Hybrid Inverter and Grid Tied Solar questions

[woe]

Hello All,

I installed a 14.8kw Grid Tied Enphase solar system in 2019. It's been great but generation buy back has really taken a hit in Texas to the point it's no longer worth it.

I'm pretty close to pulling the trigger on installing a Hybrid Inverter and some batteries so I have somewhere to put the excess power I produce. I also have switched to a Free Nights plans which has been great as I have moved my EV Charging and Pool pump to run during the free times and I've been able to move almost 90% of my usage (in winter) to the free period. I know in summer in the Houston Area the AC will change this a lot. So I'm hoping the battery will help offset this and maybe even be able to get me a negligible power bill.

And of course I want to be able to run my critical loads if the grid goes down which has happened a number of times in recent years.

Cost is a pretty big factor for me as I'm trying to justify this to my boss (wife) by cost savings.

My hope is to have Solar and Battery run all my power requirements during the day, and free nights to cover me in the evenings - while I charge my car run the pool pump and charge the solar battery.

So to my questions.
After some research I am learning towards the RUiXU RX-12K Hybrid inverter. I was looking at the EG4-18kPV but it's over $1K more and I'm not sure it will provide any benefit. Same as the Grid/FlexBoss combination. Is there anything with the RUiXU RX-12K I should be considering that I'm not? I was looking a the DEYE inverters as they are a great price point but then I read about the whole Sol-Ark debacle and the bricking so obviously that's not an option. Are there any other options I am not considering that I should.

I am looking at combining 8 x EcoWorthy 12V 280ah battery's. 4S2P. Giving me 26.88kWh. Sorry if this is a silly question but do I need a battery balancer for each of the 4 Series connected battery. I'm assuming an additional BMS connected to 4 batteries with built in BMS"s isn't something you should do.

I already have 2 panels one main one sub. The plan was to move all my critical loads to my sub panel and wire that to the load of the inverter. Wire the Enphase combiner to the GEN connectors, And the main panel to the Grid connectors. I assume the Grid panel will still be powered by my excess solar, is this correct? and the system will continue to sell back unused solar to the grid?

Maybe another silly question but in the event of Grid Down, with the critical load panel running off the battery, will excess solar produced power the Grid panel while we have enough solar production?

I also have a 12kw "portable" generator that I converted to Tri-Fuel that I have wired to an interlock in my main panel. My plan was to wire this to a dual throw manual transfer switch so I can switch from the Generator to Solar in the event of Grid down. This give me the ability to switch to the generator during extended outages if I run out of battery when the Sun isn't out (night or cloudy). Does anyone see any issues with this?

I think that's all I have for now. Any thoughts or advise you may have would be greatly appreciated.

TIA

Cam

 

[1201]

The ruixu (Saj)inverter is untested. You don't want to be the first to try it out.

 

[woe]

The ruixu (Saj)inverter is untested. You don't want to be the first to try it out.

I did see that it's pretty new but I guess someone has to give it a a go. = ) Considering it's form a known company and complies with all the required certifications I guess I'm a little more hopeful about it. Do you have any other suggestions that I should look at? Maybe pairing 2 smaller ones?

 

[1201]

I did see that it's pretty new but I guess someone has to give it a a go. = ) Considering it's form a known company and complies with all the required certifications I guess I'm a little more hopeful about it. Do you have any other suggestions that I should look at? Maybe pairing 2 smaller ones?

I would look at the solis s6 HV inverter.

For lv the srne hesp has a good rep but no warranty repair in the USA.


Also, in a grid down situation, to answer your question, the inverter disconnects from the grid so you will only have power to the backup panel

 

[woe]

I would look at the solis s6 HV inverter.

For lv the srne hesp has a good rep but no warranty repair in the USA.


Also, in a grid down situation, to answer your question, the inverter disconnects from the grid so you will only have power to the backup panel

Thank you. I'll research them a little more and thanks for the answer about the grid panel.

What about the GroWatt 11.4kw MIN11400TL-XH-US. I just saw this and need to do a little more research to see if it will do everything I need.

