Grid tied solar system.

[posplayr]

What if the grid goes down when nobody is home, or everyone is asleep? Without an automatic shut-off on the main breaker, you'll be feeding power into the grid, creating a safety hazard.

If you are referencing my diagram, IN GRID TIE mode: the transfer switch leaves both the UPS output and Generator output disconnected. The only thing the contingency is doing in GRID TIE mode is maintaining standby UPS battery power; with no discharging they will last a long time.

If the grid goes down, then the Solar inverter will shut down as required. If grid power returns before any contingency operation are invoked then power is restored and the solar inverter will simply resume operation.

The first step to invoking "CONTINGENCY MODE" is to shut off the main breaker. If you want you could use some alligator clips to attach a 120V buzzer to the grid side to let you know if power is coming back or you just look around the neighborhood to see if any other lights are on.

I don't think there is a way to screw up after that other than perhaps deep cycling your UPS batteries too far. You could get a Automatic generator transfer switch if you wanted that automatic.

The AC-DC of the double conversion prevents battery overcharging and DC-AC output should supply whatever surge requirements you plan to try and drive in contingency mode. I put 80A breakers going into the UPS since I did not want the Sunny boy to kick off if it was trying to push too much current into the UPS but it might be irrelevant.

For the cost differential of two SB5KTL SPS modules, SPS plugs and two 2.2K UPS's, the single SB10KTL and UPS6K provides full unlimited solar at close to a wash in initial cost outlay. Again the UPS6K handle surge loads or contingency overnight loads so it doe not have to be sized to full size of the SB10KTL.

[bcroe]

This is the PVwatts output. Based on a 50% probability I get 12 and 10.5 hours of
3K watt SPS daily for June and July respectively. We have had relatively cloudy monsoonal weather for most of July.

Your plots then are based on using a tracker? I can't wait to see your 10 KW tracker, please send pictures.
However a tracker won't help you compensate for clouds. Extra panels facing east and west will, as clouds
disperse the sunlight. Bruce Roe

[posplayr]

Your plots then are based on using a tracker? I can't wait to see your 10 KW tracker, please send pictures.
However a tracker won't help you compensate for clouds. Extra panels facing east and west will, as clouds
disperse the sunlight. Bruce Roe

Yes a two axis tracker (still under development ); I have not derated it for 45 degree tilt limitations but it should be mostly there with only reductions of the skirts. Spacing will be unobstructed and no shading until 45deg sun angle. The plan is Qty 6 arrays of 2x3 panels each (6 total) on a 30"x45" shop that is 15" high with flat roof. Zoning limits max height above the roof to 8". It is a new invention, and I'm told by experts that it will be operational when pigs fly, but I have gotten some other more useful information here than that.

Arizona is clear low humidity most all year except for the monsoon season which is now. Humidity climbs to about 30-40%. Specular solar is most prevalent and provides for the the high harvesting yields.

[sensij]

The AC-DC of the double conversion prevents battery overcharging and DC-AC output should supply whatever surge requirements you plan to try and drive in contingency mode. I put 80A breakers going into the UPS since I did not want the Sunny boy to kick off if it was trying to push too much current into the UPS but it might be irrelevant.

OK, if you want to have a chance of getting this to be code compliant (you seem to care about that with your tilt project), you're going to need to show that there is absolutely no way you can backfeed the grid. Simply saying "i'll remember to shut off the main breaker first" won't cut it... you'll need to plan for interlocked breakers or some other fool proof isolation technique.

The 2nd problem is that the novelty of your system revolves around the idea that you are using the UPS to "trick" the grid tie inverter into thinking the grid is present. That may work, but only as long as you have loads available to consume every single watt of power generated by the inverter (and no more). If you want to use the PV system to recharge the UPS, you'll have to deal with the fact that the power required to recharge the battery is not constant over time, so your other loads need to be variable. If those other loads are too high, the battery won't get recharged. If those loads is too low, the battery won't be able to take all the power, the system voltage will rise and the inverter will trip out, perhaps catastrophically if not managed well. As I see it, it may work, but you'll need some high quality monitoring and load shunting equipment to make sure you don't kill your inverter or your batteries.

If you revert back to just using the SPS to maintain the UPS, I think you'll have a system much more likely to succeed, which has already been proven to work. Really, I don't see how the SPS is useful except for recharging a critical loads UPS.

[posplayr]

OK, if you want to have a chance of getting this to be code compliant (you seem to care about that with your tilt project), you're going to need to show that there is absolutely no way you can backfeed the grid. Simply saying "i'll remember to shut off the main breaker first" won't cut it... you'll need to plan for interlocked breakers or some other fool proof isolation technique.

