Series or parallel for your solar?

[TobyQuest]

Just wondered how many watts solar you all have?

Connected in series or parallel?

 

[DBK]

Picking up on a thread from last year. If shading is such a problem with series wired panels what happens with a partially shaded single panel? I thought they had bipass diodes fitted to offset this problem so why does that not work with a pair of series panels?
It seems to me that a partially shaded pair of panels in series will give a higher voltage than a similar shaded pair in parallel. This would mean better performance in the more northern latitudes.

There are two ways diodes are used on panels. Virtually all of them have blocking diodes which prevent current flowing backwards through them at night. This shouldn't happen with a good regulator but it could happen if the panel was directly connected to a battery. The other type are bypass diodes which ideally should be fitted to each cell but may only be fitted to a group of cells. These allow current to continue flowing if one cell is damaged - or shaded. These diodes significantly reduce the effect of shading. However, because of the additional cost they are not normally fitted to standard panels so you need to buy one which specifically says it has bypass diodes. Expect to pay more.

 

[the1andonly]

Series or parrallel equals shading effect versus voltage curve . Ie number of collection hours (voltage above threshold ) there are videos online showing former , any body got data on later.

 

[eddie]

The truth is for a couple of panels it doesn’t really matter, people use data and equations used to calculate the difference for a house roof full of panels, South facing at an optimal angle for maximum effect.

Motorhomes move, they change direction, in the old days they even travelled, sometimes closer to the equator, sometimes further away!

We have done some extensive tests over the years, and found the absolutely most important thing to be the quality of the regulator being the critical factor.

I remember having three identical panels rigged up, and getting 1.9 amp yield to 4.2 amp when we’d tested about 12 regulators.

Shielding can be an issue, so unless there is a really valid reason to do so we don’t bother. On my camper I have three 150W panels, each wired with 4mm2 solar cable, to its own VictroN MPPT regulator.

The three regulators are connected to an adjacent single stud buss bar and a 25mm2 wire to run to the batteries.

Shielding isn’t an issues, I have built in redundancy and as I am sad enough to play with stuff swapping one out to check manufacturers claims is easy enough to do.

 

[Reallyretired]

400w in parallel with a single mppt regulator, 2x110Ah batteries 1500w inverter. I really need a bigger battery bank but weight is a problem. Lithium would solve it , at a price I'm not prepared to pay at present.

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[Raul]

There are two ways diodes are used on panels. Virtually all of them have blocking diodes which prevent current flowing backwards through them at night. This shouldn't happen with a good regulator but it could happen if the panel was directly connected to a battery. The other type are bypass diodes which ideally should be fitted to each cell but may only be fitted to a group of cells. These allow current to continue flowing if one cell is damaged - or shaded. These diodes significantly reduce the effect of shading. However, because of the additional cost they are not normally fitted to standard panels so you need to buy one which specifically says it has bypass diodes. Expect to pay more.

Just to clarify this:
The panels have bypass diodes only. The blocking diodes are in the controller only. That’s why is important to pick a good reputable controller. Also if you have ever exceeded even once the voltage open circuit from panels to controller, rest assured you lost the protection of the blocking diode, even if the controller survived and still working.
The bypass diodes are working between strings of cells on the panel. Depending on panel, a 36cell 12v panel has 2 diodes and splits the panel in half long ways. If either cell or cells on one half is shaded, the other half still works at half output. If this panel is in series with another, the shaded will bring that one down as well, to the parameters of the shaded. If two cells are shaded and each cell is in each half, it will almost kill the hole panel, and pull the series down. In parallel, each panel works individually to the vmp volt max power set by the mppt, at the given irradiance at that moment.
The 60 cell panel is better, its split into 3 cell series and has 3 diodes. In case of shading you loose 1/3 or 2/3 rather than 1/2 and nothing, comparing with the 12v 36 cells.
Fit as high voltage as possible panels and keep them in parallel or individual controllers. You can get 96cells panels with 50v+ and they have 4 diodes, splitting the panel in 4. Another good choice is the newer half cut 120 cells that have around 38-40v and are split in 6 with 3 diodes. They are in parallel 3 with 3, a total of 6cell strings. Looks much like two panels stuck together.