If an ATS separates an existing grid-tie inverters from a new off-grid system, can the same solar panels be used with both inverters?

[Not Aerosmith]

It seems that an automatic transfer switch (ATS) would activate the existing grid-tie inverters when the grid is up and work as originally installed. Therefore, an ATS could activate an off-grid inverter when the grid is down.

Since neither inverter works at the same time, it seems that the same solar panels could be connected to both inverters. Although, I believe that I need to add a relay to disconnect the solar panels from the off-grid inverter. Upon loss of grid power, the relay closes and the off-grid inverter is connected to the solar panels.

The advantage is that instead of a gasoline driven generator as backup power, we could use a solar driven inverter as backup power. In my case I would probably add 5 kw off-grid inverter with 10 KW of batteries. My current grid-tie system is (3) 5 KW inverters with 57 solar panels and no batteries.

My existing grid-tie system works great, so I don't want to revise it with new hybrid inverters not fully debugged or only works with a critical load panel. I want to add a second system for whole house backup power. Any reason why this shouldn't work? Any affordable suggestions?

 

[sunshine_eggo]

In an AC coupled system, yes. The off-grid inverter supplies the grid for the off-grid system. The off-grid inverter would need to be able to utilize phase shifting and be compatible with AC coupling. Most tier-1 hardware is.

The off-grid inverter senses the surplus power on its output, and it uses the surplus to charge the batteries.

AC Coupling

AC Coupled Solar Power System - use your existing system to feed power into a battery based inverter/charger to charge the battery bank.

www.altestore.com

 

[Not Aerosmith]

Thank you, I appreciate the response. It made me consider some things that I had missed in my original discussion, so I revised it after reading your comment.

 

[summit]

AC coupling would be the way to go for sure, but tends to be pricey. Given your 57 panels and 15kw grid-tie inverters, it's probably in your budget. On the other hand, I am in fact designing a system similar to your idea, of switch the PV output from the grid-tie inverter to a hybrid inverter during outage. But there will be a critical load panel and not supplying the whole house.

I am still worrying about potential DC arching within the transfer-switch, upon switching from hybrid-inverter back to the grid-tie inverter; as the hybrid-inverter could be pulling current from the array when grid power resumes.

 

[wattmatters]

I have a grid tied PV system (11 kW 3-phase) and use an off-grid all-in-one inverter system with grid input assist to power the home.
The off-grid system has its own small PV array (2.2 kW) and batteries (48V system).

During the day it operates in Utility First mode so the grid tied PV system powers household loads via the off grid inverter. Meanwhile the small off-grid PV array charges the batteries (and I can divert some of the grid-tied PV power to the batteries to supplement the off-grid array). For the evenings the off-grid system operates in Solar/Battery/Utility mode and runs the home from the battery.

I leave a few circuits not powered via the off-grid side, e.g. ducted aircon, oven etc. They are powered by the grid PV system during the day, and regular grid power at night.

In a grid outage those circuits are not essential and the home happily still operates from the off-grid system. I have two banks of batteries - LiFePO4 for regular daily cycling and a Lead acid bank which is for outage backup (data centre backup units, perfect for the job). The small off-grid PV array and batteries are enough for emergency power for a full day/night, more if the sun comes out, and if I really need to I can connect the generator for some supplemental charging during the day if it looks like we'll be off-line for longer.

I'm not a fan of switching PV high-ish voltage PV arrays without first shutting down loads (or done at night), which kinda negates the benefit of an ATS. High-ish voltage DC (circa 400-600 V) is not something to be toyed with. Frankly, I'd leave it well alone.

Ultimately I plan to have more PV capacity added to the off-grid side.

 

[summit]

I'm not a fan of switching PV high-ish voltage PV arrays without first shutting down loads (or done at night), which kinda negates the benefit of an ATS. High-ish voltage DC (circa 400-600 V) is not something to be toyed with. Frankly, I'd leave it well alone.

Ultimately I plan to have more PV capacity added to the off-grid side.

point well taken. The PV DC can be over 300vdc, a killer for sure. Switching upon outage from grid-tie to hybrid-inverter is unloaded, as the grid-tie inverters would be off. It's in the timing to turn-off the hybrid-inverter before the ATS reconnect the PV to the grid-tie-inverter. But yeah, have to thread carefully & slowly for sure. Thanks

 

[Ampster]

Since neither inverter works at the same time, it seems that the same solar panels could be connected to both inverters. Although, I believe that I need to add a relay to disconnect the solar panels from the off-grid inverter. Upon loss of grid power, the relay closes and the off-grid inverter is connected to the solar panels.

Another design could be both a GT inverter and a hybrid inverter that could AC couple with the GT inverter. You could have solar panels powering both inverters so you could get the benefit of both inverters all the time. Solar panels are the least expensive part of a system and it would be a shame to leave an expensive inverter idle in either of the above scenerios. The hybrid would presumable contain an ATS and the GT inverter would not need one. Your inverter capacity could be more cost effective because GT inverters are less per kW and AC coupling it to the hybrid would mean you would not need as big an off grid inverter since it could pass through the AC from the AC coupled GT inverter. You would get the generating capacity of both to meet your needs when the sun is shining and the hybrid would only have to be sized for your overnight loads.
EDIT: I did not see that earlier posts had already suggested AC coupling so consider this post a support of those ideas.
Also, as mentioned DC switching can be complicated especially since the configuration of strings on a GT inverter are often high voltage and an off grid string is usually through a charge controller that operates at lower DC voltages but higher Amps.

