SMA SPS Port to APC Transfer Switch Connected to Battery Backup

egable

I am in the process of getting a solar PV array installed on my roof. It will be a 10.08kW array which is grid tied. However, I am also interested in powering a small critical load in the event of a utility outage. They 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.

My fridge is the Samsung RF323TEDBSR:

http://www.samsung.com/us/appliances/refrigerators/RF323TEDBSR/AA

I am in the process of picking out a new freezer for my basement. The yellow label says 736 kWH per year. My freezer will be either 21.7 cubic foot freezer which uses roughly 420 kWH per year, or a 14.8 cubic foot freezer which uses roughly 360 kWH per year. The 14.8 cubic foot one is my top choice at the moment, and it is limited to 2A of current according to its labeling.

These are the two primary critical loads I want to run, as might have as much as $1.5k worth of food in both of them combined at any given time.

Any backup power system I put in place should add no more than $3k to the cost of the install, as I expect it to pay for itself in saved food spoilage costs with only two outages which are severe enough to cause food spoilage.

On top of the solar install, I am getting my house completely rewired and upgraded to a 200 Amp service panel. It is still old knob and tube style wiring (copper wire, but still almost 90 years old). Anyway, there will be an electrician putting in the house wiring and breaker boxes as a separate project from the solar PV install. So, since I am basically starting from scratch on the electrical system, I'd like to get things done right the first time and know what to have each installer put in place.

The solar install will include two Sunny Boy inverters which both provide the 1,500 watt emergency power option.

http://files.sma.de/dl/18726/EPSCompl-US-TB-en-12W.pdf

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? If there is such a device, what is it, and how much does it cost?

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?

Based on my calculations, it seems a 3.2 kWH UPS would provide sufficient battery power to run both the fridge and freezer for a day, unless I did my math wrong. I would expect the solar array to recharge the UPS during the day via the 1,500 watt emergency power output.

If I can get away with buying just one APC transfer switch and one UPS in the 1.8 kWH - 3 kWH range, then I think this can be done inside my budget of $3k.

Third, if there is no device which can combine the output of both emergency power outputs, is there a way to connect two UPS to a shared battery bank and to both outputs so that both outputs can charge the battery bank and drive a single breaker box?

Or, finally, is there a better way to do what I want in the $3k budget which I am simply overlooking? The solar PV installer said it would be $10k to do what I wanted (cost of different inverters, batteries, etc).

On top of the fridge and freezer, it would be nice to be able to flip breakers on and off for wall outlets in the living room, playroom, and bedrooms, so we can run our entertainment system (about 150 watts max when everything is in use) or our computers and phone and tablet chargers, or our LED ceiling lights.

Thanks in advance for any input anyone can provide on this.

Cariboocoot

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

Welcome to the forum.

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? If there is such a device, what is it, and how much does it cost?

I don't think so. The two outputs would not be in phase sync. On the other hand one would not expect to need a 3kW 120 Volt output anywhere; it isn't done. But nor can you stack them to provide 240 VAC do to the lack of syn of the sine wave.

Second, is it possible to attach an APC UTS6H transfer switch 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?

It is certainly possible to install a transfer switch that would allow the 'frige to be run either from the AC mains or the SMA 'emergency' outlet. There's no battery in the SMA. But it has been suggested before that the outlet on it could be successfully use to power an inverter-charger with battery which would maximize the output from the GTI and provide battery power when the sun goes down.

The issue here is whether or not you get enough power through the one outlet during the day to both run the equipment and recharge the battery for overnight use. If you can count on 4 hours with 1500 Watts available that's 6kW hours which is plenty of power. During that time a refrigerator may use a mere 200 Watt hours or even less, meaning the rest could be applied to charging batteries and/or running other equipment. In theory 50 Amps to a 24 Volt system would not be unreasonable expectation, but the current would be tapered as the battery charges. This should not present a problem, though. Rather like running a small inverter-gen for 4 hours to store up power for night (an often recommended method for campers).

