I'm moving from an ST to a GT inverter so on top af adding some panels I have to boost the voltage from 12 to 24v. I have Evergreen panels that came with some jumper plates and diodes. Looks like the jumpers go between one + and - post and the 2 diodes go between the two +'s and two -'s. I never used the diodes for my current installation. If my memory serves me I think they help in the case of partial shading which I do get early morning and late afternoon. I guess I'm looking for advice here as to advantages or disadvantages. thanks

You need the bypass diodes, if not you will burn holes in you panels where the shading occurs.

Its not an optional thing, if you damage your panel, your warranty will be voided and you out the $$

The Diodes go in parallel with the +/- of each group of cells, you should have directions that came with the panels, if not goto the Evergreen site and make sure you do it correctly!

sorry, my mistake. I just opened one of the wiring boxes on the panel and the original jumper has an integrated diode in it. The ones I have are for when I change the panels to 24v from 12v. The new jumper ties one + and one - together and the diodes go between the two + and the two - connectors according to the little wiring diagram. Thanks for stressing to me how important they are though.
On another note, I just called Sunelectric and they don't have any 102w blems which is what I have. What would hapen if I added four 110w or 115w to my four 102w in a string? Would it cause a problem? 115w blems are cheaper than new 102's.
Again, thanks for the advice.

If your doing a single string, it will work 100% fine. The stronger panel will just operate a few tenths of a volt higher and at the slightly lower current (of rated vmp) to match the other panels.

FYI, this by the way, is one of the main strenghts of running high voltage, a SINGLE series string, the panels will self balance to match the current with very little if any loss in total watts.

So get the 115watt ones, they will work great in your application

I have two of the 115 watt panels from Sunelectric and two more on the way. I have them paired up to make 24 volts and will do the same when the next two get here. I as well have two shell and two sunwize panels. I have watched to keep all my panels close to the same voltage of 17.1 to 17.3 volts so not much voltage loss. And being I am not pairing a higher amp panel with a lower amp panel it has been working great. The EC 102's are 16.2 volts, 6.3 amps and the 115's are 17.1 volts, 6.73 amps. I would try to keep two 115 watt panels paired and two 102 watt panels paired because you would loose amps by hooking a 102 to a 115. But still yet compared to buying a non blemished 102 watt panel or loosing a couple tenths of an amp or volt by hooking them together I would buy the cheaper panels.