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petes1956 avatar image
petes1956 asked

Does this output look Ok for a 355 watt panel?

Hi folks, newbie here and after some advice from the experts please.

I have a motorhome with a 355 watt half cut panel on the roof feeding directly into a 100/30 Victron mppt. This then feeds, (via the vehicles solar circuit), two110ah leisure batteries and a12 volt cab battery ( via a small bms device) .

During the sunny days I get a maximum output of about 50 watts max and around 40 volts max on the panel, and daily (depending if I'm charging peripherals like battery banks, bike computer /cameras), I'm averaging about 170-210 wh per day in the summer.

The Victron unit seems to be functioning correctly with lights such as and bulk, float working etc and it does keeps all the batteries nicely topped up , but does that output seem low?

I was expecting it to be much more on a bright sunny day to be honest, or am I missing something.

Any advice would be gratefully received as to whether I'm right to expect more production than that.

Many thanks in advance Pete.

PS: I tried to upload two photos of the screen but I'm get a "parsing failure" message for some reason. Sorry.

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1 Answer
Alexandra avatar image
Alexandra answered ·

@Pete.S1956

Yeah the picture parsing thing is a new pain.

Hard question to answer definitively over the internet. But here are a few thoughts.

Bright sunny day + flat mounted panel with no ventilation can = really poor production.

But you also saying there is no need for the generation (i.e. battery if full and floating) can that can also be a reason; as it only generates if it needs to.

How do you know your battery is fully charged? Do you have a shunt so you know what your power consumption actually is? If it matches production then you are ok.

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petes1956 avatar image petes1956 commented ·
Ah thanks, So I’m basically missing the point that it will only draw from the panel when it needs to. I just assumed it was basically registering what the panel is producing , but in reality if I understand you right it’s only drawing what is required!. That obviously makes sense but please correct me if I’ve got that wrong! .


I know when the leisure batteries are full as the vanbiz device only charges the cab battery when they are full. The cab battery ( which to be honest is knackered) is also usually fully charged by around 9.30-10am as the light goes green on the vanbiz device. Very grateful to you taking time out on a Sunday afternoon to answer. Thanks Pete
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