Based on my calculations, it seems a 3.2 kW UPS would provide sufficient battery power to run both the fridge and freezer for a day, unless I did my math wrong. I would expect the solar array to recharge the UPS during the day via the 1,500 emergency power output.

Providing it is capable of meeting the large start-up demands of the compressors, 3.2kW hours would be sufficient for a 'frige and freezer for one day.

Third, if there is no device which can combine the output of both emergency power outputs, is there a way to connect two UPS to a shared battery bank and to both outputs so that both outputs can charge the battery bank and drive a single breaker box?

You'd have to convert each output to DC first with its own charging circuit, then combine them to the common battery bank. I'm not sure you'd need the full output of both to achieve the goal, though. And of course you could always have two entirely independent systems.

Or, finally, is there a better way to do what I want in the $3k budget which I am simply overlooking? The solar PV installer said it would be $10k to do what I wanted (cost of different inverters, batteries, etc).

$10k over and above the SMA GT install? Ridiculous. Some GC2's and an inverter-charger wouldn't even cost half that, even in Canada. I'd say you're looking at <$800 for batteries and about $2000 for a really good 24 Volt inverter-charger plus some wiring and hardware.

On top of the fridge and freezer, it would be nice to be able to flip breakers on and off for wall outlets in the living room, playroom, and bedrooms, so we can run our entertainment system (about 150 watts max when everything is in use) or our computers and phone and tablet chargers, or our LED ceiling lights.

Since you're starting from scratch, put in a sub-panel for critical loads. Then you can power the whole thing from either grid or inverter, keep the batteries charged from the grid when it's up and the emergency outlet when it's down.

egable

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

Cariboocoot wrote: »

Welcome to the forum.
It is certainly possible to install a transfer switch that would allow the 'frige to be run either from the AC mains or the SMA 'emergency' outlet. There's no battery in the SMA. But it has been suggested before that the outlet on it could be successfully use to power an inverter-charger with battery which would maximize the output from the GTI and provide battery power when the sun goes down.

The issue here is whether or not you get enough power through the one outlet during the day to both run the equipment and recharge the battery for overnight use. If you can count on 4 hours with 1500 Watts available that's 6kW hours which is plenty of power. During that time a refrigerator may use a mere 200 Watt hours or even less, meaning the rest could be applied to charging batteries and/or running other equipment. In theory 50 Amps to a 24 Volt system would not be unreasonable expectation, but the current would be tapered as the battery charges. This should not present a problem, though. Rather like running a small inverter-gen for 4 hours to store up power for night (an often recommended method for campers).

You'd have to convert each output to DC first with its own charging circuit, then combine them to the common battery bank. I'm not sure you'd need the full output of both to achieve the goal, though. And of course you could always have two entirely independent systems.

I was already planning on putting in a critical load sub panel. The question is whether I need one or two and either one or two of those expensive transfer switches... The inverter charger looks like it might be the way to go, but do I need two inverter chargers to use the output from both Sunny Boy units, or are you saying that I can convert the AC from each to DC with some lower cost unit and combine the DC and then send that to a single DC charger?

Ideally, I would love to be able to use the full 3,000 watts so we can run not only the fridge and freezer, but also lights, phones, computers, network, and TV.

My problem with understanding how to do this is that I am not at all familiar with inverters, inverter chargers, AC -> DC conversion, combining, etc. I can wire an outlet or a light, and I know I can use an inverter to convert the DC from the car to AC to power things and a power supply in my computer to convert AC to DC. As for commercially available units for the type of wattage and wiring I'm dealing with for solar, I am pretty clueless.

