Solar panel selection help

[Oakgroved]

Please help.
Thank you for your time in advance. I hope you can help me with a few questions i have.
I have 2 bluetti ac 300 head units each unit has 4 batteries. Running split phase into a transfer switch with 10 circuits. In the summer I plan on installing a soft start for my AC and seeing what i can run all together. Want to run as much off grid as possible without using grid to charge batteries.

What solar panels do you recommend that will be best with my system? And most watts or volts give the best charge. And anything else you recommend my ears are open to learn. The following links and the panels i can afford.
Plan is to order 12 panels. But really help to recommend how to run them. Still learning as i go. I am very mechanical and have good home electrical knowledge but lack the solar knowledge.

Option 1
400 watt 36.8 volts 108 cell Canadian solar HiKu6CS6R


Option 2
390 watt 44.1 volts Canadian solar 132 cell HiKu Black CS3N-MS
This option is 10" longer in length.

 

[Madco]

First a disclaimer: I am not familiar with Bluetti's inverters.

SO looking at the specs and your description, It looks like each inverter can accommodate a maximum of 2.4kW of PV power with the PV voltage running anywhere between 12-150VDC with a maximum current of 12A.

Your system description indicates four B300 batteries for each inverter. These are 3.072kWh (I'm rounding that to 3 kWh) batteries, so you have a total of 12kWh of storage per phase. The system has a total of 24kWh of storage.

A couple of questions:

1. How quickly do you want to recharge the batteries? Assuming dead batteries at 10% SOC and NO A/C LOAD, it will take 4 1/2 hours to recharge if the PV inputs to each inverter are maxed out at 2.4Kw per input. This assumes ideal conditions. A more realistic estimate would assume the panels are producing 80% of the STC power and a PV to battery efficiency of 92% (Bluetti may be better than this but I couldn't find a conversion efficiency specification). Considering all that, it will take just over 6 hours to recharge (assuming the 4.8kW PV input is available for the 6 hours. Realistically, you might get 4 peak sun hours per day). That puts your system at 1.5 days to recharge from 10% SOC.

2. Given the discussion above, how many days of autonomy do you need?

On the panel layout:

OPTION 1 - A NO GO regardless of how they are configured. The panels have a Voc of 36.8V and a Isc of 13.85A. The current exceeds the maximum PV current spec of the Bluetti (12A). BTW, the maximum power current of the panels is 12.99A, also in exceedance of the Bluetti spec.

OPTION 2 - Not sure as I couldn't find the panel specs on the CanadianSolar site.

In either case, I think you will need an external charge controller for each set of batteries. You can get around this by using smaller wattage panels - you just need to find a panel with an Isc of less that 12A. Note that you'll have more panels to deal with than the 12 or so you probably envisioned.

 

[Oakgroved]

First a disclaimer: I am not familiar with Bluetti's inverters.

SO looking at the specs and your description, It looks like each inverter can accommodate a maximum of 2.4kW of PV power with the PV voltage running anywhere between 12-150VDC with a maximum current of 12A.

Your system description indicates four B300 batteries for each inverter. These are 3.072kWh (I'm rounding that to 3 kWh) batteries, so you have a total of 12kWh of storage per phase. The system has a total of 24kWh of storage.

A couple of questions:

1. How quickly do you want to recharge the batteries? Assuming dead batteries at 10% SOC and NO A/C LOAD, it will take 4 1/2 hours to recharge if the PV inputs to each inverter are maxed out at 2.4Kw per input. This assumes ideal conditions. A more realistic estimate would assume the panels are producing 80% of the STC power and a PV to battery efficiency of 92% (Bluetti may be better than this but I couldn't find a conversion efficiency specification). Considering all that, it will take just over 6 hours to recharge (assuming the 4.8kW PV input is available for the 6 hours. Realistically, you might get 4 peak sun hours per day). That puts your system at 1.5 days to recharge from 10% SOC.

2. Given the discussion above, how many days of autonomy do you need?

On the panel layout:

OPTION 1 - A NO GO regardless of how they are configured. The panels have a Voc of 36.8V and a Isc of 13.85A. The current exceeds the maximum PV current spec of the Bluetti (12A). BTW, the maximum power current of the panels is 12.99A, also in exceedance of the Bluetti spec.

OPTION 2 - Not sure as I couldn't find the panel specs on the CanadianSolar site.

In either case, I think you will need an external charge controller for each set of batteries. You can get around this by using smaller wattage panels - you just need to find a panel with an Isc of less that 12A. Note that you'll have more panels to deal with than the 12 or so you probably envisioned.

Thank you for your response. Take a look at this link on Bluestti it says you dont have to worry about exceeding amps. Does this sound correct?

AC300 PV input limits

I’ve read in other threads that you can ignore the 12A limit on the PV input so long as voltage is under 150. Is there really no limit at all on the Amp input? I’m looking at 240 watt panels with 27.08 Voc and 10.71 Isc. If I run 4S2P I will be pushing 116.32 volts and 25 amps at 32 degrees...

community.bluettipower.com

 

[Doggydogworld]

Thank you for your response. Take a look at this link on Bluestti it says you dont have to worry about exceeding amps. Does this sound correct?

