Utilize existing solar array with high PV Voltage…

[ChrisM78]

Evaluating options for adding battery backup to an existing system…. Including a ton of background info in case it affects answers or gives anyone an idea I have not thought of yet….

I have an existing grid-tied system with 2 x Fronius Inverters (one 10K and one 15K). Each inverter is fed 2 strings from a large 78 panel array. House has 400A service which is split into 2 x 200A panels. One inverter is on each panel. This system was professionally installed and works great as it sits. However…if grid power is down the inverters obviously shut down and I am without power. I have manual transfer switches in place for each panel and have a couple large portable generators I can fire up if needed. I would like to add battery backup but the inverters are not hybrid inverters and I cannot replace the inverters or modify the system due to the tax credits etc. Because of this I cannot really automate failover without going with something similar to an AC Coupled PowerWall ( which all seem to be way more $ than a DIY option). Building a 48V battery bank and inverter to power each panel in the event of a power failure would be fairly easy and would give me a manual failover to battery power instead of to the gas generators. I would like the ability to charge those batteries off the existing solar in the event of an extended outage (which is the issue I am trying to figure out). I know I can wire up switches or quick connects to rereoute the strings from the grid tied inverter to the off grid system….The problem I am running into is that these Fronius inverters support a very high input voltage for the strings (up to 1000V). 3 of my strings are in the 600V to 650V range when operating in colder weather with the exception of one that can sometimes peak around 710V with the right conditions, I cannot find any MPPT charge controllers or Hybrid Inverter units that can handle that kind of voltage. Does anyone know of a model that can handle that or a way to reduce the voltage without rewiring the existing strings (remember I cannot mess with them due to the tax credits)? If not then I think I am going to be forced into an AC Coupled battery backup system that can utilize and cycle the existing inverters….


Thanks in advance for taking the time to read this and for any ideas.

Chris

 

[AntronX]

Does anyone know of a model that can handle that or a way to reduce the voltage without rewiring the existing strings (remember I cannot mess with them due to the tax credits)?

Why can't you rewire them? Who's going to come out and check? Do you own the system or is it financed?

 

[zanydroid]

Holy paragraphing...

I cannot replace the inverters or modify the system due to the tax credits etc.

Why? That's not consistent with my understanding and I'm happily modifying/expanding my system / taking more tax credits. I'm not sure there will be many forum people that will engage with a RFP with this level of constraint, except the small subset that have the same interpretation of tax credit as you.

Since I agree with the "infinite number of systems eligible for tax credits until the expiration of IRA, the only constraint is that the installed equipment has never had tax credits claimed on it before" interpretation. I would suggest lopping off enough solar panels and putting them either in new strings or microinverters, until the strings drop below 600V and sanity is restored.

I would be much more concerned about lease or warranty issues.

The problem I am running into is that these Fronius inverters support a very high input voltage for the strings (up to 1000V).

Somebody may have violated code when installing your strings, 600V is the limit for residential.

You can AC couple a 18kpv or SolArk, you don't have to use PowerWall. Or wait about a year and a bunch more Chinese hybrids / AC batteries will come on the market.

EDIT: These can probably manage the 10K. The 15K is too big for these inverters to handle because the AC grid former charger and inverter needs to exceed the size of the AC coupled inverter's output. Assuming the K is KW-AC.

 

[ChrisM78]

Why can't you rewire them? Who's going to come out and check? Do you own the system or is it financed?

I own the system. I get solar energy credits ($) from the state that are dependent on the system producing it’s expected numbers though and I think the existing inverters only have 2 inputs each….if I split off another string they would fall short of expected production. I will double check this though.

 

[zanydroid]

I own the system. I get solar energy credits ($) from the state that are dependent on the system producing it’s expected numbers though and I think the existing inverters only have 2 inputs each….if I split off another string they would fall short of expected production. I will double check this though.

Oops, I thought you were talking about federal tax credit.

I would recommend getting an accurate view of the allowed modifications / amendments to your paperwork before getting driven down a dark path for how to adjust the system. There's a lot of moving parts here. Probably best to find someone / some post with a clear explanation of the program and share it. I have some ideas but it's all going to be an unproductive shot in the dark without the correct legal inputs. With most of what you've written, there are very few viable paths, and it's not promising to try to thread the needle only to find out the explanation of the rules was borked so it was all a big waste of time to come up with a wrong solution.

IE, how does the program handle repairs? If Fronius the company dies and your inverter also dies, how do you avoid getting screwed?

In California we are allowed to keep our ongoing incentives (20 year or so) after repairing the system, to the extent of replacing basically everything (solar panels, inverters) with functional equivalents. It is pretty flexible and sane.

