I’m planing to install a Victron MPPT 100/50 and 2x 190Wp solar panels (rated voltage 30.10V, no-load voltage 35.30V, rated current 6.68A, 2 bypass diodes inside panel , 1 bypass diode across panel) on my campervan. Both wiring the panels in series or parallel should be possible according to the maximum voltage and ampere limit of the MPPT 100/50.
Which one is preferable for maximizing the yield.
Are there differences in efficiency between both wiring methods concerning partial shading within one or two panels and the efficiency in uniform low light conditions like overcast daylight or low sun in early morning/late evening?
I’ve read in series wiring would allow charging the battery earlier in the morning and later in the evening. But I’ve also read partial shading of one panel could compromise the efficiency of the other panel as well when wire in series and parallel would then be better. Though I’m not sure this is still true with modern panels that have built-in bypass diodes, which mine have, see above.
As partial shading is quite often happening with solar panels on a campervan because of trees etc. and the partial shading may happen even midday when the yield is high, I wonder, whether minimizing any negative effect of partial shading might result in an overall higher yield per day (aka parallel probably) than starting the charging process a bit earlier and ending a bit later when solar energy is quite low anyways (aka in series).
Your question and thoughts are correct: 2 PV panels in series will result in more PV acitivity because of a higher combined voltage, cuasing the MPPT to work with less daylight.
When one of the 2 PV panels in series can get some shadow every now and then, this will cause the PV voltage to drop dramaticly, in this case it’s better to set the PV panels in parallel.
When a 12V battery needs to be charged, the Victron MPPT needs +5V more to start charging.
A PV panel with a rated voltage of 30.1V is therefore more than enought to get this done.
In this case you don’t need the 2x30.1V in series = 60.2V. It’s nice, but with shadow not adviced.
Is this still true for panels with integrated bypass diodes? I thought bypass diodes short out the shaded areas of the panel and make them in essence not harmful for the unshaded part of the panel.
E.g. one panel is 50% shaded. The other 50% still produces half of the max. PV voltage 30V / 2 = 15 V.
Wired serial the MPPT still gets 45 V (30 V from the unshaded and 15 V from the partially shaded panel) and adjusts its tracking point accordingly to get the optimum out of the 45V. Thus 75% of the total panel area is still providing energy.
Wired parallel, one panel provides 30 V the other 15 V. I’m not sure how the MPPT is dealing with this but I assume it is choosing a tracking point somewhere in the middle, not optimal for either of the 2 panels. I’m also not sure what this means for the combined energy the 2 panels provide. Is it still 75% or just 50% of the unshaded panel or even below 50% because of the not optimal tracking point?
Appreciate if you could shed some light into this. Maybe I do not fully understand the effect of bypass-diodes in combination with the MPPT controller.
Newer panels are better at handling partial shading.
On my RV, I configured the panels with the idea that if one panel was shaded, the other panel probably was too. That led me to wire them in series and it has worked well for me.
I currently have four 425 watt panels wired 2s and 2s, with each 2s string going into it’s own 150/35 controller. In a couple months, when I add two more panels at the front of the RV, I’ll change the existing four panels to 2s2p into a single 150/35 controller. The new panels will be 2s going into one of the existing controller.
I have a 48 volt system.
For those times when the RV roof is shaded, I use a set of ground deployed panels with a long extension cord.
Diodes are an important part of the panels, but what you are really talking about here is the difference between full panels, half-cut panels, and the newest 1/3rd cut panels.
In a full-cut panel, any shading will destroy almost all the panel performance.
In a half cut panel, its like having two half panels in parallel, so only the performance of the half that has some shading will be lost, so you might get say 230w from a 460w panel if it is half-cut and the bottom edge gets shaded.
Our (RoarPower) latest 460w panels for RVs are 1/3rd cut and fullscreen : RoarPower 460w 1/3rd cut, full screen panels
The 1/3rd cut means that you still get 2/3 of the power if the bottom (or top) is shaded, and the “fullscreen” means there is no lip created by the frame - ie the glass goes all the way to the edge, which is important for panels mounted dead flat on a vehicle. Full-screen means that the dust, salt, leaves etc will mostly wash off the panels when the next rain comes, where a normal panel will wash a lot of stuff down to the lowest corner, and then when the water evaporates you get a horrible triangle of dust etc which creates a shadow, as seen here;
The 1/3rd cut helps here too, but its the frames that are the primary cause of the loss of production of these panels in the picture.
Sometimes you can see that a panel is 1/3rd cut, due to two busbars visible across the panel, but often you can’t see it. It should be stated on the spec sheet, but older panels won’t say “full cut” because it wasn’t “a thing” back then (before ~2015 or so).