SMA SPS Port to APC Transfer Switch Connected to Battery Backup

egable · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

Cariboocoot wrote: »

If you use the right inverter there is zero delay between the grid going down and the inverter taking over the loads; the battery-based GTI is in sync with the grid power all the time and takes over seamlessly. The only thing that happens when the grid goes down is those items not on the critical loads sub-panel lose power and those items on it get powered from the batteries. No power will flow from the inverter to the grid.

Again, if you do not accurate measure the power need you're just guessing and will not get the best value system.

Right, but I know how much power I need; I've stated it several times. A 100 AH battery pack at 48 volts is more than enough. But you are telling me that I cannot install a battery pack that small because my inverter is so large. The inverter size is not going to go down, because I need a 10 kW array to offset the majority of my electrical usage.

I used 14.4 MWH last year and 16.3 MWH the year prior. I am taking steps to shed another 2 MWH - 3 MWH from my yearly usage, but that's about the best I can do. I am a communications system software engineer, and I work from home, so I have stuff running here all the time, including computers, switches, phones, etc, plus a treadmill desk (320 kWH per year: 350 watts for 3.3 hrs per day for 5 days a week for 52 weeks per year), a couple DVRs, fridge and freezer, and some window AC (3 MWH per year) during the summer. My lights are a combination of LED and CFL, but we are slowly phasing out the CFL bulbs as they die and replacing them with LED. Unfortunately, our kitchen has an electric range and oven, so that uses quite a bit of energy each month, especially since I work from home and cook two meals a day on it.

So, I know how much power I need for normal daily use, and I know how much I need if the utility goes down, but there is a great disparity between normal daily use and how much we need if the utility goes down. I don't want to size the entire solar array to only cover the critical load. I want to offset most of the normal daily use. That is goal #1 from this installation. Goal #2 is to have enough power available during a utility outage to cover our critical load. However, it makes no sense to me to use a 1,500 watt manually switched-on circuit for backup power, because we have several times during the year when we travel and are not around to flip a switch and run extension cords. So, if I use the array for backup power, I need to make sure it can automatically engage.

It also seems silly to limit myself to one or two 1.5 kW circuits when I have an entire array sitting on the roof which can be wired to provide power to the critical loads panel and not out to the grid so that during the day, the critical loads panel is covered with needed power for a longer duration. Doing it that way, it also lets me put the wall outlets from a couple of our rooms on the critical loads panel, too, so we can run a few other miscellaneous devices aside from just the fridge and freezer.

The real question is whether I need the battery backup at all. If I run the entire array of output into the critical loads panel during the day, the fridge and freezer will re-freeze to proper temperatures (and I can even set them lower than normal temporarily) so they will take longer to increase beyond the safe point. Yes, they would use more power during the day that way, but it would be put to good use, and there would be plenty available if I can run the entire array's output into the critical loads panel.

So, can I wire this in a way that I can get the full output of the solar array to the critical loads panel during the day even when utility power is out? And what do I need to do that?

Cariboocoot · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

egable wrote: »

Right, but I know how much power I need; I've stated it several times. A 100 AH battery pack at 48 volts is more than enough. But you are telling me that I cannot install a battery pack that small because my inverter is so large. The inverter size is not going to go down, because I need a 10 kW array to offset the majority of my electrical usage.

This is correct if you are going to use a hybrid inverter for the full GT system. That 10kW array would need two 6kW inverters and that would mean two 600 Amp hours battery banks for those inverters.

This changes if you have a separate standby system that is not 'processing' the PV output for grid tie. In your case I think you'd be better off that way, especially as you've stated the outages are not frequent nor do they last long.

Unfortunately, our kitchen has an electric range and oven, so that uses quite a bit of energy each month, especially since I work from home and cook two meals a day on it.

Yep. First thing I did in this house was get rid of the electric stove and put in a gas range. Really knocked the electric bill down (without a corresponding increase in the gas bill). Food's better too.

So, I know how much power I need for normal daily use, and I know how much I need if the utility goes down, but there is a great disparity between normal daily use and how much we need if the utility goes down. I don't want to size the entire solar array to only cover the critical load. I want to offset most of the normal daily use. That is goal #1 from this installation. Goal #2 is to have enough power available during a utility outage to cover our critical load. However, it makes no sense to me to use a 1,500 watt manually switched-on circuit for backup power, because we have several times during the year when we travel and are not around to flip a switch and run extension cords. So, if I use the array for backup power, I need to make sure it can automatically engage.

