Different size panels ?

[Westerham Womble]

I was hoping to add an extra panel on the roof of the Moho, I have an existing 120w panel and hoped to squeeze an 80w panel further forward. The existing controller is a PRS 240 so should be within parameters.
Also trying not to add more weight at the rear. When I enquire with a local stockist they said that whilst they will supply my requested size they don’t recommend it but didn’t go into specifics.
They did suggest another 120w panel and a new controller, but that will a) drain my wallet and b) add more weight on the rear (only place the panel will fit)

So can anyone tell me why ?

 

[Jamesh]

So they can sell you a controller obvs!

 

[Two on Tour]

I was hoping to add an extra panel on the roof of the Moho, I have an existing 120w panel and hoped to squeeze an 80w panel further forward. The existing controller is a PRS 240 so should be within parameters.
Also trying not to add more weight at the rear. When I enquire with a local stockist they said that whilst they will supply my requested size they don’t recommend it but didn’t go into specifics.
They did suggest another 120w panel and a new controller, but that will a) drain my wallet and b) add more weight on the rear (only place the panel will fit)

So can anyone tell me why ?

Your present solar charge controller can take up to 240 watts, so adding a 80 watt panel should not be a problem unless there is a miss-match between the voltage of your existing panel and the 80 watt panel your supplier has to offer, or the supplier is on the make for a few bob extra from you.

 

[autorouter]

The PRS 240 has two solar panel inputs. It apparently is intended for connecting two panels up to 120W each, ie 240W. I can't find any details of whether the panels need to have identical voltage, but maybe that's the case. An 80W panel with the same number of cells (probably 9 x 4 = 36) should be OK to connect, because it will probably have the same voltage.

The manual doesn't say if it's a PWM or MPPT type. It has 3-stage battery charging control, which usually indicates an MPPT, but I get the impression it's a PWM type.

 

[Westerham Womble]

I’ve been digging around and there does seem to be a thought that the charge controller will work predominantly with the smaller panel, limiting the input of the larger panel. My initial hope was to connect in series, just joining cables on the roof, rather than bringing a separate cable through to the controller. Their suggestion for a replacement controller was a Victron 75/15 but looking at the spec it seems this has a max input of 220w when the panels are both 120w

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[Two on Tour]

Don't worry about the 220 watt limit on the Victron 75/15, for one the Victron will just discard the little extra above the 220 watts, and secondly, I would be amazed if you could get the 120 watts out of the 120watt panel, even in ideal conditions.

 

[Dorwyn]

In my case I've only got one 110 amp battery and no space,
so wonder if a second panel would help anyway

 

[Two on Tour]

In my case I've only got one 110 amp battery and no space,
so wonder if a second panel would help anyway

I will at the times of the year when the sun is low in the sky. Our 410 watts of solar is overkill for most of the year but in the low sun months it can get us by for most of the time.

 

[tonka]

In my case I've only got one 110 amp battery and no space,
so wonder if a second panel would help anyway

It would help to recharge quicker and also give more charge during the cloudy / winter days.

 

[mitzimad]

In my case I've only got one 110 amp battery and no space,
so wonder if a second panel would help anyway

depends how low your currently taking the batteries down i always think of the batteries as buckets of energy if you currently draining the bucket low and not filling it an extra panel will be beneficial if your only using a third of the bucket and its full mid day it will not help

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