Here is a install diagram for a Generac 6376 Generator Transfer switch. It is transferring Generator power behind a back driven breaker, not at the main 200A supply. Electrically, driving the transfer switch using the UPS as an alternate to the gen set is the same.

Procedurally to electrocute a lineman with the gen set, you would have to flip the transfer switch switch for the generator and start it up without pulling the main. Is that possible? Yes. Are you couplable of wanton disregard for life? Probably.

In the case of the UPS you would just need to flip the transfer switch on the UPS. Is that possible? Yes probably much more likely. Are you coupable of wanton disregard for life? Possibly but less likely so less likely to be approved.

Point is there is a double safety on the generator setup that would not exist in the UPS as presented, unless some other procedural safeguard was invoked.

Leave the UPS off and or disconnected. If the UPS is not even connected is there a sufficiently reduced threat? The procedure for startup of the contingency cycle would then be to turn off the main, start the generators and plug in the UPS's . From then on you cycle the transfer switch as required and the main remains open. IS there more of a threat now if I'm running on generator v.s. UPS and I throw the main back to connect to the grid?

If that would not fly you could pre wire everything with outlets and the UPS would not even be part of the house wiring.

The 2nd problem is that the novelty of your system revolves around the idea that you are using the UPS to "trick" the grid tie inverter into thinking the grid is present. That may work, but only as long as you have loads available to consume every single watt of power generated by the inverter (and no more). If you want to use the PV system to recharge the UPS, you'll have to deal with the fact that the power required to recharge the battery is not constant over time, so your other loads need to be variable. If those other loads are too high, the battery won't get recharged. If those loads is too low, the battery won't be able to take all the power, the system voltage will rise and the inverter will trip out, perhaps catastrophically if not managed well. As I see it, it may work, but you'll need some high quality monitoring and load shunting equipment to make sure you don't kill your inverter or your batteries.

I would have thought that a smart Solar Inverter would not try to push all available power thereby exceeding overvoltage limits. With the grid, the GT inverter can't lift the line voltage and so it (the grid) will absorb anything the GTI can offer and stay within the grids voltage limits. In island mode, the AC line voltage will rise sharply if the loads can not absorb the GTI output, so the GTI should (i.e. has to) regulate the power delivered to match the load else the voltage would run away. A shunt load regulator would work, but there is already a much more efficient series regulation device in the GTI.

What is SPS but a regulated output to meet whatever demand is applied?

This really is the crux of the issue. To make this work, the UPS only have to supply surge current for variations in line voltage (due to surge) and it does not have to absorb differential power between the solar output capability and the variable load demand. The UPS will only pull power as required to restore the charge on the LA batteries(that depleted in startup surge). The GTI manages the line load.

I have seen other GTI fakeouts posted but ones that use a separate set of panels and inverter to generate the reference AC signal. What distinguishes this method is that it does that with a dual conversion UPS that provides surge capacity and utilizes the same panels at full rated power. No additional panels required. In Normal operation the UPS is not even connected or might only be connected for battery maintenance.

If you revert back to just using the SPS to maintain the UPS, I think you'll have a system much more likely to succeed, which has already been proven to work. Really, I don't see how the SPS is useful except for recharging a critical loads UPS.

I have posted both systems for comment; there is no need to revert.

[sensij]

If that would not fly you could pre wire everything with outlets and the UPS would not even be part of the house wiring.

You need an interlock on the breaker connecting the generator circuit into the main. Google "generator interlock kit" to see how it is done. You cannot satisfy NEC "procedurally", even with "double safety".

I would have thought that a smart Solar Inverter would not try to push all available power thereby exceeding overvoltage limits.

It is called a hybrid inverter. See Xantrex, Outback, Conext, etc. Expect to pay a few X more for it than for a dumb SMA grid tie inverter of equal power. You'll also need some kind of small battery for it to function properly, although it doesn't need much capacity if the rest of your contingency plan meets your needs.

I have posted both systems for comment; there is no need to revert.

The 10kW single inverter version is DOA... the only system worth discussing is the pair of 5 kW inverters in which you are getting some power from each SPS (1500 W max) in a way that does not require them to have a fixed phase difference, but otherwise running a genset and getting some surge support from the UPS. Again, this system is viable, in my opinion, if you believe that having this contingency plan is worth the money you are putting into it. I have no knowledge of how to ensure that the UPS system will be functional when you need it, but I would expect some sort of periodic test is necessary to make sure the battery capacity has not degraded.

