I found some useful info on diodes by someone named Paul Neelands that some might be interested in:

Question:

>When using a diode to stop reverse current at night with a solar panel
>what is the best type to use? The books suggest a zener type which are
>expensive. My electronics friends say any general purpose diode with a
>high enough current rating is ok. How do you decide what to use?
>


Answer:
Some comments

#1. Unsuitable diodes:
A zener diode is totally unsuitable. The function of a zener diode for
reverse voltages below the zener voltage is to block the flow of current and
for reverse voltages above the zener voltage to conduct. Also like all diodes,
it will conduct normally in the forward direction. Conceivably a zener with a
zener rating well above the maximum reverse voltage applied to the panels
might work, however the forward drop across the zener diode will be much higher
than the proper diode.

#2 Suitable diodes:
The choice is between silicon diodes and schottky diodes. Schottky diodes
have a lower forward voltage drop than silicon diodes so they are the best
choice. They are perhaps slightly more sensitive to voltage transients
than silicon diodes but the difference in recent years (they have improved in
ruggedness) is now fairly small.

#3. Ratings
A. Voltage.
The diode must have a voltage rating greater than the peak voltage
applied to the solar panels plus a safety factor to account for transients.
For a 12 volt system a 30 or 40 volt rating should be adequate. However the
loss or forward voltage drop of the diode is proportional to the voltage
rating. Thus very high voltage ratings should be avoided to minimise loss.

B. Current
The diode must have a current rating greater than the peak current
delivered by the solar panels at peak sun on the best day of the year. Some
current
margin should be used. This generally provides a slightly lower forward voltage
drop and allows for easier heat sinking.

C. Heat dissipation
The diode must be mounted on a heat sink to dissipate the heat
resulting form the forward current through the diode multiplied by the forward
voltage drop of the diode. A typical forward voltage drop under load would be
0.6 volts. Thus a 30 amps panel current, the heat to be dissipated would be
0.6 x 30 = 18 watts.

#4. Wasteful
Using a diode for the reverse blocking function is slightly wasteful
of solar energy. For example a 100 watt solar panel delivering
14 volts at 7.14 Amps if run through a good schottky with a forward
drop of 0.47 will waste 0.47 x 7.14 = 3.36 watts or about 3.36% of
the panel output. At current peak solar panel prices of about $8-9
Canadian per watt that is roughly $28. Some solar controllers use
relays for this function, others use a MOSFET switching approach.

#5. However
Frequently the solar panel is not well matched to the battery. In
particular in cold climates the panel output voltage will be quite
high. Since solar panels behave as a current limited source, inserting
a diode in series with a panel under these conditions, the panel will
just supply the required higher voltage at the same current. Thus to
the end user, not apparent change in delivered energy occurs. In warm
climates or on hot days, this is not the case and the panels may not
be able to deliver excess voltage above the battery voltage. In any
case this excess voltage still represents a system energy loss.



#7. Availability
In general these parts are readily available at electronic parts
distributors.
A few random distributors that will sell in quantities of 1 follow:
In Canada: ElectroSonic or Active Components.
In the US: Digi-Key, Newark Electronics.

#8. Prices
Prices vary but a 1Amp device should cost about $1 Canadian. A 20Amp
device should be roughly $4-5. A 50Amp device should be $10-20
again Canadian.

#9. Conclusion
This is a limited sampling of diodes from a few manufacturers. Many other
companies make schottky diodes, and there are many other distributors.
If any name in here needs to acknowledged somehow it has.

Paul Neelands
Totally off grid for 9 years.

Most of this does not apply to bypass diodes used in solar panels , which i s what your are trying to figure out on your own.

Most of what you have posted would be for blocking diodes , which in most solar systems aren't used becuase the inverter or charge controller performs this function already.

In small systems that directly connect to a battery , the blocknig diode loss is more than the night time reverse loss hence why blocking diode aren't used

Do a google search on bypass diode , its funtion is to allow voltage to bypass a shaded cell , otherwise the shading of a single cell can take out the entire production of a series string of cell/panels. It also protects the solar cell from th entire strings voltage being sourced by the shaded cell , preventing overheating and failure of the cell

No heat sink is need on bypass diodes , typical Si diodes are used , in larger panels the are paralleled for higher current production. Radio Shack has some nice 5 amp diodes I have used for 2 bucks. On a 12 volt
panel you need a bypass diode every 1/2 panel (6 volts) and if the current exceeds the rating of the diode , you need to parralel them.

in A KC-120 for example , they use 6 diodies configured 3 by 2 for the panel

Thanks Henry, I continue to learn more about electronics everyday! I got something clear now. The diodes mentioned in this article are for a different purpose. And you are right, the ones I am looking for are the bypass diodes. How dificult would it be to install these on the non-finished laminates?

Thanks,
Adiel

without the proper Jbox , very difficult. Your going to need to bring the metal strips from the laminates to some type of terminal block. All connections for wire and diodes should be made for this block , other wise your going to end up ripping off the fragile metal strip/tab and them no more power from the panel ...

I'll say this one last time ... don't buy the unfinished panels from sunelec , they have no jbox , no by pass diodes , no wires , no frame , no warrenty , just three metal tabs commnig out the back.

The fact your in need of all this info should convince you the savings of 2.40 watt vs 3.00 watt are mythical. I am pretty close to as knowledgible as they come , as I design , code the electroncs , i've installedl the part s and complete systems. With this knowledge I wouldn't buy them when offered at 1.90 watt.

So if your going to buy them you must beileve you a have better skills than me , even if your questions suggest otherwise

Here is what should be there ... the tabs come up from the bottom and connect to the terminal strip

Henry, for once in my life I am going to start paying attention. Those cheaper unfinished panels spell more "trouble" than "savings". You mentioned $3.00/Watt. Where can I get some of those??

Thanks,
Adiel

Bump

Still looking for a source of cheap panels...