Inverter and automatic transfer switch

[bass_katcher]

I am in the middle stages of planning my grid-tied solar system. I am planning an Eg4 18KPVinverter with 18kw solar panel array. Here's the catch though. My solar system will be installed a a separate building from the house (with the pole/meter in between) which means I can't utilize the automatic transfer switch (ATS) of the inverter to prevent backfeeding of the grid during power outages while still supplying power to the house. So my plan is to install an ATS at the meter so that the solar system can still feed the house during power outages. Which leads to a couple questions.

A bit of background: we are a net-metered co-op with 200a service. My electric feeds down the pole, to the meter, and back up the pole and forks at the top of the pole with a branch going to the house and a branch going to the barn. The barn electric branch is an overhead wire that I would like to utilize as my feed wire. Running solar feed lines all the way to the house (500+ feet) so that I can utilize power during an outage probably isn't realistic.

1) What ATS do I need?
2) I still feel like the EG4 18KPV is what I need as far as an inverter for the AC coupling, but is there a way to turn off the grid disconnect during a power outage? I am planning on using the barn branch wire as my output wire to the house during outages; how can I accomplish this?

 

[BentleyJ]

If its a new system, why use AC coupling which would increase costs for either microinverters or a separate string inverter? Also, with AC coupling you loose the Generator connection to the Inverter.

Technically you don't need an ATS, just a means of disconnecting the utility feeder in an outage because there is no actual transfer. Although I'm not aware of any specific products to recommend. A 200A ATS is going to be expensive but certainly would work.

 

[TM48]

Where are the panels going to be located in relation to all what you outlined?

 

[bass_katcher]

The panels will be on the barn (near the inverter)

 

[bass_katcher]

If its a new system, why use AC coupling which would increase costs for either microinverters or a separate string inverter? Also, with AC coupling you loose the Generator connection to the Inverter.

Technically you don't need an ATS, just a means of disconnecting the utility feeder in an outage because there is no actual transfer. Although I'm not aware of any specific products to recommend. A 200A ATS is going to be expensive but certainly would work.

I'm not sure I follow everything here, but I need to have any back-feed power disconnected within 2 seconds if the grid is down, which obviously needs to be automatic. Perhaps where I am confusing things, but I would like something that would automatically disconnect when the grid power is down, and reconnect once the grid is up.

I definitely need to take advantage of the net metering; in summers I should over-produce, and winters I will be underproducing.

 

[bass_katcher]

Attached is a crude sketch-up of what is existing (minus the panels and inverter which are proposed) Also, it is 250+ feet from barn to hosue, not 500. Apparently I was looking at polygon perimeters instead of distance.

 

[hwy17]

With Schneider equipment you could do this with a Backup Control Switch (BCS) located at the meter location as long as the house and barn are both fed off the load side of one main panel, rather than separately tapped straight from the meter or something.

I don't know if the 18kPV can use a similar type of upstream communicating switch.

A factor to be aware of is that your barn and house wires would have been sized for voltage drops as separate individual runs, and may not be suitable for the same amperage when their lengths are combined into one long feed from barn to house. This is probably fine as you won't be running 200A from the inverter, but if you were getting permits this could arise as a technicality.

 

[DIYrich]

Option 1: Barn Off-Grid
If the system is large enough to run the Barn in Off-Grid mode, then you can use the existing line as the Load Line from the Eg4. The ATS would then switch between Grid and EG4 for power to house. Can't export power to grid in this setup.

Option 2: Bard On-Grid
Existing line is the Grid line to the EG4. You would need a second line from the EG4 back to the Pole for the ATS to select between Grid and EG4. In this setup you could dispense with the ATS and have the House always on the Load line of the EG4. Voltage loss would be a consideration whether over time it would be cheaper to keep the house on-grid.

Option 3: Add energy storage at House, and 20amp line from Barn to House.
Energy Storage System (ESS) at house to provide power when Grid is down. If you want to be able to recharge the battery from solar during extended grid down, then run a separate 20 amp line from Barn to House. The 20amp line can provide a continuous 2kW (120v) or 4kW (240v) continuous to charge the battery. From the battery, the ESS can provide power above 20a for the house (2kW continuous is 48kWh over a 24hr period).

