All-in-One Inverter plus SCC Questions

[sandmen82]

I feel a bit like Alice in the rabbit hole, and am in need of perspective.

Situation: Designing an off grid 48v 4-5kw system w/ 36v/7.78A nominal panels (12 count). I am working around some trees that send shadows across the panels at different parts of the day. To squeeze as much as I can out of the turnip, I am trying to limit string sizes. This is problematic for a AIO string inverter because of minimum voltage requirements. Considered microinverters, but they are too pricy. Considered optimizers, but am weary about large voltage dropouts when one panel gets shaded because you still have a single string. As a result, the use of multiple SCC's on smaller arrays is appealing because it has similar performance to microinverters (theoretically).

I know that SCC's can be connected to the battery in parallel through a bus bar with no issue, as long as they have compatible charging settings, but have only seen this done, that I can find, with "old style" inverters. Of this approach, Victron seems to be very good. A straight Victron system is sadly outside my budget.

Question 1: Other than using a Victron inverter, can an AIO string inverter have SCC's added to it? More specifically, I am looking to use the on board MPPT, while adding SCC's.
Question 2: If so, does it use a common bus with the SCC's or is it something more exotic?
Question 3: Is there anything that would caution this approach? If so, what?
Question 4: What are some AIO inverters that have successfully used this approach?

I hope this makes sense. Any help is much appreciated.

 

[corndog]

Interested to hear about this too, since some of the MPP Solar AIO's are a tremendous value, if not for the wimpy PV input and charge rate.

 

[DThames]

I am not 100% sure that I understand what your thinking is but I have two Growatts connected to the same battery bank. Each Growatt has its own PV array connected to it. I have a third array and an EPEver charge controller that I plan to connect to the same battery bank in order to increase my total buck PV input so I can charge well and be driving loads at the same time. Previous to the Growatts, I had two EPEver chargers with one array each charging the same battery bank. There shouldn't be any problem to connect several chargers to the same battery bank. You might want to carefully consider where each is programmed for Boost, Float, Boost-Reconnect, etc, so they all follow a plan that makes sense.

edit, all of mine connect to a pair of large terminal blocks with a Victron Smart Shunt so I can see the net current in or out to the battery bank.

 

[corndog]

I think we're on the same page, you're wondering what happens when you parallel various make/model/size PV/SCC and PV/AIO setups onto the same battery bank?

(edit: oops ignore, mistook you for op)

 

[sandmen82]

I am not 100% sure that I understand what your thinking is but I have two Growatts connected to the same battery bank. Each Growatt has its own PV array connected to it.

This is kind of what I am getting at. There are lots of systems out there, where people have put 2 AIO inverters in parallel (Growatt, MPP, etc), I have not seen anybody add an SCC to the system. I don't want to hook SCC's up, and have the AIO freak out.

I have a third array and an EPEver charge controller that I plan to connect to the same battery bank in order to increase my total buck PV input so I can charge well and be driving loads at the same time.

How do you plan to do this? This is exactly what I am hoping to do. The SCC's will basically just dump into the battery until full. I'm not sure if the SCC load can go to the inverter when the battery is full, but that is a separate problem, for another day.

 

[John Frum]

I feel a bit like Alice in the rabbit hole, and am in need of perspective.

Situation: Designing an off grid 48v 4-5kw system w/ 36v/7.78A nominal panels (12 count). I am working around some trees that send shadows across the panels at different parts of the day. To squeeze as much as I can out of the turnip, I am trying to limit string sizes. This is problematic for a AIO string inverter because of minimum voltage requirements. Considered microinverters, but they are too pricy. Considered optimizers, but am weary about large voltage dropouts when one panel gets shaded because you still have a single string. As a result, the use of multiple SCC's on smaller arrays is appealing because it has similar performance to microinverters (theoretically).

I know that SCC's can be connected to the battery in parallel through a bus bar with no issue, as long as they have compatible charging settings, but have only seen this done, that I can find, with "old style" inverters. Of this approach, Victron seems to be very good. A straight Victron system is sadly outside my budget.

Question 1: Other than using a Victron inverter, can an AIO string inverter have SCC's added to it? More specifically, I am looking to use the on board MPPT, while adding SCC's.
Question 2: If so, does it use a common bus with the SCC's or is it something more exotic?
Question 3: Is there anything that would caution this approach? If so, what?
Question 4: What are some AIO inverters that have successfully used this approach?

I hope this makes sense. Any help is much appreciated.

Inverter

If my inverter already comes with a replacable fuse. Do i need to add an inline fuse also??? Thanks

diysolarforum.com

 

[DThames]

This is kind of what I am getting at. There are lots of systems out there, where people have put 2 AIO inverters in parallel (Growatt, MPP, etc), I have not seen anybody add an SCC to the system. I don't want to hook SCC's up, and have the AIO freak out.

How do you plan to do this? This is exactly what I am hoping to do. The SCC's will basically just dump into the battery until full. I'm not sure if the SCC load can go to the inverter when the battery is full, but that is a separate problem, for another day.

