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GRIGORIU avatar image
GRIGORIU asked

Planning for an OffGrid system with both DC and AC coupled pannels

Hi everyone and especially @Victron Staff or @Guy Stewart

I need to plan for an OffGrid system (high mountain home)

I already had an about 3Kwc enphase system installed (grid available until recently but grid is now off for more than 3 years probably).

The max power needed is about 1kw (few LED bulbs, radio/TV, GSM internet connection, Cameras and power supply for the heating (pumps mainly - works with wood).

I need to add a minimal number of DC coupled panels to be sure the system will restart in case of heavy snow covering the panels.

Need also to limit investment and more important the number of DC coupled panels because of place on the roof (environmental/architectural/personal restrictions)

The planning is the following:

EasySolar 48/3000 (expecetd < 2k€)

One or two Pylontech USS5000 (expected < 3k€)

400W Solar panels (expected <1k€)

All the connection stuff 'expected (<0,5 k€)

So I have a few questions:

1. The 1:1 power rule will have to take into account the DC coupled panels ?

2. what is the minimal number of panels ( 400W Voc around 38 V, Icc around 13-14 amps) ?

3. am I missing something big ?

4. Parsed the forum but do you have some link to doc/tutos and technical recommendations for such a system

5. tips for keeping cost low/lower ?

5 I am a former electronic/informatic engineer and installed for some time a number of photovoltaic systems mainly with enphase microinverters and some Huawei but no experience with Victron until now.

Thanking you in advance

BG

cerbo gxoffgridAC PV CouplingMulti RSenphase
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Alexandra avatar image Alexandra ♦ commented ·
@bgrigoriu

The community guidlines are clear. This forum is not for system design.

Neither is it an ask victron forum. While the Victron staff do spend time on here this is not an official ask victron site.

There may be some other voltunteers who will answer one or two questions. But they are best directed to a distributor or supplier near you.

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Alexandra avatar image
Alexandra answered ·

@bgrigoriu

1. No with DC coupled the 1:1 rule is not applied.

2. Minimum number of panels depends on system battery voltage and choice of MPPT. And how fast you want the system to self recover from black start.

3. I have added more tags additional resources are in a box on this page. You can sign up for training on Victron Professional.

4. Tips for keeping costs lower. There really aren't cheap ways to install. Especially if you are including all the correct protective gear. And following local regulations if there are any.

If you are offgrid you are not using ESS. So ov inverter assistant. Do you need some form of charging from an alternative source? If not then consider using the new RS inverter. It has by default got frequency shifting in inbuilt. Then make sure you choose an AC PV inverter that responds to frequency shift.

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GRIGORIU avatar image GRIGORIU commented ·

Hi, Thanks a lot for the answer !

Q's

2. Battery voltage will be 48V I suppose since I would like to use Pylontech. But any cheaper suggestion is welcome.

3. Thanks for the links. For the training I have already looked at almost all videos. Very clear and nice to see but still had to look for the technical manuals.

4. Nobody think that it can build well with cheap equipment; However I am always trying to optimise costs as hard as possible and here experienced people are invaluable

5. I already have the "inverter" as the enphase system was running until recently. However landslides have made the grid unavailable and no repairing is planned for at least three years. So I am stuck with this equipement which i need to use. Moreover the place available on the roof is limited and I am not allowed (and I will not) cut trees for puting extra panels !! . The main question is if the MPPT 250/70 included in the Easy solar 48/3000/ will work ok with three pannels( means starts enough early in the winter mornings) or it is better to plan to install separate elements ( Multi II 48/3K + cerbo+MPPT 150/35 or /45 . Is there a real difference ?


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JohnC avatar image
JohnC answered ·

@bgrigoriu

Consider removing the Enphase and rewiring your existing panels to that Easysolar. It can easily handle 3kW. You'd end up with a simpler, and just as capable system.

Sell the enphase, and spend the savings on (not) buying the extra panels on a small genset.

You may never actually want the grid back. I don't, and it's just 60 metres away for me..

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GRIGORIU avatar image GRIGORIU commented ·
That was an option BUT

1. Big trees around so some shading occurs continously. One of which served a a chrismass tree for years of my youth, my kids and maybee more

2. The seven IQ on the second had market will not worth more than 4-500€ which will go on the new cable conectors and so on

3. I will eventually more some pannels from AC to DC coupling but for the moment I think I have a max place for three or four extra pannels and I wonder how it will work on a 250/70 ppt copared with a 150/XX one. Do you have data (measurable) on that ?

4. We have a small (3kw) generator but not been used for years. It scares hinds and dam nearby.

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JohnC avatar image JohnC ♦ GRIGORIU commented ·
@bgrigoriu

The 250/ just allows you to have more panels in a series string than the 150/. Otherwise they work identically. For 48V batteries I'd use a minimum of 3 typical panels (say 35Vmp) in a string, 2 may not be enough in poor light.

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GRIGORIU avatar image GRIGORIU JohnC ♦ commented ·

Thanks , I will go for the EasySolar I think. A bit cheaper and a lot simplier .

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GRIGORIU avatar image
GRIGORIU answered ·

By the way, I do not know who has created the excel file for calculation and MMPT simulation but I thank him and Jacques Noel (a Victron employee I suppose) for the presentation (https://www.victronenergy.com/upload/software/Guide%20pour%20VE.MPPT-calculateur%20(v3.1)%20-%20FR.pdf)

and the excel file:

Truly useful.

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