First 48v Off-Grid System Build - Advice/ Recommendations Needed :)

[Alanrc]

Hello everyone! I've been reading the forums for the past few weeks, digesting information and learning all about off-grid systems. I'll explain my situation then provide info on what I believe to be a good scalable entry point. Hoping to get some feedback on a few elements!

The Property/ Background

• Fully off grid summer cabin of appx. 750sq/ft in the Vernon, BC Canada
• South facing roof where we plan to install the panels (appx 30' from the planned electronics shed)
• The west side of the cabin is a very large tree. The roof gets full sun until about noon at which point it begins to shadow from W->E. By about 3:30pm the full roof is shaded by the tree.
• Cabin will be used from mid May through mid September and then winterized
• Our typical daily power usage is around 3.8kWh
• Our fridge, some lighting, and water pumps are all 12V DC
• We may add a 12000btu 120v heat pump in the future
• This is a shared family cabin passed down from my grandfather, and the other co-owners are incredibly price sensitive. I would be willing to pay a larger portion for a more robust and hassle free system (within reason).

Planned Setup
The goal of the setup is to have something simple, reliable, cost effective, scalable and relatively easy to troubleshoot. As I mentioned above, relatives will be at the cabin when I am not there so I would need to be able to walk a complete newbie through troubleshooting on the phone.

• 8 or 9 x 380w Heliene panels in either 3S3P or 4S2P. I was thinking 3S3P to add a panel and the extra string in parallel would help minimize impacts of shading
• EG4 3000 EHV (though this wouldn't work with a 3S3P due to low voltage risk and higher current w/ input rating of just 18A).
• 1 x ecoworthy 48V 100Ah LifePO4 battery (add more as needed if heat pump or other appliances etc installed)
• 48v to 12v converter
• 10AWG wiring from panels to SCC.
• 2AWG wiring from battery to controller

Questions/ Concerns

1. Am I overthinking 3S3P vs 4S2P? Will it make that much of a difference in the real world?
2. EG4 idle consumption is significant, and with it unable to run 3S3P should I be looking at alternatives 2 in 1's or should I consider separating SCC and Inverter?
3. Should I go with a 6000w EG4 Inverter w/ split phase for a 240v heat pump, though this would have the same voltage and current issues as above.
4. How risky is it having only 1 battery, therefore no redundancy, and of course only 1 day of autonomy (pre heat pump, obviously that would need more batteries)
5. Am I missing anything?

Thanks in advance!!!!

 

[hybe022]

Am I overthinking 3S3P vs 4S2P? Will it make that much of a difference in the real world?

I don't think 3S will work. The 3000EHV MPPT startup voltage is 120V.
Your panels are 40.65Vmp.
I'd personally will do minimum 5S on each string. More headroom.

Should I go with a 6000w EG4 Inverter w/ split phase for a 240v heat pump, though this would have the same voltage and current issues as above.

If you have the money, the 3000EHV only outputs 120V, single MPPT

How risky is it having only 1 battery, therefore no redundancy, and of course only 1 day of autonomy (pre heat pump, obviously that would need more batteries)

4.8kWh of backup can also be too tight
You only mentioned 3.8kWh daily typical use, not maximum use.

Your first upgrade might probably be a second battery.

Am I missing anything?

By about 3:30pm the full roof is shaded by the tree.

By 3:30pm you will be using a bulk of your batteries then.
You should definitely add that to your calculation if 4.8kWh will be enough.

 

[Alanrc]

I don't think 3S will work. The 3000EHV MPPT startup voltage is 120V.
Your panels are 40.65Vmp.
I'd personally will do minimum 5S on each string. More headroom.

Am I being overly concerned about minimizing shading impact? Do you think the bypass diodes in a 5S2P would be sufficient vs running 3S3P? If shading is going to be a big impact, I'm open to using something like a Victron 250/(85 or 100) MPPT SCC and a separate inverter to run more strings in parallel. Or will having 5S2P be over paneled enough even with shading impact as long as I buy 2 batteries?

With the two MTTP's of the 6000XP - would I run 5 panels in series to each? Or does it matter since I'll be well below the max voltage with 5S2P anyways?

 

[hybe022]

Am I being overly concerned about minimizing shading impact? Do you think the bypass diodes in a 5S2P would be sufficient vs running 3S3P?

microinverters handle shading better, idk if you might want to look into that.

i just can't be of much help with it though since i haven't tried microinverters myself

With the two MTTP's of the 6000XP - would I run 5 panels in series to each

i stand corrected, you said it faces the same direction
and gets fully shaded anyway so having 2 mppts
might not make much of a difference for the same amount of panels

Or will having 5S2P be over paneled enough even with shading impact as long as I buy 2 batteries?

i think this will be your best bet for going string-type.

--------------;

Your panel spec:
9.41Imp
40.65Vmp

i'm not certain if
4s will work (160v)
but 5s definitely should (200v).

going 3P (28.23Imp) might get wasteful
as you'll probably clip a lot on full sunlight
with the 3000ehv having only 18A max input.

 

[hybe022]

appreciate anyone to chime in, i'd just like to make sure i'm giving good advice

 

[Bongbong]

If you are looking at a couple of hours of reasonably good sunshine on the panels, you will need about 3kW in solar (expect about 80% of the rating), 8 panels should be enough. At 12V this means you will be charging with 200A per hour, this is not a small current for the size of that system. So make sure your solar charge controller, batteries, wiring (between solar charge controller and battery) and BMS can cope with those currents.

I think it is doable and given that everything runs of 12V, it's not worth going higher. If your things are rated properly and the work is done correctly, you might want to keep the battery in the house though, LiFePo4 is fairly safe.

 

[Alanrc]

If you are looking at a couple of hours of reasonably good sunshine on the panels, you will need about 3kW in solar (expect about 80% of the rating), 8 panels should be enough. At 12V this means you will be charging with 200A per hour, this is not a small current for the size of that system. So make sure your solar charge controller, batteries, wiring (between solar charge controller and battery) and BMS can cope with those currents.

I think it is doable and given that everything runs of 12V, it's not worth going higher. If your things are rated properly and the work is done correctly, you might want to keep the battery in the house though, LiFePo4 is fairly safe.

About half of our current power usage is 12v DC and half 120v AC; so I was thinking of using 48v batteries with a 48 -> 12v converter alongside the EG4 3000 or 6000. This would give a max charging current of 63 - 79 amps (8 panels or 10 panels @ 380watts.)

The only real consideration for going with the 6000 is it's ability to operate a larger 240v heatpump to cool our cabin on hot summer days, but again not sure this is worth the added cost vs just running a slightly smaller 120v heatpump for longer.

Seems like 2S5P is the way to go given the minimum voltage requirements of the EG4 3000/6000, and hopefully the internal bypass diodes on the panels help reduce shade impact.