djingis avatar image
djingis asked

Optimal connections and correct MPPT for mix of panels?

I have an existing panel and am planning to add two panels and a new MPPT. Not sure how to connect them and what MPPT to use for most efficiency.

All three panels will be fitted on the deck of my sailing boat and will get partially shaded (no way to avoid this. Two of the panels will be fitted under the boom, one on the deck under the boom and the other on the spray hood. The third will be fitted in front of the mast and will get partially shaded from the sails.

- How should I connect these panels (serial of parallel)?

- What is the best suited MPPT for these panels (depending on if they are serial or parallel connected?

- Would it be better to replace the existing 55W solar panel with two new 18W solar panels?

New solar panel on spray hood (Sunbeam Tough T70F):
Pmax: 70 W
Voc: 22.1 V
Isc: 4.26 A
Vmp: 17.6 V
Imp: 3.98 A

New solar panel in front of mast (Sunbeam Tough+ TP56F2):
P max: 56 W
Voc: 23.6 V
Isc: 3.3 A
Vmp: 17.6 V
Imp: 3.18 A

Existing solar panel under boom (M-Series 55W S220P43):
Rated output (Pmpp) Wp: 55 W
Short-circuit current (Isc): 2.54 A
Open-circuit voltage (Uoc): 27.13 V
Voltage (Umpp): 22.88 V
Current (Impp) 2.40 A
System voltage: 24 V
Reverse current carrying capacity IR: 12 A

Optional 2 new 18W panels instead of existing 55W panel (Sunbeam Tough 18w L):
Pmax: 18 W
Voc: 23.7 V
Isc: 0.99 A
Vmp: 19.4 V
Imp: 0.92 A

Sunbeam and Solara are using a bit different terminology for the data, hope this is ok.

MPPT ControllersSolar Panelsolar sizing
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

1 Answer
JohnC avatar image
JohnC answered ·

Hi Djingis. Given your shading and some mismatching of panel specs, I'd be inclined to parallel wire them into a single 75/15.

You could go series into a 100/15, but if the panels have no Jboxes that will mean adding bypass diodes, and the shade might cancel out the usefulness of such an approach.

The 18W options I wouldn't bother with.

Note this isn't a 'by the book' way to do it, but it should work ok.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Related Resources

MPPT Product Page

MPPT Error codes

MPPT 150/60 up to 250/70 Manual

Additional resources still need to be added for this topic