 

[Not Aerosmith]

I agree that having everything working together would maximize the benefits and increase solar productions.

My concern is that when I read the owner manuals on the new hybrid inverters, they don't have instructions for interfacing with existing grid-tie systems. The owner manual barely provides enough instructions for setting up only their hybrid inverter and connecting to the basics components. Often the instructions are very unclear and the wording is really misleading.

 

[Ampster]

My concern is that when I read the owner manuals on the new hybrid inverters, they don't have instructions for interfacing with existing grid-tie systems.

Not all hybrids can do AC coupling. That is a feature set that I know Schneider, Outback and SolArk can do. Reportedly SMA can also do that. I don't know the product mix available to you in Panama but that may be a constraint. I know you mentioned it is 240/120 volt like North America

 

[summit]

Besides Schneider/Outback/SolArk/SMA (high cost), which hybrid/all-in-one can even turn on GT ? let alone AC coupling ?

 

[Ampster]

which hybrid/all-in-one can even turn on GT ? let alone AC coupling ?

Those are the only ones I am familiar with from reading posts on this forum. There could be more. You might have to search vendor sites. There is only one concept called AC coupling. A GT inverter will only turn on if it sees the grid or a grid forming inverter that has the necessary firmware to control a GT inverter. It is not likely a feature that can be implemented in low cost hybrid inverters.

 

[summit]

A GT inverter will only turn on if it sees the grid or a grid forming inverter that has the necessary firmware to control a GT inverter. It is not likely a feature that can be implemented in low cost hybrid inverters.

exactly, AC coupling is indeed an elegant solution to utilize the GT, particularly coupling to micro-inverters since there is no DC access at ground level. Has anyone successfully tested to turn on a micro-inverter, say an Enphase, from a hybrid-inverter AC output ? controlling the GT inverters is another level of complexity, though they simply shut-down upon no "grid" AC

 

[Ampster]

Has anyone successfully tested to turn on a micro-inverter, say an Enphase, from a hybrid-inverter AC output ? controlling the GT inverters is another level of complexity, though they simply shut-down upon no "grid" AC

Yes I have done it with Enphase and SolarEdge from my Outback Skybox. If the GT inverter is UL1741 compliant it should work. There is no equivalent spec that I know of that gaurantees that a hybrid can AC couple other than manufacturers specs.

 

[summit]

bought an used M215 Enphase off ebay, planning to test with a low cost hybrid-inverter (MPP-U5648GK) one of these days

 

[Not Aerosmith]

Well, it seems that the more I learn ... the less I know. Several people have mentioned AC coupling and DC coupling. which I had always assumed was the two normal methods for connecting solar batteries. Either charge the batteries before the inverter with DC to avoid conversion losses or after the inverter with AC to DC conversion losses. I had always assumed that this was a given for hybrid inverters or off-grid inverters using batteries.

I looked again at SunGoldPower hybrid inverter TP6048 and they don't say AC Coupling even though they connect to batteries. I also looked again at SunGoldPower hybrid inverter IP6048 and they do say "AC Coupling IP65" and this inverter is about $700 higher than the TP6048. SunGoldPower website even break down their inverters into five product types: hybrid solar inverters, low frequency solar inverters, on off grid hybrid solar inverters, parallel solar inverters, and AC coupled inverters. The SunGoldPower IP6048 is listed in 4 out of 5 product types, and is the only SunGoldPower inverter listed as an AC Coupled IP65 hybrid inverter. So obviously, Ampster is correct when he stated, "not all hybrids can do AC coupling."

 

[Not Aerosmith]

Besides Schneider/Outback/SolArk/SMA (high cost), which hybrid/all-in-one can even turn on GT ? let alone AC coupling ?

The SunGoldPower IP6048 and MPP Solar LVX6048WP manufacturers have provided a schematic showing these inverters as AC Coupling. The SunGoldPower inverter has free shipping with a $150 discount or about $1900 versus MPP Solar from Watts247 at about $2200 without free shipping. SunGoldPower indicate that they are in stock and MPP Solar is still pre-order. With that said other, things do change from day to day plus other suppliers will have different prices. Still this gives you an approximate cost that these inverters are not very expensive. Both designs were release 2022 and there not much information on their performances and reliability.

 

[summit]

is SunGoldPower from mainland China ? couldn't tell from the web page. MPP is Taiwan co.

 

[Not Aerosmith]

is SunGoldPower from mainland China ? couldn't tell from the web page. MPP is Taiwan co.

SunGoldPower was established in 2010 and have sales with support in America, Australia, Europe and Southeast Asia. I have been in contact with SunGoldPower in Ca, USA vial email. They normally respond within 24 hours from sales@sungoldpower.com.

SunGoldPower products ship usually in 5 days via Amazon distribution centers in USA and Europe. I called last week and the IP6048 is in stock. The MPP Solar LVX6048WP is still pre-order.

 

[wattmatters]

SunGoldPower was established in 2010 and have sales with support in America, Australia, Europe and Southeast Asia.

Who is their local support in Australia? Never heard of them. Website mentions nothing other than they've sold to customers here but no mention of local support. None of their inverters are suitable/designed for our electrical system.

They look like a clone manufacturer.

 

[summit]

I have an MPP hybrid-inverter, and SunGold's manual looks just like MPP's