 

[ChrisM78]

Holy paragraphing...


Why? That's not consistent with my understanding and I'm happily modifying/expanding my system / taking more tax credits. I'm not sure there will be many forum people that will engage with a RFP with this level of constraint, except the small subset that have the same interpretation of tax credit as you.

Since I agree with the "infinite number of systems eligible for tax credits until the expiration of IRA, the only constraint is that the installed equipment has never had tax credits claimed on it before" interpretation. I would suggest lopping off enough solar panels and putting them either in new strings or microinverters, until the strings drop below 600V and sanity is restored.

I would be much more concerned about lease or warranty issues.


Somebody may have violated code when installing your strings, 600V is the limit for residential.

You can AC couple a 18kpv or SolArk, you don't have to use PowerWall. Or wait about a year and a bunch more Chinese hybrids / AC batteries will come on the market.

EDIT: These can probably manage the 10K. The 15K is too big for these inverters to handle because the AC grid former charger and inverter needs to exceed the size of the AC coupled inverter's output. Assuming the K is KW-AC.

Thank you. Tesla supposedly can (or at least the design team says they can) manage both inverters with 2 of their 200A gateways (one on each panel) and 2 powerwalls hooked to each…way more $ than I was hoping to spend though. I already took the tax credit on the existing inverters so my understanding was that I could not take another tax credit on replacement inverters? I was debating going with the SolArk 15k inverters from the start and really wish I had at this point. At the time I was not as worried about long term off grid power but with current times it sure would be nice. The 600V limit is interesting and something I did not know. I think I will talk to my installer about it. Maybe they would be willing to rewire things at a discount to give me a 5th string and bring it all down to a reasonable voltage and within code if 600V is the limit. That would preserve the warranty on the install and I own the equipment so no lease problems. Issue is I don’t think my existing inverters have an additional input on them…I will need to double check this

 

[glandpuck]

Evaluating options for adding battery backup to an existing system…. Including a ton of background info in case it affects answers or gives anyone an idea I have not thought of yet….

I have an existing grid-tied system with 2 x Fronius Inverters (one 10K and one 15K). Each inverter is fed 2 strings from a large 78 panel array. House has 400A service which is split into 2 x 200A panels. One inverter is on each panel. This system was professionally installed and works great as it sits. However…if grid power is down the inverters obviously shut down and I am without power. I have manual transfer switches in place for each panel and have a couple large portable generators I can fire up if needed. I would like to add battery backup but the inverters are not hybrid inverters and I cannot replace the inverters or modify the system due to the tax credits etc. Because of this I cannot really automate failover without going with something similar to an AC Coupled PowerWall ( which all seem to be way more $ than a DIY option). Building a 48V battery bank and inverter to power each panel in the event of a power failure would be fairly easy and would give me a manual failover to battery power instead of to the gas generators. I would like the ability to charge those batteries off the existing solar in the event of an extended outage (which is the issue I am trying to figure out). I know I can wire up switches or quick connects to rereoute the strings from the grid tied inverter to the off grid system….The problem I am running into is that these Fronius inverters support a very high input voltage for the strings (up to 1000V). 3 of my strings are in the 600V to 650V range when operating in colder weather with the exception of one that can sometimes peak around 710V with the right conditions, I cannot find any MPPT charge controllers or Hybrid Inverter units that can handle that kind of voltage. Does anyone know of a model that can handle that or a way to reduce the voltage without rewiring the existing strings (remember I cannot mess with them due to the tax credits)? If not then I think I am going to be forced into an AC Coupled battery backup system that can utilize and cycle the existing inverters….


Thanks in advance for taking the time to read this and for any ideas.

Chris

This is only my opinion. I have a similar situation to yours, but with SMA inverters. Part one of my solution was to install a second system with a hybrid inverter and batteries to supply half of my home. If this is not grid connected, it will not affect your net metering and you can back it up with a generator which you already own. New hybrid inverters discussed on this site often have integrated 3-4 500 Voc mppt controllers built in with amps of 15-25 for each mppt. So you will need to string your panels in series to say reach about 450 volts open voltage. My arrays have 12 panels in series and 8 panels in series. My voltage is 350 to 450. What is required is that you install a high DC voltage circuit breaker. Midnite solar DIN rail breakers go to I believe 600 volts. Then you would add a DIN rail solar fuse rated for 1000V DC. Lastly, you add a DC disconnected rated for about 1.56% your expected amps and 500-600 volts DC.

