Announcement

Collapse
No announcement yet.

Isolating generator from solar system

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Isolating generator from solar system

    I have a customer who just had a whole house generator installed at their home where I had put solar panels a couple of years ago. The solar system backfeeds the main panel through a 40-amp breaker. The power to the house comes underground for a pedestal about 150' from the house. The electrician put the transfer switch by the pedestal and ran power down from the generator which is off in a different direction. Normally I would either tie the solar into a line-side tap on the utility side of the transfer switch or connect the solar to the main panel by way of a normally open contactor that is tied to the dry contacts in the transfer switch (when utility power fails, the contactor opens). Currently there is no way that I know of to tell where the power in the house is coming from (utility or generator) and no way to connect the solar to the transfer switch way down at the pedestal. (Apparently the conduit to the house is thought to be damaged, so pulling the main feed to the house and adding a signal wire is not possible).
    Anybody got any ideas?

    #2
    Does the solar have a negative impact on generator performance? Since the solar only adds capacity but still needs the 60 cycles as a reference for the inverter to produce output.

    Comment


      #3
      Originally posted by mopowr steve View Post
      Does the solar have a negative impact on generator performance? Since the solar only adds capacity but still needs the 60 cycles as a reference for the inverter to produce output.
      If the solar comes on when the generator is running, it has the potential to backfeed the generator causing significant harm.

      Comment


        #4
        Would using a low voltage 2-wire cable rated for direct burial that's placed at least 6 inches below the surface work for a low voltage signal line at 30V or less? This would drive the contactor you mentioned, and so worst case if the wire gets cut the solar won't operate. It could be fused to offer additional protection in the low voltage circuit if appropriate.

        Comment


          #5
          This could work. It wouldn't be too hard to run a small trench through the lawn.

          Comment


            #6
            I'm sure this situation is going to come up more and more frequently.

            There is no physics reason that says you _can't_ have the solar power system running with the generator. It is all about the controls.

            When the solar panels/inverter are supplying more energy than the home is consuming, and the system is not connected to the grid, then _something_ has to give, preferably is a well defined fashion that permits continued operation, but the _something_ could be the magic smoke that keeps everything working.

            Do there exist solar inverter and generator combinations which are smart enough that when operated without the grid connection, if solar production exceeds house consumption, that the system will simply do the right thing and reduce solar production?

            -Jon

            Comment


              #7
              Originally posted by winnie View Post
              I'm sure this situation is going to come up more and more frequently.

              There is no physics reason that says you _can't_ have the solar power system running with the generator. It is all about the controls.

              When the solar panels/inverter are supplying more energy than the home is consuming, and the system is not connected to the grid, then _something_ has to give, preferably is a well defined fashion that permits continued operation, but the _something_ could be the magic smoke that keeps everything working.

              Do there exist solar inverter and generator combinations which are smart enough that when operated without the grid connection, if solar production exceeds house consumption, that the system will simply do the right thing and reduce solar production?

              -Jon
              There are such systems, but they most often include a battery bank and an inverter capable of off-grid operation from the battery bank as well as grid interactive operation. Pure grid interactive systems with throttling are rarer but are marketed in countries that prohibit feed back into the grid completely.

              Comment


                #8
                Originally posted by GoldDigger View Post

                There are such systems, but they most often include a battery bank and an inverter capable of off-grid operation from the battery bank as well as grid interactive operation. Pure grid interactive systems with throttling are rarer but are marketed in countries that prohibit feed back into the grid completely.
                You might could make this happen with a SolarEdge inverter and their Electricity Meter.

                Comment


                  #9
                  I would go the trench route to the transfer switch. I remember having to do a similar setup. The generator and service were near the house and the PV interconnection was in a building pretty far from the house, back-feeding a subpanel.

                  As an alternative, you can set up the PV system with a dropout relay to trip off on loss of AC and require a manual reset to turn it back on. There will be a loss of AC between when the grid goes down and the generator picks up the load, even with an automatic transfer switch. The homeowner needs to be involved and they need to do things right. They can't reset the PV system when on generator power. They can't manually switch from the energized grid to the running generator with the transfer switch without manually shutting the PV system down, depending on the reaction speed of the dropout relay.

                  Comment


                    #10
                    Originally posted by MikeBalst1
                    Power is most often expressed in dBm or milliwatts; less often, peak power in volts is indicated. However, it is most convenient to understand using dBm. Since, using them, it is easier to go to the attenuation and length of the cable, which can be called with the help of such a generator.
                    Yes, if you're talking about RF signal generators with a source impedance of typically 50 ohms or sometimes 75 ohms. And usually with coaxial cables with the same characteristic impedance.

                    However, this forum deals primarily with AC power at 60 Hz or 50 Hz, and usually dealing with watts, kilowatts, megawatts, or more. And matching the load impedance to the source impedance (which is typical when using RF transmission lines) is usually a very bad thing in AC power distribution and usage

                    Comment


                      #11
                      Originally posted by MikeBalst1
                      Power is most often expressed in dBm or milliwatts; less often, peak power in volts is indicated.
                      Power in Volts?

                      Comment


                        #12
                        I think MikeBalst1 might be some kind of bot. They made another weird post to a different group.

                        Comment


                          #13
                          If at all practical I would and hard wire a control circuit. I would be a little concerned of AC driving a small relay at that distance though due to capacitance. DC would be a better choice.

                          Comment


                            #14
                            Originally posted by smithgordonm View Post
                            I have a customer who just had a whole house generator installed at their home where I had put solar panels a couple of years ago. The solar system backfeeds the main panel through a 40-amp breaker. The power to the house comes underground for a pedestal about 150' from the house.
                            Anybody got any ideas?
                            Just out of curiosity whats the make, model and kW rating of the generator?
                            And the Make, model kW rating of the inverter?
                            Its becoming quite common to synchronize several generators instead of installing one, I doubt it would be a problem for them to synchronize.
                            https://selinc.com/solutions/Generat...izing-Systems/
                            However it would be expensive.


                            Originally posted by smithgordonm View Post
                            If the solar comes on when the generator is running, it has the potential to backfeed the generator causing significant harm.
                            Can you elaborate on this ?

                            Comments based on 2017 NEC unless otherwise noted.

                            Comment


                              #15
                              Originally posted by tortuga View Post

                              RE: "If the solar comes on when the generator is running, it has the potential to backfeed the generator causing significant harm."


                              Can you elaborate on this ?
                              I can. If the PV system is connected on the generator side of the transfer switch when the generator is running, and if the PV system recognizes the output waveform from the generator as the grid, and if the demand from the loads falls below what the PV system is producing, the PV system will backfeed the generator, which would be bad news for most generators.

                              Comment

                              Working...
                              X