AC300 PV input limits

I’ve read in other threads that you can ignore the 12A limit on the PV input so long as voltage is under 150. Is there really no limit at all on the Amp input? I’m looking at 240 watt panels with 27.08 Voc and 10.71 Isc. If I run 4S2P I will be pushing 116.32 volts and 25 amps at 32 degrees...

community.bluettipower.com

Sounds correct. A MPPT should present the panels with an open circuit (infinite resistance) as they first wake up in the morning. So V = Voc, I = 0. The MPPT then lowers the effective resistance, reducing panel voltage and increasing current, in search of the max power point. It shouldn't let current increase beyond its 12A limit, though.

If you put 6 panels on each Bluetti you'll have to go 3S2P to keep cold weather Voc below 150V. Peak sun current would then be 25A or so. The Bluetti won't let it go above 12A, so you'll get less than half the potential power.

BTW, I don't understand the Bluetti's 2.4 kW rating. Max of 150V and 12A is only 1.8 kW.

 

[Oakgroved]

Sounds correct. A MPPT should present the panels with an open circuit (infinite resistance) as they first wake up in the morning. So V = Voc, I = 0. The MPPT then lowers the effective resistance, reducing panel voltage and increasing current, in search of the max power point. It shouldn't let current increase beyond its 12A limit, though.

If you put 6 panels on each Bluetti you'll have to go 3S2P to keep cold weather Voc below 150V. Peak sun current would then be 25A or so. The Bluetti won't let it go above 12A, so you'll get less than half the potential power.

BTW, I don't understand the Bluetti's 2.4 kW rating. Max of 150V and 12A is only 1.8 kW.

Bluetti wouldnt be my first choice. I was given the Bluetti by my uncle and i want to make the best out of it as a starter and in the future go with a better home system. So i want to purchase panels i will be able to use on another system in the future. I dont understand how to wire the system like you said. Do you have a drawing or something to explain it better. With my lack of knowledge i was thinking of doing them 3 in series, 3 in series and so on.

 

[Doggydogworld]

3 in series in each AC300 works fine. That's 6 panels total. (Some "solar generators" have two separate MPPT inputs, but if I read the AC300 specs correctly it only has one).

You plan to buy 12 panels. Instead of just storing the other 6 in your garage, connect a second 3-panel string in parallel to each AC300 (3S2P). Like this diagram from this article on another site. You won't get more peak power due to the 12A limit, but you will get more power on cloudy days and in mornings and evenings.

 

[Oakgroved]

3 in series in each AC300 works fine. That's 6 panels total. (Some "solar generators" have two separate MPPT inputs, but if I read the AC300 specs correctly it only has one).

You plan to buy 12 panels. Instead of just storing the other 6 in your garage, connect a second 3-panel string in parallel to each AC300 (3S2P). Like this diagram from this article on another site. You won't get more peak power due to the 12A limit, but you will get more power on cloudy days and in mornings and evenings.

View attachment 199283

Each AC 300 unit has a splitter that creates 2 inputs each takes 1200 watts. So i would have 4 inputs total each 1200 watts up to 150 volts. Thank you for the help. How would you recommend this with 4 inputs?

 

[Oakgroved]

Each AC 300 unit has a splitter that creates 2 inputs each takes 1200 watts. So i would have 4 inputs total each 1200 watts up to 150 volts. Thank you for the help. How would you recommend this with 4 inputs? Each unit has 2 separate mppts. See this video 3:12 into the video shows the solar input. Will prowse.

 

[Doggydogworld]

Wow, two separate MPPTs is great. They should make their spec sheet clearer. You're right, just connect two 3 panel strings to each AC300. You should get close to full power. Getting back to your original question, the 400s will be current-limited in peak conditions. You may not care. The 390s reach 50Voc around -25 deg C. That could be an issue in Minnesota. I'd probably play it safe and get the 400s.

 

[Oakgroved]

Wow, two separate MPPTs is great. They should make their spec sheet clearer. You're right, just connect two 3 panel strings to each AC300. You should get close to full power. Getting back to your original question, the 400s will be current-limited in peak conditions. You may not care. The 390s reach 50Voc around -25 deg C. That could be an issue in Minnesota. I'd probably play it safe and get the 400s.

2 three panel strings in series to each AC300 head unit? I have about hundred feet from head units to solar panels. If i run them in series i would have to pull 8 wires in total from panels to ac300 head unit? What gauge wire would you recommend? I think 8 gauge but let me know what you think. Do i run each series of wires into individual 25amp solar disconnects? Indoor or outdoor? Better closer to panel or mppt? Thanks again for your help.

 

[Doggydogworld]

8 wires (4 pairs) is the only way I see to get full power from your 12 panels. If you put more than 3 panels in series you'll exceed the AC300's Voc limit. Parallel connections reduce the number of wires, e.g.
One big 3S4P array - one wire pair (not recommended here for various reasons)
Two 3S2P arrays - two wire pairs

But you'll lose power due to the AC300's 12A limit. For example, a 3S2P array could push 20-25A in full sun, but the AC300 will limit that to 12A so you'll only get about half your potential power. As I mentioned before, this may or may not be OK in your situation. There won't be much effect when cloudy or at low sun angle because array current in those conditions can't get much higher than 12A anyway.

8 vs. 10 vs. 12 AWG wire depends on how much voltage drop you're willing to accept. Voltage drop calculators can help you decide this. For example, 100 ft of 8 AWG might cause a 1% voltage drop at 12A, 10 AWG 2% and 12 AWG 4%. I just made those numbers up, but they should be in the general ballpark.