So, going with what I know, can I buy two power supplies of some sort which convert the AC to DC and then go through a combiner and into a DC battery charger which charges a bank of batteries which is connected to an inverter which goes to an automatic transfer switch to switch the load from grid to batteries? And then how do the batteries charge when connected to the grid? Is there an inverter charger which accepts three AC inputs for charging batteries (grid + 2 others for the Sunny Boy units) which also has the automatic transfer switch, DC combiners, and battery charging unit built in?

Cariboocoot

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

egable wrote: »

I was already planning on putting in a critical load sub panel. The question is whether I need one or two and either one or two of those expensive transfer switches... The inverter charger looks like it might be the way to go, but do I need two inverter chargers to use the output from both Sunny Boy units, or are you saying that I can convert the AC from each to DC with some lower cost unit and combine the DC and then send that to a single DC charger?

To utilize two you would either have to have both run a battery charger or (and this is better) use one to power the AC IN on an inverter-charger and have the other power a stand-alone battery charger.

Ideally, I would love to be able to use the full 3,000 watts so we can run not only the fridge and freezer, but also lights, phones, computers, network, and TV.

Pick a unit like the Outback VFX3524: 3.5 kW of output power (about two full household outlets of 15 Amps @ 120 VAC), built-in transfer switch so it will start inverting the moment power goes down (even if you're not there). One of the SMA's feeding the batteries through a charger, the other on a transfer switch to change the AC IN from grid to emergency outlet. I think the SMA outlets have to be manually started every time. That would be a bit of a drawback.

My problem with understanding how to do this is that I am not at all familiar with inverters, inverter chargers, AC -> DC conversion, combining, etc. I can wire an outlet or a light, and I know I can use an inverter to convert the DC from the car to AC to power things and a power supply in my computer to convert AC to DC. As for commercially available units for the type of wattage and wiring I'm dealing with for solar, I am pretty clueless.

Well there's really only two types of solar: supplying DC current to charge batteries (off-grid or grid-tie hybrid) or supplying AC current to supplement the grid (standard grid-tie).
Inverters either take the DC from a battery bank and use it to supply a steady VAC for power, or they take the DC current from panels and convert it to AC current.
There are variations within the inverter realm, but it pretty much boils down to input Voltage, output power, and what extra features they have.

So, going with what I know, can I buy two power supplies of some sort which convert the AC to DC and then go through a combiner and into a DC battery charger which charges a bank of batteries which is connected to an inverter which goes to an automatic transfer switch to switch the load from grid to batteries? And then how do the batteries charge when connected to the grid? Is there an inverter charger which accepts three AC inputs for charging batteries (grid + 2 others for the Sunny Boy units) which also has the automatic transfer switch, DC combiners, and battery charging unit built in?

Yes except you can make use of the built-in transfer switch and battery charger of something like a VFX, and then use the other outlet on an Iota battery charger to the same bank. Might have to do some thinking about the AC IN side in terms of manual or automatic transfer for that.

The inverter I'm talking about: http://www.solar-electric.com/outback-power-pure-sinewave-inverter-vfx3524.html
An Iota battery charger: http://www.solar-electric.com/ioten25amp24.html

vtmaps

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

Cariboocoot wrote: »

Yes except you can make use of the built-in transfer switch and battery charger of something like a VFX, and then use the other outlet on an Iota battery charger to the same bank. Might have to do some thinking about the AC IN side in terms of manual or automatic transfer for that.

The inverter I'm talking about: http://www.solar-electric.com/outback-power-pure-sinewave-inverter-vfx3524.html
An Iota battery charger: http://www.solar-electric.com/ioten25amp24.html

I think it would be simpler (but more expensive) to have two stand-alone battery chargers and a stand-alone inverter. That way you can draw whatever your batteries and inverter can handle. If you use an inverter/charger your AC load cannot exceed the output of just the one sunnyboy that is powering the inverter/charger.

I would suggest you find a power factor corrected battery charger... not the Iota. A 1000 watt Iota will use all the capacity of the 1500 watt outlet.

