Help for 3.2KW offgrid inverter

italianuser

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Hi there everyone, I'm going into details with the project for my new low-budget solar system.

I need some help to understand pros/cons for the inverter, I did some research but this is actually new for me. My first system was a good experience for me, a small 12V system, 4x 50W panels, 20A regulator, 1500W inverter; now the new system could be 24V (I also examinated a 48V system, it seems to me that my specs are at limit between a 24V and a 48V system, am I right?).

After some analysis I arrived to something like this (my wife simulated fainting when I told her total expense was 1500€, not much really, 1EUR=1.20USD :p):
  • 4x 280W 60 cell class A poly panels Voc 39.0V Isc 9.27A in 4s1p configuration, total 1120W (will become 6 panels later, total 1680W).
  • 4x 100Ah AGM 12V batteries in 2s2p, total 200Ah 24V (could go for 4x 120Ah 2s2p, total 240Ah 24V).
  • Offgrid Inverter 60A 3.2KW (when I started searching I was first looking for an 6000W inverter and an 80A solar regulator, two devices, but offgrid inverted seemed more suitable).
Electricity in most apartments in Italy is single phase 3.3KW at 220V. Considering I don't want to swap/sell/give electricity to grid my questions are mainly about the offgrid inverter, please tell me if you see something wrong:
  • Noise: They seem to be quite noisy so I couldn't keep it inside (I have a sort of big open space room), so I could consider keeping it outside on the balcony. Temperatures in winter barely go below 0°C and in July/August normally go up to 40-42°C (104-107°F). I would use an external ABS enclosure, and support some efficient temperature control.
  • Hybrid: would I really have any advantage using a hybrid system? Considering I don't want to give electricity to grid.
  • KW requirements: House requirements for electricity are normally quite low, well under 2KW, with not-so-often higher peaks of 3KW for maximum 30-60 minutes per time (oven, kitchen appliances). I'd go for 3.2KW inverter model although I don't like to be at specs limits... I had a look at 5KW, too, but it's 48V. In this period I'll be monitoring house KW usage for a more detailed insight on peak loads. My current usage is 220-240KW/month (7-8KW/day average).
  • Make/model: yes, I know that I shouldn't look at cheap products, but budget wins over everything. I was looking at models like Powland SMR 3.2K 24V (very similar to Easun and PowMr products) in the 300-350€ range. https://www.aliexpress.com/item/33024632564.html. If you tell me these are not reliable I'll rethink the thing.
offgrid1.jpg
Plus, what I don't like of offgrid inverted is that batteries are charged from grid also, do tell me if I got it wrong, but it seems inefficient to me to charge DC batteries to then convert it again to AC to give current to the house. If this is what happens I think I'd prefer to have separate inverter and charge regulator and avoid charging batteries from the grid, controlling power source switching in some other way.

TIA
 
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Question Why so high of PV input voltage? since you donot have room for many panels? The mppt operates from 120v to 450vfrom solar panels you would 3 in series on a perfect day. https://powland.aliexpress.com/stor...html?spm=a2g0o.detail.100008.7.6b71218aDmCREU has almost the same specs but its mppt operates at 30~115 VDC 2 in series get you to 80v-100vdc.
Batteries can be charged from the grid if hooked to the grid, doesn't mean you have to charge from the grid. you can disable charging from the grid in most inverters
later floyd
 
A more expensive inverter can be in same room as you without Noice... But since you have la batteries they should not be in the house and they should be well ventilated unless sealed high quslity One.


And as Floyd Said the voltage. You need more panels in series for that inverter.
 
@floydR: you speaking about "MPPT Range @ Operating Voltage 30~80VDC" parameter (from SMR 3.2K 24V datasheet). You're absolutely right, that's a new parameter for me; so my choice could be SMR 3.2K 24V model which has a max capacity of 1800W for PW panels and support for 1s/2s within the 30-80VDC

@daromer: batteries are AGM very high quality, I buy them from a professional local dealer. Actually I'm keeping my current set of sealed AGM batteries in the house. I'll check this solution out, I don't wont to risk get poisoned!

