Auto Transfer Switch for Battery Back up

[SJKLLC877]

Hello all, first post on the forums. I'm currently doing solar down here in Florida and we are starting to get into battery backup systems. We have a local outfit that has their own brand of battery. Company is call Vudu Energy if anyone is interested. Anyway, Im having a hard time finding an Auto Transfer switch that I can pair with the battery. From all the searching I've done, it seems all the auto transfer switches are made specifically for a back up generator. Customer is looking for a whole home solution. Any help or suggestions would be appreciated. TIA.

 

[ron]

The transfer switch would transfer AC power downstream of your solar inverter, just like the ones for generators.
Tesla makes a packaged unit called a Powerwall which is expensive because it is Tesla but it provides a small household load either utility or solar / battery.
I'm sure you could create one for the entire house yourself, but there would be a large solar / battery system needed.

 

[SJKLLC877]

The transfer switch would transfer AC power downstream of your solar inverter, just like the ones for generators.
Tesla makes a packaged unit called a Powerwall which is expensive because it is Tesla but it provides a small household load either utility or solar / battery.
I'm sure you could create one for the entire house yourself, but there would be a large solar / battery system needed.

Yeah, its a large solar system. I’ve looked online and called my local supply house. All they had was Generac transfer switch which only works with a Generac generator. If anyone can point me to a transfer switch that just operates off utility power to switch on and off that would be ideal.

 

[roger]

Have you looked into ASCO, Russelectric, or Zenith? They can probably help you but will most likely have healthy price tags.

Roger

 

[hillbilly1]

Yeah, the Generac switches are “dumb” switches, the switch is controlled by the controller in the generator.
As Roger said, you need a switch with the controller built in, such as Asco, or Kohler, but look carefully, not all of those are smart switches. Look for one that has a two wire generator start contact. You will not need the contact, but those are generally smart switches. They have built in timers and sense voltage source loss. The switching is powered by the available source, so generator or generator battery power would not be required.

 

[Jraef]

Something is amiss here. If you need a "transfer switch", it implies that your system is grid connected. You CANNOT connect an inverter to a grid unless it is specifically listed as a "Line Interactive Inverter", meaning it AUTOMATICALLY detects when the grid goes away and turns off the grid feedback capability, so as to not kill a utility lineman. So what I'm saying is that if you are doing this correctly, you would NOT need an Automatic Transfer Switch, the batteries would feed the inverter all the time so when the utility power goes off line, the household is unaware (unless you specifically want indication of it).

So your asking for an ATS might, to me, indicate that you are in over your head here because you are possibly using an inverter that is NOT listed /rated to be used in a grid connected system, making your installation illegal and potentially deadly.

 

[hillbilly1]

The OP may not be grid tied, if I get what he is trying to do, when the solar fails, it automatically backs up with utility. So he would be perfectly legal to do that. The system would not have to be listed for grid tie. The emergency side of the transferswitch would be tied to utility, while normal would be connected to the inverter., even if he is using it as a backup (a lot of wasted money on solar) he could still do it without being grid tie rated.

 

[Jraef]

The OP may not be grid tied, if I get what he is trying to do, when the solar fails, it automatically backs up with utility. So he would be perfectly legal to do that. The system would not have to be listed for grid tie. The emergency side of the transferswitch would be tied to utility, while normal would be connected to the inverter., even if he is using it as a backup (a lot of wasted money on solar) he could still do it without being grid tie rated.

OK, I can see that possibility. In that case, a transfer switch is a transfer switch if it is on the AC side of the inverter.

 

[hillbilly1]

One issue I could foresee, is time delays. They would need to be at least an hour to allow the batteries to build back up sufficiently, or short cycling may occur.

 

[SJKLLC877]

Appreciate all the replies. When it comes to batteries I am out of my element, which is why I've come to these forums for some answers. Let me back up and explain what I'm trying to do. My solar company is considering partnering up with the battery company, during this process the owner of the battery company came to us with an idea. Essentially what his idea is, is to put a battery in line with the solar system so in the event of a power outage the battery would trick the solar system(enphase system with IQ7 micro inverters) that there is still grid power when in fact there is not. So, Line side of 200A transfer switch is utility grid power. Load side of transfer switch will feed to line side of MSP. At the line side of the main service panel and on the load side of the transfer switch the solar system with battery in circuit will line tap there. In the event of a power outage, ATS will open utility side leaving only the solar system with battery tapped into MSP. If this is too confusing I will attempt to upload a line diagram to better illustrate. Now if this is illegal of course I won't attempt it, but I was under the assumption that the Auto Transfer Switch would suffice as protection from keeping the system back feeding grid?

Edit: I forgot to mention, the idea behind this set up is not to power the house at night during an outage only to supply people with power during the day from the solar. The battery we are using is rather small in comparison to a true battery backup set up.

 

[GoldDigger]

OK, I can see that possibility. In that case, a transfer switch is a transfer switch if it is on the AC side of the inverter.

There are at least two possibilities here..
1. A hybrid inverter (capable of both line interactive and standalone operation) can contain or be used with an isolation switch that simply disconnects the system and its loads from the utility connection allowing the inverter to change to stand alone mode.
2. A purely standalone inverter can be used with a normal transfer switch which switches the critical loads between grid and inverter. The batteries may charge from PV or from a separate line powered charger.

