Glass and diode question

[prasath_ragavan]

Hello,

I bought some 40 solar cells from eBay and started building my panel. I have some basic questions.

a) What kind of glass can be used.Most of the websites suggest to use anti-reflective coated glass but I tried my best to get it in my city which is like impossible now to get in my town. People suggest an alternate to use textured ultra clear glass? I really want to know if its ok to go with this glass.

b) Is it wise to build panels with just two glasses glued together with sealant and framed with aluminum frame or a wooden hallow box and glass on top of it?Which one is weather proof? and heat resistant? I also see on many forums like people complain about their panels catching fire when they build it with wooden box during extreme heat condition. I live in a city where the temperature raises up to 47 deg Celsius during summer. So do I need to leave some gaps at the bottom for the heat to escape from the panel, will that damage my cells? or does it really matter if we have some vapour inside the panel? What will be the alternate? If we need to provide some gaps for the heat to escape where can those be?

c) I'm working on 12v panel with a charge controller so is it really necessary to use a bypass and blocking diode? I think I don't need a blocking diode since the charge controller can take care but how about the bypass diode?

Thanks

[DeltaFox 25]

A. You should use a low iron glass , I have to use just a hardened glass , Low iron is very exspensive.
B. If you just put two glass's togeather and seal it wiht silicone you will get moisture traped in with the cells and that will kill your cells. If you have a wooden box you have a chance of it catching on fire. I have seen pictures of the burn't wooden box's. Even if you have a vent there.
C. The charge controler will take care of it.

. http://photobucket.com/Wayne_2010

[prasath_ragavan]

So which one is ok to proceed with? two glasses? or wooden box and glass? Sounds like both has its own disadvantages!

[DeltaFox 25]

How about one glass , one aluminum frame , solar cells and encapsulatent ;

Try to click on my diagram on the last thread see if you can enlarge it. It will show you what I'm doing to make a solar panel.

http://photobucket.com/Wayne_2010

[prasath_ragavan]

Sorry I can't enlarge the picture! Do you have a larger version of it? Also I heard encapsulatent sealing will not allow heat or cool expansion of cells and potentially might damage the cells! So I need to understand the practical issues on this!

[DeltaFox 25]

I'll look for a way to enlarge the picture.

Dow Corning has made a cemical called sylgard 184 that is made for PV's to encapsulate them. Your cells do exspand with this on it. Check out Dow Corning Encapsulation .

[DeltaFox 25]

Now instead of eva and tedlar put in encapsulane and cells

[prasath_ragavan]

Thanks for the image @deltafox 25! That helps me a lot. I have another question. I bought a charge controller (TW-910) The spec says -
# Handles up to 5 amps of array (solar panel) current
# Rated Voltage: 12V
# Max input power: 60W.

Now since I got 40 solar cells rated with
# Average Power (Watts): 1.75 Wp
# Average Current (Amps): 3.5 Imax
# Average Voltage (Volts): 0.5 Vmax

I'm in a confusion that if I can use this charge controller practically! Because if I connect all the cells in series I will get ~70W, ~20V and ~3.5A.

Since the charge controller is rated just 60W can I still use it. I have a bit confidence where it says that it can handle up to 5 amps of array (solar panel) current. So is it ok use this charge controller or do I need to buy and use other CC rated higher than this? may be ~100W, ~30V, ~10A something like this??

Thanks

[DeltaFox 25]

You should allways think of exspandtion . You will probly add on in the furture. It probly would be best to get a larger one.

[Mike90250]

re charge controllers. You get what you pay for. Sometimes you get junk too. Stick with the name brands: Morningstar, Xantrex, Blue Sky, Outback, Rogue. Other stuff from China or fleabay, just is not what I would use to charge and maintain my expensive battery bank. Morningstar has a nice 45A MPPT controller that runs 99% efficient. Very slick. http://store.solar-electric.com/motr45ampmps.html

CC faq: http://www.windsun.com/ChargeControls/ChargeCont.htm
a store with many choices: http://store.solar-electric.com/chco.html

[prasath_ragavan]

Agreed I haven't thought about the expansion in future. But mike I think its kind of ok to go with normal CC from the brand you mentioned, rather than the MPPT. because as of today MPPT CC's are very expensive in my view.

On a long run if I built some more powerful panels I will surely get a MPPT one, for now for my DIY panel is it ok to go with what I have in my hand or do I still need to get one with higher ratings?

[Mike90250]

MPPT controllers are usefull for matching high voltage (low line loss) arrays, to lower voltage batteries, 48V 5A array, to a 12V battery @ 20A