The auto engagement is not difficult to achieve. I do agree that the SMA SPS system is a pain for having to be manually activated. It's possible that process could be automated in some way, especially as there would be battery-based power available to run a timer and relay to reset the SPS every day.

It also seems silly to limit myself to one or two 1.5 kW circuits when I have an entire array sitting on the roof which can be wired to provide power to the critical loads panel and not out to the grid so that during the day, the critical loads panel is covered with needed power for a longer duration. Doing it that way, it also lets me put the wall outlets from a couple of our rooms on the critical loads panel, too, so we can run a few other miscellaneous devices aside from just the fridge and freezer.

Yes, and you could make use of that of that power with AC coupling during the day. Otherwise again you'd need the massive battery bank for storage and it would sit around aging most of the time. If you go with the AC coupling option I'd recommend using all SMA inverters because they work together much more smoothly for this than any other configuration.

The real question is whether I need the battery backup at all. If I run the entire array of output into the critical loads panel during the day, the fridge and freezer will re-freeze to proper temperatures (and I can even set them lower than normal temporarily) so they will take longer to increase beyond the safe point. Yes, they would use more power during the day that way, but it would be put to good use, and there would be plenty available if I can run the entire array's output into the critical loads panel.

That would be another option, but one that requires manual intervention. You can do a lot more if you're around to manage the power rather than leaving it to automation.

So, can I wire this in a way that I can get the full output of the solar array to the critical loads panel during the day even when utility power is out? And what do I need to do that?

Without batteries your only GT output option is the SPS @ 1500 Watts each. Hardly full power. With even a small battery system you could make use of the AC coupling to utilize more of the PV power and have at least some of it available 24 hrs. Otherwise you're looking at a huge battery bank to make use of 10kW (roughly 1600 Amp hours @ 48 Volts) and even then there would be losses; battery systems are never as efficient as direct grid-tie.

Yet another possibility (albeit an expensive one) is the XW 600 V MPPT controller which can handle GT-style array Voltages and charge a 24 or 48 Volt battery bank. But at $1,200 each I don't think it's a good choice most of the time.

techntrek · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

Yes, you can rely on thermal carryover (staying cold after power is removed) for up to 12 hours assuming it isn't hot (in a garage in summer) and you keep milk jugs 3/4 full of water in the empty spaces of the freezer to help. The milk jugs will cut your normal operating costs, too.

Usually around here people suggest using a good inverter-generator for backup power, even with a grid-tie system. I'll make that recommendation. Save the extra money for the inverter, batteries, charger, and whatever extra the "emergency power" Sunny Boys cost, and go with a normal grid-tie inverter. Then spend $1200-1500 on a Honda or Yamaha in the 2-3kw range. Keep 20 gallons of gas in the shed with Stabil and rotate it every 6 months into your car.

My original emergency power system was a 12 kw genset and a 22 kw battery. I could run most of the house all night and all day on the batteries, powered by a large UPS, and then charge in the morning and night. This was for 2 fridges, a freezer, DVRs, wood stove fan, etc. Inverter generators make that obsolete when you will only burn $10-15 in gas per day. You can get large UPSs very, very cheap, but the batteries are never cheap. Another interesting option is in the link in my signature.

egable · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

Cariboocoot wrote: »

This is correct if you are going to use a hybrid inverter for the full GT system. That 10kW array would need two 6kW inverters and that would mean two 600 Amp hours battery banks for those inverters.

The roof of the house is 60 degrees (really steep), and faces south east. So, given wiring, combiner box, and inverter inefficiencies, the 10.08 kW array will output probably only 8.3 kW AC. That is assuming 88% of the rated output on the panels due to solar orientation and excessive tilt angle, 98% of that reaching the inverter due to wiring and combiner box, and 96% efficient inverter. The installer has me spec'd for a Sunny Boy 4000 and a Sunny Boy 5000. As far as I can tell, you cannot get them anymore without the emergency power. If you know otherwise, please let me know.

