3.3 KW off Grid System

Barbar0ssa

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Joined
Mar 3, 2021
Messages
77
This will be my build thread for my off-grid 48v system on my garage roof for backup and charging my electric car.

My roof area is about 25'x 25' which should fit 8 72-cell panels nicely. I planned the racking with Unirac Ubuilder.

I purchased my 3kw all-in-one (xindun LSM-30248) before I had planned on charging the electric car so I only have 120v. If I want to charge quickly, I may need to add a 240V inverter in the future.

I have 20 x 271 CATL cells (16 for this project an 4 for a smaller 12v setup) coming next Wednesday!

Right now I am trying to choose the best panels for my setup and that seems to come down to bi-facial vs mono-facial. I will be roof mounting so there will be much less reflection from the surface but I have heard that bi-facial are more efficient on cloudy days and my area has far far too many cloudy days so I am leaning that way right now.

With my current space, amperage, and voltage constraints, it looks like I will be designing 4 parallel strings of 2 panels.

The two front-runners at the moment are:

LONGi Solar LR4-72HPH-445M- These are called bi-facial but say that they have a white backsheet and mono-perc? They would be $0.59/w delivered and this company has all of the racking I need so it would be very convenient order.

Solorever 440w - made in the US, $0.53/w delivered. Signature Solar doesn't have the racking I need so I would likely have higher overall costs if I buy here.

I am definitely open to suggestions if there are better options out there.
 

Barbar0ssa

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Mar 3, 2021
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77
I went with 8 of the Longi panels. They are bi-facial and RES Supply was great to work with.

PXL_20210914_154449442.jpg
They dropped the pallet at the road and we inspected each panel, loaded them in the truck, and hauled them down the driveway. I need to get better pictures but it was threatening rain.
PXL_20210914_160629593.jpg
 

Barbar0ssa

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Mar 3, 2021
Messages
77
PXL_20211001_001450398~2.jpg

I have 20 x 280a CATL cells (16s and 4s packs) that will take about a week to charge with my little 10a power supply. I really like this cart for battery storage but I don't think it will hold 16 on one shelf without sagging over time.

I think I'm getting some scaffolding to get the panels on the roof this weekend!
 

740GLE

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Joined
Apr 30, 2021
Messages
521
Good luck with too balancing 20 cells at a time. What’s your current resting voltage?
 

chrisski

Photon Sorcerer
Joined
Aug 14, 2020
Messages
2,365
I have 20 x 280a CATL cells (16s and 4s packs) that will take about a week to charge with my little 10a power supply. I really like this cart for battery storage but I don't think it will hold 16 on one shelf without sagging over time.
Thanks for the pics. I’m top balancing and capacity testing a smaller 25 ah bank now and not very fun.

My 280s will be here in a few weeks. I am planning on putting them in an 8S pack on a 35 amp charger for a few hours prior to top balancing. Should shorten the process. Probably 3 hours to get 105 amp hours in each cell before the top balancing process. That should leave 35 - 45 ah left in each cell and shorten the top balance process.
 

Barbar0ssa

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Mar 3, 2021
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77
PXL_20211001_121931474.jpg

Last night they were sitting at 3.295 and this morning 3.319 so I should be almost at 90%. Call it 2kw remaining at 36w for about 55 hours, but it will probably take a day more than that as the amperage will taper off.

This will definitely take forever but the plus side is a beautiful top balance on a system I'm not ready to use with no chance of overcharging any cell.

I could break down the pack into a 4s and a 16s and hook up each BMS and charge them both in a few hours and then break them down into parallel again and then top balance for a day. This just involved less thinking and I can let them run for a week if they have to.

On to panels!
 

Barbar0ssa

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Joined
Mar 3, 2021
Messages
77
I rented a bucket lift for the weekend and wrapped up all of the roof work!


PXL_20211009_195632735.jpg

When it was time to move the panels, I turned the bucket into a tiny fork lift. Then careful use of rachet straps allowed me to get the panels in place.

PXL_20211011_113037164.jpg

One neat trick was to undo the rachet and use the strap to gently lower the panel onto the roof in a controlled manner.

PXL_20211010_162754412.jpgPXL_20211010_162747348.jpg
 

Barbar0ssa

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Joined
Mar 3, 2021
Messages
77
The end clips for the unirac were particularly difficult. It seems the trick is to have them in place before you bring the panel anywhere near the rack so you can wiggle it in. If it stops moving, a hammer will destroy the clip far before it slides it home.

PXL_20211010_190155897.jpg

I had to cut an inch off both the top rails to get that row to fit but that allowed me to plan the bottom rail slightly better so no rail trimming was necessary on those two.

I used a weatherhead for the roof penetration.
PXL_20211011_161942846.MP.jpg

It took so much longer than expected, but I'm thrilled with the results!
 

new off grid

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Joined
Jan 27, 2020
Messages
45
This will be my build thread for my off-grid 48v system on my garage roof for backup and charging my electric car.

