East west configuration

[Tony54]

Hi first post, I couldn't find a new member forum so hope its ok diving straight in.
Im planning an off grid system that will reduce my bill by some 80%, my average daily wattage use is 10kwatts.
I have a shallow east west roof and am considering buying a Must, 3000w-24v-mppt-50a with max input pv voltage of 100v.
My battery will be a 8 segment 230amp, 24v system with bms. So over 5kw. Im not fussed about extra battery capacity because i will just switch back to the house supply.
I am thinking about buying JA 450 watt panels and placing 4 on the west facing and 4 on the east side of roof, so total panels some 3200 watts.
I plan to put the 8 panels into 4 series pairs, so the input into the inverter will be 90v (oc) and 22amps from the east panels and the same in the afternoon from the west panels.
The literature for this Must inverter states that the max pv should be 1500watts, so maybe I should buy the 60amp inverter which allows 2000 watts of pv. I dont know how the east and west facing panels power would combine, in a high sun both sides of the roof receive sun light but not at a productive angle.
One last question, my Must inverter has a mains input connection for charging the batteries and providing power if the solar and battery power is not sufficient. The output of my system would be totally independent of the existing electrics so do i need to run a separate earth wire or would the mains input to the inverter provide an adequate earth.
Will these components and panel array work together in my planned way. Thanks for reading and I know there lots of questions.
Ps would my panels need a seperate earth when only at 90voltd oc. I intend to fuse all panel strings.
Is there a newer Must inverter that would be suitable?

 

[pollenface]

I would keep each array on a separate charge controller (eg. east array on your AIO unit, west array on a separate controller)

I imagine the max PV is your output, not your input as is with most mppts.

 

[Tony54]

Thanks that would make more sense.
So if Im powering a 2.5kw water boiler, the max solar power would be 1500watts and the other 1000 watts would come from the battery.

 

[meetyg]

Another possibility is to put both strings in parallel, but to use a blocking diode on each string. That way one string won't "pull down" the other.

I have recently received a MUST PH1800 Plus, 3kw 24v inverter.
I haven't fully installed it yet, just doing some testing for now. My model has the 60A mppt.
I am also planning to parallel two different strings. My setup will have both strings facing East, but each string is at a different angle. I'm planning on using diodes as I suggested. From my research, this should solve the problem.
Worst case I will just add another small MPPT SCC.

 

[Tony54]

Hi Meetyg,
Sorry for late reply. Thanks for your advice, I'm also looking at the same Must inverter but it says it has a maximum of 2000 Watts pv input.
I was thinking about putting 1800 Watts pv on my West roof and because of the 2000 restriction I was going to put the east roof panels through a seperate charge controller. Because my roof is a low angle, in the summer both West and East panels would receive sun and might tip me over the 2000 limit.
It looks like you may use a seperate charge controller like myself.
I don't know much about Must be here in Spain wc solar, and autosolar. es are selling them so assume they must reliable.

 

[meetyg]

Hi Meetyg,
Sorry for late reply. Thanks for your advice, I'm also looking at the same Must inverter but it says it has a maximum of 2000 Watts pv input.
I was thinking about putting 1800 Watts pv on my West roof and because of the 2000 restriction I was going to put the east roof panels through a seperate charge controller. Because my roof is a low angle, in the summer both West and East panels would receive sun and might tip me over the 2000 limit.
It looks like you may use a seperate charge controller like myself.
I don't know much about Must be here in Spain wc solar, and autosolar. es are selling them so assume they must reliable.

If you have a local supplier that's good.

Please note that the MUST inverter does NOT automatically bond Neutral to Ground!
If you plan to have AC IN connected, this might be complicated to do when the inverter switches to off-grid mode.

Seems like most newer inverters also don't have automatic bonding. So just check that the inverter you get meets your requirements.

P.S. I am working on a "hack" to read the inverter's mode using the communication port via a microcontroller, in order to dynamically switch an external N-G bond relay. While I hope I succeed, don't count on it.

 

[Tony54]

If you have a local supplier that's good.

Please note that the MUST inverter does NOT automatically bond Neutral to Ground!
If you plan to have AC IN connected, this might be complicated to do when the inverter switches to off-grid mode.

Seems like most newer inverters also don't have automatic bonding. So just check that the inverter you get meets your requirements.

P.S. I am working on a "hack" to read the inverter's mode using the communication port via a microcontroller, in order to dynamically switch an external N-G bond relay. While I hope I succeed, don't count on it.

