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doug70 asked

Help Expanding motorhome off grid system

Hi, I can't find any posts that I can understand sorry. So hopefully someone can guide me in this journey.


Currently We live in a 12 metre bus totally off grid for probably 90% of the time. We have been traveling permanently for 7 yrs.


My set up right now, is as follows.

6 x 260W 20V 60 cell solar panels wired in pairs, series & parallel at the DC RCD box.

Victron multiplus 12/3000/120-50

Blue Solar MPPT 150/85

12/24/36/48V-85A

3 x 340ah LiFePo4 batteries in parallel to give me 1020AH

I used to have AGM batteries with slightly less total AH.

I have found that the LiFePo4 batteries seem to take a lot longer to reach 100% than the AGM's did.

I also am changing to an induction cooktop and electric instant water heating. These will require a larger current demand.


My questions are

1) Do I need to get a 2nd MPPT and/or inverter?

2) if above is yes, do they need to b Victron or could they be another brand like Epever maybe.

3) What size of above would I need, do they have to be exactly the same.

4) Obviously I need to increase the total power demand capability, but I am not sure how.

5) I have enough roof space for another 4 panels only.


I think that's about it. I would greatly appreciate any assistance to help me move forward.

Cheers Doug





system design
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4 Answers
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kevgermany answered ·

1 probably not. Unless you're in an area where you can get max power out of the panels for much of the day.

4/5 Best option is to add the extra panels with a separate, dedicated MPPT. You appear to have some monitoring, so sticking with Victron allows integration.

Whether extra panels will be enough will depend on electricity use. An audit would help give clarity.Same goes for upgrading the inverter capacity. How much power will the new loads draw, and for how long?

It might be worth checking the existing installation/panels firstly for problems (are all panels delivering full output?) And is the output comparable to what you're going to get with new panels covering the same roof area. Big cost, but if your electricity needs are higher than supply, it may be a way forward.

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doug70 answered ·

Thanks for that. You touched on 1 area I have been trying to work out. How do I measure the true output of each pair (or single panel). It would be good to know exactly what each panel is actually producing.


If I have a second dedicated MPPT, that handles the extra input and sends it to the batteries, yes?


With a potential max current requirement of 5000W would the current inverter handle that?


Thanks for assisting.


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kevgermany avatar image
kevgermany answered ·

Simplest way to measure output is to run on single strings and compare results. Be sure to isolate panels or cover before disconnecting

Second MPPT behaves as you think. Make sure output/battery settings identical and check you don't exceed battery charge rating.

Your multiplus is rated at 3000VA or, depending on load type, 2400W. It will not provide 5000W. If you want 5000W output, it might be a good time to review the system and consider increasing the house battery voltage . This power will draw over 400A from your batteries and it's unlikely that the existing cabling will be adequately sized. Are your batteries rated for this current?

Suggest you get the old system/planned upgrades reviewed by an expert.

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doug70 answered ·

Thanks very much for the help. I am consulting a couple of off grid design companies to get a better handle on all this. But your information has certainly helped.

Cheers

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