My roof area is about 25'x 25' which should fit 8 72-cell panels nicely. I planned the racking with Unirac Ubuilder.

I purchased my 3kw all-in-one (xindun LSM-30248) before I had planned on charging the electric car so I only have 120v. If I want to charge quickly, I may need to add a 240V inverter in the future.

I have 20 x 271 CATL cells (16 for this project an 4 for a smaller 12v setup) coming next Wednesday!

Right now I am trying to choose the best panels for my setup and that seems to come down to bi-facial vs mono-facial. I will be roof mounting so there will be much less reflection from the surface but I have heard that bi-facial are more efficient on cloudy days and my area has far far too many cloudy days so I am leaning that way right now.

With my current space, amperage, and voltage constraints, it looks like I will be designing 4 parallel strings of 2 panels.

The two front-runners at the moment are:

LONGi Solar LR4-72HPH-445M- These are called bi-facial but say that they have a white backsheet and mono-perc? They would be $0.59/w delivered and this company has all of the racking I need so it would be very convenient order.

Solorever 440w - made in the US, $0.53/w delivered. Signature Solar doesn't have the racking I need so I would likely have higher overall costs if I buy here.

I am definitely open to suggestions if there are better options out there.
My system is similar to yours , been running 2 years so far , with zero issues
4.5kw panel ( 375w x 12 / 1 x 3 in serial / 4 x 3 in parallel )
Midnite classic 150 CC
10kwh/48v Meritsun Lifepo4 battery pack
7k/48v Reliable Inverter
MOES ATS
Power whole 1.2k sq home , off grid ( not the 230v dryer thou )
total around $10k back then , a bit cheaper now ?
 

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Barbar0ssa

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Mar 3, 2021
Messages
77
PXL_20211031_204648856.jpg

All the DC side is functional (though my batteries are completely full so there is no charging happening yet). One more stop at the hardware store should flesh out my AC side.

The battery switch is a 2 battery switch so I have #1 link to a pre-charge resistor that jumps to #2. As long as I rotate clockwise, there will always be some pre-charging on connecting the batteries to the all-in-one.

I definitely need some more cable management, and I am planning on insulating the lower shelf both to keep it warmer and to prevent any accidental shorting.

The primary load will be a 12amp charger for my Chevy Bolt (1440w). I am guessing I can get around 26 miles a day.
 

Barbar0ssa

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Mar 3, 2021
Messages
77
This inverter might not be good enough. I have 110v from N to L, 75v from L to PE, and 30v from N to PE (at .48hz?!?).

The air compressor is happy. The car charger is giving me a ground fault.
 

Supervstech

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DO NOT CHARGE IN SERIES UNLESS A BMS IS IN PLACE...

Destroyed cells are frustrating.
 

Barbar0ssa

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Mar 3, 2021
Messages
77
The only charging without a BMS was in parallel to a power supply limited at 3.65v. It is now in a 48v system with a BMS.
 

Barbar0ssa

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Joined
Mar 3, 2021
Messages
77
I attempted to charge my car but the charger gave me a ground fault. Thanks to all the help here, I was able to prove that I have a good ground when the inverter is plugged into the house system. My circuit was floating.

So yesterday, I made a little bit of power!

Screenshot_20211104-091249.png
 

Barbar0ssa

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Joined
Mar 3, 2021
Messages
77
Today I attempted to recharge my batteries instead of applying an AC load.

I've been playing with it today, and SmartESS says I have made 4kwh of solar. The highest peak I saw was 1400w, which seems awful. My xiaoxiang bms app says I added about 1.5kwh to my batteries. The wattage the BMS saw going into the battery was always at least 300w less than what the inverter app was saying. Sometimes it was 600w less. Either one of my apps is inaccurate or I am losing a ton of power somewhere.

I have a lot of figuring out to do. I am not sure which apps can be trusted. I will try to measure the current at various locations compared to the apps to see how if any of them are accurate.

So far, this is an incredibly disappointing day but there is time yet.
 

chrisski

Photon Sorcerer
Joined
Aug 14, 2020
Messages
2,365
Your panels are not he roof, so this is hard, but one way I test panels is to shade them and monitor production. If I shade a panel in full sunshine and the power does not go down, I know that that panel and everything it is connectors to in series is not making any power. When I shade a panel output for that string should drop to 1/4th to 1/3rd starting power. If there are other strings still active, 2P etc.. then that drop will not be as extreme.

Nearly every time I set up my portable panels, there is troubleshooting involved.

The only other thing I see is the shading on post 10, but that could be an early morning shadow that goes away quickly.

If you’re losing 300 watts, I’d expect some heat. I have a ammeter I could clamp over connections to see if something is odd.
 

740GLE

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Joined
Apr 30, 2021
Messages
521
Everything has an % accuracy, I’d trust what the BMS is telling you more than a cheap SCC.

Do the voltages of the BMS and SCC read the same? Any voltage drop is losses, but 300w of losses is pretty huge.

As for low output, what your latitude? This isn’t high output months for us in northern hemisphere.
 
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