Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Alan Bloom]

In case anyone's interested, I decided not to go with Solar City.  I 
think they would have done a fine job of installing a standard, 
off-the-shelf solar system with a 20-year warranty that would have 
worked fine as far as providing solar power.  I was planning to buy it 
outright rather than lease and I'm convinced that the investment would 
have paid for itself in reduced electricity costs.


But I was worried about RF interference from the inverter, basically a 
3000-watt switching power supply attached to the side of my house.  So 
instead I have decided to go with a local company that is willing to 
work with me on RFI issues, even though their price is higher.  Rather 
than one big inverter, their system uses "micro-inverters" mounted on 
each solar panel.  They did some research and found that it is possible 
to get extension cables to go between each micro-inverter and its panel 
and between each micro-inverter and the power bus.  The extra length can 
accommodate a common-mode choke by wrapping several turns of the cable 
through a ferrite core.


So the plan is to install the system without chokes and see if there is 
any interference.  If so, then I will buy the extra cables and ferrite 
cores and install the chokes.  For testing purposes I can just 
temporarily disconnect all the panels but one and then apply whatever 
works with one to them all.


Alan N1AL


On 07/18/2016 07:32 PM, Alan Bloom wrote:

I am now leaning on going with a local company rather than Solar City.
They quoted a higher price for a lower-power system, but because of some
convoluted accounting it will actually end up costing me less.  And they
are at least willing to talk about adding some common-mode chokes. Their
system uses micro-inverters on each panel, which potentially should
cause less interference because all the switching  electronics is
localized with short connections.  Only 240 VAC 60 Hz comes out of the
panels.

Alan N1AL


On 07/18/2016 06:49 PM, John Kaufmann wrote:

My advice on Solar City is to avoid them at all costs.  Their systems,
manufactured by SolarEdge, generate horrendous broadband RF noise

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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Tom Azlin W7SUA]

Hi Jim,

On 7/19/2016 12:51 PM, Jim Brown wrote:


Remember that whether or not you hear more noise with the system running
will depend on how much OTHER noise there is in your neighborhood. Some
(many?) of us have background noise in the range of S8, others in the
range of S3. The difference is 25 dB.


Good point. When not in Monsoon season my K3 S meter is around S2 with 
my 160 meter inverted V up about 50 ft with about 150 ft of RG8 type 
coax. Right now jumps up much higher during static crashes but storms 
all around us. We live in a rural area long way from high voltage power 
lines and perhaps from plasma TVs and electric fences.



It's worth looking for a quiet MPPT charge regulator. Just like any
other electronics that generate or use square waves, it can be done well
or it can be done badly. Since badly is cheaper, and done well requires
more technical design expertise, badly is by far the most common. The
Genasun regulators are pretty quiet, but so far, they only make units
for much smaller systems.


I'll keep looking for quiet MPPT charge controllers. My battery bank is 
1200 amp-hr at 12 volts. Thanks!


73, tom w7sua



73, Jim K9YC



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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Jim Brown]

On Tue,7/19/2016 10:23 AM, Tom Azlin W7SUA wrote:


We put in a 10KW array on our garage roof using two SMA 5000TL-US-22 
inverters to grid tie. I could not see any difference in noise floor 
or moving noise bands with the inverters running or with both the DC 
and AC disconnected. Perhaps just lucky? 


Remember that whether or not you hear more noise with the system running 
will depend on how much OTHER noise there is in your neighborhood. Some 
(many?) of us have background noise in the range of S8, others in the 
range of S3. The difference is 25 dB.


They also said for just charging my station batteries using the 700 
watt legacy solar array that came with the house that I should use a 
PWM charger rather than the noisier MPTT chargers. Have not picked a 
charger yet. The local solar guy also provided that 700 watt array to 
the original owners of our house as it was an off-grid solar home. 



It's worth looking for a quiet MPPT charge regulator. Just like any 
other electronics that generate or use square waves, it can be done well 
or it can be done badly. Since badly is cheaper, and done well requires 
more technical design expertise, badly is by far the most common. The 
Genasun regulators are pretty quiet, but so far, they only make units 
for much smaller systems.


73, Jim K9YC

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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Tom Azlin W7SUA]

Hi Alan,

We put in a 10KW array on our garage roof using two SMA 5000TL-US-22 
inverters to grid tie. I could not see any difference in noise floor or 
moving noise bands with the inverters running or with both the DC and AC 
disconnected. Perhaps just lucky? We used a local solar company that has 
been around 30 years who was aware of RFI issues. The local panel 
distributor is a ham by the way. As an aside both inverters can provide 
up to 1500 watts at 120Vac if the grid is down. One inverter feeds that 
1500 watts to the kitchen and the other to the shack.


My HF dipole runs above the roof mounted panels with the feed about 70 
ft south of the garage.  I did not do any thing special for RFI. 
Electricians provided the UFER ground to the inverters. The two 240Vac 
lines from the inverters run underground about 75 ft over to the utility 
panels on the north side of the house.


They also said for just charging my station batteries using the 700 watt 
legacy solar array that came with the house that I should use a PWM 
charger rather than the noisier MPTT chargers. Have not picked a charger 
yet. The local solar guy also provided that 700 watt array to the 
original owners of our house as it was an off-grid solar home.


You can see the panels on my QRZ page's aerial view.

73, tom w7sua

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.