[posplayr]

You need an interlock on the breaker connecting the generator circuit into the main. Google "generator interlock kit" to see how it is done. You cannot satisfy NEC "procedurally", even with "double safety".

So you are saying that installation manual would not satisfy NEC correct?

It is called a hybrid inverter. See Xantrex, Outback, Conext, etc. Expect to pay a few X more for it than for a dumb SMA grid tie inverter of equal power. You'll also need some kind of small battery for it to function properly, although it doesn't need much capacity if the rest of your contingency plan meets your needs.



OK, so the 10kW single inverter version is DOA...

OK I'll take you word on it but find it hard to believe that the GTI has no safety feature to prevent it's output from rising too far to an overvoltage condition without shutting down. Maybe that is really why it wouldn't work, the voltage would rise (it is not voltage regulated) with load and the GTI would shut down due to overvoltage. It is a "dumb SMA grid tie inverter" not even as smart as a dumb UPS.

How does the GTI even push the first watt of power unless it can regulate it's output voltage above the grid?

Seems like this industry has a ways to go yet if that is the case.

[sensij]

So you are saying that installation manual would not satisfy NEC correct?

I'm saying that what you've illustrated in your drawings is nothing like what the installation manual shows. In your sketches, you are using the transfer switch to toggle between the generator and the PV system, with the loads receiving power from whichever is selected. Those same loads are also connected to the grid, with only the main circuit breaker in between. Not ok.

The installation manual shows the transfer switch toggling between grid power and generator power, with a few critical circuits moved off the main (slots 6/8 and 11) and into the switch's load center or a critical loads subpanel. The switch is interlocked so that the generator can never feed back into the grid, or any loads other than the critical ones that were relocated. Again, your sketch is using this interlock feature to prevent the generator and PV system from seeing each other... necessary for the function of your system, but insufficient to meet code. You need a hard interlock between the grid and your other sources of power, or you need a device that has that safety mechanism built in.

OK I'll take you word on it but find it hard to believe that the GTI has no safety feature to prevent it's output from rising too far to an overvoltage condition without shutting down. Maybe that is really why it wouldn't work, the voltage would rise (it is not voltage regulated) with load and the GTI would shut down due to overvoltage. It is a "dumb SMA grid tie inverter" not even as smart as a dumb UPS.

Seems like this industry has a ways to go yet if that is the case.

Believe what you'd like, but if you spent as much time reading as you have filling the forum with your posts, you wouldn't have to take my word for it. Residential PV is purely about cost... inverters that are stripped down to nothing is the only way the economics of it works. Better inverters are out there for people who want to do what you'd like, but you have to pay for it.

How does the GTI even push the first watt of power unless it can regulate it's output voltage above the grid?

Google "grid tie inverter as a current source" for a better explanation than one I can provide.

[inetdog]

...
OK I'll take you word on it but find it hard to believe that the GTI has no safety feature to prevent it's output from rising too far to an overvoltage condition without shutting down. Maybe that is really why it wouldn't work, the voltage would rise (it is not voltage regulated) with load and the GTI would shut down due to overvoltage. It is a "dumb SMA grid tie inverter" not even as smart as a dumb UPS.

How does the GTI even push the first watt of power unless it can regulate it's output voltage above the grid?

Seems like this industry has a ways to go yet if that is the case.

The GPS does not regulate its voltage output at all. It regulates the current that it outputs, proportional to the voltage waveform that it sees and proportional to the available panel power at the moment.
It does NOT actually raise its voltage a little bit above the line voltage, since it sees only its terminal voltage, not the unaugmented line voltage. If the current it pushes causes a voltage drop in the wiring back to the service entrance, then the GTI voltage will indeed be higher than the grid voltage, but that is a purely passive result of the resistance in the wire.
Since it does not know the "real" grid voltage, all that the GTI can do is shut down if the "grid" voltage it sees goes too high. That may be enough to protect an off-grid inverter or generator that the GTI is trying to sync to, but it is an all or nothing response.

The SunnyBoy/SunnyIsland combination is unique in the industry in that the GTI (the SI) will proportionally decrease its power output in response to an increase in frequency of the SunnyIsland output.

A hybrid inverter and the Sunny Island have in common the presence of an internal shunt located where it can sense the direction of power flow on the external source side of the connected loads, not just the voltage present. This also requires that the "grid/generator" interface goes in series through the SI and the internal transfer switch to get to the the loads.

[posplayr]

I'm saying that what you've illustrated in your drawings is nothing like what the installation manual shows. In your sketches, you are using the transfer switch to toggle between the generator and the PV system, with the loads receiving power from whichever is selected. Those same loads are also connected to the grid, with only the main circuit breaker in between. Not ok.

