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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