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Getting ready to make my PV panel
By ibedonc, Section Solar Posted on Fri Sep 17, 2004 at 04:48:27 PM MST
none

Well I got them and out of 96 cells , I only got 4 that I would not use in a full panel, did not look like anyof them were broken due to USPS , these guy are now wrapping them in 1/4 lb lots with brawny Paper towels then 4 of those in large bubble wrap in a small box , then the 2 lbs were wrapped again and put into a larger box
I WILL be buying 5 more lbs . I got 92 full size unchipped cells
so what would be the best to use for a backing and best volts to wire for a 12v setup
checked on glass and for 1/8 tempered it would cost $80 for a 26" x 71" piece

Getting ready to make my PV panel | 17 comments (17 topical)

Re: Getting ready to make my PV panel (3.00 / 0) (#1)
by richhagen on Fri Sep 17, 2004 at 06:07:27 PM MST

I would measure the current from each cell and make the panel from cells which output reasonably similar current, connecting in series to the required voltage, usually about 36 cells per 12 volts of battery charging. Keep having fun, Rich Hagen
'A Joule saved is a Joule made'

Re: Getting ready to make my PV panel (3.00 / 0) (#2)
by zmoz on Fri Sep 17, 2004 at 06:08:18 PM MST

A 12v panel should be 17-18v worth of cells. For a backing you might want to look for a peice of ~1/4" thick plastic. I think that's what I'm going to do with the same cells.

Re: Getting ready to make my PV panel (3.00 / 0) (#3)
by jacquesm on Fri Sep 17, 2004 at 06:12:34 PM MST

Don't forget to put bypass diodes in there ! (anti-parallel to the cells, one every two or three cells will do)
www.greenbits.com

Re: Getting ready to make my PV panel (3.00 / 0) (#5)
by tecker on Fri Sep 17, 2004 at 07:31:50 PM MST

What the heck is anti parallel

[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#7)
by jacquesm on Fri Sep 17, 2004 at 09:00:37 PM MST

parallel but opposite polarity. Cathode = negative, Anode = positive to make a diode conduct. In this case you only want it to conduct when the voltage across the panel is negative (shaded panel!), the diode will bypass the panel, so you have to reverse it (Cathode goes to positive pole, Anode to Negative).
www.greenbits.com
[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#10)
by tecker on Sat Sep 18, 2004 at 05:57:46 AM MST

You mean your concerned about reverse bias internal to the panel. A blocking diode is most certainly nessesary ( schottky power type Less voltage drop).

[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#11)
by jacquesm on Sat Sep 18, 2004 at 08:03:14 AM MST

Hey Tecker,

That's not true, blocking diodes are NOT required, but bypass diodes are.

For a nice little schematic and some more info on the internals of solar panels have a look at this site.

I usually mean exactly what I say :)
www.greenbits.com
[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#13)
by tecker on Sat Sep 18, 2004 at 08:43:06 AM MST

If this is the only charger you got on the bank you don't or it you don't have inductive load or relays etc back emf will do some damage. Yeah that's bypass diodes between panels not individual cells.

[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#14)
by Ungrounded Lightning Rod on Sun Sep 19, 2004 at 11:40:01 AM MST

Quoting the site: Bypass diodes are not needed on 12V panels, optional on 24V, necessary on 26V.

Paraphrasing: The purpose of a bypass diode is to route current around shaded cells, to prevent damage from overheating due to the unshaded cells forcing current through it.

My impression is that in a 12V panel the forcing voltage across a single shaded cell will be sufficiently low that the extra heat will be acceptable - but in a 36V panel the voltage difference between the remainder of the panel and the battery is sufficiently high that a lot of power is available to be be dissipated in the shaded cell.

Also with respect to the blocking diodes: According to the site such diodes are needed to prevent panel leakage from pulling significant power from the batteries at night, but most charge controllers already have them (or something equivalent) internally. So you only need them if you're connecting the panels directly to the battery (using a "self-regulating", i.e. low-voltage, panel and accellerated water level checks, or a dump load for overcharge protection without charge-side regulation).

