Adding more panels to a 15 year old system.

 I'm helping a friend that has a small 12v system. He wants to add 4 more
panels to his existing 4 panel 12v system.

Should we worry about adding diodes to avoid problems?

   - jim

  Where would you put the diodes?

If they are all in parallel and all the same voltage, I see no problems

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 When there is uneven lighting they have attempt to have different output
voltages.

 Gymmie,

I would suggest you actually do some reading before giving advice , you
show a lack of practical lack of knowledge , it helps no one.

You can parallel solar panels just fine , blocking diodes are not needed.
Solar panels are current source devices , not voltage source. If one panel
is 12 volts and the other is 15 volts it makes no difference except that the
vmp is slightly different. All this means is you won't get the rated power
out of the panels since the will be operating slightly off vmp when
paralleled.

In the case of shading a panel , first the bypass diodes kick in and the
remaining cells operate at a higher voltage (closer to open circuit). If the
entire panel is dark , the panel will sink current , but it at a rate about
1/100th that of the rating of the panel. I have measured the loss into my
large 3kw array by hooking up a power supply to it at night ... it barely
pulled any current (dark outside) until I got the voltage to about 70 volts
(48 nominal array) , at about 80 volts it was sinking about 1 amp ....

www.solar-guppy.com/forum

 Since the gloves are off.

Try rereading what I posted and try a basic English comprehension course
before you make a complete fool out of yourself again.

Your information violates the laws of physics. You don't apparently know the
difference between voltage and current and have successfully demonstrated
you don't understand parallel or series circuit networks.

If one panel is totally dark and another (in parallel) is lit up, the dark
one produces no current because it cannot match the others (12v base)
15-18vDC or so. This means it has the lit up panels voltage accross it.
***If*** this could cause damage then you need series diodes.

Thanx for your experimental information. This is good to know. However I
tend to go by the manufacturer's information. They provide the warranty.