Good points, I understand a bit more, thanks a lot for your replies(y)
 
Update:
I did some more research and downloaded a few inverter manuals to understand settings. Yes, I usually do exaggerate with research before buying ehm :giggle: I understood that hybrid inverters are my choice and that I can choose to charge batteries from solar only (no grid charging), and that's what I want; also I love the feature these inverters have of automatically switching to grid when batteries are undervoltage, I find that perfect for me.

I'm seriously thinking to go for a 5KVA model and not a 3.2KVA one because I'm right at specification limits for 3.2 models and I don't like running a device at it's limits for most of the time (I would have about 60A coming out of panels in sunny days). Budget for inverter is around 400€.

Also I'm considering connecting all 6 panels in series at this point (234V DC, yes, I know it's a high voltage) otherwise I won't be in "MPPT Range" parameter (>120V DC).

So my configuration is still: 6x 280W panels, 4x 100Ah or 120Ah 12V batteries plus the hybrid inverter. Now I'm looking into cables, they cost so much!

EDIT: I started collecting data from my ACS712 sensor (in AC version, arduino software very different from DC version), here's the graphs for average usage and peak current usage.

20210416.jpg
(16th April 2021)

20210417.jpg
(17th April 2021)

As usual any advise is welcome! Thanks a lot(y)
 
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Update: ordered Panels and Off-Grid Inverter(y):giggle: (photo below); tomorrow I should be able to order the batteries (my local dealer doesn't have them, so I'll get the on Ebay from a solar-specialized vendor).

I think it will be a month or maybe two before I get everything mounted and fully running, the hardest part will be making the structure to hold the panels outside and the enclosures for inverter and batteries; and the arduino systems for monitoring.

Final configuration for my offgrid system:
  • 6x 280W PERC polycrystalline, Imp 8.64A, Isc 9.27A panels (strangely enough I had a better experience with poly compared to monocrystalline ones);
  • Panels mounted in 2S3P configuration;
  • Inverter is Axpert V_PF1 5KW 48V, MPPT range 60-115VDC (thanks guys for advise on that); max charge 60A from PV + 60A from grid (wont be using AC charging from grid); max.panels 3000W;
  • Batteries, I'll try and find a good price for 4x 120Ah @12V AGM Deep Cycle; mounted in 4S for 48V; I'm avoiding no-brand and cheap ones.
Now, what I really didn't think about when buying the inverter is this... a 5KW unit is useless in my case, although I do prefer having an over-dimensioned unit. It's useless because all the cables in italian houses are 2.5mm2 (13AWG) for heavy loads and 1.5mm2 (15AWG) for lights & co., that is:
  • Grid supplies maximum 3.3KW;
  • Electrical system mounts:
    • 25A 220V RCCB followed by two MCBs;
    • 16A 220V MCB (3520W) for heavy loads circuit;
    • 10A 220V MCB (2200W) for lights.
If by any chance I permitted the inverted to give 5000KW around the house I would have cables really be at limit and overheat, risking a meltdown. Now, this is a real problem, not sure if inverter has a setting for limiting inverted AC output (I didn't see it), so I'll surely add a relay to handle >3300W per 5 or 10 seconds.

Axpert_5KW.jpg

What's missing: cables... 2AWG and 8AWG they are expensive! Metal bars to support panels. Enclosures for mouting inverter, batteries and control stuff.

Next step: open a new thread in Solar section when pieces arrive!:sneaky:
 
t think about[/B] when buying the inverter is this... a 5KW unit is useless in my case, although I do prefer having an over-dimensioned unit. It's useless because all the cables in italian houses are 2.5mm2 (13AWG) for heavy loads and 1.5mm2 (15AWG) for lights & co., that is:
  • Grid supplies maximum 3.3KW;
  • Electrical system mounts:
    • 25A 220V RCCB followed by two MCBs;
    • 16A 220V MCB (3520W) for heavy loads circuit;
    • 10A 220V MCB (2200W) for lights.
If by any chance I permitted the inverted to give 5000KW around the house I would have cables really be at limit and overheat, risking a meltdown. Now, this is a real problem, not sure if inverter has a setting for limiting inverted AC output (I didn't see it), so I'll surely add a relay to handle >3300W per 5 or 10 seconds.