This is work, but it can be done quite easily. Once you have the array voltage sized for your inverter and your battery bank connected, you will need to connect your generator and have an electrician create your load panel to meet your needs.

With the remaining panels, you can replace your existing inverters and add batteries and this will not void your net metering in CA. The only thing that voids it is if your add panels or replacements that add more than 1 kW of size to the system and you would not be doing that. The replacement second inverter should be the same model as the first so that you can monitor both at the same time. Two 12k or 15k inverters, one net metered and one off grid will do the job with your generators and batteries.

 

[zanydroid]

My understanding is as long as each piece of solar property (equipment) was placed in service and has at most a single federal tax credit taken in its lifetime (IE you aren't taking credit on used equipment that already had a tax credit taken), you can do whatever you want. Install it, generate some power, and then remove and go crush it in a junkyard and it's fine /s. You should be good to sell the used inverters too, it's net neutral cost to the government for you to buy two inverters and claim two credits. Vs you not selling it to the other person, and you taking one credit and them taking one credit on new equipment.

I don't know why you would want to ask them to rewire it to 600V other than to get it more code compliant / avoid problems with potentially exceeding the voltage rating of some of your wiring. If they used regular THHN the rating is being regularly exceeded. I guess that's a good reason to do it.

If they messed up and are actively causing a long term safety or warranty hazard then they need to pony up and add hardware as needed to address the issue. Small claims court or licensing board complaint.

 

[SunDave]

Since I agree with the "infinite number of systems eligible for tax credits until the expiration of IRA, the only constraint is that the installed equipment has never had tax credits claimed on it before" interpretation. I would suggest lopping off enough solar panels and putting them either in new strings or microinverters, until the strings drop below 600V and sanity is restored.

Hi Zanydroid,
Doesn't this link agree with you 100%? I don't get why google's top results say one thing, and people argue about this but rarely go to the source of the information. Am I reading this wrong? I wonder why there would be an argument about this when the IRS says clearly:

The credit has no annual or lifetime dollar limit except for credit limits for fuel cell property. You can claim the annual credit every year that you install eligible property until the credit begins to phase out in 2033.

Residential Clean Energy Credit | Internal Revenue Service

If you invest in renewable energy for your home such as solar, wind, geothermal, biomass, fuel cells or battery storage, you may qualify for a tax credit.

www.irs.gov

Am I reading this wrong, or looking at the wrong program? Can't take it twice on the same property, but clearly can take the credit for NEW eligible equipment.

 

[ChrisM78]

Oops, I thought you were talking about federal tax credit.

I would recommend getting an accurate view of the allowed modifications / amendments to your paperwork before getting driven down a dark path for how to adjust the system. There's a lot of moving parts here. Probably best to find someone / some post with a clear explanation of the program and share it. I have some ideas but it's all going to be an unproductive shot in the dark without the correct legal inputs. With most of what you've written, there are very few viable paths, and it's not promising to try to thread the needle only to find out the explanation of the rules was borked so it was all a big waste of time to come up with a wrong solution.

IE, how does the program handle repairs? If Fronius the company dies and your inverter also dies, how do you avoid getting screwed?

In California we are allowed to keep our ongoing incentives (20 year or so) after repairing the system, to the extent of replacing basically everything (solar panels, inverters) with functional equivalents. It is pretty flexible and sane.

Thank you. I did get the federal tax credit but in addition I get $ from IL for meeting my production numbers. My agreement is to produce X amount of power over 15 years. The inverters are actually covered under warranty for 10 years but I guess if one were to die and the manufacturer was out of business I would have to replace it with something similar at my own expense or forfeit the remaining credits…at least that is how I read it. So I guess with that understanding I probably could pull these inverters out and replace them with a SolArk or something similar but I think it would be at my own expense and without tax credits. But I don’t think the SolArk handles these voltages either so I would still need to solve the voltage issue. The system is only 2 years old so I prob need to talk to my installer at this point and gracefully bring up that all the voltages are over the 600V limit for residential that zanydroid mentioned and see if I can possibly work something out on that end…

 

[zanydroid]

Hi Zanydroid,
Doesn't this link agree with you 100%? I don't get why google's top results say one thing, and people argue about this but rarely go to the source of the information. Am I reading this wrong? I wonder why there would be an argument about this when the IRS says clearly:

The credit has no annual or lifetime dollar limit except for credit limits for fuel cell property. You can claim the annual credit every year that you install eligible property until the credit begins to phase out in 2033.