--vtMaps

Cariboocoot

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

vtmaps wrote: »

I think it would be simpler (but more expensive) to have two stand-alone battery chargers and a stand-alone inverter. That way you can draw whatever your batteries and inverter can handle. If you use an inverter/charger your AC load cannot exceed the output of just the one sunnyboy that is powering the inverter/charger.

I would suggest you find a power factor corrected battery charger... not the Iota. A 1000 watt Iota will use all the capacity of the 1500 watt outlet.

--vtMaps

Except that you would have no automatic transfer of critical loads that way unless you put in an auto transfer switch.

The inverter charger at 3.5 kW could in fact power more than the two 1.5 kW SMA outlets combined, if need be. Set the limit on the AC IN and it will drop it if the load demand exceeds that just as it would with a generator. Or use the GVFX and utilize gen support function to supplement the 1500 Watts of the SMA with the 3500 Watts of the inverter if necessary.

vtmaps

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

egable wrote: »

I was already planning on putting in a critical load sub panel. The question is whether I need one or two and either one or two of those expensive transfer switches.

I'm not too familiar with the sunny boys, but I recall reading that the 1500 watt emergency outlet does NOT automatically power up when the grid is out... you need to manually engage it. Also, I'm not sure you can hardwire the emergency outlet to a transfer switch or critical loads subpanel.

Another thing you should check into is neutral-ground bonding. I have no idea where the bond is in your sunny boy system. If you try to wire a battery based inverter into your critical loads panel, where will that inverter's output have its bond?

--vtMaps

Cariboocoot

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

vtmaps wrote: »

I'm not too familiar with the sunny boys, but I recall reading that the 1500 watt emergency outlet does NOT automatically power up when the grid is out... you need to manually engage it. Also, I'm not sure you can hardwire the emergency outlet to a transfer switch or critical loads subpanel.

I'm wondering about this too, as I believe the first reports were ambiguous as to how the SMA outlet worked. I think you have to start it when the power goes out, but then it stays working.

Which leads me to suggest a hybrid of vtMaps suggestion and mine: the inverter-gen with AC IN connected to the mains, but both emergency outlets powering chargers connected to the batteries. With that, when the power is up the grid will keep the batteries charged. Power goes off the inverter will take over the critical loads instantly. You turn on SMA outlets to keep batteries charged.

Another thing you should check into is neutral-ground bonding. I have no idea where the bond is in your sunny boy system. If you try to wire a battery based inverter into your critical loads panel, where will that inverter's output have its bond?

--vtMaps

The N-G bond should be in the main service panel. The SMA system being grid-tied would not have a separate one, now would an FX inverter. Since neutrals and grounds are common throughout, there should be no need for any sort of bond switching.

egable

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

vtmaps wrote: »

I think it would be simpler (but more expensive) to have two stand-alone battery chargers and a stand-alone inverter. That way you can draw whatever your batteries and inverter can handle. If you use an inverter/charger your AC load cannot exceed the output of just the one sunnyboy that is powering the inverter/charger.

I would suggest you find a power factor corrected battery charger... not the Iota. A 1000 watt Iota will use all the capacity of the 1500 watt outlet.

--vtMaps

Wouldn't it make more sense to have the PV installer install something like the Sunny Island to charge the batteries? I assume that is what the Sunny Island is for? I have been finding it rather difficult to find anyone giving a good description of what my different equipment options are and what each piece of equipment does. I cannot seem to find any good, plainly written documentation describing the difference between a Sunny Boy and a Sunny Island in terms of what functions they provide.

If I interpreted what I read and the videos I watched correctly, then it seems like the Sunny Island is the ideal piece of equipment. It sounds like it is basically a Sunny Boy but with the added ability to charge a battery bank and to draw on the battery bank to deliver power to the house. It also sounds like it can use a Sunny Boy as a slave and direct it on what to do with its power output. If that is the case, then it seems like all I really need is one Sunny Island and one Sunny Boy instead of two Sunny Boys and a small battery bank. It sounds like the smallest battery bank the Sunny Island will take is a 100AH bank. But that seems like almost the ideal size for my needs. So, the incremental increase in equipment cost for having the installer switch one of the Sunny Boy units to a Sunny Island and install a 100AH battery bank should be fairly small, shouldn't it? At least, it should be less than $3k for that, wouldn't it? Or am I once again just missing something?

