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joeriwa asked

Easysolar II gx: solar array, fusing and grounding

Hi! I’m a bit of a solar energy newbie, trying to install a 5000w off-grid system. I’ve got the Easysolar II gx 5000 which has the MPPT 250/100 inside, 10 Trinasolar Vertex 505w panels and 3 Pylontech US3000c batteries. I thought it would be simple to connect but I’m struggling a little with the following question. Would greatly appreciate your opinion here!!


1. How do I best connect these panels? I now realise with 10 panels I bought a silly number. 2 parallel series of 5 panels exceeds the 250v limit (Vmpp 43,0, Impp 11,75, Voc 51,9 (- 0.25%/°C), Isc 12,35 (0.04%/°C). 5 parallel series of 2 panels leaves me with a very high current, probably needing a quite massive bar to connect them and thick cables (am I right here?). I’ve used the online calculator and it says 5x2 is okay though. What would you do? Or shall I rather put them as 3x3 and leave one panel off or buy 2 more and make 3 parallel series of 4 panels. This would potentially give me over 6kW PV array, whereas the manual says max 5.8kW, nevertheless the online calculator says it’s okay.


2. How do I fuse the system? So far my understanding is that best practices would be:

* One 20amp DC fuse (this is the panel’s max series fuse rating) for each parallel series of panels to avoid too much current flowing in from the other strings in case of short circuit.

* From there I lead the parallel series together and add a DC fuse/switch before going into the Easysolar. Am I correct in understanding it should be a 70amp fuse as the MPPT’s max PV short circuit current is 70A?

* Should I add a DC fuse/switch to the batteries? I’m off grid so I normally won’t want to disconnect the batteries unless I need to replace them. The manual says the recommended fuse is 200A, just for my understanding why would it be this high if the max output current is 100A?

* I will connect de AC out to my small house the house has a regular fuse box in place with a 32A main fuse and after this, several groups for the different areas with 16-20A fuses. I assume I don’t need to change anything here?


3. How do I ground the system? My house is grounded from the main fuse box, so every plug etc has a ground wire coming into the fuse box and one thick wire goes to the pin in the ground.

* Should I add a ground wire from the chassis of the Easysolar directly to the same pin?

* Should I add a ground wire from the chassis of the solar panels to the same pin?

* Should I add the ground wire in the AC out and where does it go? Should this be added to my house’s grounding system or should it replace it (ie instead of my house’s ground wire to the pin, I redirect it into the AC out of the Easysolar (and the Easysolar redirects it via the chassis to the pin??)

* Do I need to add any grounding to the batteries in any way?


Many questions, I know! I hope someone of you is kind enough to spend her/his precious time in writing me an answer and I also hope this may help others who may have similar questions. Thanks so much in advance!!

MPPT SmartSolarEasySolar All-in-OneSolar PanelfusesGrounding
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6 Answers
nhuillard avatar image
nhuillard answered ·

I'll answer some of your questions. I'm not an expert, but report from what I've read, seen and built.

1. I'd say that the 250V limit is when producing, thus the Vmmp must be lower (and actually is). There is a second absolute (higher) limit in the controller, which the Voc should never surpass. I remember having read about that in this very forum. I'd trust the MPPT calculator, as long as you input everything, including the lowest expected temperature.

2. Battery DC fuse: the 200A is to allow for transcient currents, way above the sustained power output. You don't want to blow the fuse when starting a high load which will remain below the sustained power, but will initially draw much more.

3. Add a ground wire the same size as the PV wires (6mm2), from the panels to the PV fuse box. Connect the Multiplus and Pylontech grounds to it, and connect that fuse box ground to your existing ground bar. The AC-out ground should also be connected to the main fuse box as any other.

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joeriwa avatar image
joeriwa answered ·

Hi nhuillard,

Thanks so much for your quick answer!