Residential Clean Energy Credit | Internal Revenue Service

If you invest in renewable energy for your home such as solar, wind, geothermal, biomass, fuel cells or battery storage, you may qualify for a tax credit.

www.irs.gov

Am I reading this wrong, or looking at the wrong program? Can't take it twice on the same property, but clearly can take the credit for NEW eligible equipment.

Same program.

One failure mode is that people read "clean energy property" as "the property (address, heh) at which you installed the solar panels & whatnot". Versus "clean energy property" as "some tangible thingie that generates clean energy, that you can buy and install." Since most people are installing it again at the same address repeatedly, they assume they have one shot to install the system at that address ?

 

[ChrisM78]

My understanding is as long as each piece of solar property (equipment) was placed in service and has at most a single federal tax credit taken in its lifetime (IE you aren't taking credit on used equipment that already had a tax credit taken), you can do whatever you want. Install it, generate some power, and then remove and go crush it in a junkyard and it's fine /s. You should be good to sell the used inverters too, it's net neutral cost to the government for you to buy two inverters and claim two credits. Vs you not selling it to the other person, and you taking one credit and them taking one credit on new equipment.

I don't know why you would want to ask them to rewire it to 600V other than to get it more code compliant / avoid problems with potentially exceeding the voltage rating of some of your wiring. If they used regular THHN the rating is being regularly exceeded. I guess that's a good reason to do it.

If they messed up and are actively causing a long term safety or warranty hazard then they need to pony up and add hardware as needed to address the issue. Small claims court or licensing board complaint.

I think beyond the possible safety issues I need to get the voltage down because I haven't really seen any hybrid inverters that can accept the higher voltage input…. Which makes more sense to me know that I know about the 600V limit.

 

[zanydroid]

The system is only 2 years old so I prob need to talk to my installer at this point and gracefully bring up that all the voltages are over the 600V limit for residential that zanydroid mentioned and see if I can possibly work something out on that end…

I would suggest asking an electrical question (here or on a electrical help forum) about regularly exceeding 600V on your wiring. Unless the contractor installed PV wire (1000V rated) all the way down to your inverter MPPT inputs, and all junction boxes it goes through are 600V rated. It is in a bit of a gray area.

Those inverters might not be officially rated for 1000V either in the US. Depends on if the particular one you have is explicitly for residential market.

 

[SunDave]

Same program.

One failure mode is that people read "clean energy property" as "the property (address, heh) at which you installed the solar panels & whatnot". Versus "clean energy property" as "some tangible thingie that generates clean energy, that you can buy and install." Since most people are installing it again at the same address repeatedly, they assume they have one shot to install the system at that address ?

I see. What was funny to me is that all of the ways I could think of searching for the answer online returned the wrong answer until I found the site on IRS.gov and just bookmarked it. I plan to bring it to my tax preparer to avoid any confusion.

I just appreciate seeing others who read it the same way.

 

[ChrisM78]

Same program.

One failure mode is that people read "clean energy property" as "the property (address, heh) at which you installed the solar panels & whatnot". Versus "clean energy property" as "some tangible thingie that generates clean energy, that you can buy and install." Since most people are installing it again at the same address repeatedly, they assume they have one shot to install the system at that address ?

That is actually is exactly how I was interpreting it. Like the tax credit covers you for the inverters for my postal address one time. Make the wrong choice and too bad you used your tax credit opportunity…. The way you guys explained it makes more sense and gives me better / cleaner options for adding battery capabilities without having redundant inverters, etc.

 

[zanydroid]

I see. What was funny to me is that all of the ways I could think of searching for the answer online returned the wrong answer until I found the site on IRS.gov and just bookmarked it. I plan to bring it to my tax preparer to avoid any confusion.

I just appreciate seeing others who read it the same way.

Yeah, who would have thought, the internet is clogged with bad information.

The part I have an impossible time understanding is stacking federal credits with other rebates. Generally doesn't apply with solar in my state, but there are a lot of local heat pump rebates that may interact with the federal heat pump credit.

 

[ChrisM78]

I would suggest asking an electrical question (here or on a electrical help forum) about regularly exceeding 600V on your wiring. Unless the contractor installed PV wire (1000V rated) all the way down to your inverter MPPT inputs, and all junction boxes it goes through are 600V rated. It is in a bit of a gray area.

Those inverters might not be officially rated for 1000V either in the US. Depends on if the particular one you have is explicitly for residential market.

I do remember there being an up charge on the wire due to the fact it was being pulled through underground conduit ( panels are on my Morton outbuilding and inverters are in my house ) and needed to meet certain requirements. So maybe it is the higher rated wire. I will take a look at the specs on the wire and see. I do know the inverters can be used for commercial installs as well since they quoted me the same 10K model for my office building.