Solar Panels - Series or parallel?

[Stemar]

I have a pair of panels, 100W each, IIRC, but I've lost the paperwork, and they don't seem to be available any more. They were mounted under the boom, so were wired in parallel. I'm moving them to a frame above the davits, so they shouldn't be shaded, and I'm considering adding another similar, but not identical pair, all fed into an MPPT controller.

Plan A is to wire each pair in series, and the pairs in parallel. Does this sound reasonable?

 

[Refueler]

Isn't the answer in the potential total voltage of each pair - deciding series or parallel ? can the controller accept such voltage ?

 

[lustyd]

They should have a label on the back with details of voltage etc.
you probably want a second mppt for best performance.

 

[jakew009]

Generally speaking you are better putting identical panels in series up to the limit of your MPPT, unless they are likely to be shaded.

If they are not identical, better putting them in parallel, but they need to be similar vmpp or its better to put them on a second mppt.

 

[tillergirl]

I have a pair of panels in series. The only recommendation was to match the pair, jakew009 is right. Parallel if not identical. The purpose for me is to have 24v.

 

[Baggywrinkle]

Quick explanation of the maths.

On top of this, modern half-cut solar cells combined with MPPT solar controllers improve partial shading performance further by dividing modules into two independent, parallel-connected, top-and-bottom halves.

 

[Stemar]

Quick explanation of the maths.

Om top of this, modern half-cut solar cells combined with MPPT solar controllers improve partial shading performance further by dividing modules into two independent, parallel-connected, top-and-bottom halves.

Thanks for that - I'd seen something like it before, but couldn't find it.

 

[Bobc]

I find that I get the most out if my panels in series.

 

[lustyd]

Bear in mind that in parallel, the strings might need fuses (usually for 3 or more, but check the details of your panels). Not an issue with series.

 

[Graham_Wright]

Mine are selectable by a rotary switch. OFF, PORT, STBD, PARALLEL or SERIES.
It is interesting to see how twiddling the knob varies the derived charge current.

 

[kwb78]

It's generally better to have them in series if possible:

The cable loss is much lower with higher voltage - power lost is proportional to the square of current, so doubling the voltage results in a a quarter of the cable loss.
MPPT chargers work better when the input voltage is higher than the battery - they can start up earlier and you will get charging at lower light levels. Not all MPPTs will do boost conversion.

Caveats:

The panels should be similar types.
The string of panels should be unshaded. If there are shadows on one panel in a series string, it will drastically reduce the output of the whole string.
Panels where shading is common should be in parallel, as the shaded panel won't drag down the reast of the string.

4 panels in series gives best efficiency providing the MPPT controller has wide enough input voltage range.
4 panels in parallel gives the best resistance against power drop due to shading.
2 in series and 2 in parallel is a good compromise for pairs of panels in different locations, as long as each pair isn't too prone to being shaded.

 

[Stemar]

Thanks, everyone.

I'm off to the boat later this week to move the two panels I have. I'll wire them in series, as they're unlikely to be shaded. I'll also see if the stickers are still on the backs, so I know the voltage and current output, and I'll then see if I can match them. If I can, I think that, provided the maximum voltage of the controller allows, I'll put all four in series, if not, it'll be each pair in series and the pairs in parallel.

If I can't, I'll do whatever works best, according to Baggy's video, or get all new ones and sell the old ones.