I am assuming that your apartment or house does have split your loads on more then 1 or 2 circuits, right :)

A 2,5mm2 circuit can handle 16A continues (3,5kW), a 1,5mm2 13A (2,8kW). Your service panel will surely be rated to 80A. So in your case you are actually better of with your 5kW off-grid system feeding into your load panel. But you need to feed the grid and inverter through a Transfer switch. That power will distribute to your various circuits. You just cannot put all the 5kW on one circuit.
 

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@Roland W , yes house two circuits, a 16A one and a 10A other one. I wanted to connect everything to the inverter and have PV+Battery as main source and Grid AC as a backup :unsure:I will obviously try everything in the lab first, before attaching anything in the service panel.

A Manual Switch like in your circuit, between Grid AC and Inverter yes, does make sense to completely disconnect/isolate inverter and run from Grid only. I'll consider that, thanks(y)

This is the schema I'll be following, it's a typical one, similar to what I'm already using on my (small) labs PV system.

schema1.jpg

Extras will be:
- DC MCB between Panels and PV IN;
- DC MCB and fuses between Batt and BATT IN;
- AC MCB between Utility Grid AC220V and AC IN;
- Industrial Relay just on top of RCCB 25A to open circuit if load >3.3KW for more than <n> seconds;
- Monitoring on everything (I'm paranoid about this LOL): voltage, current and temperatures, all cables are a concern for me.

I'll check @daromer 's videos, thx a lot!
 
@Roland W , yes house two circuits, a 16A one and a 10A other one. I wanted to connect everything to the inverter and have PV+Battery as main source and Grid AC as a backup :unsure:I will obviously try everything in the lab first, before attaching anything in the service panel.
And you cannot split those 2 circuits into more separate ones? There is only 2 sets of wires coming into your service panel for loads? Must be a very small apartment, right?
 
And you cannot split those 2 circuits into more separate ones? There is only 2 sets of wires coming into your service panel for loads? Must be a very small apartment, right?
Uhm split it... I could have a look at that , there's actually 4 sets of wires leaving the service panel, two 16A and two 10A, I suppose it could be left side and right side of the flat. Why could it be convenient to manage it in 4 segments instead of 2, for a more granular management?:unsure:
The flat isn't big, should be 130-140m2, it's quite big for italian standards where a 90m2 flat is considered a medium side house. Small ones are 40m2, usually good for singles and just married couples.
 
Uhm split it... I could have a look at that , there's actually 4 sets of wires leaving the service panel, two 16A and two 10A, I suppose it could be left side and right side of the flat. Why could it be convenient to manage it in 4 segments instead of 2,

In a modern installation, you would protect each individual circuit with a separate breaker. If there is a problem with a device, you would not lose the electricity of half of your house. And today, people of course as well do have much more devices. You can easily overload a breaker, if there are more then one circuit connected at it. If your panel has space for 2 more breakers, just give each set of wires a breaker. You will distribute your loads more evenly and no need to worry about overloading anything, if you really have to pull 5kW from your inverter someday.
 
In a modern installation, you would protect each individual circuit with a separate breaker. If there is a problem with a device, you would not lose the electricity of half of your house. And today, people of course as well do have much more devices. You can easily overload a breaker, if there are more then one circuit connected at it. If your panel has space for 2 more breakers, just give each set of wires a breaker. You will distribute your loads more evenly and no need to worry about overloading anything, if you really have to pull 5kW from your inverter someday.
That's true, does make sense, yes. I actually have no idea how they divided the circuits but I think they maybe did a bit of a mess:censored:
I think they mounted the minimum required by law over here (minimum 2 separate circuits for heavy loads and light loads and MCB+RCCB, actually I added RCCB, there was none). You know my MCBs never tripped in 15 years, the grid AC trips after seconds for overloads >3.3KW so no way my MCBs will ever catch an overload LOL.

I thought there was a reason to split circuits having to do with using solar as main source. If my wife will ever use oven + microwave + hair dryer all together I'm sure inverter will be happy to give a lovely 5KW and melt all the cables in the house :D:D no way those 2.5" multicore wires would last long with 22 amps going round them ahhhh, they already become nice and hot with 12-13 amps!
 
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