Good luck with your hack. I want to be off grid but having the mains input connected for the inverter battery charging would be useful.
Do you know or, anyone know, what I need to do to earth my inverter, I had assumed that by connecting the mains input supply that it would be earthed to the house mains earth point. I watched a utube video where someone connected the earth to the neutral inside the victron eguipment.
Let me know how you get on, it would be useful to me. I'm just about to pull the trigger on an inverter. The two sellers above here dont seem to have the 1800 series which I assume is a newer model so might have to aliexpres it.

 

[Tony54]

Good luck with your hack. I want to be off grid but having the mains input connected for the inverter battery charging would be useful.
Do you know or, anyone know, what I need to do to earth my inverter, I had assumed that by connecting the mains input supply that it would be earthed to the house mains earth point. I watched a utube video where someone connected the earth to the neutral inside the victron eguipment.
Let me know how you get on, it would be useful to me. I'm just about to pull the trigger on an inverter. The two sellers above here dont seem to have the 1800 series which I assume is a newer model so might have to aliexpres it.

Ps, I am going to earth my panels to an earth rod, 4foot in the earth., whether that be suffient in the drier environment I don't know. In Cyprus it was necessary to go down 200 foot to reach the water table.
I am still considering how to earth the inverter, the deeper you dig into this subject the more confusing it becomes.

 

[meetyg]

Good luck with your hack. I want to be off grid but having the mains input connected for the inverter battery charging would be useful.
Do you know or, anyone know, what I need to do to earth my inverter, I had assumed that by connecting the mains input supply that it would be earthed to the house mains earth point. I watched a utube video where someone connected the earth to the neutral inside the victron eguipment.
Let me know how you get on, it would be useful to me. I'm just about to pull the trigger on an inverter. The two sellers above here dont seem to have the 1800 series which I assume is a newer model so might have to aliexpres it.

Let's separate two issues:
1. Earthing the inverter - yes, if you connect AC IN with ground, the inverter will be grounded/earthed.

2. Ground to Neutral bonding - your home power most likely has a Ground to Neutral bond. It's either done at the power company transformer, or at the power entrance to your house. This is done for two reasons: First so that RCD devices will work correctly and any faults will not shock a person but rather go to Ground and trip the RCD. The second is so that you will not have a floating Neutral. Some electronics do not work well with floating Neutrals.

When the inverter is in off-grid mode (powered from solar and/or battery), you loose that N-G bond. The problem is that you can't just bond it yourself in a permanent way on AC OUT, because if/when the inverter works in bypass mode (for example if battery is too low to power loads), it will revert to the AC IN and you will have two N-G bonds in your system. There needs to be only one N-G bond in any system, or else current will also flow on the ground wires, which is not good/not safe.
That's why we need dynamic bonding, that will engage only when inverter is in off-grid mode.

 

[Kornbread]

Hi first post, I couldn't find a new member forum so hope its ok diving straight in.
Im planning an off grid system that will reduce my bill by some 80%, my average daily wattage use is 10kwatts.
I have a shallow east west roof and am considering buying a Must, 3000w-24v-mppt-50a with max input pv voltage of 100v.
My battery will be a 8 segment 230amp, 24v system with bms. So over 5kw. Im not fussed about extra battery capacity because i will just switch back to the house supply.
I am thinking about buying JA 450 watt panels and placing 4 on the west facing and 4 on the east side of roof, so total panels some 3200 watts.
I plan to put the 8 panels into 4 series pairs, so the input into the inverter will be 90v (oc) and 22amps from the east panels and the same in the afternoon from the west panels.
The literature for this Must inverter states that the max pv should be 1500watts, so maybe I should buy the 60amp inverter which allows 2000 watts of pv. I dont know how the east and west facing panels power would combine, in a high sun both sides of the roof receive sun light but not at a productive angle.
One last question, my Must inverter has a mains input connection for charging the batteries and providing power if the solar and battery power is not sufficient. The output of my system would be totally independent of the existing electrics so do i need to run a separate earth wire or would the mains input to the inverter provide an adequate earth.
Will these components and panel array work together in my planned way. Thanks for reading and I know there lots of questions.
Ps would my panels need a seperate earth when only at 90voltd oc. I intend to fuse all panel strings.
Is there a newer Must inverter that would be suitable?

