Any sources left to buy a pallet of new solar cells?

rmay635703

Several years ago I was scouring the internet to find a low volume source of solar cells to build a couple odd voltage trickle chargers for my 2 evs and I found a post mentioning buying them in bulk $500 bulk at a time. The cost over 2 years ago was $.31-$.65 a watt depending on tabbed, volume etc. Back then I didn't want $500 worth of cells but now after looking at ebay I could just get rid of the extras.

Anyone know of any places that sell moderately small amounts of solar cells without ripping me off. I really don't want to pay $1.76+ a watt for cells when I can buy the whole panel for less than ebay. Heck If I would have pulled the trigger sunelec had them for under a buck a watt and they were about the right voltage too

I also do not want to buy $5500 worth of cells either

Also I was told that country crews sell off old panels, that might be another option but the voltages I need are odd. Any ideas of what companies in Wisconsin would handle cleaning out highway crew pulls from road signs?

Thank YOu
Ryan a solar wannabe.

BB.

Re: Any sources left to buy a pallet of new solar cells?

Do you need battery/energy storage (large caps)?

If so, you could use a "standard" MPPT type solar charger (probably effective down to 100 watts or so of panels) to, say 12 volts... Then use ~80-90% efficient down converters to your special voltages.

If your needs are smaller--then you get into the trade-off where you end up paying as much or more for the converters vs just buying "extra panel wattage" and just using analog/PWM voltage regulators and only getting 50% or less efficiency (but very low regulator costs).

In general, defining the loads gives us a better handle on how to suggest various solar PV power system options.

-Bill

niel

Re: Any sources left to buy a pallet of new solar cells?

i'd be curious what base battery voltage you are talking about as it may be possible to obtain smaller pvs and place them in series. your problem may be in the regulator being non-standard and difficult to find one readily available to suit.

rmay635703

Re: Any sources left to buy a pallet of new solar cells?

I was hoping to build a trickle charger for both, one is 48v AGM (58v absolute max) the other is 72v FLA. One of the setups might be moving to 50v silicate batteries.

Anyway lead acid batteries last much longer if they have a small trickle charge, even when they are fully discharged a small charge can keep them alive. So I was hoping to build a small inexpensive solar panel that would not output enough current to overcharge my FLA considering I drive the car every weekday and have 2 days off on weekends. Since I charge at night and drive in morning then the car sits during the day partially charged the panels could be quite large and still not overcharge the battery even without a charge controller.

If the price were cheap enough I would build a panel to fit the 4x8' area on the roofrack of the zx40 mini-van ev. But more realistically I just need something that can trickle a small current to save my batteries and run my desulphator circuit.

And yes I prefer CELLS, I am not really looking for panels. Panels on cars don't always agree but I guess if they aren't real expensive like those $58 60 watt panels from sunelec a while back...

Back in the day I thought $500 minimum for cells for too much now I wish to god I still had the bookmark, they were a long standing US based company and one of the few that would send you a pallet of cells out. Even if I didn't use them for little experiments I'm sure I could clear them out considering the rediculous prices people pay for cells broken or whole.

I always figured a smart cut off switch would be the easiest charge controller if someone has a diy to make a ciruit to sense the pack voltage and cut a contactor or relay once its met and stay that way.

Cheers
Ryan

niel

Re: Any sources left to buy a pallet of new solar cells?

if you can get cells to agree on cars, more power to you. we have had discussions on diy panels, but to put the cells on a car just will not be viable cost wise, let alone last. i would find some decent small pvs and wire them in series for a good voltage. controllers are workable for 48v, but at 72v you'd need something special. if you must do the individual cells then consider placing them say under the rear window for protection. i know that's not optimal for collection, but you will know the weather won't hit them directly that way. other factors will still be detrimental such as condensation and if one smokes that would get to them also.

rmay635703

Re: Any sources left to buy a pallet of new solar cells?

niel wrote: »

if you can get cells to agree on cars, more power to you. we have had discussions on diy panels, but to put the cells on a car just will not be viable cost wise, let alone last. i would find some decent small pvs and wire them in series for a good voltage.

That was what I was thinking and no I don't smoke, I figured a small set along the angled surface of the window, it sits way larger than I need to view so the cells could even be left along the top edge without issue.

And $0.50 a watt isn't that expensive to put on a car, especially when I really only need maybe 5-30 watts. (depending on how much area I can find and the wattage of individual cells) Solder isn't expensive either, they would be after all tabbed.

Photowhit

Re: Any sources left to buy a pallet of new solar cells?

If your worried about a minimal charge to help the battery from complete discharge ruining the but worried about overcharging them...

Just put in a diode to drop the voltage(zener?), this could reduce/incapacitate the solar chargers ability to reach the higher voltages to over charge, but be high enough to apply a charge to a relativly discharged battery.

niel

Re: Any sources left to buy a pallet of new solar cells?

photowhit,
it really isn't as simple as a zener diode as this often requires a resistor of the proper value and power dissipations need to be observed for all components. this is a possibility though as one of the simplest type of regulators.