Thanks again

 

[1201]

Thank you. I'll research them a little more and thanks for the answer about the grid panel.

What about the GroWatt 11.4kw MIN11400TL-XH-US. I just saw this and need to do a little more research to see if it will do everything I need.

Thanks again

The battery for the growatt min are on the expensive side

 

[woe]

The battery for the growatt min are on the expensive side

Yeah thanks. Just noticed you need specific high volt batteries for it. So I guess I'm back to the RUIXU RX12k or the EG4 18kpv. Still researching the support Solix S6. But it doesn't look like it has an input for the AC solar. How do I wire it in?

Please give my ignorance but when would I need HV vs LV?

Couple more questions if you have the answers.

Do I need a battery balancer if I connect 4 12v batteries in series?

I'm pretty sure the answer is yes but just wanted to check with the AC coupled solar connected to the inverter, the solar will still cover the circuits on the grid panel while the grid is up?

Thanks for all you knowledge

Cam

 

[1201]

Yeah thanks. Just noticed you need specific high volt batteries for it. So I guess I'm back to the RUIXU RX12k or the EG4 18kpv. Still researching the support Solix S6. But it doesn't look like it has an input for the AC solar. How do I wire it in?

The Solis has 4 mppts up to 600v.

It can also ac couple on the load side, or ac retrofit in the grid side

Please give my ignorance but when would I need HV vs LV?

Just whatever you are more comfortable with and whichever is the best value.

Couple more questions if you have the answers.

Do I need a battery balancer if I connect 4 12v batteries in series?

I've heard it's not a good idea to do that but I don't know exactly why. I'll try to find the link I read

I'm pretty sure the answer is yes but just wanted to check with the AC coupled solar connected to the inverter, the solar will still cover the circuits on the grid panel while the grid is up?

Yes that is correct

Thanks for all you knowledge

Cam

 

[1201]

Here is a thread on the topic of 12v batteries in series

S

Thread 'LiFePO4 Battery in Series'

Mar 9, 2023

As a novice in battery making I see that so many people are connecting 4 LIFPO batteries in series to make 48v, and for my understanding this seams to be a very bad practice as there is no way to keep the batteries balanced and the failure of one battery or BMS can create huges problems and thermal runaway as the voltage is way to high for the 12v batteries, it would seam like you would at least need a external type of BMS to monitor the 4 string voltage of individual battery that would trip a breaker to shut off the charging. If one of the mosfet for charging fails as the 3 other ones are...

• Skari
• Replies: 18
• Forum: DIY Solar General Discussion

 

[woe]

Here is a thread on the topic of 12v batteries in series

S

Thread 'LiFePO4 Battery in Series'

Mar 9, 2023

As a novice in battery making I see that so many people are connecting 4 LIFPO batteries in series to make 48v, and for my understanding this seams to be a very bad practice as there is no way to keep the batteries balanced and the failure of one battery or BMS can create huges problems and thermal runaway as the voltage is way to high for the 12v batteries, it would seam like you would at least need a external type of BMS to monitor the 4 string voltage of individual battery that would trip a breaker to shut off the charging. If one of the mosfet for charging fails as the 3 other ones are...

• Skari
• Replies: 18
• Forum: DIY Solar General Discussion

Thanks for that. I read though it and past the first few replies most seem to be saying it's okay. The batteries I'm looking at are listed as 4s4p by the manufacturer. But I'm still concerned.

I believe the main concern is a one of the 12v batteries dying and having a thermal runaway issue but if each of the 12v batteries has a BMS with thermal monitoring, shouldn't that kill the battery before that happens?

Please know I'm not disputing you, I really just started learning all this 2 weeks ago, but just trying to understand.


I understand if you can get 48v certainly do it but there is a 50% price increase per kWh if I don't want to build my own batteries. (Which I may end up doing it I need to). I was hoping 4s with a balancer 2s would work.

I looked more into the Solis S6 but I can't find anything about a split phase version outside of AliExpress. They all seem to be single phase. I read you can wire single phase inverters for split phase but is that normal?

