My Off-Grid EV Solar Charger is... DONE!!! (and it even WORKS!)

[TheDoctorUSA]

Hey everyone!

I finally reached the point in my build where I turned everything on this morning, and... IT WORKS!!!

I would like to thank @Will Prowse for his video, if it wasn't for him, I would have never realized how easy and accessible solar is...

This is my 39feet trailer, everything was done with lag screws in the roof attached to brackets and unistrut, I got the idea from @mmmmmdonuts and they were so kind to provide me with all the links to buy everything + instructions.


AFTER incentives, I have spent a little over $5,000, which I hope to gain back in 2 years.

Now, I definitely have to clean the cables up, add conduit, add a fork to the ground wire and hide it. But this is what it looks like so far:


- Sungoldpower 10kw
- Yixiang DIY 16kWh
- 2 series of 6 430w bifacial SEG panels (12 panels total 5.1kw)
- 2 DC breakers
- 50 + 20 Amp outlet with a NEMA 14-50 and a GFCI 20amp outlet

I even put some juice in my Tesla!!!


I do have some questions though:

1) Does anyone know how Sungoldpower neutral ground bond works? I tried asking them but they could not give me a straight answer, here's my problem:

When I first wired everything up, I was measuring 120V between L1 and G, which technically means bonded, right? Now here's the issue: not only I wasn't getting any continuity between N and G, but my Tesla charger was throwing a "bad ground" error.

I ended up bridging N and G bars in my outlet panel and it worked... So what does that mean? Did I have a bond at the inverter or not? Definitely don't want to end up with a ground loop.

2) I have a ground rod driven in the soil next to the shed, my set up right now goes underneath the shed (touching the metal sheetings) and then in the ground rod, is this a decent way to include my metal shed in the grounding?



For my usage, I will charge my Tesla a couple times a week, and use the remaining for my trailer!

As for panel production, I am very satisfied as of now, I had a peak of 3.8 kW which is on par with what PVWatts says, so if the predictions are right, I will end up producing almost 8000kWh in a year (which is already $3200 in savings!!!)



You can see the times I shut everything off to make adjustments, but minus that... the production seems great. I also tried to charge my tesla first at 32A and then 16A, the inverter did not bat an eye...

I'm so thankful for everyone in this forum who helped me make this dream real! Thank you guys!

(Another special thanks goes to @BaylentheSky and @1ufvlsi6x for helping me understand grounding)

P.S. I'm adding some closed cell spray foam in my shed very soon, with some ventilation, so should be interesting!

 

[BaylentheSky]

1. You’re fine as long as it is a stand alone off grid system, not connected to another system like the grid, or another inverter. Back in the day when people built a system solely for the purpose of charging an EV like yours, they used to have to manually bond the N and G together to circumvent the ground fault error that many EV’s would display. In fact I remember Ian from watts247 showed this in one of his videos from years back. There is no ground loop if your inverter is the only thing grounded in the whole system.

2. If you measure 120V between L and G, there is a potential shock hazard if you’re touching both the shed and any of the 2 L’s at the same time. However this is even less likely than you touching the inverter’s panel and L at the same time WHILE it’s on, so I wouldn’t be worried about it.
Always turn off the inverter before working on it, and you’re safe!! Never attempt even the easiest physical operation with it before turning it off!

 

[TheDoctorUSA]

Thank you so much for the reply!

I guess the only question that remains is how is it possible for me to measure 120V between L1 and G and NO continuity between N and G?

I thought I would only see 120V between L1 and G if G was bonded to N, but I guess it's not the case this time

 

[jorby]

Your meter is very high impedance (10 million ohms) and can measure leakage from neutral to the ground (case) of the inverter that the continuity test does not see. The neutral of a split phase inverter often has high value resistors and capacitors between it and the case. This is far from "bonded" like you now are. The evse (AKA charger) does not like the floating neutral or in this situation (240v), the floating ground which it can easily pull to a voltage far away from the 120v you measured with it unplugged. I had the same problem with a 230v inverter until I bonded the "neutral" line.

 

[TheDoctorUSA]

Hi Jorby! Thank you for the clarification, that makes sense.

I'm glad everything works now! Excited to keep it on and see my production in the next days.

