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Old 03-16-2012, 08:30 AM   #1
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Solar and generator interface?


I am considering adding solar panels to my home to generate electricity. I will not add batteries however (to expensive) so when the grid goes down I won't get energy from the panels (you need a special inverter and batteries) so I want to add a portable gas generator for those, hopefully, limited cases.

I just wondered how the solar wiring gets interfaced into my system (breaker panel?) and can I later add a transfer switch or interlock switch when I add the generator?

Or should I do that at the same time (perhaps the interface is complicated)?

Thoughts?

Thx

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Old 03-16-2012, 07:02 PM   #2
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Solar and generator interface?


Think about installing an change over switch first,
Then on the genny side of the change over switch,
can be another DPDT switch (can be auto or manual)
witch selects either the genny or the solar panels via invertor.

EASY !

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Old 03-16-2012, 07:51 PM   #3
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Solar and generator interface?


Thanks. Not sure I got all that but i did hear from a PV folk and they say they can just do a line tap so I am ok later with adding a transfer switch or interlock.
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Old 03-16-2012, 08:49 PM   #4
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Solar and generator interface?


Quote:
Originally Posted by dmxtothemax View Post
Think about installing an change over switch first,
Then on the genny side of the change over switch,
can be another DPDT switch (can be auto or manual)
witch selects either the genny or the solar panels via invertor.

EASY !
This does not work. That solution is fine for a grid-independent solar system with a battery bank, but cannot be used without batteries. What he needs is a grid-tie inverter and a net metering setup. He needs to install the generator and transfer switch as normal, and also install a grid tie inverter, net meter (supplied by the power company), and required disconnects. The inverter and metering equipment go ahead of the transfer switch, on the utility input side.
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Old 03-16-2012, 11:06 PM   #5
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Solar and generator interface?


Quote:
Originally Posted by mpoulton View Post
This does not work. That solution is fine for a grid-independent solar system with a battery bank, but cannot be used without batteries. What he needs is a grid-tie inverter and a net metering setup. He needs to install the generator and transfer switch as normal, and also install a grid tie inverter, net meter (supplied by the power company), and required disconnects. The inverter and metering equipment go ahead of the transfer switch, on the utility input side.
Correct.

Also, I wouldn't put the output of the solar inverter on the generator side of the transfer switch. I seriously doubt that the waveform of a small generator would be compatible with an inverter, plus if the utility were down and the solar output exceeded the load, the generator would become a motor and very likely overspeed.

The best bet would be to install the system as described above, and add a transfer switch downstream of the solar inverter.

True enough, the solar system doesn't produce any power when the utility is dead, but it's better than destroying equipment.

Rob
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Old 03-17-2012, 12:54 AM   #6
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Solar and generator interface?


If he has no batteries, then he can only get power from the panels via an
invertor when the sun shines.
If no sun, then he has to use the genny.
And if he uses an DPDT switch, as I suggestted,
then there would be no problems,
because it would be either invertor or genny
not both.
Thats the function of the DPDT switch.
it isolates the genny from the invertor.
So spikes would not be a problem.

Its not an ideal set up,
but it would sort of work.
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Old 03-17-2012, 07:30 AM   #7
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Solar and generator interface?


The solar folks told me they do this:

There will need to be a disconnect from the grid so that your generator doesn’t back feed onto the grid when folks are working on the power lines. The best way to approach this situation with a solar electric system would probably be for us to do a line side tap when we tie the system into your breaker panel. With a normal solar installation (without a generator), we tie the system into your breaker panel from the load side. If we do a line side tap, we are tying the system into your breaker panel from the line side (utility side). Whether you have an interlock or transfer switch, it will cut off power coming from the utility. Since the solar electric system would be wired to come into your breaker panel from the line (utility) side, it would also cut off power from the solar electric system. So this would ensure that the generator and solar electric system would not interact with each other.
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Old 03-17-2012, 12:33 PM   #8
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Solar and generator interface?


Quote:
Originally Posted by desmo907 View Post
The solar folks told me they do this:

There will need to be a disconnect from the grid so that your generator doesn’t back feed onto the grid when folks are working on the power lines. The best way to approach this situation with a solar electric system would probably be for us to do a line side tap when we tie the system into your breaker panel. With a normal solar installation (without a generator), we tie the system into your breaker panel from the load side. If we do a line side tap, we are tying the system into your breaker panel from the line side (utility side). Whether you have an interlock or transfer switch, it will cut off power coming from the utility. Since the solar electric system would be wired to come into your breaker panel from the line (utility) side, it would also cut off power from the solar electric system. So this would ensure that the generator and solar electric system would not interact with each other.
That will work, and be code compliant.

Rob
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Old 03-18-2012, 02:22 PM   #9
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Solar and generator interface?


Interesting stuff....which made me think of a different question. How do the solar systems keep from backfeeding when the utility looses power?
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Old 03-18-2012, 04:16 PM   #10
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Solar and generator interface?


the 'grid-tie' doesnt allow power down the utility lines if it doesnt see voltage coming from POCO.
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Old 03-18-2012, 04:35 PM   #11
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Solar and generator interface?


Quote:
Originally Posted by dmxtothemax View Post
If he has no batteries, then he can only get power from the panels via an
invertor when the sun shines.
If no sun, then he has to use the genny.
And if he uses an DPDT switch, as I suggestted,
then there would be no problems,
because it would be either invertor or genny
not both.
Thats the function of the DPDT switch.
it isolates the genny from the invertor.
So spikes would not be a problem.

Its not an ideal set up,
but it would sort of work.
This really doesn't work. Solar panels cannot be used to power an inverter directly without batteries, except in a grid-tie system with a maximum power point tracking (MPPT) inverter. You cannot simply connect a bunch of solar panels to an inverter and use it to power stuff. The reason for this is that the panels' output power characteristics do not match the load's requirements. Batteries are needed to provide short term (milliseconds to minutes) power storage so the load can draw the power it needs when it needs it, while the panels provide the power they can produce when they can produce it. This is why net-metered grid-tie systems are so convenient. They use the grid in place of batteries to provide effective instantaneous power storage.
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Old 08-27-2012, 11:26 AM   #12
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Solar and generator interface?


So electrician is here and said they wil install the solar to 2 breakers on panel. So when i lose the grid (power outage), before i use my generator (either with an interlock panel or switch) that i turn OFF the breakers to the solar arrays. They say this will prevent backfeed into the generator from the solar.
Else they do a line side tap and install some fuses...

Little beyond me but I guess the former makes sense since I do not have batteries and have to turn on breakers anyway for the generator, etc.

Thoughts?

Quote:
Originally Posted by desmo907 View Post
The solar folks told me they do this:

There will need to be a disconnect from the grid so that your generator doesn’t back feed onto the grid when folks are working on the power lines. The best way to approach this situation with a solar electric system would probably be for us to do a line side tap when we tie the system into your breaker panel. With a normal solar installation (without a generator), we tie the system into your breaker panel from the load side. If we do a line side tap, we are tying the system into your breaker panel from the line side (utility side). Whether you have an interlock or transfer switch, it will cut off power coming from the utility. Since the solar electric system would be wired to come into your breaker panel from the line (utility) side, it would also cut off power from the solar electric system. So this would ensure that the generator and solar electric system would not interact with each other.

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