The installation manual shows the transfer switch toggling between grid power and generator power, with a few critical circuits moved off the main (slots 6/8 and 11) and into the switch's load center or a critical loads subpanel. The switch is interlocked so that the generator can never feed back into the grid, or any loads other than the critical ones that were relocated. Again, your sketch is using this interlock feature to prevent the generator and PV system from seeing each other... necessary for the function of your system, but insufficient to meet code. You need a hard interlock between the grid and your other sources of power, or you need a device that has that safety mechanism built in.

OK the answer to my question is that the drawing does meet NEC and it does it by a mutually exclusive interlock. It accomplishes that without flipping involving the main, but it only works for selected loads not the entire panel.

but if you spent as much time reading as you have filling the forum with your posts,

I'm really trying to take that the right way; I really really am...................

Google "grid tie inverter as a current source" for a better explanation than one I can provide.

I'll read what inetdog has to say, he seems to have a better idea.

[posplayr]

The GPS does not regulate its voltage output at all. It regulated the current that it outputs, proportional to the voltage waveform that it sees and proportional to the available panel power at the moment.
It does NOT actually raise its voltage a little bit above the line voltage, since it sees only its terminal voltage, not the unaugmented line voltage. If the current it pushes causes a voltage drop in the wiring back to the service entrance, then the GTI voltage will indeed be higher than the grid voltage, but that is a purely passive result of the resistance in the wire.
Since it does not know the "real" grid voltage, all that the GTI can do is shut down if the "grid" voltage it sees goes too high. That may be enough to protect an off-grid inverter or generator that the GTI is trying to sync to, but it is an all or nothing response.

I figured that it would have to monitor line current to have any hope of working but apparently no voltage control even at it's own terminal other than shutoff.

[/QUThe SunnyBoy/SunnyIsland combination is unique in the industry in that the GTI (the SI) will proportionally decrease its power output in response to an increase in frequency of the SunnyIsland output.

A hybrid inverter and the Sunny Island have in common the presence of an internal shunt located where it can sense the direction of power flow on the external source side of the connected loads, not just the voltage present. This also requires that the "grid/generator" interface goes in series through the SI and its internal transfer switch.

OK , I guess there is just not the market demand for such a feature. Things are segmented Grid Tie and Off Grid and not too much in between although SMA seem to be starting to fill it in (e.g. SPS and SB/SI).

Thanks for your considerate response; it is seemly rare.

[inetdog]

I figured that it would have to monitor line current to have any hope of working but apparently no voltage control even at it's own terminal other than shutoff.

It is easy for it to monitor its own current output. But to prevent back driving an inverter or generator it has to be able to monitor the current at that source only. That requires a separate shunt placed in the circuit. And to distinguish between the two directions of energy flow it has to sense the phase angle of the current as well as the magnitude.

[posplayr]

It is easy for it to monitor its own current output. But to prevent back driving an inverter or generator it has to be able to monitor the current at that source only. That requires a separate shunt placed in the circuit. And to distinguish between the two directions of energy flow it has to sense the phase angle of the current as well as the magnitude.

In my simplistic way of thinking as long as the terminal voltage at the output of the solar inverter was within range then there would be no danger of over driving anything. This would require some sort of DC-AC sine wave generation (like in the UPS) but apparently this just some type of coupled current source without any regulation. Without a schematic it is hard to discuss. You don't happen to have anything representative do you?

[inetdog]

In my simplistic way of thinking as long as the terminal voltage at the output of the solar inverter was within range then there would be no danger of over driving anything. This would require some sort of DC-AC sine wave generation (like in the UPS) but apparently this just some type of coupled current source without any regulation. Without a schematic it is hard to discuss. You don't happen to have anything representative do you?

The problem is that when the standalone source is no longer actually supplying any power, and the GTI is able to produce more power than the load can absorb.
At that point the results will depend on just how the output voltage is regulated on the inverter or generator. In some cases the regulator will allow the voltage to rise to the point where the GTI cuts out. In other cases the circuitry of the standalone source will be damaged as it tries to reduce its output power below zero.

[sensij]

In my simplistic way of thinking as long as the terminal voltage at the output of the solar inverter was within range then there would be no danger of over driving anything. This would require some sort of DC-AC sine wave generation (like in the UPS) but apparently this just some type of coupled current source without any regulation. Without a schematic it is hard to discuss. You don't happen to have anything representative do you?

Too simplistic. The inverter as a current source makes sense because the solar panels are as well. Regulating the inverter *input*,not output, is the answer you are looking for.