Cariboocoot

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

The Sunny Island is an off-grid inverter, but one that can AC couple to the Sunny Boy in perfect harmony. It can be an excellent choice for back-up power, however it will not make use of the emergency outlets we were discussing earlier; it is entirely separate from that.

It does not sell back to the grid the way the Sunny Boy does either, nor does it have a PV input (when used alone the PV connects to the batteries through a charge controller). As such you would not have as much grid-tie PV with one Sunny Boy and one Sunny Island. They also are a tad pricey at just over $4,000 for the 4.5kW version.

egable

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

Cariboocoot wrote: »

The Sunny Island is an off-grid inverter, but one that can AC couple to the Sunny Boy in perfect harmony. It can be an excellent choice for back-up power, however it will not make use of the emergency outlets we were discussing earlier; it is entirely separate from that.

It does not sell back to the grid the way the Sunny Boy does either, nor does it have a PV input (when used alone the PV connects to the batteries through a charge controller). As such you would not have as much grid-tie PV with one Sunny Boy and one Sunny Island. They also are a tad pricey at just over $4,000 for the 4.5kW version.

So, I would basically need the two Sunny Boys and a Sunny Island in order to charge the batteries and feed back to the grid?

Cariboocoot

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

egable wrote: »

So, I would basically need the two Sunny Boys and a Sunny Island in order to charge the batteries and feed back to the grid?

Yes. As you can see that makes the system more expensive. That's one of the reasons they came up with those outlets; no battery needed for power during daylight.

vtmaps

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

Cariboocoot wrote: »

The N-G bond should be in the main service panel. The SMA system being grid-tied would not have a separate one, now would an FX inverter. Since neutrals and grounds are common throughout, there should be no need for any sort of bond switching.

But he wants to wire the battery based inverter to a critical loads subpanel. The subpanel does not have a neutral-ground bond.

--vtMaps

Cariboocoot

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

vtmaps wrote: »

But he wants to wire the battery based inverter to a critical loads subpanel. The subpanel does not have a neutral-ground bond.

--vtMaps

It does not need one because the neutral and ground are not switched from the main panel. Therefor the bond at that point is still active.

vtmaps

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

Cariboocoot wrote: »

It does not need one because the neutral and ground are not switched from the main panel. Therefor the bond at that point is still active.

But if he transfers the subpanel from the main panel to the battery based inverter, won't the subpanel will lose its bond? --vtMaps

Cariboocoot

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

vtmaps wrote: »

But if he transfers the subpanel from the main panel to the battery based inverter, won't the subpanel will lose its bond? --vtMaps

No, because the only switching is done on the hot wire; neutral and ground are carried through the inverter.

vtmaps

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

Cariboocoot wrote: »

No, because the only switching is done on the hot wire; neutral and ground are carried through the inverter.

OK.. I was assuming that it was being used as a stand-alone battery based inverter with no AC input. --vtMaps

bill von novak

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

vtmaps wrote: »

I'm not too familiar with the sunny boys, but I recall reading that the 1500 watt emergency outlet does NOT automatically power up when the grid is out... you need to manually engage it.

Yep. There's a switch you need to turn on (wired separately.) If you lose power temporarily (clouds) it will try to restore emergency power after the sun returns, but after the sun sets and rises the next day the switch must be reset to continue to provide emergency power.

Also, I'm not sure you can hardwire the emergency outlet to a transfer switch or critical loads subpanel.

The "emergency outlet" is just screw terminals so it has to be wired to something to be able to use it.

