[Elecraft] OT: RF noise in solar photovoltaic system

[Jim Brown]

Alan,

There are TWO major noise sources in solar systems -- the charge 
regulator, which switches square waves, and the inverters.  If the solar 
vendor "will not work with you," run like hell in the other direction. 
This is my advice for ANY kind of purchase that involves a known 
engineering problem. System wiring is also a VERY big part of the 
engineering problem.

Study my tutorial, k9yc.com/RFI-Ham.pdf  and follow the guidelines for 
RG8 coax chokes for chokes that you add to circuits carrying DC circuits 
with noise on them. Snap-on ferrite cores are USELESS at HF unless you 
wind enough turns through them to place the parallel resonance where the 
noise is. Also study http://k9yc.com/KillingReceiveNoise.pdf  and see my 
comments on the QST article.

One of the most useful points in the QST article is the use of steel 
conduit for ALL of the wiring AND the use of twisted pair for the 
circuits carrying noisy DC and AC.  This cannot be emphasized enough.

I can't comment on the number of chokes used nor their design, because i 
don't know enough about engineering details of the system. One of the 
criticisms of the piece is the specific recommendations for chokes.

73, Jim K9YC


On Mon,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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to jim at audiosystemsgroup.com
>