 

[TheDoctorUSA]

Updating here for anyone reading this in the future:

I just connected my trailer with a 50ft 50amp RV extension chord (unfortunately the solar shed is in front of the trailer and the plug is in the back lol), I have the main AC on, my laptop charging, lights, fridge, Starlink... The sungold is doing amazing and I'm even charging 1kW to the battery!!!

Only thing I can't understand is, my Yixiang says it's at 99% on its display, but the inverter says it's at 66... What's gonna happen when the battery is actually full?

 

[jorby]

Do you have battery communication connected and working with the inverter?

 

[TheDoctorUSA]

Hey @jorby ! I don't have any communication connected, should I? I know Will never does.

 

[BaylentheSky]

Hey @jorby ! I don't have any communication connected, should I? I know Will never does.

That means your inverter is just “guessing” the battery’s true SOC. There’s no way of it knowing without comms.

 

[jorby]

I won't say you should, but it is the reason that they don't agree right now. Eventually, the inverter will decide that the battery is full based on parameters set in the inverter, and then it will also report full. You can view and adjust these parameters in most inverters. It is common for them do disagree in "open loop" operation.

 

[TheDoctorUSA]

Thanks to both.

Is it as easy as connecting the RS485 cable between the two, or is there any settings I should be aware of?

 

[BaylentheSky]

Thanks to both.

Is it as easy as connecting the RS485 cable between the two, or is there any settings I should be aware of?

I've always run my batteries open loop (no communications) but I believe there are 3 things you must do to get comms:
1. Yes, use that cable.
2. Set the right communication protocol. This depends on your battery's BMS. Check your battery manual to see what protocol it uses, then set it in your inverter settings.
3. You may have to change battery type to Lithium in the inverter settings, again, consult your inverter manual to see what it wants this battery type to be when you have communications.

 

[TheDoctorUSA]

Thank you!

Do you think running open loop is better? This is what I see in my inverter's manual, so I suppose I need to check the BMS comm port as well.

I do not care about seeing wrong SOC on my Inverter, more so I hope I don't fry anything by overcharging etc.

 

[BaylentheSky]

If you run open loop, the inverter doesn’t care about its own display of the battery’s SOC. It only cares about the charging voltage you set, and will perform exactly to that setting. It’s not like it “guesses” the battery SOC is 100% and stops charging, rather, it will charge the battery to the bulk voltage that you set. If you haven’t already, watch Will’s recommended LFP charging voltages video (he recommends 58V Bulk and 54.4V Float). If you are a bit conservative, you can do 57.6V and 54V respectively.

Remember if you want the BMS balance function to trigger, the cells have to be charged to above a certain voltage before the BMS starts its balancing process. I’ve seen this balance voltage to be as high as 3.55V on some BMS (JBD).

 

[TheDoctorUSA]

Thank you as always. I just changed some settings on the inverter.

Battery type: USER
Max discharge 46.8
Max charge: 58V
Float: 54.4V

I think I will leave open loop right now, I don't have enough knowledge for letting the BMS communicate with the inverter, and I think set voltages might be better for now.

Update on today: yesterday night I used air fryer, microwave, laptop, battery only dropped to 70% and this morning it started charging back up again!

I have produced over 10kWh and it's still 12:35PM. I think i might go over the predicted 18!

Very satisfied with the system so far, it's so cool seeing the panels on the trailer and thinking that I'm using energy out of the sun!

Also, not sure what that little drop in production is, only lasted 5 mins, probably either a temporary shade or bird sitting on a panel... No clouds today lol.

 

[BaylentheSky]

Can I recommend a little bit higher of a discharge voltage? I generally like to leave mine at about 50V, especially if I have larger loads. Reason why is, as you probably already know, voltage under load is always lower than true (resting) voltage of the battery. So when you pull a load, let’s say 4KW, that would be roughly 80A pulled from the battery. In my crude observation, every 5A load drops the battery voltage by 0.1V, so a load of 80A can drop its voltage down as high as 1.3V. That means a battery resting at 52V will drop to 50.7V under such load.

So generally under that particular scenario, I like to plan my discharge voltage as follow:
1. I want to discharge to about 10%, which is roughly 51V resting. So I will set my discharge voltage to 49.7V (51-1.3).
2. I set the recovery point voltage (back to battery) to 52V. This will ensure that if there is more capacity to the battery if the inverter cuts off early due to a larger load, then go ahead and use it.

