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automation-noob asked

Maximizing PV capability

I want to be off-grid on a new home. So, I'm planning to install a EasySolar-II 48/5000. The target is to have an acceptable production on very cloudy days (so, minimize battery capacity).

500W panels seems to fit "perfectly" for the 250V limit (JA Solar JAM66S30-500). The Voc of 45,6V makes an array of 5 produce 228V. My plan is to have 3 parallel arrays.

I would consider -10ºC, as temperature value for calculation at my location (42ºN). But almost never goes under -8.

That makes 249V at the worst case scenario. Cabling of each array will be 20 meters long (that adds some voltage drop).


Is it way too tight?

Can something bad happen if I open the circuit with some contactor (DC rated) if 249V is reached? (and then return after conditions are suited better).


Thanks

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pwfarnell avatar image pwfarnell commented ·

Do not forget that on a clear calm winter night black surfaces can cool down below the air temperature by radiation. The question is, are they still cold as the sun rises. I do not know the answer but it is something you should consider.

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kevgermany avatar image kevgermany ♦♦ pwfarnell commented ·
@automation-noob

4 strings of 4 would be safer.

Also check the Isc rating of the panels against the MPPT.

Don't size the batteries too small. The Victron recommended sizes are there for a reason.

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automation-noob avatar image automation-noob kevgermany ♦♦ commented ·

Thanks for the observation.

With 4 strings, 550W panels can be used. Isc= 14A

EasySolar II-GX has MPPT 250/100, that can handle 70A.


About batteries, I'm thinking of 2 packs of Pylontech / Tensite 4,8kWh. It is possible that I would need to start a generator some times in winter. But, I want to know the real needs before buying a third one.


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kevgermany answered ·

Some background.

You may see less than 10% output from the panels in winter. But looks like you're well aware of that.

With Pylontechs, correctly installed, charging is controlled by the battery BMS.

You have a max solar output on the MPPT of 100A at about 50V, or 5kW. This will be sustained while there's enough light, unless the BMS throttles it, or heat causes downrating. As long as you don't exceed the input specs of the MPPT, your overpanelling is ok.

Generator charging through the built in multiplus is a separate consideration. This is limited to 70A at about 50V, or about 3.5kW. Unless BMS or heat reduce it.

Size the batteries as large as you can.

You're creating a critical system based on a single box. It's a very reliable box, but if something fails you are completely powerless until an off site repair can be done. Might be worth considering redundancy. E.g. 2x3kW multiplus, 2xMPPTs, Cerbo.


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beat avatar image beat commented ·
Cerbo will still be the critical component.

Putting Mulitpluses in parallel or 3-phase systems doesn't make them redundant: One fails, all stop. It would then require manual reconfiguration of each remaining Multiplus, on the VE.Bus or if it still works remotely through VRM with bidirectional comms enabled.

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kevgermany avatar image kevgermany ♦♦ beat commented ·
At least manual reconfiguration gets you going...
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beat avatar image beat kevgermany ♦♦ commented ·
Indeed better than having nothing. But that works fine, if in 7 or 12 years from now, when/if the unit fails, you are not away on a trip and still remember how to reconfigure a Multiplus II, and still have the MK3 adapter around :-)
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nesswill avatar image nesswill beat commented ·
With my x2 Inverter RS Smart 48/6000 in parallel if one fails the other one keeps going so no interruption in power supply . I too am completely off grid.
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automation-noob avatar image automation-noob commented ·

I see your point about redundancy. But, also size matters. In my case, I need the smallest package. And price wise, is also a plus.


I take the advice of battery sizing. Thank you.

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Alex Leo avatar image
Alex Leo answered ·

Be careful if you oversize the array and also be carefull choosing the batteries.I also have Easysolar2 48/5000 with 2 pylontech US3000c and 9 Jinko Bifacial 555w N-type ( 3 strings ) that can push easily over 4000w when its sunny.But when the load on the MPPT is bigger than 60A (about3kw) the MPPT will stop and pass the loads solely on the batteries.You will not get any errors or alarms,the MPPT will just stop,and start,and stop and so on until the load is close to 60A or lower.Victron recommends 4 x US3000C for the Easysolar 2 48/5000.So there is no point in oversizing the array if you can only use 3kw of PV....it will only help you if its cloudy,but when its sunny it will give you problems...

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automation-noob avatar image automation-noob commented ·

@Alex Leo Thank you for your comment.

I can put a contactor on each array, so to select how many arrays to work with at any given moment. So the MPPT will make the panels always work near the maximum.


For me, the point in oversizing is to always have production. Even on the worst days of winter, make enough energy to spend a whole day (and night).

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beat avatar image beat commented ·
With a lithium battery in parallel, I don't see why the MPPT would deliver more than 60A and thus go into stop mode, in my ESS setting, when MPPT are maxed, the additional current needed is provided by batteries, when they are above minimum SOC. And that feature imho does not depend of ESS.
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Alex Leo avatar image Alex Leo beat commented ·
I have 3 of them now with a combined charge/discharge rate of 111A,the MPPT still stops at 60A.Just stops and starts again and so on.Cant figure out whats wrong.
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kevgermany avatar image kevgermany ♦♦ Alex Leo commented ·
The MPPT is controlled by the batteries via the GX.
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Related Resources

EasySolar 1600 product page

EasySolar-II GX 3000 & 5000 product page

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