Glass + Sylgard fail anyone yet?

[martinjsto]

hi

I also agree with you sunking, its seems like you have experienced these efforts before and see the failures stack up, its good for experimenters to be told the limitations of there projects before they start, can save a lot of waist (time, money, tears, wife etc). there is no doupt that to try to re-create the wheel is a difficult road to venture down, however i also believe its the person in there back shed trying different idears out and experimenting that spawned some of our greatest inventions and idears. i too am trying to create my own panel using silgard 184, research on the product shows it is reccomended by the panel manifacturers ndustry, it is used as a potting resin for fine electronics encapsulation, is acid free, non conductive, drys flexible but stiff uv resisant and the only one known not to discolour in the sun, the use of EVA as a laminate is the more predominant method used to make panels, under vacume and heat multilayers of eva and another backing material that escapes me now, sandwiched together.
lots of money to try to reproduce that but encapsulation is viable, still expencive product but if you want to get at least a chance of success you have to use it,
im trying to encapsulate my cells between glass and a tough plastic backing using a similar method of vacumm encapsulation used by the fiberglass industry. i have a vacumm pump from my a/c tech days, i should not get bubbles as there wont be any air, i will flush with nitrogen prior to vavumm, and should only use about 1/2 tub of sylgard for a 80w panel.
im using toughend glass from shower recess. i want to know the best wiring arangement to fix the mismach from shadow using diode's, i have got a great site with instructions, pics and drawrings but its the first ive found and wouldnt mind other opinions
the link is

http://rifraf.dyndns.org/solar/

not sure if i found it on here or another solar forum.
thanks and good luck

[Mike90250]

Diodes are tough, you have to leave access to them, in case something frys them, and you need to replace one.

[rhjames]

It seems to me that the diodes can be connected external to the panel in the connection wiring. This gives easy access for replacement. Wiring from all panels would go to a weather proof junction box, which includes the diodes.

[Mike90250]

There also need to be several bypass diodes for each panel, which need to be at the panel, not remote mounted.

[rhjames]

I guess that depends on the size of the panel. If there are 36 cells in one panel to give 18V, then as I understand it, no diodes are used within this panel, but would be used to connect multiple panels of this size. Please correct me if I'm wrong.

[Sunking]

silgard 184, research on the product shows it is recommended by the panel manufacturers industry, it is used as a potting resin for fine electronics encapsulation, is acid free, non conductive, drys flexible but stiff uv resistant and the only one known not to discolor in the sun, the use of EVA as a laminate is the more predominant method used to make panels, under vacuum and heat multilayers of eva and another backing material that escapes me now, sandwiched together.

There is the crux of the problem. You cannot recreate millions of dollars of special tooling, machines, and processes the manufactures use.

I do not blame anyone for trying and experimenting on a very small scale, but in the end, you are better off just buying commercial made panels.

[Mike90250]

I guess that depends on the size of the panel. If there are 36 cells in one panel to give 18V, then as I understand it, no diodes are used within this panel, but would be used to connect multiple panels of this size. Please correct me if I'm wrong.

You asked.
Every 3 or 5 volts worth of PV in a panel, needs to have BYPASS diodes, which allow a portion of the panel to be shaded, and the power of the rest of the panel, use the diode bypass. Otherwise, and especially if you have panels in series, the dark portion of the panel, goes high resistance, and can be burnt or damaged by the other active cells.

Blocking diodes, are used to prevent a battery bank from discharging at night, thru the panels.

No diodes are needed to connect multiple panels of any size. Fuses are used when panels are connected in parallel, to prevent a bad or damaged panel from being burned from the other active panels.

[rhjames]

Thanks - that clarifies it nicely.

[martinjsto]

thanks, that helps heaps, so keeping them in the junction box is the go, I think one of the pics shows that. i have a old bp panel that has 3 in it and a wiring chart, need to replace the bus but should work fine, what about heat from the diode's, i guess being external it should be ok?

[rhjames]

So I just purchased 72 cells to make two 18V panels. Two diodes (T6A100L) were also supplied. I assumed these to be blocking diodes, which I would wire in series with each panel. Some literature claims that for low voltage systems such as this, bypass diodes aren't necessary. What diodes are used for bypass?

[RifRaf]

3 diodes in junction box appears fine for smaller panels like 100w or less, for a decent size, like 72 6x6 cells, i would use at least 6, which is very easy to incorporate between rows like bus wire, the sylgard is easy to remove if diodes need replacing, have just modified 2 large panels removing the sylgard and silicon and successfully installed bypass diodes, then cover with more silicone, and can replace again if needed.

this is a big advantage of not having a backing on the sylgard, repairs are able to be made so a bad cell or junction can be fixed, you can neatly remove a cracked cell and replace it, then mix up a tiny amount of sylgard to embed the repair.

can this be done with the epoxy methods that have been talked about, has anyone tried the epoxy stuffs yet?

[Mike90250]

T6A100L 6A 6 Amp 1000V 1KV Axial Diode Rectifiers

Are cheap crap for solar usage. 20 cent diodes, high forward voltage. For high efficency, you want Schottky diodes, which have low forward (conducting. on.) voltage.

a better choice for bypass diodes would be a 6A 60V schottky diode, here's one thats close:
SB560 5 Amp 60V Schottky Rectifier Diode

Many vendors carry a wide selection of diodes, in many package styles.

heres's a Dual diode in a TO-220 package which may be easier to handle / mount.

[martinjsto]

with those schottky diodes how do you wire them as they have 3 legs in the to-220 package. i know there anode, cathode, anode, does that mean you can just use one for two circuits ?
if so which do you wire to the common, pos or neg?.
best price on diodes is from mike at world wide electronics. im not affiliated or get any kickbacks etc from here.

http://members.iinet.net.au/~worcom/browse_catalog.php?search_by_terms=diode

16CTQ100 SCHOTTKY DIODE DUAL 100V 16 AMP $2.50
would these be good?, i have seen similar used on other sites.

[rhjames]

Mike - re multiple panels - if blocking diodes aren't used on each panel, and the panels are connected in parallel - if one panel is shaded, couldn't the others discharge through it?

[Mike90250]

My thought was to use the handy TO-220 package, just use one diode, and ignore the other. Trying to use both diodes and keep wires short, maybe it's not worth the trouble, and the diodes are cheap.