Hi I have 6.2 kw's of solar panels running to my 48v 12KW Growatt inverter and 600 ah of lithium batteries, it has been working very well for a year and a half now. But now I'm starting to run out of solar power to keep my batteries charged back up every day. I've purchased a little over 8 kw more of used solar panels that I'm wanting to add to my system. I am wanting to buy enphase inverters to go on the used solar panels I just purchased with the envoy controller. My question is can I purchase a reliable disconnect switch or relay that I can connect to the 48v dc battery bank and have it to kill the 240 volt power that is supplying the enphase envoy power once the battery reaches a set voltage to shut the envoy and solar array off to keep from over charging my 600 ah 48v Lithium battery bank .
Adding more solar panels with enphase inverters to my existing 12 kw offgrid growatt inverter with 6 kw's of panels
- Thread starter hotrod
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BentleyJ
Solar Wizard
Does the Growatt have an Aux output that could be configured to change state at a certain battery voltage? Alternatively. there are several choices of Voltage Monitoring Relays available. I don't have a specific model number to recommend but this subject has been discussed on the forum several times in the past. Do a few searches here and on Google.
I think all it has is a dry contact for starting a generator when voltage is low.
I am using a Batrium for my BMS on my batteries, I'm using the watchmon core with two K9's I know the Batrium has relays that can be programmed to do what I'm wanting to do but I need a good switch or disconnect that can be turned off and back on by the Batrium I would like for it to be able to cut off the 240 volts to the envoy when the voltage gets to around 54.6 volts and then turn the power back on to the envoy when the voltage drops to around 53 volts.
ncsolarelectric
Engineering Support CEO
May I suggest Hoymiles inverters with a zero-export meter, to prevent them from back feeding into the Growatt inverter? It requires,
Wifi
Hoymiles DTU-Pro-S-Wifi w/RS485
Hoymiles microinverters
CSS WattNode utility meter w/RS485 and 2 CT's
I found it easy to configure for zero-export, just now. Supposedly, as the load is reduced, the inverters will automatically throttle back. I don't know if they will be fast enough to protect the Growatt 100% of the time, but if you can avoid switching large loads on and off, it's likely to work well.
PS: I'm testing the SolarEdge meter to see if it works the same as the WattNode, because it looks identical to the WattNode but much lower cost. I haven't connected it yet, just looking at the software.
Wifi
Hoymiles DTU-Pro-S-Wifi w/RS485
Hoymiles microinverters
CSS WattNode utility meter w/RS485 and 2 CT's
I found it easy to configure for zero-export, just now. Supposedly, as the load is reduced, the inverters will automatically throttle back. I don't know if they will be fast enough to protect the Growatt 100% of the time, but if you can avoid switching large loads on and off, it's likely to work well.
PS: I'm testing the SolarEdge meter to see if it works the same as the WattNode, because it looks identical to the WattNode but much lower cost. I haven't connected it yet, just looking at the software.
Why do you need to worry about an AC microinverter over-charging your battery bank? Won't the Growatt curtail the Enphase if there isn't sufficient demand?
BentleyJ
Solar Wizard
I looked up the Growatt manual and it does have a dry contact but wasn't clear if the setting were sophisticated enough to give you the exact turn off and back on voltages desired. The Batrium does have an Aux relay and I believe its contacts are rated for 30V. You could use a definite purpose HVAC relay, like a 2 pole 30A with a 24V coil. You would need a source of 24V and the contactor would be a parasitic load when it is on. Forgot to ask before, does the Growatt support AC coupling? If its not UL1741SA compliant, it could be a problem.
I am not grid tied so I will have to have somewhere for the solar power from the Enphase system to go. once the battery gets fully charged the Growatt will stop charging the battery but then the Enphase inverters want have anywhere for the solar power to go if there isn't enough ac load to take care of the incoming power from the Enphase system, I'm pretty sure the system would destroy itself .
Yes I believe the HVAC contactor would work just fine. I don't know why I didn't think of that. And I don't think the Growatt is set up for AC coupling. I'll have to research that to make sure. I didn't think about that issue so if the Enphase is producing 240v power to my distribution box that the Growatt is supplying 240v to, it could back feed 240v into the output side of the Growatt is this correct and will that cause a problem if the Growatt is not ac coupled compatible.
BentleyJ
Solar Wizard
Yes, back-feeding the LOAD side of the Growatt could cause a problem if its not capable of doing 2 things.
1) Converting excess AC to DC at the proper voltage for charging the batteries.
2) If the batteries reach full charge, there has to be a method to curtail the output of the grid tie inverters. This is generally done by frequency shifting.
Most likely the Growatt would have to be replaced with a UL1741SA compliant grid forming inverter. Schneider 6848 Pro, Outback Mojave, Sol-Ark, SMA
Ok thank you for pointing that out to me. I'm glad I ask before following thru with this idea. My Growatt inverter has 2 PV strings I was told that the specs were for both strings combined. I called Growatt this week and they informed me that the specs were for each string not the combined 2 strings. They told me I could send up tp 7000 watts to each string safely with out damaging anything. So I should be able to just add more panels to the inverter I have.
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svetz
Works in theory! Practice? That's something else
The Growatt's battery charger regulates charging the battery, so you don't need to worry about overcharging the battery.
Any grid-tied inverter is a current-source, so you do want some way to control them. Unlike a voltage source, they'll up the voltage trying to move the power. AC-Coupling is the common solution.
If you were grid-tied, zero export is a great feature ... the problem with the feature is they leak a little bit around big power changes (e.g., pump shutting off). It's only for a few milliseconds at a time and as they are not "perfect" current sources they do have an upper voltage. But, I've no idea as to how much that might chip-away at your electronics over time.
Other than AC Coupling, the sure-fire way to do this is called "PV Shedding", basically it's exactly as you suggest... a battery sensor trips a relay that opens the microinverter's PV input. All the microinverters would then go into anti-islanding until 5 minutes after the circuit closed. You'll find this is how some AC Coupled solutions work behind the scenes.
If it has that, it probably has a way to stop the generator too. It's probably something simple, like the dry-contact is closed whenever the generator should be on.
That sounds like the best solution! Hope to see you post some photos in the show 'n tell forum!
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Quattrohead
Solar Wizard
If there is no power draw, the system will not blow up LOL
Electricity is not like filling a balloon with water or air until it explodes. This does baffle a lot of new people to electricity though.
svetz
Works in theory! Practice? That's something else
It's rare that everything is off. For example, a TV that is "off" is usually really in standby and still drawing current. Also, the Growatt must obviously be on or the microinverters would switch to anti-islanding mode. With a current-source (e.g., grid-tied inverter), anything that wasn't disconnected would be subjected to higher than normal voltages, which would cause more current through those devices.
SniperX
Solar Enthusiast
- Joined
- Apr 1, 2021
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Did you end up doing this and has It worked out well for you? I am getting ready to set mine up. I know it was 250V per pv string but just came across this and I thought it was 7000w total (3500w per string) but it makes more sense that it could be up to 7000w per pv connection too. Just need to know if you tried it and had no issue.
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