretty and they were heavy as rock slabs (mostly silicon) but they were very efficient. The goal was to make them flexible. We sprayed them on stainless steel panels and scraped them off using a spatula. We added all sorts of neutral stuff to give it flex but never really got it right. I gave up playing with them after a year or so and now see that the technique has been successfully applied to rubber mats that you can put on the roof of your car and trickle charge your battery on sunny days or use for charging motor home batteries.

Sometimes, I'm a dreamer. Then reality strikes. I just love the idea of paper batteries that can also charge themselves.

-- Ray

I understood that you meant future. I was just throwing in a little reality check on just how much power you can expect to get period. You aren't going to harvest more power than the sun is providing. When you take the total area of the earth it is an ENORMOUS amount of energy, but the amount that actually falls on the covering of a plane is quite modest and most hobbists are not going to go out for some super light weight exotic plane just to say it is solor powered.

You are still bound by physics. Average solar power is ~146 watts/square meter. Peak solar power is `600 watts/square meter. That's the best you can do unless you turn up the sun ;)

Jim

Well you could have a 747 equipped with mirrors flying above it to deflect extra sunlight on it.

I reckon that with a perfectly efficient power train, you can *just* stay aloft at 3W/lb. Realistically you need about 12W/lb to do it with normal props/motors etc.

At 150W/sq meter, you can just about crawl a 10lb model off the ground with a square meter of wing.

The wing loading would be ~14 oz per sq foot. So its not totally pie in the sky. You could probably get the weight well below 10lb on a square meter of wing too. If you could get cheap >30% efficient lightweight photocells its probably a goer.

Not a hugely interesting model to fly..wouldn't knife edge a damn :-) but it would probably fly..

Sounds very eco-logical ;)

Exactly, for "real" flying you need a bit more umpf.

Until that cloud passes over. LOL

Sure, they have even done a full scale with a passenger using only solar power. You would die of old age before you got anywhere AND it was so flimsy that even a stiff breeze would buckle the wings, but it did fly.

Solar is great for using on massive scales where it is impossible for all the collectors to be out of commission. As a point source, it is pretty iffy. That's why most people off the grid use combination systems and still have to have a backup generator just in case.

Jim

| Even if you get get 100% efficiency (and you can't) the MAXIMUM power | you can get from 1 square meter of sunlight is ~100 watts.

Actually, sunlight is about 1000 watts/square meter at ground level at the equator assuming no clouds or haze. Above our atmosphere but still near the Earth, it's almost 1400 watts/m^2. You're off by a factor of 10.

(You did say MAXIMUM and 100% efficiency, after all.)

This 1000 w/m^2 figure is for the equator, but as long as your solar panel is directly facing the sun, you can still get most of that as long as your latitude doesn't go too high (causing the sun to go through lots and lots of atmosphere before it reaches you.)

100 watts per square meter is actually be a reasonable real-world value (during bright sunlight, not the average), considering panels that aren't pointed exactly into the sun and not being directly on the equator. If everything is perfect, 150 watts/m^2 isn't unheard of -- but it does require that everything be just right.

| That's a lot of covering to get that kind of power. Take into | account real world efficiencies and so on and you are looking at a | pretty crappy power system for a sport RC plane, even if just to | charge a flight pack.

If the solar cells were extremely light, it might work reasonably well to keep a flight pack charged on a sunny day. But to power an electric plane, you'd need a plane designed around this, and perfect conditions -- and then it would barely fly. But it's been done, many times. I think I've even seen solar powered ARF or kit planes!