46.8V might be a bit too close to the BMS’ cut off voltage, which might trigger it going into sleep mode, requiring you to wake it back up manually if the inverter doesn’t have such function.

 

[TheDoctorUSA]

Just changed the setting, thank you for your advice.

I put the max discharge at 50V. The threshold for restoring the load is 52V by default so I'm gonna leave it like that!

Also, is it normal that the battery is taking A WHILE to balance? It seems like the V difference is definitely getting closer and closer, but it's been saying "310A of 314" for the capacity for the last 3 hours! I'm guessing it's actually lower than that and it's slowly going up.

Also, if the battery is fully charged, and I'm leaving for let's say 7 days, is it ok if I turn everything off, with the battery at full charge? Or should I leave it on to let it "float"?

 

[TheDoctorUSA]

To add to my question, I'm not always at my off-grid trailer, and the shed is getting super hot right now, so while I figure out what to do with portable ac, closed cell foam etc, I don't want to leave the system on in there baking, I would rather it be hot but with the system completely turned off.

When I'm at the trailer, I usually leave the shed open so it airs out.

 

[BaylentheSky]

Just changed the setting, thank you for your advice.

I put the max discharge at 50V. The threshold for restoring the load is 52V by default so I'm gonna leave it like that!

Also, is it normal that the battery is taking A WHILE to balance? It seems like the V difference is definitely getting closer and closer, but it's been saying "310A of 314" for the capacity for the last 3 hours! I'm guessing it's actually lower than that and it's slowly going up.

Also, if the battery is fully charged, and I'm leaving for let's say 7 days, is it ok if I turn everything off, with the battery at full charge? Or should I leave it on to let it "float"?

1. A new battery will require several full charge before it’s fully equalized and allowing you access to its full capacity. Don’t worry, just keep charging to full and you’ll have it at max capacity in no time.
2. Please try not to leave a full battery sitting in such state of charge for too long. I recommend 80% if you’re leaving it for a week or two, and around 50% if you plan to be away for more than a month.

 

[BaylentheSky]

To add to my question, I'm not always at my off-grid trailer, and the shed is getting super hot right now, so while I figure out what to do with portable ac, closed cell foam etc, I don't want to leave the system on in there baking, I would rather it be hot but with the system completely turned off.

When I'm at the trailer, I usually leave the shed open so it airs out.

You probably already do this, but please make sure to turn off the PV disconnect switch as well as the battery’s breaker before leaving. You don’t want to chance all these currents going into your inverter even if it’s off.

 

[TheDoctorUSA]

1. A new battery will require several full charge before it’s fully equalized and allowing you access to its full capacity. Don’t worry, just keep charging to full and you’ll have it at max capacity in no time.
2. Please try not to leave a full battery sitting in such state of charge for too long. I recommend 80% if you’re leaving it for a week or two, and around 50% if you plan to be away for more than a month.

Thank you, that makes sense.

Welp not to fret, sun is going down and my AC is still on I will probably stop using it once battery goes down a little.

Also, PVWatts estimated 587 kWh in October, or 18.93 kWh. And guess what... it's 4:11pm and I have produced 21.2 kWh!!! I still have an hour of sun left so I will let you guys know how much I end up producing.

 

[TheDoctorUSA]

Final day update... 22.3 kWh produced!

 

[BaylentheSky]

Sorry to tell you it's not going to stop there. As people in this forum will tell you, there's no such thing as enough power. Once you're bitten by the solar bug, it's not going to stop even if you've eliminated all your electricity bill. Once you're there, the thirst just does not satiate, you're going to actively search out family and friends to "help" them, but in reality you're just looking for that next hit, chasing that dragon.

Will created this forum as an online SA (Solar Anonymous) spot for junkies like us to congregate, else we'd be standing at street corners begging people to let us "help" them go solar.

 

[TheDoctorUSA]

LOL you are so right. I found myself today compulsively looking at the inverter's dashboard... admiring production and trying to analyze every single piece of data...

I was already thinking of how much better my setup would be with a second battery and more panels!

 

[ConnerLabs]

2. Please try not to leave a full battery sitting in such state of charge for too long. I recommend 80% if you’re leaving it for a week or two, and around 50% if you plan to be away for more than a month.

This is especially important if it’s stored at high temperatures. Combo of high temp and high SoC is known to send all kinds of lithium ion batteries to an early grave.