Option 4: Add energy storage at House, 20 amp line barn to pole, and MTS at pole.
Depending upon the cost of the wire, you can do a line back to the pole, and an MTS at the pole. The reason for the MTS is that you have to reconfigure the ESS to know that grid is now limited to 16amps (80% of 20 amps) before you flip the switch.

Option 5: Add energy storage at House, 20 amp line barn to pole, and ATS at pole.
Same as Option 4 but you limit the grid to 16 amps at all times, and let the ESS do its thing with the battery.

Option 6: Manual Disconnect at Pole. Manual Disconnect at Pole would disconnect Grid power at Meter (keep connection between House and Barn). MTS at Barn would switch line from Pole from Grid to Load. You have to be careful to switch in the proper sequence - MTS at barn back to grid before reconnecting to Grid. ESS at Home could bridge the transfer time (minutes to hours).

 

[bass_katcher]

Permits are pretty sparse in these parts; I don't think permitting will be my problem.

With Schneider equipment you could do this with a Backup Control Switch (BCS) located at the meter location as long as the house and barn are both fed off the load side of one main panel, rather than separately tapped straight from the meter or something.

I think I understand this; the wires to the house and the barn are physically spliced at the top of the pole; they aren't separately tapped. Both lines then run to a respective breaker panel.

 

[bass_katcher]

Option 1: Barn Off-Grid
If the system is large enough to run the Barn in Off-Grid mode, then you can use the existing line as the Load Line from the Eg4. The ATS would then switch between Grid and EG4 for power to house. Can't export power to grid in this setup.

Option 2: Bard On-Grid
Existing line is the Grid line to the EG4. You would need a second line from the EG4 back to the Pole for the ATS to select between Grid and EG4. In this setup you could dispense with the ATS and have the House always on the Load line of the EG4. Voltage loss would be a consideration whether over time it would be cheaper to keep the house on-grid.

Option 3: Add energy storage at House, and 20amp line from Barn to House.
Energy Storage System (ESS) at house to provide power when Grid is down. If you want to be able to recharge the battery from solar during extended grid down, then run a separate 20 amp line from Barn to House. The 20amp line can provide a continuous 2kW (120v) or 4kW (240v) continuous to charge the battery. From the battery, the ESS can provide power above 20a for the house (2kW continuous is 48kWh over a 24hr period).

Option 4: Add energy storage at House, 20 amp line barn to pole, and MTS at pole.
Depending upon the cost of the wire, you can do a line back to the pole, and an MTS at the pole. The reason for the MTS is that you have to reconfigure the ESS to know that grid is now limited to 16amps (80% of 20 amps) before you flip the switch.

Option 5: Add energy storage at House, 20 amp line barn to pole, and ATS at pole.
Same as Option 4 but you limit the grid to 16 amps at all times, and let the ESS do its thing with the battery.

Option 6: Manual Disconnect at Pole. Manual Disconnect at Pole would disconnect Grid power at Meter (keep connection between House and Barn). MTS at Barn would switch line from Pole from Grid to Load. You have to be careful to switch in the proper sequence - MTS at barn back to grid before reconnecting to Grid. ESS at Home could bridge the transfer time (minutes to hours).

I guess I should state my goals. Goal #1 is to reduce my electric bill. if I get close to the expected output, it should be significant. With net metering, I should be able to build up enough surplus in the summer to pay for most of my winters. Powering through an outage is a distant second.

In theory, if I was willing to go dark during an outage, could I just hook the grid connection on the EG4 and leave the load empty?

If I'm reading this correctly, that is effectively what Option 6 is saying, just with manually switching wires from grid to load during an outage. The only problem with this is monitoring for when the power is back.

As you can tell, I'm desperately trying to avoid running lines.

I suppose theoretically I could run my solar lines from the barn to the house and install my inverter there, which would kill power at my barn during an outage (no big loss) but 250+ feet of solar wire (x3 for the 3 strings I'm thinking) seems like a lot of waste.

