I want to add two panels to my existing 4x panels. The two new panels will have the same angle and direction of the other four.

Now the one new panel will get slight shade late in afternoon due to my fireplace chimney, will this have a negative effect on my existing panels production or will the losses be minimal on my existing system. 

In other words is it still worth adding a panel that will get shade or is it better to just rather leave it out completely?

If you are very cunning you can add a mirror somewhere else to cancel out the shade (allegedly!).

On 2020/01/31 at 7:08 PM, Gerrie said:

Now the one new panel will get slight shade late in afternoon due to my fireplace chimney, will this have a negative effect on my existing panels production or will the losses be minimal on my existing system. 

I got the answer after doing a little test with a blanket over the panels.

I installed two new panels as a string on its own. I through a blanket over them and there pv power output fell away completely, but it did not effect my other two strings pv output as the old ones were still generating power as normal. I also pulled the fuses on the new string, it has the same effect as throwing a blanket over that string.

So my conclusion is don’t put pv panels in the shade unless you have another plan. Now I just need to convince my wife I want to borough her dressing table mirror for a while and fit it on the chimney for my final test as Deepbass9 allegedly suggests 😁

I have the same situation where the chimney shadow will obstruct one string after about 3. If I understand correctly from your measurements I will lose the power from that one string when it is partially in the shadow but the other ones will still operate normally without any additional equipment, e.g. diode protection?

P.S. I am comfortable with losing the one string, I was more worried if I need to split them to different inverters or add diodes in series.

8 hours ago, Otto ES said:

I will lose the power from that one string when it is partially in the shadow but the other ones will still operate normally

Yes, that is correct you will loose only the string that has the shadow, your other strings will  still be generating power as normal.

I use a Axpert 5KVA so I don’t know if other inverters will have the same effect.

I remember reading (in other words I don't have the faintest whether this is correct) that if the shadowed panel is part of a string, only that string will be affected. It, does, in other words impact the other panels to which it is connected to in series. Not those to which it is connected to in parallel. The other thing I remember is that the shadowed parts of the panel will heat up... even to the extent of possible damage? Can anyone confirm?

I can't comment on parallel strings, but I can show the effect of partial shadow on a panel of a single string...

My two strings are 12S each (2 separate strings with 12 panels in series each) connected to separate MPPT controllers on a single InfiniSolar inverter.  In the mornings I have a roof overhang that creates some shadow on a few of the panels in string 2:

It does limit the output of that string (lower voltage & current = lower wattage), but it definitely does not "kill" the complete string!

As far as I understand 72 cell panels like mine have three have bypass diodes built in to cater for exactly this type of situation:

Indeed they have: