Alan,
There's a local electrician here in Santa Rosa that I have used for a
couple of projects. He is presently installing a new 800A 3P service for
me. His prices are fair and I know he has done a number of PV
installations. He's accommodating & I'm sure would be willing to deviate
from a formulaic install to allow such things as wiring to be in conduit
and winding CM chokes as specified by you.
He's a big fan of the Enphase microinverters. I don't have any specific
info about their RFI performance, although they are HQ in Petaluma and I
understand that their tech support people are accessible. He gave me an
Enphase microinverters to dissect, so we can open it and see at least if
it looks like the design includes expected filtering. For what it's
worth, I see that it's externally labeled "complies with part 15" and
"operation...may not cause harmful interference" so at least they
acknowledge their responsibility!
I'm fairly certain that he would give us a tour of one of his installs
in operation where we could sniff around and see for ourselves what sort
of junk the Enphase inverters are producing. I would be very interested
in the results. Let me know off list if interested and we can try to sked.
73,
Josh W6XU
On 7/18/2016 12:05 AM, Alan Bloom wrote:
I am contemplating having a solar photovoltaic power system installed
on my roof. There was an article by K1KP in April 2016 QST about the
hoops he had to jump through to reduce the noise level from his system
low enough that he could operate the HF bands.
My system should be less troublesome than his since it would not have
power optimizers (basically switching power supplies) on each solar
panel. The panels have no electronics in them. So I think all I need
to worry about is the noise from the inverter (the device that
converts DC from the panels to 240 VAC to connect to the electric
company).
The inverter already includes an AC line filter, so hopefully that
should reduce differential-mode noise into the power line. So I think
I'm talking about common-mode chokes on both sides of the inverter -
the side that connects to the electric utility and the side that
connects to the panels up on the roof.
Solar City is not interested in working with me on this - they just
want to do a standard installation like they have done thousands of
times before. However, I see in their plans that they connect to the
meter main breaker box with 3/4-inch EMT (electrometallic tubing) and
also use 3/4 EMT for the solar panel connections. You can buy snap-on
ferrite chokes, FairRite P/N 0431177081, which have a 1-inch ID, so it
should be possible to simply snap them on over the EMT. These chokes
are basically the same as the ones used in the article (type 31, 2"
OD, 1" ID, 1.5" L) except that they are snap-on types.
My question is, how many chokes do I need? K1KP used 30 (!) in series
on the power-line side of his inverter. That seems excessive. The
FairRite data sheet says the impedance is about 80 ohms at 2 MHz,
rising to 240 ohms at 30 MHz. I'm thinking a half-dozen or so of
these on each side would be reasonable. Does anyone have any
experience with this kind of thing?
Alan N1AL
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