The inverter part of the All In One units will draw power to produce output. Most draw directly from the battery, while another part of the same unit is charging the battery. Some draw from a common internal DC bus which is powered by solar, the grid, or the battery. In either case, they use the power available to then based on their setup settings. If they need power from the battery and the battery voltage is not below some voltage setting, they get power from the battery. They don't care how the power is delivered to the battery. So another charger, from solar, generator, grid, whatever can be charging the battery to keep up (or try to keep up) with the inverter's demand.

I will just connect my PEEver charger's output to the common terminal block and turn it on. I will likely set its boost and float a bit lower than the Growatt's settings, so this third charger comes in when the system is under a load that is enough to pull the battery down more than the Growatt can keep up with.

 

[sandmen82]

Inverter​

If my inverter already comes with a replacable fuse. Do i need to add an inline fuse also??? Thanks

diysolarforum.com

smoothJoey:
I like the ladder analogy. It is helpful.

I will just connect my PEEver charger's output to the common terminal block and turn it on. I will likely set its boost and float a bit lower than the Growatt's settings, so this third charger comes in when the system is under a load that is enough to pull the battery down more than the Growatt can keep up with.

Between smoothJoey, and what you say here, I think I may be starting to get it. How does this sound?

As long as the SCC's are not charging the battery at a rate higher than the AIO's settings, the AIO just think of any additional SCC as part of the battery. So if the SCC is charging at 51V, and the AIO floats at 51V, the AIO will stop charging/float. Basically, the AIO needs to govern the maximum parameters. Is that about right?

 

[DThames]

smoothJoey:
I like the ladder analogy. It is helpful.


Between smoothJoey, and what you say here, I think I may be starting to get it. How does this sound?

As long as the SCC's are not charging the battery at a rate higher than the AIO's settings, the AIO just think of any additional SCC as part of the battery. So if the SCC is charging at 51V, and the AIO floats at 51V, the AIO will stop charging/float. Basically, the AIO needs to govern the maximum parameters. Is that about right?

Not incorrect but not right or a rule, so to speak. Each charger will do exactly what you program it to do. If it thinks the battery is low, it will charge. If one goes into boost and the other one doesn't, one will charge and the other one will not charge.....because the float of the second one will be lower than the current voltage....headed towards boost voltage because the first one is charging hard. If there is high demand, the battery is below float, and there is sun, all should be charging.

 

[DThames]

smoothJoey:
I like the ladder analogy. It is helpful.


Between smoothJoey, and what you say here, I think I may be starting to get it. How does this sound?

As long as the SCC's are not charging the battery at a rate higher than the AIO's settings, the AIO just think of any additional SCC as part of the battery. So if the SCC is charging at 51V, and the AIO floats at 51V, the AIO will stop charging/float. Basically, the AIO needs to govern the maximum parameters. Is that about right?

Today I had the chance and turned on all three chargers. Two Growatts, and one EPEver all charging the same battery bank. The Growatt units are connected to a 1800w array and a 1500w array. The EPever is connected to a 1200w array. Consider how a charge will act when the battery gets to the boost voltage level. The charger will start backing off of the amps so the volts don't go over the boost setting. For one of several different reasons, one of the charges will see boost voltage first and as it backs off its amps, it will back off to almost zero. This is often the charger that is delivering the most power to the battery, as (if all things are equal) it will have a slightly larger voltage drop over the wire to the battery and will think the battery voltage is a bit higher than what the other chargers will measure. The last man standing will hold the boost level for the determined time and then drop to float level. My early experiences with this behavior confused me a bit....to the point that would turn off the working charger to make sure the other one was still functioning properly. So when you have such a setup, only expect normal charging, on all chargers, when the battery voltage is below the boost voltage setting.

In the image below, the Growatts show over 1000w each. The only update about once every 10 minutes. A cloud came over the the screenshot shows the EPEver at less than 200w but it was over 800w not long before.

 

[RCinFLA]

If you need to keep to multiple parallel PV strings due to a lot of shading you run SCC to battery voltage to keep the number of series panels count low, keeping the series stack voltage low.

You can always run a separate SSC feeding direct to battery charging. You can run an all in one PV supplied inverter and also a separate SSC direct to battery charging, just stay below maximum charge current for battery AH size and make sure their charging float and absorb voltage are set the same. Because the battery SSC is low voltage PV input and AIO SSC is high voltage PV inputs it requires two separate sets of panels arrangements.

High Frequency (light weight) AIO inverters inject their PV power to inverter's internal high voltage DC point. The SCC in HF inverter is a DC to DC boost converter. This is why they take relatively high PV voltage input, but must stay below the HF inverter's internal HV DC voltage. This is typically 230 to 280 vdc for 120 vac only units and 400-480 vdc for 240 vac units. Their DC to DC boost SSC requires a relatively high minimum PV input DC voltage to keep their SSC efficiency high.

LF (heavy transformer) AIO inverters have the equivalent of a separate GT inverter, internal and in parallel with hybrid LF battery to AC inverter AC output. It is like a LF hybrid inverter with AC coupling of a separate GT inverter with the exception that the AIO has directly hard-wired control over GT inverter power output.