Time to change from grid-tie to hybrid

[GlenB]

Hello,
I currently run two grid-tie systems, 8kw Fronius, and a 6kw SMA. The 8k is under contract with GA Power going to a separate meter,, paying me $0.096/kw.
The 6kw is going to the house panel, a 'normal' grid-tie.

I want a new hybrid inverter to replace the SMA, and add LFP batteries. I see myself possibly expanding this system, perhaps to 10 or 12kw, so two parallel hybrid inverters.

I get confused reading the specs on these hybrid inverters. I kind of had my eye on the MPP Solar LVX6048. I am not sure it will do what I want it to.
This is what I want, so tell me if it will do it:
1. Normal grid-tie with solar charging the batteries first.
2. Battery backup of the house when the grid goes down (understand that I will have to install a 200 amp smart transfer switch).
3. Use the batteries at night or when there is little sun to obtain a net-zero condition.

Thanks in advance,

GlenB
Moultrie, GA

 

[Ampster]

@GlenB
You have a number of alternatives to accomplish adding battery backup depending on your overall goal. You may not even need to replace any of the grid tie inverters depending on their age and ability to AC couple with a modern hybrid inverter.

Is the separate meter no longer economical? How do the two inverters serve the house loads? Is your rate plan better to have just one grid tie connection?

 

[BentleyJ]

I get confused reading the specs on these hybrid inverters. I kind of had my eye on the MPP Solar LVX6048. I am not sure it will do what I want it to.
This is what I want, so tell me if it will do it:
1. Normal grid-tie with solar charging the batteries first.
2. Battery backup of the house when the grid goes down (understand that I will have to install a 200 amp smart transfer switch).
3. Use the batteries at night or when there is little sun to obtain a net-zero condition.

1. This statement is confusing in that one has to understand the difference between AC coupling and DC coupling. If you are replacing the SMA with an Inverter/MPPT Charger then its really NOT a "normal" grid-tie system anymore. Terminology is important. MPP Solar Inverters do not have sell back capability, their AC input is for utility power or generator power to charge the batteries in case solar is not enough to meet demand. Take a look at Outback Skybox, Schneider Conext Pro, Sol-Ark Etc. These are more expensive products that have feature sets you will need, Specifically UL 1741 SA compliance.
2. Whole house back-up is certainly an option, I did the same thing. You will either need to stack 2 Inverters or practice some kind of load control so as not to overload if only 1 inverter is used.
3. The Products mentioned above generally do have "peak load shave" features that will allow you to reduce or eliminate utility use during certain hours.

 

[Ampster]

I agree with @BentleyJ that the hybrid inverters he mentioned might be a better fit depending on your goals. Most of them contain transfer switches and have several modes to prioritize charging from solar.
They also may be able to work with your existing grid tie inverters. Are there reasons to keep or get rid of some of those system components? The more you can help us by answering some questions the more we can help.

 

[GlenB]

Thanks guys, this was the missing piece. I guess that is why the others cost DOUBLE! It seems as if they are marketed as hybrid inverters, but if they cannot do grid-tie, they are NOT hybrids!!!

 

[Ampster]

The missing piece for me in order to provide more advice is whether you intend to give up the separate meter? Can the electricl panel be consolidated as sub panels under one meter?That will determine the mix of components. Who is your electrical provider and what are the Net Metering options? I see there is a similar thread here that may answer some of my questions; https://diysolarforum.com/threads/hybrid-system-conversion.15702/

Cost is related to features and UL compliance. Economics should drive the decisions because a hybrid may be able to AC couple to one or more of your Grid Tie inverters and save your investment in those devices. Part of that will depend on the age of the GT inverters and whether they are built to the latest standards. The number to look for is UL 1741 or UL 1741SA.

 

[iamrich]

The MPP LVX6048WP seems to check all the needed boxes, but much like a unicorn, no one has seen this mythical beast...

https://www.mppsolar.com/v3/catalogs/LVX6048WP.pdf

 

[BentleyJ]

The MPP LVX6048WP seems to check all the needed boxes, but much like a unicorn, no one has seen this mythical beast...

https://www.mppsolar.com/v3/catalogs/LVX6048WP.pdf

Will did a review of this product recently, overall it was favorable. However, as far as I know the MPP Solar 6048 is NOT UL1741SA compliant for use in the US with the grid-tie option enabled.

 

[iamrich]

Will did a review of this product recently, overall it was favorable. However, as far as I know the MPP Solar 6048 is NOT UL1741SA compliant for use in the US with the grid-tie option enabled.

LVX6048WP is a completely different animal...

 

[GlenB]

I agree with @BentleyJ that the hybrid inverters he mentioned might be a better fit depending on your goals. Most of them contain transfer switches and have several modes to prioritize charging from solar.
They also may be able to work with your existing grid tie inverters. Are there reasons to keep or get rid of some of those system components? The more you can help us by answering some questions the more we can help.

Well, grid-tie is very important to me during the day because my net rate is around $0.14/kw. I want to mitigate the bill. Selling power back using the 6kw is not important, since I am only paid $0.03/kw for excess power, hardly worth doing. Most days, the 6kw will cover the house 'idle power' of around 1200 watts, and the 3.5kw for the A/C. I have a wife who is not solar friendly, doing laundry at 8am and 9pm. I told her only to do the laundry starting at noon, but she does not pay any attention. Of course, I pay the electrical bill, and buy all the solar ;-)
To hook any inverter to the house, it would have to be UL (IEEE ??) compliant, which the SMA is.

 

[iamrich]

To hook any inverter to the house, it would have to be UL (IEEE ??) compliant, which the SMA is.

I would check with whatever entity governs your grid (power company/city/county, etc.). I have been going back and forth with my provider (who is a private rural provider) and their stance is the inverter "must meet UL-1741 standard" to be in compliance. Now, obviously every place is going to be a little different, but I wouldn't just dismiss options without checking, especially if you live out in a rural area. Obviously, safety should be #1, but if an inverter is listed with another company (ETL or TUV for instance) and is UL1741 compliant I would not dismiss it.

 

[Ampster]

The only difference between UL1741 and UL1741SA is that the SA version requires as an option that the inverter be able to respond to frequency Watt changes with variations of power. All that means is that AC coupling is easier because the GT inverter will modulate instead of turning on and off. The SA is the newer specification.

 

[Mr. Sunshine]

Sorry to jump in but I have a question about my micro inverter on my PV system which reads:
APsystems YC500A
Safety Class Compliance UL 1741 , CSA C22.2, No. 107.1-01, NEC2014 690.12
Grid Connection Compliance IEEE 1547
Does this mean these micro inverters will be compatible with an AC coupled inverter/charger to shut down with the change of frequency when power is no longer needed from the panels? Sorry if this is a dumb question, I am just looking into this and trying to learn if it is even possible on my system.

 

[Ampster]

As far as I can tell they are UL1741 which means they will shut down in an AC couple situation when the controlling inverter increases frequency. It does not look like they are UL1741SA compliant, which means they cannot modulate. They will be either all on, or all off.

 

[Mr. Sunshine]

Thanks, nice to know it is possible. Still have much to learn.