jurjenhoekstra avatar image
jurjenhoekstra asked

Venus GX setting SOC battery

What would be the ideal settings/recommendations for SOC for the Venus GX/MPPT to maximise the use of solar power and minimise the use of (expensive) grid or generator power on a yacht. Details: battery OPzS 980 Ah, Victron Quattro 24/8000, MPPT 100/50, 4 x 350 Wp solar array, grid 230 V 16 A, generator 4 Kw.

During the day there is a discharge of about 4.1 Kwh when not present. When just visiting during the day and using some equipment discharge will lead up to 5-6 Kwh. Fully living on the yacht will lead up to 9-10 Kwh per day. Yacht is fully equipped with fridge/freeze, oven, dishwasher, microwave, combination washing machine/dryer, central heating, led lights, etc.

My idea was to let consumers discharge the battery to 40 % before the grid/generator kicks in and the Quattro will start charging. Should the Quattro then charge to say 70 % and let the solar take over to charge to 100 %? Or maybe it is better to let the Quattro charge to 100 %?

Any thoughts?

Venus GX - VGXSOCsolar
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3 Answers
Michael Riley avatar image
Michael Riley answered ·

We also live on a yacht (sailing catamaran) but full time so some differences. The approach we use is that I maximise the solar yield so that charging occurs during the day. At around dusk we are ending the solar yield so I then use the generator to: a. charge house bank (28 V LiFePO4) to 90-95%, run desalinator to top up water and cooking equipment (microwave, induction cooker etc). In this manner I am maximising the solar yield for whatever it is. I also often heat hot water (cylinder for showers) from solar during the mid afternoon as it is quicker to charge LIPO than heat water and I want to run the generator at maximum load for as short as period as possible. Generator runs at 1.8l/hr so not so expensive as yours. I am also thinking that this is a 'single' charge cycle per day not multiple 'top-ups'. Location will also obviously affect my solar yield (mid Coast NSW - Australia at present). I am awaiting the 'load shedding' configuration for VenusGX to assist with this profiling.

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jurjenhoekstra avatar image
jurjenhoekstra answered ·

@Michael Riley, thanks for your reply. I understand how you use the solar, but you are still using the generator quite a bit is my impression. I intend to use shore power or generator as little as possible (self-consumption). So I would run as much equipment as possible during the day (also the desalinator, washer/dryer, dishwasher), continue depleting the battery with cooking equipment in the evening and use the solar the next day to recharge the battery. Only when the battery would be below a certain critical percentage, say 40 % (no sun, use to much equipment), would I connect the shore power or (auto) start the generator. And then (that was my question) should I let the shore power or generator let the batteries charge to say 70-80 % or to 100 %?

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JohnC avatar image
JohnC answered ·

Hi @jurjenhoekstra

You're pretty much onto it. And how far you charge with these 'slugs' is really determined by where you're happy to be, given you have a night to get through, and they can be long in winter.

Depends on what your batts are too, how low is too low for you at sunup?, and the next day's solar forecast might impinge your decision as well. And your loads.

I only use a generator, and don't autostart it because all these little factors make programming it in too hard. And I only run it when solar is done for the day, and I've checked my VRM graphs. No point running a genny either with a trickling charge, and I'll shut it down when I can't get value from the fuel usage. I hardly use it at all outside the three winter months, but the poor solar days and long nights give it a little work (VRM says 2% of my annual charge. A painful 2%)

So it's almost impossible to give you specifics on how to operate your system. You'll learn it yourself. And I wish you well with it.

A side observation - your unattended usage is quite high. Absorption fridges or something? I dumped mine. :)

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Related Resources

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Venus GX manual

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