Grid tied solar system.

[Mike90250]

go to youtube and search LDS Prepper. Look at his system he just put up. He is originally from Houston, moved to Idaho. He knows his stuff and has plenty of videos of his system.

We could spend all day wandering the web looking at neat stuff, but this is more of a forum, where folks interact with each other, a blind reference to a site where there are nnnyyyzzz is not really on topic. If there was a specific question, and you know of a specific answer (like we often refer folks to the Smartguage site where they lay out the math about how bad parallel batteries can be) that's much more in line with what we like to see.

[mmyler]

Check this guy and system out

go to youtube and search LDS Prepper. Look at his system he just put up. He is originally from Houston, moved to Idaho. He knows his stuff and has plenty of videos of his system.

[Mike90250]

.....
Apparently the Hybrid Inverter, essentially performs this function by generating a programmable DC voltage source (from high voltage solar DC) to charge a battery bank(the load) which are subsequently used to generate AC which presumable is regulated and terminal voltage adjusts to the load. This is like the DC to AC conversion in a dual conversion UPS......

Not really. The Hybrid Inverters generally do NOT have a solar PV charge controller. That is a separate box, to keep the batteries charged. They take DC from the battery bus, and invert it to AC. Some are rated to be able to back feed the grid, they have internal safety interlocks that pass UL testing. Some also sync with and work with generators when the solar is insufficient. As to the internal circiuts that manage the voltage and ability to supply AC amps, their design department can tell you more than I can.

[posplayr]

You are getting good input from Inetdog. When a power supply is built, it typically is a voltage or a current
source (within practical limits). The PoCo is a voltage source, supplying whatever current the load conducts
while maintaining a stable voltage. For a GTI to supply the PoCo, it must be a current source, supplying
whatever power it has available as current into a stable voltage. A supply cannot be a voltage and a current
source at the same time; that operating point will be determined by the impedance of a load.

If a GTI were to change to output voltage reg at a defined point, it would cut off every time the line voltage
rose slightly. It the point was set way high, it would operate higher than the voltage desired when not PoCo
line connected. The only way to solve this is a method to change the inverter mode from one to the other,
which is not a feature generally available. Bruce Roe

Without characterizing the GTI as either current source or voltage source, it is just basic ohms law that if the grid AC voltage envelope is surging, the GTI AC output voltage envelop would have to float and follow just above that grid level to maintain a positive AC current flow into the grid. Within limits as you describe looks more like an AC current source with a floating output voltage that follows the grid undulations. There is no hard voltage control at the GTI terminals; with a grid you would never be able to do pull the grid voltage around with a GTI of any reasonable capacity.

[posplayr]

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.

OK I guess we have to discuss this without a representative schematic.

I understand now that a GTI has no output voltage regulation. If it did it would have to maintain that voltage on top of any Grid line variation probably as measured through output current sensing. So it would basically be an AC current source with additional AC Voltage limits all synced to the prevailing AC voltage (i.e. grid ). From a practical standpoint if the voltage were to be limited it would be by series regulation v.s. shunt as the GTI would have to massive to shunt for example: 10Kwatts of solar if there was no load.

Apparently the Hybrid Inverter, essentially performs this function by generating a programmable DC voltage source (from high voltage solar DC) to charge a battery bank(the load) which are subsequently used to generate AC which presumable is regulated and terminal voltage adjusts to the load. This is like the DC to AC conversion in a dual conversion UPS.

It is not impossible, just not what GTIs do; a GTI can not regulate it's output based on load except the SB TL with SPS which does it on a limited basis (1500 watts per plug).

EDIT: I have been reading alot and I thought I read a comment that the SPS was a simple mod, to the existing GTI. That sort of flies in the face of the current discussion so I might not be remembering that correctly.

EDIT EDIT: As per the other discussion on potential Contingency GT implementations, you run into the NEC safety interlock requirements with the grid. That is the biggest impediment to having full solar output at the GTI terminals without the grid. Not impossible just messy without doing a complete house transfer switch. The dual SB SPS is looking better.

[bcroe]

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?

You are getting good input from Inetdog. When a power supply is built, it typically is a voltage or a current
source (within practical limits). The PoCo is a voltage source, supplying whatever current the load conducts
while maintaining a stable voltage. For a GTI to supply the PoCo, it must be a current source, supplying
whatever power it has available as current into a stable voltage. A supply cannot be a voltage and a current
source at the same time; that operating point will be determined by the impedance of a load.

If a GTI were to change to output voltage reg at a defined point, it would cut off every time the line voltage
rose slightly. If the point was set way high, it would operate higher than the voltage desired when not PoCo
line connected. The only way to solve this is a method to change the inverter mode from one to the other,
which is not a feature generally available. Bruce Roe

[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.

[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.

[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]

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]

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.

[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.

[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.

[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.

[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.