Thanks again for all of your help

 

[going_commando]

The S6 US is split phase with built in backup capability. They are making a MID (microgrid Interconnect Device) that will allow more options, but I don't think it's available yet. Search for Solar Guppy for his install and experiences. High voltage batteries are a different animal, but more and more options are coming out all the time, and they are looking like the future. I've been looking into the S6 quite a bit to use as a grid tie inverter for now, and maybe adding 10kW or so of backup battery in the future.

The Growatt requires an autotransformer or an MID to provide backup power, depending on which version you get of the same part #, which could be argued is an incredibly stupid idea. Why they wouldn't make a different part # for an essentially different inverter is mind boggling. In fact, they made 3 different versions of the same part # of that inverter within 2-3 years of it coming out, and they make at least 2 of them at the same time.

Here is a link to the S6 available in the US. It's available from a bunch of online retailers, I just knew it was easy to get to from signature solar's website. https://signaturesolar.com/solis-s6...-high-voltage-energy-storage-hybrid-inverter/

 

[Solar Guppy]

Here is a link to the S6 available in the US. It's available from a bunch of online retailers, I just knew it was easy to get to from signature solar's website. https://signaturesolar.com/solis-s6...-high-voltage-energy-storage-hybrid-inverter/

Wow, had no clue that SS was now selling the Solis S6, great to have more retail options.

Running HV is much simpler for high power than 48V, most don't understand the true costs for 400-800 amp battery banks until they build one, it isn't cheap, or easy to work with.

I added 50kWh recently for ~5k USD, so the hit for HV is just the initial battery, parallel more as needed and they don't require communication's to work as the primary battery will proportionally provide energy and SOC will be close enough for the pack.

 

[woe]

The S6 US is split phase with built in backup capability. They are making a MID (microgrid Interconnect Device) that will allow more options, but I don't think it's available yet. Search for Solar Guppy for his install and experiences. High voltage batteries are a different animal, but more and more options are coming out all the time, and they are looking like the future. I've been looking into the S6 quite a bit to use as a grid tie inverter for now, and maybe adding 10kW or so of backup battery in the future.

The Growatt requires an autotransformer or an MID to provide backup power, depending on which version you get of the same part #, which could be argued is an incredibly stupid idea. Why they wouldn't make a different part # for an essentially different inverter is mind boggling. In fact, they made 3 different versions of the same part # of that inverter within 2-3 years of it coming out, and they make at least 2 of them at the same time.

Here is a link to the S6 available in the US. It's available from a bunch of online retailers, I just knew it was easy to get to from signature solar's website. https://signaturesolar.com/solis-s6...-high-voltage-energy-storage-hybrid-inverter/

Thank you!

I read though the manual of the S6 and it brought a few questions.

It says that when AC coupled I can wire the ACPV to either the grid side or backup side. But if I wire to the backup side it says the ACPV can't exceed the nameplate size of the inverter. My existing solar array is 14.8kW. and the S6 11.4kW.

So does this mean I need to wire the ACPV onto the grid side. And if I do this won't it get disconnected with the grid is down?

It also says if the solar consumption on the grid side is more than the name plate side when the grid is present an overload could occur. I have an EV charger which will be in my grid side that well pull more than 11.4kW by itself. This sounds weird an I reading it right? Why does the inverter care if it's on the grid side?

 

[woe]

Wow, had no clue that SS was now selling the Solis S6, great to have more retail options.

Running HV is much simpler for high power than 48V, most don't understand the true costs for 400-800 amp battery banks until they build one, it isn't cheap, or easy to work with.

I added 50kWh recently for ~5k USD, so the hit for HV is just the initial battery, parallel more as needed and they don't require communication's to work as the primary battery will proportionally provide energy and SOC will be close enough for the pack.

I need to read more about HV! 50kWh for 5k sounds amazing.

Can you confirm what batteries and configuration you used to help in my research?

Thanks!

 

[1201]

I added 50kWh recently for ~5k USD, so the hit for HV is just the initial battery, parallel more as needed and they don't require communication's to work as the primary battery will proportionally provide energy and SOC will be close enough for the pack.