Go with a larger inverter so you can add more pv for cloudy days or increased loads.

What is the VOC of the JA panels you intend to purchase? Max pv 100v is pretty low.

Blocking diodes; been some discussion on the subject. Some say they help, others say there is no need as even a shaded pv panel generates enough voltage to prevent becoming a draw on the system.

Dynamic bonding; I would prefer the inverter did nothing at all with bonding. IMO, makes it easier to figure out safe wiring solution.

 

[Tony54]

Thanks for your replies. I had been thinking about increasing the west facing roof with 5/6 panels at 450 watts= 2900 West and thus a larger inverter. My initial thinking was that the Must inverters were readily available in spain and I wasn't too bothered about being totally off grid. I'm evolving as I go along.
I do have more duration of sunlight on my west roof, and it is shade free so think I could go with a 5/6 panels on West and 3 on east. I will start looking at higher pv input inverters at about 3.5 kwatts.
Any suggestions for a 5 or 6 series string with string open cct voltage of 5 x 50v =250v or 6 x 50v= 300v.?
The panels on the east shaded roof I will put into scc. and connect the 24v directly into the 5kw lifepo4 battery. Will that work?

As regards the bonding, will bond the panels to an earth spike and leave the inverter bonding until I have more info.
Thanks for the help.
Tony

 

[Tony54]

I've just found an inverter at a reasonable price which will allow me to have a series string of 6, 450 panels. =2700 watts
It has a reasonable amount of good comments on autosolar.es so it may be a contender. I'm happy that I've gone for more pv on the west facing roof and pv is fairly cheap so why not. This inverter gives me more charging current as well at 40amps and more.
I am processing the paper work for the town hall building works approval, which will cost about 60 euros and then can submit my plans for final approval to the town hall.

 

[Tony54]

Ps it's a Inversor Híbrido 3000W 24V Voltronic Axpert VMIII

 

[Tony54]

Ps it's a Inversor Híbrido 3000W 24V Voltronic Axpert VMIII

Pps I assume 3000w is va and not rms power which would be about 2.4kw.

 

[Kornbread]

Thanks for your replies. I had been thinking about increasing the west facing roof with 5/6 panels at 450 watts= 2900 West and thus a larger inverter. My initial thinking was that the Must inverters were readily available in spain and I wasn't too bothered about being totally off grid. I'm evolving as I go along.
I do have more duration of sunlight on my west roof, and it is shade free so think I could go with a 5/6 panels on West and 3 on east. I will start looking at higher pv input inverters at about 3.5 kwatts.
Any suggestions for a 5 or 6 series string with string open cct voltage of 5 x 50v =250v or 6 x 50v= 300v.?
The panels on the east shaded roof I will put into scc. and connect the 24v directly into the 5kw lifepo4 battery. Will that work?

As regards the bonding, will bond the panels to an earth spike and leave the inverter bonding until I have more info.
Thanks for the help.
Tony

IIRC, NEC here in the states does allow an earth ground at the pv panels but it's not the preferred method. Bonding is 'typically' referring to connecting neutral and ground at the breaker panel.

Voltronic Power is a large Chinese manu of solar inverters which often get rebranded as MPP, Growatt, eg4, etc..

 

[Tony54]

Kornbread, it seems like everything is made in China these days. I bought a bafang mid drive motor and 48v battery for it from a lie press and I am very impressed with bafang and lifepo4 battery, its takes me for 60kms rides with easy.
Anyway, thanks for your input, I didn't know that voltronic was the master company of these other decent brands.
Do you know how one bonds these inverters.?

 

[Tony54]

Motor for ebike

 

[Kornbread]

Kornbread, it seems like everything is made in China these days. I bought a bafang mid drive motor and 48v battery for it from a lie press and I am very impressed with bafang and lifepo4 battery, its takes me for 60kms rides with easy.
Anyway, thanks for your input, I didn't know that voltronic was the master company of these other decent brands.
Do you know how one bonds these inverters.?

Voltronic Power is notorious for their severely lacking manuals. If, when, how it handles bonding may be something you have to figure out yourself.

 

[Tony54]

Thanks kornbread, I had read this as well, I will look at other options too. Who needs problems, but it's useful to have forums like this to resolve or evade problems.

 

[Tony54]

Another aspect is reliability, personally I would prefer low frequency inverter (I assume that means a transformer based inverter) because in high frequency application the switching fets, mosfets etc have a reputation of burning out.