Another thing you should check into is neutral-ground bonding. I have no idea where the bond is in your sunny boy system. If you try to wire a battery based inverter into your critical loads panel, where will that inverter's output have its bond?

Good question. The wiring diagram suggests that the ground and neutral remain independent during SPS operation but it doesn't say so explicitly.

egable

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

vtmaps wrote: »

OK.. I was assuming that it was being used as a stand-alone battery based inverter with no AC input. --vtMaps

Cariboocoot wrote: »

It does not need one because the neutral and ground are not switched from the main panel. Therefor the bond at that point is still active.

Ground bonds are not really an issue anyway -- remember I am having the whole house rewired on top of doing the solar PV install, so I can ask them to wire it whatever way I need it.

I did some Googling and found the Xantrex Hybrid Inverter/Charger system by Scheider Electric. I know they make the Square D QO Load Centers and breakers which I trust more than any competing brands, so I would trust them with an inverter, as well. It looks like maybe I should ask the solar PV installer to install two of these Xantrex systems. Their documentation seems to plainly state that it can take DC in from the PV array and convert it to AC, deliver to a battery for charging or pull from a battery in the event the grid goes down, and deliver AC to the grid or throw an automatic transfer switch (built in) to deliver AC to the house directly. That seems like exactly what I am looking for. Did I read it correctly? It almost seems too good to be true. Anyone have any experience with these?

On solarhome.org, I priced out a Xantrex system which would do 10.5 kW of inverter capacity with battery charging along with 110AH @ 48V of batteries for about $7,200. This would cost about $3k more than the dual Sunny Boy setup, but would give me full use of the 10 kW array during the day and enough battery capacity to run the fridge and freezer all day long if needed. In fact, during the day, I could even run AC or do some cooking on top of watching TV or using computers. There seem to be other benefits, as well. It looks like these things are modular to the point that even the inverters can have the faceplate removed and you can swap out circuit boards inside. This means I wouldn't have to replace an entire inverter if something failed. Having the battery backup power and solar would also probably allow me to stop buying UPS systems for my computers and DVRs. Eliminating that cost would allow me to afford new batteries for the solar PV system every 5 years or so (or if it is longer than that, would save me money). It would also eliminate any food spoilage costs, and the cost savings on repairs would probably end up paying for the difference over a 20 year period.

Thoughts?

Cariboocoot

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

Couple of things.

First would be that if you use a hybrid inverter such as the XW (4kW or 6kW) or Outback's Radian (which is 8kW) you need 100 Amp hours of battery per kw of inverter. This gets confused often. That means an XW needs six times the amount of battery you were planning.

If you read through the forum here about XW6048 inverters you may change your mind entirely about having one. They are known to be 'buggy' and not have the best customer support. You need an expensive 'dongle' to upgrade the firmware.

Now look at it in a power outage situation: 600 Amp hours @ 48 Volts (for one XW6048 ) would supply about 7kW hours @ 25% DOD. Will you need that much power? Knowing how much you'll need is critical to making a good decision here. You should get a Kill-A-Watt meter and measure your power usage on what you want to keep running and see what it comes out to.

Putting your money into a large battery bank that is going to go bad whether or not it is used just to accommodate occasional emergency power needs is not a wise expenditure. Especially if it comes at the cost of GT capacity that could do more for you in terms of offsetting the electric bill.

egable

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

Cariboocoot wrote: »

Couple of things.

First would be that if you use a hybrid inverter such as the XW (4kW or 6kW) or Outback's Radian (which is 8kW) you need 100 Amp hours of battery per kw of inverter. This gets confused often. That means an XW needs six times the amount of battery you were planning.

Why do you need 100 amp hours per kw of inverter? What dictates that?

Cariboocoot

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

egable wrote: »

Why do you need 100 amp hours per kw of inverter? What dictates that?