How did you add the 50kwh? The post you linked does not provide details

 

[1201]

Thank you!

I read though the manual of the S6 and it brought a few questions.

It says that when AC coupled I can wire the ACPV to either the grid side or backup side. But if I wire to the backup side it says the ACPV can't exceed the nameplate size of the inverter. My existing solar array is 14.8kW. and the S6 11.4kW.

Correct, that is true of pretty much all ac coupling systems. Look up the Victron factor 1 rule for explanation.

Does your 14.8kw system ever produced more than 11.4kw at any point in time?

Are you and to supply the system up into two different outputs? Some going to backup sides and some going to grid side?

So does this mean I need to wire the ACPV onto the grid side. And if I do this won't it get disconnected with the grid is down?

Yes if is connected to the grid side you will not have solar when the grid is down but your inverter will still operate off battery . Do you have a lot of grid down time?

It also says if the solar consumption on the grid side is more than the name plate side when the grid is present an overload could occur. I have an EV charger which will be in my grid side that well pull more than 11.4kW by itself. This sounds weird an I reading it right? Why does the inverter care if it's on the grid side?

This is a good question. I read that too and was confused

 

[bhbaker220]

If you think free nights plans will be available for many years, why not just go with a relatively cheap off grid inverter and cheap 48v batteries. Charge the batteries at night and utilize the fully charged batteries during the day. Look at the YouTube videos of "East Texas Homestead" to see how he has been doing this. Unless you think ERCOT is going to be begging you to put power back on the grid at specific times of the day, not sure the incremental cost of the hybrid is worth it. Of course, who knows what the future holds.

 

[1201]

If you think free nights plans will be available for many years, why not just go with a relatively cheap off grid inverter and cheap 48v batteries. Charge the batteries at night and utilize the fully charged batteries during the day. Look at the YouTube videos of "East Texas Homestead" to see how he has been doing this. Unless you think ERCOT is going to be begging you to put power back on the grid at specific times of the day, not sure the incremental cost of the hybrid is worth it. Of course, who knows what the future holds.

That's for people who don't have an interconnection agreement.

Since he already is interconnected a hybrid is going to be a much better solution

 

[bhbaker220]

That's how people who don't have an interconnection agreement.

Since he already is interconnected a hybrid is going to be a much better solution

I also have an interconnection agreement and have gone to an off grid inverter as an alternative for a portion of my needs. I'm on Entergy and their cost avoidance calculation that they do annually for the Public Utility Commission sets their buy back rates. What was about $0.05/kWh in 2023 went to $0.03/kWh in 2024. Given the abundance of wind and solar in Texas, it's doubtful in my mind that this buy back rate is going back up. I suspect the OP is seeing the same trend from an independent plan on ERCOT. If we eventually go to a Time of Use model in Texas, then the hybrid could be the way to go. He can keep his current hybrid for that use case if and when it occurs.

 

[Solar Guppy]

I need to read more about HV! 50kWh for 5k sounds amazing.

Can you confirm what batteries and configuration you used to help in my research?

Thanks!

I've posted before about this previously, here is one example

Also off the shelf, plug and play Seplos Hitens for 2440 per 20kWh, linked in another post

 

[1201]

I also have an interconnection agreement and have gone to an off grid inverter as an alternative for a portion of my needs.

I'm on Entergy and their cost avoidance calculation that they do annually for the Public Utility Commission sets their buy back rates. What was about $0.05/kWh in 2023 went to $0.03/kWh in 2024.

That's not the big benefit. Still, 3 cents can be better than zero cents. With off grid, when the battery is full you just lose all the potential power. Why not get the 0.03 per kWh for it?

Since the op is already connected he can support ALL loads via solar and battery. With an off grid inverter he can only support BACKUP loads and never home loads. So with interconnection he can get by with a smaller inverter and less battery and still save the same or more

 

[1201]

I've posted before about this previously, here is one example

So you are able to use 48v batteries in series to match the voltage of the seplos and byd?

How many different 48v batteries?

Each 48v battery has its own bms?

You're not worried about issues with having different BMS in series?

