Live in the sticks Generator switch?

   / Live in the sticks Generator switch? #11  
. I'm not sure about two generators coupled to the same electrical system. I think some generators are not built to receive power, and they would be connected to each other electrically via the 120V busses in the service panel.

Please elaborate about this two generator thing and generators not being built to receive power???

The Two links I provided both systems supply power to all circuits. I can't imagine why people install those little ding dong four or six circuit only transfer panels.
 
   / Live in the sticks Generator switch? #12  
Please elaborate about this two generator thing and generators not being built to receive power???

The Two links I provided both systems supply power to all circuits. I can't imagine why people install those little ding dong four or six circuit only transfer panels.

All I know is what I have been told. The installers of my grid-tied solar system said to disconnect the solar inverter from the service panel (open its breaker) before switching to generator power. They claimed the solar output could harm some generators by feeding them power. ????
 
   / Live in the sticks Generator switch? #13  
Ahhhhhhh makes much more sense now.
The solar system should be isolated when on generator power when using a single bi-directional power meter for net metering. I'm going to read up on that tomorrow in the latest code book.
 
   / Live in the sticks Generator switch? #14  
Ahhhhhhh makes much more sense now.
The solar system should be isolated when on generator power when using a single bi-directional power meter for net metering. I'm going to read up on that tomorrow in the latest code book.

I have two meters, and IN and an OUT. The solar system produces a maximum of 16.2 Amps, ~4200 watts.

I don't think the meter(s) was the issue, it was damage to the generator they were warning about. I don't know if that is a code issue, or if there would be anything regarding that in the code?

This generator was connected to the house without isolating it from the grid when the power was restored:
Beware of Backfeeding - How NOT to Connect a Portable Generator


I'm not sure synchronization (phase) would be an issue for a grid-tied solar system since it gets it 60 Hz clocking from the service panel power.
Do 2 5000 watt generators = 1 10000 watt generator - Straight Dope Message Board
You can't just chain generators together like batteries, they have to be running in phase or you'll get one "pushing" while the other is "pulling" in the AC cycle and the result would be interesting.

There is a Honda EU series unit made to run in parallel with another Honda, but they are designed for that.
 
   / Live in the sticks Generator switch? #15  
400 amp automatic switch gear. Power company knows about the generator and if they get concerned or have a problem they will come pull my meter to stop back feeding then reinstall after the work is complete. But they also call and tell me if they must shut down power for scheduled service. Storm damage or line failures are no warning but they can't do anything about that.
 
   / Live in the sticks Generator switch? #16  
I have two meters, and IN and an OUT. The solar system produces a maximum of 16.2 Amps, ~4200 watts.

I don't think the meter(s) was the issue, it was damage to the generator they were warning about. I don't know if that is a code issue, or if there would be anything regarding that in the code?

This generator was connected to the house without isolating it from the grid when the power was restored:
Beware of Backfeeding - How NOT to Connect a Portable Generator


I'm not sure synchronization (phase) would be an issue for a grid-tied solar system since it gets it 60 Hz clocking from the service panel power.
Do 2 5000 watt generators = 1 10000 watt generator - Straight Dope Message Board
You can't just chain generators together like batteries, they have to be running in phase or you'll get one "pushing" while the other is "pulling" in the AC cycle and the result would be interesting.

There is a Honda EU series unit made to run in parallel with another Honda, but they are designed for that.

If there are two meters , with the solar panel's inverter connected direct to the grid. Then there are no concerns about backfeed or paralleling the standby generator and the solar inverter when a proper generator transfer switch is used.
 
   / Live in the sticks Generator switch? #17  
It is true that you could cause some issues running a generator with solar. If you have a large solar output and little load, the inverter wants to push power out onto the grid. If the "grid" is a generator, the inverter will raise the voltage it is supplying to drive to drive it's full power. This increase voltage will cause the voltage regulator (on a better generator design) to back off the output of the generator, since the voltage will be too high. This will all happen within a second or two and the likely outcome is the inverter will shut down due to overvoltage, and restart again. It is unlikely to damage the generator. If there is a reasonable load at the time, they may work well together.

