new project

[KTP]

In my other thread I mentioned wanting to purchase a few of the "satellite" quality multijunction solar cells.

The thing I want to build is sort of trivial, but some might find it amusing.

I have a few different models of the tiny flying devices (one is a helicopter, the other is more of a spinning rotor driven by two fans) which use a very small li-ion battery to give 5 to 10 min of flight time.  They are really cheap (under $15) so not a big deal if you lose them.

My idea is to interface a msp430 and a 3 axis accelerometer to the flying device, along with a couple of solar cells capable of recharging the li-ion battery over several hours (how long doesn't really matter).  I would also like some way of righting the device if it lands upside down (some sort of muscle wire lever?).  No real point to the device right now, just want to build it for fun.

[Simon]

so are you saying that you want the cells to be on the flying machine or just as a "charging launchpad" ? not sure why you want the accelerometer I don't think you've explained the whole project ? is it going to fly itself ?

[Zad]

For what aerospace grade solar panels cost you could buy an entire helicopter, not just a model. I would have thought looking at price per watt would be a better performance indicator.

[KTP]

For what aerospace grade solar panels cost you could buy an entire helicopter, not just a model. I would have thought looking at price per watt would be a better performance indicator.

It is not like I need a 1000 watt panel or something.  I just want about 0.25 to 0.5 watts.  I had thought perhaps some company might sell chipped aerospace grade cells for a discount.  For example, if a new, 30% efficient triple junction GaAs 0.5V 1 amp cell (or whatever they are made of now) is $300, then maybe a chipped cell would be $30.  Maybe I am dreaming.

The amorphous cells will give me voltage in very low light (they power the msp430 in a room with a single 60 watt bulb at the ceiling) where the monocrystalline cells will not give squat.  In full sun, the monocrystalline cells are about 17 to 20% efficient where the amorphous cells are about 6%.  It was my understanding that the newer aerospace triple junction cells work well at a wide range of wavelengths and at low light levels...

If the helicopter lands in full shade, I wanted it to be able to recharge itself to move away, even if it took a few days.


Simon: yes, I meant the helicopter would be autonomous and carry the solar cells with it.

[Simon]

I'm not sure of the weight of the cells you have in mind but a model helicopter will cope with not much more than it's own weight, thats why we still don't have solar powered cars, solar cells are heavy

[cksa]

I beg to differ. The fact that solar cells are heavy are not why we don't have solar powered cars, but the fact that cars nowadays are far to heavy, requiring a lot of power to run - power which cannot be supplied by solar power alone, and also by their cost.

solar panels can be quite light, depends on what type of encapsulation you use.

[Simon]

yes your right my main point was just how cumbersome they are and their power to weight ratio, think of the weight of your standard 20 pannel and then try and put it on a chasis with a motor,

Of course the project in discussion does not require 1:1 power delivery as batteries can be charged over a period of time and there are specialized panels but that all needs thinking out very carefully

[TechGuy]

I beg to differ. The fact that solar cells are heavy are not why we don't have solar powered cars, but the fact that cars nowadays are far to heavy, requiring a lot of power to run - power which cannot be supplied by solar power alone, and also by their cost.

solar panels can be quite light, depends on what type of encapsulation you use.

The issue is that the Sun only puts out 1.4KW per square meter. and thats in the best of weather conditions. The Sun doesn't provide sufficient energy to power a car, nor would it contribute a significant amount of energy to be practical.

Nobody wants to buy a car that weights just a couple hundred pounds to make the power to weight ratio feasible. I don't even like sub-compact cars, especially when the majority of drivers drive large SUV's and large trucks weighting tens of tons on the road. One small mistake in a ultra-light car, and your instant hamburger meat, and ultra-light sun powered cars would provide any useful space to transport any significant loads. It would basically be the size of coffin with just barely enough room to fit a thin person.

[EEVblog]

Nobody wants to buy a car that weights just a couple hundred pounds to make the power to weight ratio feasible. I don't even like sub-compact cars, especially when the majority of drivers drive large SUV's and large trucks weighting tens of tons on the road. One small mistake in a ultra-light car, and your instant hamburger meat, and ultra-light sun powered cars would provide any useful space to transport any significant loads. It would basically be the size of coffin with just barely enough room to fit a thin person.

And that is the unfortunately state of today's society. We have been bought up on big heavy fast cars and they dominate the roads. Changing to smaller more practical electric cars and bikes won't be quick or easy.
Ironically, if we all had slower more compact electric cars and bikes that were only half the speed of today's big heavy fossil fuel cars we'd almost certainly get where we want to go quicker and safer!

Dave.

[Simon]

very true, I usually never exceed 55mph and get there as fast as anyone else and get to all junctions finding them que free because I've taken it easy and the last car of the cue is pulling off just as i arrive, no breaking, stopping, revving and changing from 1st gear up again, just coast through and carry on. My car weighs 1.8 tons and has a 1.8L engine (115 hp) yet I've got as much as 47 mpg* around town ! surely the same consumption of a lighter car driven by an average driver, if people only understood how to use energy efficiently we would already have half the carbon foot print we do.

*using 99 octane petrol from shell