But, what about a single Sunny Boy 10 kW inverter? I found one for $3k online, and the other two combined look like they would be $4k - $4.5k. If they are really 50% more to buy 2 of them, I think I'd rather buy 1 and take the extra risk of an outage. It would take a nearly year long outage to make up the cost difference.

Cariboocoot wrote: »

This changes if you have a separate standby system that is not 'processing' the PV output for grid tie. In your case I think you'd be better off that way, especially as you've stated the outages are not frequent nor do they last long.

I'm not sure what you are saying here. What do you mean by having a separate standby system that is not 'processing' the PV output for grid tie? Also, which way are you saying I would be better off?

Cariboocoot wrote: »

Yep. First thing I did in this house was get rid of the electric stove and put in a gas range. Really knocked the electric bill down (without a corresponding increase in the gas bill). Food's better too.

We plan on remodeling our kitchen at some point, and will switch over to a gas range and convection oven at that time, but right now we have old custom cabinets set up in a very non-standard way which does not make it easy or affordable to try to swap out the electric range and oven.

Attachment not found.

Cariboocoot wrote: »

The auto engagement is not difficult to achieve. I do agree that the SMA SPS system is a pain for having to be manually activated. It's possible that process could be automated in some way, especially as there would be battery-based power available to run a timer and relay to reset the SPS every day.

Yes, and you could make use of that of that power with AC coupling during the day. Otherwise again you'd need the massive battery bank for storage and it would sit around aging most of the time. If you go with the AC coupling option I'd recommend using all SMA inverters because they work together much more smoothly for this than any other configuration.

How would you wire it so that when the grid goes down, the AC to the grid from the inverter is disconnected so it meets code, but yet it still powers the critical load panel when the sun shines? If I understand correctly, the SMA detects the grid failure and shuts down for a minimum of 5 minutes and then it looks for a sine wave coming in to detect when the grid is back and only turns back on if the grid is seen. So, how could you wire it in such a way that it still disconnects from the grid but also still provides power to the critical load panel if you don't have any battery backup power?

Cariboocoot wrote: »

Without batteries your only GT output option is the SPS @ 1500 Watts each. Hardly full power.

This sounds like you are saying what I just asked is not possible to do. Is that correct?

Cariboocoot wrote: »

With even a small battery system you could make use of the AC coupling to utilize more of the PV power and have at least some of it available 24 hrs. Otherwise you're looking at a huge battery bank to make use of 10kW (roughly 1600 Amp hours @ 48 Volts) and even then there would be losses; battery systems are never as efficient as direct grid-tie.

I thought you said it is not possible to have a small battery bank if I have the whole array turned into AC and fed into the critical load panel? Am I missing something? I don't need to store a full 10 kW every hour for an entire day and then use that all up at night. Like you said, that would be over 1,000 amp hours. If I put any batteries in the system at all, I want it to be as small as I can possibly get away with. I have no interest in storing and entire day's worth of array output. All I would want is just enough to either cover the 5-minute period when the Sunny Boy shuts down the grid before it turns the output back on, or just enough to power the critical load until the next day, whichever is the most practical smallest amount I can get away with.

Cariboocoot wrote: »

Yet another possibility (albeit an expensive one) is the XW 600 V MPPT controller which can handle GT-style array Voltages and charge a 24 or 48 Volt battery bank. But at $1,200 each I don't think it's a good choice most of the time.

I don't understand how the XW 600 V MPPT would fit into the picture unless the batteries are on the DC-side and the solar inverters draw entirely from battery if the grid goes down? And then don't I still need something to block the inverter power from going to the grid? My understanding is that the SMA shuts down entirely if the grid goes down and doesn't turn back on unless it sees a pure sine wave coming in from the grid connection point, and then only after being shut down for 5 minutes.

Cariboocoot · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

egable wrote: »

The roof of the house is 60 degrees (really steep), and faces south east. So, given wiring, combiner box, and inverter inefficiencies, the 10.08 kW array will output probably only 8.3 kW AC. That is assuming 88% of the rated output on the panels due to solar orientation and excessive tilt angle, 98% of that reaching the inverter due to wiring and combiner box, and 96% efficient inverter. The installer has me spec'd for a Sunny Boy 4000 and a Sunny Boy 5000. As far as I can tell, you cannot get them anymore without the emergency power. If you know otherwise, please let me know.

