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Solar Panel

In some part of our country, the cos phi is 0.9 while in some other is still 0.8. The higher the cos phi the better. The power is belong to government (say the name is MAINS). Different cos phi is possible as the they are on a a different network, in a different island.

I would like to install 150KVA ON-GRID solar panel using a 330 Watt output power of each panel (output of a single independent panel theoretically is 330 watt. By connecting some panels parallel and invert it to AC from DC, expected will meet the requirement). The output of the panels we will use internally. But as no guaranty that the power the panel produce will be enough for our need (as could be cloud, rain, etc), the solar panel system will still be (inter)-connected to the MAINS. Once the power produced by the solar panel is not enough, than system will draw from MAINS by the ON GRID inverter. Means, there will be two electric sources for us. From MAINS and from solar panel.

Then my question is, what will happened to all the electric equipment or to our network if the cos phi are not same? Say, the MAINS' cos phi is 0.9 while our cos phi is 0.8 or something like that.

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  • \$\begingroup\$ PF is the current phase consumed not supplied \$\endgroup\$ Nov 28, 2019 at 4:41
  • \$\begingroup\$ Are electrics generated from many source (like water turbine, gas turbine, etc) produce electric all in phase? Sorry to ask you as I got confuse regarding my friend's explanation who working in the MAINS. He said, due to the generator's limitation, then not all can be produced in phase. \$\endgroup\$ Nov 28, 2019 at 14:27
  • \$\begingroup\$ The grid load may have more motor loads and be lower PF. This can be raised.. Passive bank caps , Active PFC ( usually only local to PSU to make PF=1). Every load is different, the average is what you heard as the net PF of all loads. The Grid must maintain a much lower impedance by design that all these load variations to maintain the supply voltage, in spite of changes in loads AND PF or cos phi \$\endgroup\$ Nov 28, 2019 at 15:53

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The AC from the solar panel inverter and the AC of the grid do have to be in phase. Both the inverter and the grid do their best to be a voltage source. The power factor caused by a reactive load puts requirements on both the inverter and the grid. Hopefully, the inverter can handle any reactive load you may be presented to it. The grid can handle it, but it causes transmission losses.

The power factor is a property of the load you is being driven, not the source, so your question is a bit confused.

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  • \$\begingroup\$ The power factor is a property of the load you is being driven, not the source. This is interesting. I will come back shortly after I do some checking regarding this. Thanks for the info. \$\endgroup\$ Nov 28, 2019 at 14:24
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To take power from PV panels and feed that power into a utility grid, you need a device known as a Grid tie inverter. (From a regulatory perspective, you would also need a power meter that supports net metering and an approval from your local utility company to feed power into their system. They would lay down a number of conditions mostly related to quality of your Grid tie inverter and how well it would deal with different sort of grid problems like sudden power outages).

My understanding is that you would buy a grid tie inverter(it’s design is something which is a fairly complex case of power electronics). The grid tie inverter ensures that before it ties up with the grid, the phase angle difference between the voltage waveform produced by inverter and the utility waveform is zero. If the grid tie inverter does not do that, it would instantly blow up the fuse or trip the circuit breakers because utility is a very deep source of power and would’nt allow an invertor of any size to disturb utility supply’s own phase angle.

The good part is that almost all grid tie investors take care of this problem.

There is one more phase angle that comes into this debate and that is the phase angle of the current waveform when compared to the voltage waveform. The phase angle of a current waveform depends on the load and not the source. For a grid tie inverter, it would usually supply current into the grid by almost replicating the voltage waveform with no phase angle difference and then “very slightly” trying to raise the voltage amplitude as compared to utility in order to start power flow into the grid. The difference of voltage here again has to be kept really small as grid is a very powerful source of power that won’t run on terms(voltage, phase angle, frequency) of a very small power producer.

So in short, if any device tries to tie in with grid while it’s voltage waveform does not exactly replicate the phase angle, frequency and amplitude of utility voltage waveform, a short circuit would happen triggering safety devices like fuses and circuit breakers.

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