Here was what I was secretly hoping (that I figured was a pipe dream) which was to dumb down my smart inverter to always be chucking power out to the grid, (basically shutting off its safety function), leave the load lines empty and letting the safety function be taken over by a ATS at the meter. This would allow me to avoid an extra line, and it would still power the house during an outage.

 

[hwy17]

I think I understand this; the wires to the house and the barn are physically spliced at the top of the pole; they aren't separately tapped. Both lines then run to a respective breaker panel.

If there's just a straight up splice there, after the meter, without any main breaker on the pole, and it goes from the splice to each panel, then that's actually what I meant by separately tapped.

 

[bass_katcher]

Attached is what I was dreaming of doing. Having the inverter only connected to the grid (and no load) so it always fed the grid. The ATS would take care of the disconnect as if I were running on generator power. This seems straight forward if the inverter can be overridden.

HOWEVER, if I can't trick the inverter like that, can I trick it by splicing my wires and running a leg to load and another leg of the same wire to grid? This seems sketchy and unnecessary since the inverter is capable of net metering, but I feel like there would be issues. This is sort of like Option 6, but less manual.

 

[DIYrich]

If you don't care about backup, then

Growatt 11.4kW Grid-Tie Inverter | MIN11400TL-XH-US

Optimize your grid-tied solar system with the Growatt 11.4kW Inverter (Model MIN11400TL-XH-US), delivering efficient energy conversion and reliable performance for residential and small commercial applications.

signaturesolar.com

Export whatever you produce, and let net metering handle it.

 

[bass_katcher]

If you don't care about backup, then

Growatt 11.4kW Grid-Tie Inverter | MIN11400TL-XH-US

Optimize your grid-tied solar system with the Growatt 11.4kW Inverter (Model MIN11400TL-XH-US), delivering efficient energy conversion and reliable performance for residential and small commercial applications.

signaturesolar.com

Export whatever you produce, and let net metering handle it.

That is certainly a much cheaper option. I was trying to future proof a bit by adding the ability to add batteries at a later time and a way to power the house with the eg4 during outages, but this checks all the other boxes for less than 1/2 the price. So, is it worth hassling with a bunch of extra lines and components and $3k more just for the inverter for something I MIGHT do in the future? hrmmm

I do assume that the EG4 kpv would let me do the same connection as well and strictly net-meter? (obviously, the EG4 would only be worth it if I eventually added more features)

 

[WorldwideDave]

in the photo, what are the two wires on the right side of the power meter? I know what the two red lines you have labeled on the left are for. I know one of them is the line in for the meter.
Or do you have 2 meters - an 'ag' meter (lower rate) for barn, and a 'residential' meter for the house?

 

[bass_katcher]

in the photo, what are the two wires on the right side of the power meter? I know what the two red lines you have labeled on the left are for. I know one of them is the line in for the meter.
Or do you have 2 meters - an 'ag' meter (lower rate) for barn, and a 'residential' meter for the house?

that was the hypothetical ATS installation that would be necessary if I tried to utilize the existing line to the barn as the feed to the house with the grid down. I only have the one meter. The first image "solar plan" is existing condition. (minus the solar panel and inverter labels)

I can't tell if I am overcomplicating things, or trying to oversimplify, or both.

If I go "dumb" and only grid connect, I think I have a good handle on things. I also think if I do that, I would have a way smarter inverter than I need if I went with the EG4 18kpv.

I like the idea of having power with the grid down and the sun out, but that is not the #1 goal. I also like the idea of eventually having a battery backup, but again, not the immediate goal.

 

[WorldwideDave]

so what is the immediate goal?
Think long term. Plan for grid outage. Save for battery backup. And design accordingly.

 

[bass_katcher]

so what is the immediate goal?
Think long term. Plan for grid outage. Save for battery backup. And design accordingly.

Immediate goal is to save money. With net metering in Missouri, I have 12 months to use credits. I can go with a dumb(er) inverter for that and I have a decent handle on that. As diyrich pointed out, if I stopped there, I could go with a much cheaper inverter.