Filtering the AC ripple current.

egable

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

OK, after going over everything you mentioned and taking prices into consideration, what if I did this:

1) Connect the main output of the Sunny Boy inverters to the critical loads panel which also connects to a battery inverter/charger with a small battery bank attached to it.
2) Wire the battery inverter/charger to an automatic transfer switch and then to the main breaker box where the grid is connected.

Basically, this wiring diagram:

http://www.aeesolar.com/sites/default/files/graph-ac-coupling.jpg

Source: http://www.aeesolar.com/grid-tied-solar-systems-with-backup-power

So, will this outback inverter you mentioned work in this type of setup? Will this setup provide the full capabilities of the solar array during the day? Will it automatically shut off power to the main breaker box so it isn't sending electricity out to the grid? How much of a battery bank do I have to buy to make this work? Is there anything else needed other than the inverter/charger, automatic transfer switch, batteries and DC inverter breaker required? What batteries do you recommend I get? Which automatic transfer switch should I get?

Cariboocoot

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

egable wrote: »

OK, after going over everything you mentioned and taking prices into consideration, what if I did this:

1) Connect the main output of the Sunny Boy inverters to the critical loads panel which also connects to a battery inverter/charger with a small battery bank attached to it.
2) Wire the battery inverter/charger to an automatic transfer switch and then to the main breaker box where the grid is connected.

Basically, this wiring diagram:

http://www.aeesolar.com/sites/default/files/graph-ac-coupling.jpg

Source: http://www.aeesolar.com/grid-tied-solar-systems-with-backup-power

So, will this outback inverter you mentioned work in this type of setup? Will this setup provide the full capabilities of the solar array during the day? Will it automatically shut off power to the main breaker box so it isn't sending electricity out to the grid? How much of a battery bank do I have to buy to make this work? Is there anything else needed other than the inverter/charger, automatic transfer switch, batteries and DC inverter breaker required? What batteries do you recommend I get? Which automatic transfer switch should I get?

Not all inverters work with AC coupling. The Sunny Island will (it's designed to) but the Outback FX series will not; it has no way to regulate the power input from the GTI.

Again you need to figure out how much back-up power you require before choosing a plan. Ultimately that dictates the minimum battery capacity. Otherwise you will either have not enough or spend too much to have more power than you'll use.

bill von novak

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

egable wrote: »

1) Connect the main output of the Sunny Boy inverters to the critical loads panel which also connects to a battery inverter/charger with a small battery bank attached to it.
2) Wire the battery inverter/charger to an automatic transfer switch and then to the main breaker box where the grid is connected.

Yes, this is AC coupling. Here are the caveats:

1) Battery inverter must be bidirectional. (Trace SW series, Outback GTFX series etc.)
2) Grid tie inverter(s) must be rated lower than battery inverter.
3) Battery bank must be able to handle the power from the GT inverter(s).
4) You need a relay to disconnect the GT inverters when battery voltage is high. If you have more than one GT inverter you may need more than one relay (with associated controls.)

Note - in this case you do not need a transfer switch. It can always be connected to the critical loads panel.

egable

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

Cariboocoot wrote: »

Not all inverters work with AC coupling. The Sunny Island will (it's designed to) but the Outback FX series will not; it has no way to regulate the power input from the GTI.

Again you need to figure out how much back-up power you require before choosing a plan. Ultimately that dictates the minimum battery capacity. Otherwise you will either have not enough or spend too much to have more power than you'll use.

The fridge and freezer use roughly 1200 kWH per year, combined. So, they should average about 3.3 kWH per day. I only need them to run on battery for 18 hours, not 24, assuming the whole array is used to recharge the batteries. On a 10.08 kW array, I am assuming that they will be able to fully power the load and charge the batteries very early in the morning and quite late into the evening. Perhaps I only need 12 - 16 hours of battery power, but I will assume I need 18. So, that means I need about 2.5 kWH of usable battery capacity or 3.125 kWH of total capacity assuming I don't discharge below 20%. At 48 volts, that means I need 4x 65 AH 12V batteries, right? I see 110 AH 12V batteries for about $200 each. Based on the pricing I have been looking at, that is roughly $1k worth of batteries for 110 AH @ 48V or 5.28 kWH of backup power. That is far more than I need for just my critical load, so I would have some extra built in for running my LED lights, recharging phones, using our laptops, or watching a little TV.