[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#16)
by jacquesm on Sun Sep 19, 2004 at 12:09:58 PM MST

yes, I read it too (I posted the link :), check out my other reply.

j.
www.greenbits.com
[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#17)
by Ungrounded Lightning Rod on Sun Sep 19, 2004 at 01:06:56 PM MST

yes, I read it too (I posted the link :),

Sorry, jacquesm. I didn't mean to imply that I was talking to you. I was just pulling out the significant details from your link and posting them, since your summary didn't seem to cover it ...

check out my other reply

... which DID cover the same stuff nicely. (I should have read ahead before jumping in.)

[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#6)
by ibedonc on Fri Sep 17, 2004 at 08:19:07 PM MST

I am going to do that in my charge controller , so the cells will not be directly connected to the batteries , will be using a charge pump to match the required charging volts , also I will be converting to 370 vdc using a MSW inverter , since these will be a ways from my house , the other reason is that my FULL SINE INverter that I am building will take 340dc volt input

[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#4)
by richhagen on Fri Sep 17, 2004 at 06:20:00 PM MST

I left this out, most current commercial panels have an open circuit voltage of around 20V in full sun for 12V charging. Similar to a wind genny, as the conditions improve, you will produce more voltage and current. From what information I have read and measurements from my panels, I believe that maximum power occurrs not far (a couple of volts or so on a 12V system) below the opencircuit voltage, and that lowering the voltage across the load beyond that does not increase the current greatly, and in fact reduces the power (P=IV) output. However I suspect this may vary somewhat with different cell types. The reason for matching the current of the cells in the string is that like a chain, the string of cells will only be as good as its weakest cell. If you put a .25 amp cell in a string of 1 amp cells, the output of the whole string will be brought down. You can see this by hooking a bad or weak cell and a good cell in series and measuring the short circuit current. Also, some people use 1/8" steel for backing, for my simple panel, I used glass, commercial manufacturers often laminate high strength plastics to the pack of their panels. Have fun building the panel and keep us updated. Rich Hagen
'A Joule saved is a Joule made'

Re: Getting ready to make my PV panel (3.00 / 0) (#15)
by Ungrounded Lightning Rod on Sun Sep 19, 2004 at 11:45:22 AM MST

Another reason the voltage is so high on a panel is that it drops when the panel gets hot - like 20% at 150F - so you need extra cells to keep the voltage high enough to drive current into your batteries.

This is why it is important to give the cells a way to cool (i.e. a backing that conducts heat well - metal or thin fiberglass - and an air gap behind the panels if mounted over a roof.)

Or add more cells to make up for poor cooling.

[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#8)
by veewee77 on Fri Sep 17, 2004 at 10:09:44 PM MST

You got yours in far better shape than I did! I only had about 54 that were usable.

Not a happy camper!

Doug

Re: Getting ready to make my PV panel (3.00 / 0) (#9)
by ibedonc on Fri Sep 17, 2004 at 11:55:43 PM MST

when did you order yours ?

[ Parent ]

Re: Getting ready to make my PV panel (3.00 / 0) (#12)
by jacquesm on Sat Sep 18, 2004 at 08:12:00 AM MST

Let me amend that a bit...

The case for bypass diodes is one that has to do with shading a panel or a cell within a panel. In that case all the current runs through the shaded cell and it can get hot, and possibly break. To avoid this bypass diodes are used, but these only have effect if you have a long string of cells. In a short string there isn't enough capacity for damage to mandate a bypass diode. If a panel is made for a 12 V only setup then you can probably get away without them. But since the future is an uncertainty and most people grow their systems over time what is a 12 volt panel today may well become part of a 24 or 48 volt string at some point in the future.

So unless you are making these panels for your car or boat I would highly recommend putting those bypass diodes in there, to make your panels future proof even if you only intend to use them on 12V today. Inserting them into your sealed panel a few years down the line will be a nasty job at best. It will also help their resale value in case you ever decide to offload them onto someone else.

Blocking diodes are only needed if you do not have a charge controller, and with all respect for people running banks with manual off switches I think that is being penny wise and pound foolish. A chargecontroller will save you many times over compared to messing up a $4K battery bank and will result in much less water depletion of your batteries.

If in spite of that you are going to go without a charge controller then you DO need a blocking diode at the + pole of each panel (or string for a multi-panel setup), rated at at least 2x the continuous current that the panels can produce.

take care,

Jacques.

www.greenbits.com

Getting ready to make my PV panel | 17 comments (17 topical)

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