Alas, planning long term, means that eg4 inverter is still viable if I execute those plans of outage and battery backup power. That also means some combination of a "remote" ATS, running new lines, or some combination. THIS is what I'm really trying to wrap my head around is if I can do this without running a bunch of new wire and/or rewiring anything else.

 

[DIYrich]

IMHO: Start with the GW I linked to (high voltage battery version). price seems to be an issue for you.
When you are ready to add batteries:
1) Install 2nd wire back to pole or house
2) Install ATS at Pole or House
3) buy Growatt 10000TL-HU-US, or other 48v battery inverter that can AC Couple (note feature is TBD for the GW).
4) AC Couple existing GW into new inverter. Maybe move some of the PV to the new inverter.

The two GW are about the same price as the 18kPV, Maybe when you are ready to add batteries, Inverter prices come down enough that the net cost is about the same as doing it now.

 

[bass_katcher]

Thanks! Price isn't really an issue aside from I don't want to invest money on features I'm not going to use.

But I think you're right; I am going to wire it up as-is with grid connect only. At some point, I'll install a line where all my power feeds to the barn first and then to the house. This also eliminates the need for a separate ATS as I can let the inverter handle that disconnect.

Thank you guys so much for your help and talking me through it.

 

[WorldwideDave]

Time is ticking on that 12 months to use the credits I guess. Set aside a weekend to figure that out and place order and move on with life? Can always buy just one battery and 18K for now. Not cheap, i know.

 

[bass_katcher]

Time is ticking on that 12 months to use the credits I guess. Set aside a weekend to figure that out and place order and move on with life? Can always buy just one battery and 18K for now. Not cheap, i know.

Sorry, I should have been more clear. Let's say my anticipated generation for May exceeds my usage, that excess gets carried over as a credit to the next month and then the next month etc etc up to 12 months. Based on pvwatts, December, January and February will be my lowest generation. I currently have zero credits. But I can't start earning until I finish designing and building!

That aside, I already have a 14kwh battery. But as we've covered, to install a system that tolerates battery output would require additional construction time: I want to do this as soon as possible. I do think a good hybrid system is what I will go with, just because I DO plan on installing those other features sooner than later.

 

[WorldwideDave]

what battery did you go with

 

[bass_katcher]

what battery did you go with

This is a bit of an odd story. Bet you didn't think you'd end up with a story from that question!

A month or so ago, we bought a junked 2010 Polaris Ranger EV that we decided to retrofit it with LiPo batteries. Well, turns out solar folks have the most comprehensive review of batteries. During that research, I kept stumbling across solar ideas, and finally the idea stuck that, "Hey, I can do that!"

Anyway, I bought 4 12v 280ah Eco-worthy batteries for it; the ones with bluetooth and cold weather charging cutoff. 200a/250a continuous, 800a peak. Anyway, even when I purchased them, I thought that if I didn't like those for that purpose, I could use them as trolling motor batteries or battery storage for solar. No, they aren't rack mount, not smart, and yes, they are cheap chinese, but they reviewed well and deconstruction looked like they were relatively well assembled. Anyway, I decided to do a more traditional 'golf cart' battery for the ranger (105ah, 200a continuous, 600a peak, which will be enough to power my ranger 95% of the time, and the other 5% will require a 32-second waiting period) and eliminate several connections in the process, so I have 4 batteries currently without a home.

 

[bass_katcher]

Current immediate plan is to install inverter only connected to the grid. No additional lines will immediately be required. This also means I don't need a ATS or other disconnect; the inverter will handle it. (I'm still looking into the GroWatt versus the Eg4; if GroWatt will be adding a battery capable/direct power option soon, the 2 inverter combo might be viable.) I will be installing per the plan below relatively soon after. (I woudl say within a year or 2)

A new line will be ran from the meter to the barn. The current connection at the meter will be terminated as now all power will run from the pole to the barn and then the house. this is effectively a slight tweak of Option 2 form DIYrich.
Positives: no splices at pole and everything is easily isolated.
Cons: everything runs through the barn which means extra exposure to line breaks.

Something that I don't fully understand though; in options 4 and 5, there is a 20% reduction in amps. why?