So, assuming I do a 110 AH, 48V battery bank, where do I go from here on selecting an inverter/charger and other components, assuming I want the Sunny Boy units to output to the critical load panel?

michaelc

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

You need an additional piece of equipment to hook to one of your sunnyboys called an AC coupler such as the magnum units. I am going to do this in the future with my SB5000. Here is a block diagram. Mike


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Blackcherry04

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

michaelc wrote: »

You need an additional piece of equipment to hook to one of your sunnyboys called an AC coupler such as the magnum units. I am going to do this in the future with my SB5000. Here is a block diagram. Mike

There is no piece of equipment called a " AC Coupler " in this system . AC Coupling is a concept where the output of a Grid Tie Inverter is used to energize the AC buss that a bi directional Inverter is attached to supply the reference voltage, the current is back driven through the bd inverter and that charges a set of batteries. The back driven DC current is hard to control and has ripples, that is why you see the load controller and load on the batteries. While it does work, there are many pit falls trying to make it successful. At present your much better off with a hybrid Inverter rather than a two inverter system IMO. Who knows what the future may hold with equipment development.
.

michaelc

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

OK it was late took pen to paper and I meant to say ac coupling is a method of using your array to power critical loads when your grid tied and it goes down, The Magnum series have so many different options it is worth a look at. I have been wanting to do this for a long time but ran out of money. The batteries are the PITA not the converters. The pit fall is without buying to many additional things you can only dedicate one of your two (I have two SB inverters also) into powering your critical loads while staying isolated while the grid is down. I don't see anywhere in my instruction where the OP has to keep flipping his SPS switch except to restore grid operation when it come back on. Clouds will just reduce output, at night also but come back on at dawn. But researching did also convince me that the Outback Radian would do the job of powering critical loads nicely with a 10KW array and also use small gen Honda or Yamaha and the radian will start the generator when the grid goes down. But the Radian is expensive and you still need batteries, That was one of the first questions I asked on this forum and someone was nice enough to make the AWESOME answer a sticky at the top of the off grid thread (can you implement a Outback Radian into your solar project without batteries). The Radian is a nice unit though with many options from a good company

egable

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

Well, at the moment I am starting to think the best bet might be to wire it using the new diagram but with an automatic transfer switch or some other automatic disconnect set up between the inverter and the grid such that when the grid goes down, the inverter still detects it and shuts down, but then comes back on after the 5 minute delay, except only powering the critical load panel. I'm just not sure how to do that, exactly. It seems like I might still need some sort of battery inverter and battery to generate a sine wave to the SMA inverter so it thinks the grid is back, but somehow leave the disconnect tripped so the solar inverter's power doesn't reach the grid. Then, at some future point I could go through the expense of doing an "upgrade" to add battery backup to the system or a gas generator.

Thoughts?

Cariboocoot

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

egable wrote: »

Well, at the moment I am starting to think the best bet might be to wire it using the new diagram but with an automatic transfer switch or some other automatic disconnect set up between the inverter and the grid such that when the grid goes down, the inverter still detects it and shuts down, but then comes back on after the 5 minute delay, except only powering the critical load panel. I'm just not sure how to do that, exactly. It seems like I might still need some sort of battery inverter and battery to generate a sine wave to the SMA inverter so it thinks the grid is back, but somehow leave the disconnect tripped so the solar inverter's power doesn't reach the grid. Then, at some future point I could go through the expense of doing an "upgrade" to add battery backup to the system or a gas generator.

Thoughts?

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.