Additional solar panel matching

[chris-s]

Our new-to-us boat has a single 80watt rigid panel mounted on the doghouse. For the most part I'm sure this will be sufficient but want to be able to connect in a second 'wandering' panel temporarily for a boost as needed. The plan would be to connect it in parallel with the existing panel. I cannot swap out the existing panel for a larger one in its position and I do not want to do something like replace it with two permanently connected 100watt panels hanging off the side. I swapped out the original charge controller for a Renogy DCC30S which has a max solar voltage of 25v/400W, plenty for my expected use. For those not familiar with this controller it separates the engine and house batteries but includes a dc-dc charger to charge the two sets from a combination of alternator and solar power sources. House batteries currently consist of a pair of old 100ah AGM that are likely to get replaced this season, most likely like-for-like although the Renogy charger will support lithium house and flooded engine batteries. We haven't really worked out the electrical consumption on the new boat yet, but I think I feel the current battery setup is sufficient...for now.

So everything I read about mixing mismatched panels suggests the world is going to end, ok, probably a slight exaggeration. But just how closely do they need to match to avoid significant losses?

The existing panel is 80W, open circuit voltage (Voc) 22.5v and operating voltage (Vmp) of 18v.

As some examples, I was looking at some of the Renogy flexible and 'folding suitcase' options like these...

1) 100W Voc 22.5v Vmp 18.9v
2) 100W Voc 21.6v. Vmp 18.0v
3) 120W Voc 23.8v Vmp 19.8v
4) 175W Voc 23.9v Vmp 19.5v

As it happens, I do have the solar setup from the previous boat, a rigid Renogy 80w panel that pretty much matches the specs of the existing panel on the new boat and a Victron mppt charge controller. But I would prefer to use a lighter flexible less bulky panel and avoid having to wire in a separate charge controller if the world isn't going to implode.

Thanks

Chris

 

[Baggywrinkle]

Mixing solar panels – Dos and Don’ts • SOLAR POWER SECRETS

This site shows you how to calculate losses when mixing panels in series or parallel. You just need a basic understanding of P=I x V and the calculation rules for connecting in series or parallel.

 

[Grith]

Mixing solar panels – Dos and Don’ts • SOLAR POWER SECRETS

This site shows you how to calculate losses when mixing panels in series or parallel. You just need a basic understanding of P=I x V and the calculation rules for connecting in series or parallel.

I know this but it’s excellent info for others.
720w of removable panels On a trailer sailer.

 

[Trident]

Either of the first two on your list will be fine - the voltages are near enough and its all theoretical anyway - 4 identical panels in a row can have varying light, shadow and so forth and put out several volts difference and work find in to the MPPT charger you have and work ok. Its not the most efficient way but the world will not end and the batteries will get more charge

 

[chris-s]

So it is that simple. Thanks!

 

[Baggywrinkle]

So it is that simple. Thanks!

Do bear in mind that energy lost is produced by the larger panels and dispersed in the smaller ones, heating them up ... so don't make the difference too big.

 

[andsarkit]

Do bear in mind that energy lost is produced by the larger panels and dispersed in the smaller ones, heating them up ... so don't make the difference too big.

I believe that most panels have a blocking diode to prevent any reverse current from the battery at night and will also stop the larger panel sending power to the smaller one.
In a parallel connection the output voltage of the larger Voc panel will drop as current is drawn until it as low as the output voltage of the smaller Voc panel which will then start to deliver current. I don't think heating of the smaller panel will be a problem but there will be a loss of efficiency as the maximum power point of the panels may be different and the controller will have a compromised setting.