On 1. I´m just reading a little more and don´t think your answer is right. This is one post I got out of Quora (https://www.quora.com/Which-voltage-Voc-or-Vmp-of-the-solar-panel-should-I-consider-while-rating-the-charge-controller):

"The VOC rating is critical. A solar charge controller can be destroyed if the voltage goes too high. So you need to be sure that the maximum voltage will never exceed the controllers rating. There are times when the charge controller will unload the solar panel, so the panel output can rise to the VOC (voltage open circuit) and if the panel is cold, it can exceed that rating as well, so you need to calculate any voltage rise from cold as well. Most people recommend leaving a 20% margin to ensure you don’t cook the controller on the first sunny and cold winter morning.

The VMP rating is still important, but not as critical. If the VMP (Voltage Maximum Power) of the panels added up is too low, the MPPT controller will not be able to maximize the solar production so you will lose some efficiency.

Your series group of solar panels should have a VMP about 10 volts higher than the maximum battery voltage, and a VOC 20% lower than the maximum input voltage of the charge controller."

So this brings me back to mininum 2, maximum 4 panels in series (which is also what the online calculator gave me). Question remains: Is it a good idea to put 5 series of 2 panels in parallel? The MPPT can handle it (according to the online calculator), but it´s quite a high current. Is this smart?? Or better 3x3 or 3x4?

On 2. Thanks for the clarification. Would greatly appreciate any further opinions on de fusing.

On 3. Thanks, this matches with what I though makes sense.

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nhuillard avatar image nhuillard commented ·

1. I agree re. Voc vs. Vmpp. The issue is to match those to the actual specs of the MPPT controller. Just follow the advice of the MPPT calculator, not forgetting the lowest temperature anticipated, which you apparently did.

Re. parallelizing panel strings: take into account the maximum input current of the MPPT controller, which is not that much. I have a 450/100 and 2 parallel strings on one tracker. Each tracker is limited to 18A, which is easily reached on hot sunny days, when heat reduces voltage, increasing current. This just limits the power delivered, with no adverse effect (there is a 20A absolute limit, applicable to reverse voltage). On the other hand, during cold sunny days, the voltage increases, leaving more room to the current, which produces a much higher power, partially offsetting the shorter days.

3. Forgot to add to ground the batteries too, using same-length cables (but it's explained in the Pylontech doc, and you actually read docs)

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philippem answered ·

Hi, following my experiences I always recommend to have a safety margin with all power electronic products from at least 30%, means you have to degrading for example for a MPPT 250/60 I never go over 200 V and 40 A, for a 3000va inverter I never go over 2000va. By doing this you decrease the heating, the noise and the life expectation of the products will increase a lot. Concerning the grounding, better to do a new one near the panels and to connect all them together.

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philippem answered ·

sorry I don t answer you about the fuses, more is the better, sometimes it is good to experience and check. Put your installation in maximum power, full solar power and full consumption and check were you are getting hot points, if the fuses are still cold you can start to decrease the value until they are getting too hot so you will be on the safest side possible. I recommend to put your installation 1 time per month under full stress to check everything too many solar installations are burning.

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joeriwa avatar image
joeriwa answered ·

Hi philippem,

Many thanks for your answers!

I think I will go with:

- 3x3 (or 3x4) panels -> 4mm cables -> each of the 3 string going into a 20A (500v 2P DC MCB) circuit breaker -> which are connected by a comb busbar to a 63A (1000v 2P DC MCB) circuit breaker and a lightning protector (2P40KA) -> from the 63A circuitbreaker goes an 8mm cable to the Easysolar.

- Between the batery and the Easysolar I will put a 200A blue sea MRBF fuse.

- I will ground the Easysolar chassis, the bateries, the chassis of the PV and the lighting protector, together with the grounding of my house in the earth pin (which is under the (tiny) house, so close to everything), all with 10mm cable. Since I´m fully off grid, also without genset, the Easysolar will automatically connect the neutral to its chassis ground.

I think with this I should be ready to start building, but if anyone is seeing an error, please do let me know!

PS. for those with similar questions, i came across this document while researching yesterday. I wasnät aware of this yet and it´s very very informative!

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

Best regards!

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philippem avatar image
philippem answered ·

Hi, looks good, I will use 6mm for the solar panels it is the same price, just 1 detail for the solar use solar cable they are double isolated.

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