What the OP now seems to be proposing (Enphase with small standalone inverter to simulate the grid) will not work as there is no way to throttle the Enphase output to less than full power when it is lightly loaded.
In addition the standalone inverter would have to be capable of supplying the full load while the Enphase "qualified" the incoming AC.

Sent from my XT1585 using Tapatalk

 

[ron]

If this is too confusing I will attempt to upload a line diagram to better illustrate.

Please do.
I'm also interested in where the inverter is to convert the battery voltage to AC to interface with the rest of the system.

 

[SJKLLC877]

Ok, forgive my artistic ability(I have none, lol) this is how I was planning to wire it up.

 

[Todd0x1]

I can't see this ever working....The grid tie inverter will fight the pony inverter trying to push power into it. If you want to be able to island, you need hardware capable of doing so.

 

[SJKLLC877]

I can't see this ever working....The grid tie inverter will fight the pony inverter trying to push power into it. If you want to be able to island, you need hardware capable of doing so.

Im very skeptical as well, but I figure we could give it a try. It's one of the other owners house that we are planning to test it out on.

 

[jaggedben]

Appreciate all the replies. When it comes to batteries I am out of my element, which is why I've come to these forums for some answers. Let me back up and explain what I'm trying to do. My solar company is considering partnering up with the battery company, during this process the owner of the battery company came to us with an idea. Essentially what his idea is, is to put a battery in line with the solar system so in the event of a power outage the battery would trick the solar system(enphase system with IQ7 micro inverters) that there is still grid power when in fact there is not. So, Line side of 200A transfer switch is utility grid power. Load side of transfer switch will feed to line side of MSP. At the line side of the main service panel and on the load side of the transfer switch the solar system with battery in circuit will line tap there. In the event of a power outage, ATS will open utility side leaving only the solar system with battery tapped into MSP. If this is too confusing I will attempt to upload a line diagram to better illustrate. Now if this is illegal of course I won't attempt it, but I was under the assumption that the Auto Transfer Switch would suffice as protection from keeping the system back feeding grid?

Edit: I forgot to mention, the idea behind this set up is not to power the house at night during an outage only to supply people with power during the day from the solar. The battery we are using is rather small in comparison to a true battery backup set up.

In order for this to work, at a minimum, your battery inverter(s) (do you even have them selected?) would have to do frequency shifting to turn off or throttle the output from the solar inverters when the micro-grid is disconnected from the grid. There is a discussion in this thread. It is possible to do, but frankly it sounds like the people involved are out of their depth. This battery company should be developing their own complete solution or looking for an partner to work with that will build their own transfer switch (technically a 'micro-grid interconnect device') and inverter product. If they are asking you as an electrician to spec a transfer switch then ... I would run away. There's a whole world of UL listing standards that may be code required in your state. You'd be better off going with Powerwall or some other fully engineered solution that has done the required homework already. Enphase will soon be shipping their own solution too which will be best for working with their micro inverters. (But, of course, then the battery company that wants to do this will be out of the equation so of course they won't want to go along.) Either that or, if the system is big enough (doesn't sound like it with a 200A service), then a properly qualified engineering firm should be involved to build and field-list a custom system.

 

[jaggedben]

After taking a look at the battery company site, yeah they are not selling everything that is required. You might be able to use their batteries with Outback or Schneider's XW line of inverters. These are not the most streamlined solutions available right now. Lots of homework for whoever does it.

 

[jaggedben]

...

What the OP now seems to be proposing (Enphase with small standalone inverter to simulate the grid) will not work as there is no way to throttle the Enphase output to less than full power when it is lightly loaded.
...

Actually Enphase IQ do have throttling capability. But you need a controlling battery inverter with the right capabilities.

 

[SJKLLC877]

Really good info guys, thanks again. Yeah, Im fairly confident we will end up going with enphase ensemble line of integrated products. The big allure to vudu was the price. They were gonna sell direct to us for almost half what enphase wants for their batteries. But I’m coming to realize they’re only offering half a solution.

 

[texie]

In order for this to work, at a minimum, your battery inverter(s) (do you even have them selected?) would have to do frequency shifting to turn off or throttle the output from the solar inverters when the micro-grid is disconnected from the grid. There is a discussion in this thread. It is possible to do, but frankly it sounds like the people involved are out of their depth. This battery company should be developing their own complete solution or looking for an partner to work with that will build their own transfer switch (technically a 'micro-grid interconnect device') and inverter product. If they are asking you as an electrician to spec a transfer switch then ... I would run away. There's a whole world of UL listing standards that may be code required in your state. You'd be better off going with Powerwall or some other fully engineered solution that has done the required homework already. Enphase will soon be shipping their own solution too which will be best for working with their micro inverters. (But, of course, then the battery company that wants to do this will be out of the equation so of course they won't want to go along.) Either that or, if the system is big enough (doesn't sound like it with a 200A service), then a properly qualified engineering firm should be involved to build and field-list a custom system.

Very well said.