Panels do not have to be mounted on the same plane as the roof; they can be tilted either way to improve output. If you're spending this kind of money you should study all the aspects of panel angle and system efficiency vs. total Watt hour output both throughout the year and in respect to any TOU plan with your utility. As far as I know the SPS is an option, but that may have changed.

But, what about a single Sunny Boy 10 kW inverter? I found one for $3k online, and the other two combined look like they would be $4k - $4.5k. If they are really 50% more to buy 2 of them, I think I'd rather buy 1 and take the extra risk of an outage. It would take a nearly year long outage to make up the cost difference.

There is definitely a savings with one larger inverter rather than two smaller ones because there's no duplication of the 'basics' necessary to invert; just higher current capacity. A new SB 4kW is about $2,000 whereas the 8kW is $3,350. $1,350 is nothing to sneeze at.

I'm not sure what you are saying here. What do you mean by having a separate standby system that is not 'processing' the PV output for grid tie? Also, which way are you saying I would be better off?

With a hybrid grid tie system all the PV goes to batteries then to the inverter then to loads including the grid. As such the battery bank has to be large enough to 'filter' it all. If you have only a small back-up battery bank as a separate system it can be sized to suit those needs only. So rather than have a battery bank capable of handling a 10kW array you'd be better off with one that is large enough for your back-up needs only, and have the rest of the array capacity be direct grid-tie. Much cheaper and more efficient.

How would you wire it so that when the grid goes down, the AC to the grid from the inverter is disconnected so it meets code, but yet it still powers the critical load panel when the sun shines? If I understand correctly, the SMA detects the grid failure and shuts down for a minimum of 5 minutes and then it looks for a sine wave coming in to detect when the grid is back and only turns back on if the grid is seen. So, how could you wire it in such a way that it still disconnects from the grid but also still provides power to the critical load panel if you don't have any battery backup power?

It's about the input and output of the battery-based inverter involved. There will be one set of terminals for the grid connection and another for the load connection. With the GTI on the load terminals it can continue to supply power for loads and charging without back-feeding the grid. But you have to have the right inverter. Using all SMA equipment solves this problem. The shut down, wait 5 minute, start up is for the standard GTI system; it checks every 5 minutes to see if there is proper grid power to feed to whenever it has sufficient input power to work with.

I don't understand how the XW 600 V MPPT would fit into the picture unless the batteries are on the DC-side and the solar inverters draw entirely from battery if the grid goes down? And then don't I still need something to block the inverter power from going to the grid? My understanding is that the SMA shuts down entirely if the grid goes down and doesn't turn back on unless it sees a pure sine wave coming in from the grid connection point, and then only after being shut down for 5 minutes.

That charge controller was specifically designed to take input from GT arrays in the even of a power outage and use it to charge batteries. Power goes out: simply switch the array output from the GTI to the XW 600. The controller's output is connected to the battery bank, as is an inverter-charger. The built-in charger keeps the batteries up while the grid is available, the high Voltage charge controller makes use of the existing array when the grid goes down.

egable · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

With your extensive assistance, I was able to have an intelligent conversation with my PV installer about my options, and I was able to get my point across on what exactly I'm looking for. They are going to provide me with a few different options for cost comparison, and then I can choose which one fits my budget. They said they usually use either Magnum or Outback battery inverter/chargers when AC-coupled, and they also did not recommend going with the Xantrex systems. Apparently they used them quite extensively for a while, and then Xantrex did a recall of all the units they had installed and they had to go back out to all the sites they installed them at and replace things. That must have sucked.

I also spoke with my electrician and had them revise their quote to include installing a critical loads panel, a surge arrestor on the main panel, and a large raceway between the two panels located either above or below the panels with some excess slack in the circuits for the wall outlets for the living room, bedrooms, server rack in my basement, attic space that we eventually plan on finishing, and the playroom. That way, if I decide to move any of those circuits over to the critical loads panel at some point in the future, I can do so without needing to extend the wires. The extra breaker box, extra 60 amp breaker for the solar hookup, raceway, and surge suppressor, plus additional labor for installing it all added about $1k to the electrical install costs. Is that reasonable? I figured it's probably about $500 for the extra parts, given the prices I saw online. Is there anything else I should include in this?