The Solis is still able to track soc accurately?

So many questions

Also off the shelf, plug and play Seplos Hitens for 2440 per 20kWh, linked in another post

Looks like shipping is another 2500. I'm not against this if one can get say 20kwh for 5000 then parallel more diy stuff as needed.

Would you be able to do a detailed write up on how you set up the 48v batteries for HV?

Thanks

 

[Solar Guppy]

Would you be able to do a detailed write up on how you set up the 48v batteries for HV?

Thanks

The nominal battery pack voltage in my system, which is 128S 3.4V LFP cells or (8) 51.2V batteries is series is 409.6V nominal in 3 strings, each string as its own circuit breaker and a combined voltage / current meter so I can watch current sharing for charging ( its so far dam near perfect ) likely due to the low current involved, so the voltage drop is not an issue that 49V systems has. I charge at 10 amps ( 4kW ) which is only 20% of the inverter rating, system is whole home backup only and I'm grid tie with 15kW solar.

2 of the 3 stings are 50Ah each ( 100Ah total ) and after the circuit breaker(s) is parallel with the BYD batterybox HV ( 10 kWh ) which has canbus closed loop with the slave S6.

The 3rd is 30Ah parallel after the circuit breaker with the Seplos Hitens ( which are parallel each 20kWh) and is closed loop with the master S6, technically 55Ah total

Solis S6 Hybrid 11.4kW * 2	Closed Loop Battery	Open Loop Battery
Master	Seplos Hiten 20kWh * 2	Generic 12kWh
Slave	BYD 10kWh	Generic 20kWh * 2

The primary concern / issue with series battery's is when one battery in the string discharge mosfets in a generic BMS goes offline you can have very large voltage across the offline battery as the positive of the total string will go to ground from the inverter battery positive, could be up to negative 3XX volts which would have the BMS FETS blow up. ( single series string )

So when a "dumb" string is paralleled with a string with communications, it is protected as the two possible cases are:

• Communicating battery goes offline, inverter shuts down the battery port, naked battery safe
• No communications battery goes offline, communicating battery maintains the string pack voltage so no large voltage differentials on an individual battery.

Wire size:

Since this is HV, the S6 has a maximum continuous rated battery current of 50 amps and the pack voltage is ~409V is well above the inverter rating of 11,400 watts. And at 11.4kw that's only a draw of ~28 amps , so 10 awg is fine for the battery and that is actually less as that is split between 3 battery's, less than 10 amps each at full rated load.

One can use lower pack voltages, but you need ~230 as a minimum @ 50A for the 11.4kW rating and just keep in each battery cell count an even divisor of the total pack voltage of the battery with closed communications to the inverter of the parallel pack voltages are the same.

As for concerns about current sharing the parallel packs, uneven discharge will rotate from pack to pack as the charge or discharge ( ohms law ), but be close enough for bottom and top SOC anything in-between is unknown and doesn't have any functional value as one has no control even if all batteries were perfect in reporting SOC.

The down side of this is this system isn't UL9540 ( BYD and S6's are is but nothing else )

Works great, fun project to build and keep me busy, your mileage will vary if you should choose this path.

 

[LanePilot]

Do you have separate breakers on the AC grid side for each S6? If so, what size breaker are you using? On the AC backup side, do you have separate breakers on each S6? If so, what size breaker are you using? I have not yet commissioned mine yet, but are you able to set current limits on both Grid and Backups so as not to over current the busbar if you don't have a 200 amp panel?

 

[bhbaker220]

That's not the big benefit. Still, 3 cents can be better than zero cents. With off grid, when the battery is full you just lose all the potential power. Why not get the 0.03 per kWh for it?

Since the op is already connected he can support ALL loads via solar and battery. With an off grid inverter he can only support BACKUP loads and never home loads. So with interconnection he can get by with a smaller inverter and less battery and still save the same or more

You don't have to give up the existing inverter and selling back some solar. I've still got my grid-tied inverter, but I maximize the solar value by utilizing the off-grid inverter and batteries until batteries are at 100% and then utilize the grid-tied inverter if I have excess solar.