There is a bigger issue. Most grid tie inverters have a very narrow range of frequencies that they will operate with to supply power. On my Fronius 10KW, the range of allowable frequency is 59.3-60.5 Hz Outside that frequency window, it will not sync and connect. Since the generator is quite a bit less accurate in terms of absolute frequency control, it is unlikely to be an issue. I have had several day long runs of outage with my genset running (9.8 KW diesel) and I have left the solar enabled (9.2 KW). First I always have some base load, and I saw that when the solar would connect (when the genset frequency was within the window) it would only last a few up to about 10 minutes, and then go off line again. I saw times when the solar was feeding and a fridge or well would kick on, and the motor starting would cause a momentary dip in frequency and trip the solar off. All in all, on a day where I would normally see 30-40 KWh of solar, I saw maybe 2 KWh of solar supply, supplied a few minutes at a time.

One is certainly safer disconnecting the solar from supplying during genset operation, but with all of the frequency and voltage interlocks on a modern grid tie inverter, it is likely that it may not connect at all, and if it does it will be only for a few minutes when conditions of the gen power and load are just right.

paul
 
   / Live in the sticks Generator switch? #18  
It is true that you could cause some issues running a generator with solar. If you have a large solar output and little load, the inverter wants to push power out onto the grid. If the "grid" is a generator, the inverter will raise the voltage it is supplying to drive to drive it's full power. This increase voltage will cause the voltage regulator (on a better generator design) to back off the output of the generator, since the voltage will be too high. This will all happen within a second or two and the likely outcome is the inverter will shut down due to overvoltage, and restart again. It is unlikely to damage the generator. If there is a reasonable load at the time, they may work well together.

There is a bigger issue. Most grid tie inverters have a very narrow range of frequencies that they will operate with to supply power. On my Fronius 10KW, the range of allowable frequency is 59.3-60.5 Hz Outside that frequency window, it will not sync and connect. Since the generator is quite a bit less accurate in terms of absolute frequency control, it is unlikely to be an issue. I have had several day long runs of outage with my genset running (9.8 KW diesel) and I have left the solar enabled (9.2 KW). First I always have some base load, and I saw that when the solar would connect (when the genset frequency was within the window) it would only last a few up to about 10 minutes, and then go off line again. I saw times when the solar was feeding and a fridge or well would kick on, and the motor starting would cause a momentary dip in frequency and trip the solar off. All in all, on a day where I would normally see 30-40 KWh of solar, I saw maybe 2 KWh of solar supply, supplied a few minutes at a time.

One is certainly safer disconnecting the solar from supplying during genset operation, but with all of the frequency and voltage interlocks on a modern grid tie inverter, it is likely that it may not connect at all, and if it does it will be only for a few minutes when conditions of the gen power and load are just right.

paul

That all sounds logical, thanks. I don't intend to test it, but maybe someday I will due to forgetfulness. :) I didn't look up my inverter's frequency tolerance but I recall it is a narrow range.

I typically don't have that much to gain even if it did work. Power outages here usually come with bad weather, or slippery winter roads, when sunshine is lacking. The last two were overnighters from late afternoon to early the next morning.
 
   / Live in the sticks Generator switch? #19  
With two power meters. The solar system could be connected parallel to the utility side of the transfer switch. In that case back feeding form solar is not an issue. If the solar system meter is in series with the main utility power meter, then yes. The solar unit could back feed. As previously stated it would however sync, then un-sync with the generator.
 
   / Live in the sticks Generator switch? #20  
:smiley_aafz:When I want to ask a rookie question I sometimes find the answer in the search box which is great but does this stop others from putting their input in on a topic without getting slammed by somebody say check search? I do have a questions and seek your knowledge that I could not find and it has to do with generators and switches .

We have two 30 amp generators at 7500 and 7600 outputs and are tired of running cables when there is a outage. I have been looking at what is called the interlock or the transfer switch to hook our house when there is a blackout. My main concern is that is there is no back feed in the lines that could harm a worker.

Which would you chose and why?

Simply put; a transfer switch or an interlock, correctly sized and properly installed, will each work as intended and NEITHER will allow for backfeed to your utility line. As has been pointed out, each serves a different purpose/function; the interlock allows all or select main panel breakers to be in use while on generator supplied power, the transfer switch can be limited to # of circuits in the transfer switch, so may offer less functionality/ choices if only a few circuits are switchable at the transfer switch. Either will work, and is safe, so long as the generator does not exceed the switch's rated capacity.
 

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