I will let you guys know what my new pricing options are for the solar PV install when they get back to me, and I will keep you all informed on how the whole process goes, just for documentation purposes to refer others to this thread.

Cariboocoot · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

Don't ask me about prices: I live in Canada. Nothing is reasonable here.

jaggedben · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

My two cents...

(Note: I have not read the entire thread thoroughly, so apologies if the points have already been raised. Also, sorry if my cutting and pasting your early comments and later comments is confusing.)

egable wrote: »

...[utility outages] do not happen frequently enough around here to make it cost effective to do a fully grid-interactive system which can fully utilize the solar capacity and run the whole house on batteries. However, a small amount of emergency power would be nice for my fridge and freezer.

egable wrote: »

...It also seems silly to limit myself to one or two 1.5 kW circuits when I have an entire array sitting on the roof

I think it's worth comparing your original statement to your more recent one, to make sure you're not losing perspective on what's silly. :cool:

egable wrote: »

... So, my first question, is it possible to install some device which allows me to combine the two 1,500 watt emergency outputs into a single 3,000 watt output? ...

No. The SPS on the SMA TL inverters is not a grid interactive output, and is not designed to work with any other sources in any way.

Second, is it possible to attach an APC UTS6H transfer switch (http://www.apcmedia.com/salestools/KBOK-74JRFQ/KBOK-74JRFQ_R3_EN.pdf) to the emergency output of an inverter and then use the transfer switch in combination with a battery backup to provide uninterrupted power to my fridge and freezer for an entire night until the sun starts shining the next day?

There's not much point in attached an automatic transfer switch to the SPS output because the SPS output requires manual activation. If you're doing things manually, might as well save money and use a manual transfer switch. Also, SMA may not warranty the SPS output if connected to anything other than an outlet, as described in the installation manual.

The real question is whether I need the battery backup at all.

I would suggest rephrasing that to...

"Do I want full battery backup so much that I'm willing to pay a lot of money for it? Or would I be content with the (very cheap by comparison) back up power provided by two SPS outlets, which I would only very occasionally need, and which could be used to charge an (also much cheaper) UPS?"

Since you have talked about rewiring the entire house anyway, may I suggest a compromise...

Have wiring for the SPS outlets installed to two locations in the house that would be very convenient for your critical loads. E.G., one right next to the fridge and one right next to the electronics you want to run. Then when you suffer the occasional outage, you can easily switch cords over and back.
Just a thought....

SkiDoo55 · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

Quote
"Apparently they used them quite extensively for a while, and then Xantrex did a recall of all the units they had installed and they had to go back out to all the sites they installed them at and replace things. That must have sucked. "

The recall was on the grid tied inverters, they got paid $300 for each installed inverter and it takes less than 30 minutes to install the kit that was supplied free from Schneider?

not saying Zantrex/Conext inverters are what it go with but just wanted to point out that the installer maid a "Lame Excuse" about them. I am sure he made good money off of the recall and should not have been any cost to his customers.

Cheers

vtmaps · March 2014

Re: SMA SPS Port to APC Transfer Switch Connected to Battery Backup

jaggedben wrote: »

My two cents...
<snip>
Just a thought....

Jaggedben gave you some good advice. I would also add techntrek's advice:

techntrek wrote: »

Usually around here people suggest using a good inverter-generator for backup power, even with a grid-tie system. I'll make that recommendation. Save the extra money for the inverter, batteries, charger, and whatever extra the "emergency power" Sunny Boys cost, and go with a normal grid-tie inverter. Then spend $1200-1500 on a Honda or Yamaha in the 2-3kw range. Keep 20 gallons of gas in the shed with Stabil and rotate it every 6 months into your car.

Techntrek's advice is particularly appropriate and cost effective if you really mean what you wrote in the first post:

...[utility outages] do not happen frequently enough around here to make it cost effective to do a fully grid-interactive system which can fully utilize the solar capacity and run the whole house on batteries.

--vtMaps

SMA SPS Port to APC Transfer Switch Connected to Battery Backup

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