Photowhit

Re: Any sources left to buy a pallet of new solar cells?

He is only talking about 30 watts.

I have some 4/5watt 6 volt panels setup this way for 3rd world countries to us with basicly any 12 volt sorce (using them in series and parrellel) for a minimal light source, they shipped with a 4 watt florescent and a base and a couple panels.

I suspect higher wattage would create a problem but did not think 30 watts would be, I am certainly not an electrician, just someone who has been around solar for a long tiime.

niel

Re: Any sources left to buy a pallet of new solar cells?

Photowhit wrote: »

He is only talking about 30 watts.

I have some 4/5watt 6 volt panels setup this way for 3rd world countries to us with basicly any 12 volt sorce (using them in series and parrellel) for a minimal light source, they shipped with a 4 watt florescent and a base and a couple panels.

I suspect higher wattage would create a problem but did not think 30 watts would be, I am certainly not an electrician, just someone who has been around solar for a long tiime.

i'm sorry as i should clarify a bit more. when a zener regulates it must pass a great deal of the power and shunt it to ground. this would be the voltage difference between the zener voltage and that which is inputted along with the amount of current passing through it. say for instance you are floating at 13.5v and the input voltage is 15v (pvs are usually much higher than this) and the load is taken off or out of the circuit. this would press that voltage difference (1.5v in my example) at the full current if there's nothing slowing it like a resistor. even if the pv is a modest 5a that would be 5a x 1.5v = 7.5w. this is a modest example possibility as most conditions would press higher voltage differences with even higher current levels. there are high power zeners out there, but they are high in cost and are like a huge screw in power diode in appearance. most zeners are in the 1w area and appear as other small duty rectifying diodes do.
there are ways of extending the power handled by a zener with the simplest being a resistor and even better results with transistors added. it does not go by how small the pv watts are as this is certainly able to pop some zeners depending on the design circuit and wattage values for the parts involved. it is possible your z diodes could have popped and are looking like opened fuses doing nothing if they passed more power than they are rated for.

Photowhit

Re: Any sources left to buy a pallet of new solar cells?

Ok, since he's building his own it would be simple to reduce the number of cells until his VMP is below an over cahrge level and be fine for rescueing the batteries from a catastrophic low?

niel

Re: Any sources left to buy a pallet of new solar cells?

varying the number of cells may help, but i did not advise against using regulars and more specifically zeners as a regulator. in fact he should try to employ an even better regulator if he can, but my point to you was that it is just not as simple as you think to do with zeners as more planning and design needs to be done than just buying a zener.

Photowhit

Re: Any sources left to buy a pallet of new solar cells?

Thanks for trying to help me, I don't have a problem though and am just trying to help him.

niel

Re: Any sources left to buy a pallet of new solar cells?

you're welcome, but i didn't try to 'help you' as the post was to help rmay and if i address something you brought up as help to him, i can address it too.

Photowhit

Re: Any sources left to buy a pallet of new solar cells?

.... my point to you was that it is just not as simple as you think ...

Just looked like after I ageed ('OK...')that you decided to show your superior knowledge rather than address a some what interesting manner of addressing the problem.

I believe the reduction of cells would work, be nice if you wanted to address this rather than returning to a point I accepted. Don't see a reason it wouldn't, perhaps you do?

He is not trying to fully charge rather than provide a some charge to keep the battery from bottoming out.

niel

Re: Any sources left to buy a pallet of new solar cells?

if it is your opinion i am wrong then you may still advise him. don't be so touchy as i'm not trying to belittle you, but i'm trying to help him. if i have to be somewhat technical because i'm called out on my advice then what did you expect? in any case i'll not address this further as it is trivial.

myocardia

Re: Any sources left to buy a pallet of new solar cells?

Hi, Ryan. For the reasons mentioned by Niel (condensation being your #1 enemy in this instance), attaching solar cells to the interior of the windows of your EV(s) would be an exercise in futility, to say the least. Also, solar panels/solar cells must be pointed directly at the sun to be able to produce anywhere near their rated power. They lose a large amount of their output capability when they aren't. Like in the neighborhood of 1% loss per degree that they are off. Add to that the fact that no manufacturer has made a flat automobile window since the 1940's, and that while solar cells are as thin as paper, they bend about as well as glass, and you can see why you would be the first person ever to attempt mounting solar cells to the interior surface of your vehicle windows.:D

For the purpose you mention, you'll want to use six "12V" panels for the 72V minivan, and four 12V panels for the 48V EV. They'd need to be mounted to the roof, so you'll actually get some usable output from them during the highest insolation period of every day, ~11 AM-1 PM. Luckily for you, this is when the sun is directly overhead, and flat on the roof is the perfect location. Well, it's about as perfect as is possible with an automobile, at least.

As far as panel sizing goes, you'll want to use a minimum of 10 watt panels, although my best guess would be that you'd me much, much happier with the ~1A of actual output that you'd get from six 20 watt panels. 10 watt panels are only rated for .6A max, so you'll only get ~1/2A of actual output from them. By the way, if you're interested in a link to the EV forum that I moderate, just shoot me a PM.

Robert