Help for 3.2KW offgrid inverter

italianuser

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Feb 25, 2020
Messages
87
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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floydR

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Aug 23, 2017
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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
 

daromer

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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.
 

italianuser

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Feb 25, 2020
Messages
87
@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)
 

italianuser

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Joined
Feb 25, 2020
Messages
87
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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