[snip]


Alan N1AL
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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Bill Steffey NY9H]

In 2010 I had installed a 10kw system, about 400 feet down from my tower.
Before selecting SMA as the inverter manufacturer, I went to two 
sites with my little Kenwood TF6A.  It has  am fm ssb  bdcst to 
uhf... using the am broadcast band and built in loop antenna, the 
only noise I could discern was when the handheld was held several 
inches from the inverter cabinet. Nothing heard on other bands. 
Lightning took out the inverters, Thor came into the inverters on the 
RS422 control lines, not the AC outputs, blowing the interface cards 
& control circuity. Insurance covered the replacement  SMA 5000TL 
transformerLESS inverters. Thankfully the loss of transformers did 
not change the cleanliness of the SMA boxes. Being in the boonies, 
allows an s3 noise level...and the SMA do not change that !!!


pix at my google/picasa site
https://picasaweb.google.com/102281425518350961470/SolarElectric

EIS Energy Independent Systems in Pittsburgh did a great job...
.no affiliation other than a customer ...

bill   ny9h/3

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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Jim Brown]

You're moving in the right direction, Alan. Study the QST article to 
learn as much as possible about the concepts. Remember that RF is 
radiated by CURRENT flowing on conductors that are not shielded, and 
that differential current on a transmission line is not radiated. 
Twisting helps that tremendously.


Study my RFI piece. I'd be happy to chat if you want to work through 
some ideas and concepts. Yes, inverters integral to panels can minimize 
RFI IF the units are properly designed, but that can be a very big if. 
:)  Also, buy Henry Ott's excellent EMC text and study it. Published by 
Wiley, you want the latest edition (c.a. 2007-8).


73, Jim K9YC



On Mon,7/18/2016 7:32 PM, Alan Bloom wrote:
I am now leaning on going with a local company rather than Solar City. 
They quoted a higher price for a lower-power system, but because of 
some convoluted accounting it will actually end up costing me less.  
And they are at least willing to talk about adding some common-mode 
chokes. Their system uses micro-inverters on each panel, which 
potentially should cause less interference because all the switching  
electronics is localized with short connections.  Only 240 VAC 60 Hz 
comes out of the panels.

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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Alan Bloom]

I am now leaning on going with a local company rather than Solar City. 
They quoted a higher price for a lower-power system, but because of some 
convoluted accounting it will actually end up costing me less.  And they 
are at least willing to talk about adding some common-mode chokes. 
Their system uses micro-inverters on each panel, which potentially 
should cause less interference because all the switching  electronics is 
localized with short connections.  Only 240 VAC 60 Hz comes out of the 
panels.


Alan N1AL


On 07/18/2016 06:49 PM, John Kaufmann wrote:

My advice on Solar City is to avoid them at all costs.  Their systems,
manufactured by SolarEdge, generate horrendous broadband RF noise

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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[John Kaufmann]

Sorry, I forgot to add my call to my post below.  It's W1FV (John).

 

From: John Kaufmann [mailto:jkaufm...@alum.mit.edu] 
Sent: Monday, July 18, 2016 9:50 PM
To: 'elecraft@mailman.qth.net'; 'n...@sonic.net'
Subject: Re: [Elecraft] OT: RF noise in solar photovoltaic system

 

My advice on Solar City is to avoid them at all costs.  Their systems,
manufactured by SolarEdge, generate horrendous broadband RF noise.  One of
my neighbors installed a Solar City system on his house and ever since, I've
been plagued with extremely bad RF noise, especially on 6m, whenever I beam
in the direction of his house.  On 50 MHz, it raises my noise floor by 25
dB, which makes it impossible to work anything but very strong signals in
the direction of the neighbor's house.

 

The neighbor has been very cooperative in trying to work with Solar City to
get the problem fixed for me, but Solar City is technically incompetent or
not seriously interested, or both, in trying to eliminate the noise.  They
claimed the noise was originating in their optimizers, so they replaced them
with different units.  However, that barely made a dent in the noise.  I ran
some tests and determined that both the inverter and the optimizers are
generating noise.  At this point Solar City is trying to wash their hands of
the whole mess.

 

The neighbor leases the system from Solar City, so neither he nor I can
really make any modifications to the hardware, like adding chokes and the
like.  I would like to get the FCC on the case, but I seriously doubt that
will ever come to pass.

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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[John Kaufmann]

My advice on Solar City is to avoid them at all costs.  Their systems,
manufactured by SolarEdge, generate horrendous broadband RF noise.  One of
my neighbors installed a Solar City system on his house and ever since, I've
been plagued with extremely bad RF noise, especially on 6m, whenever I beam
in the direction of his house.  On 50 MHz, it raises my noise floor by 25
dB, which makes it impossible to work anything but very strong signals in
the direction of the neighbor's house.

 

The neighbor has been very cooperative in trying to work with Solar City to
get the problem fixed for me, but Solar City is technically incompetent or
not seriously interested, or both, in trying to eliminate the noise.  They
claimed the noise was originating in their optimizers, so they replaced them
with different units.  However, that barely made a dent in the noise.  I ran
some tests and determined that both the inverter and the optimizers are
generating noise.  At this point Solar City is trying to wash their hands of
the whole mess.

 

The neighbor leases the system from Solar City, so neither he nor I can
really make any modifications to the hardware, like adding chokes and the
like.  I would like to get the FCC on the case, but I seriously doubt that
will ever come to pass.

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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Alan Bloom]

On 07/18/2016 01:42 PM, Joe Subich, W4TV wrote:

> Make sure they are quoting *everything.*  When I looked into solar a
> few years ago, the quote specifically excluded building permit(s).

Good point.  The contract states, "SolarCity will obtain any necessary 
permits, at SolarCity's cost."  So I think I'm covered there.


Alan N1AL
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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Josh Fiden]

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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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Jim Brown]

Yep. Just like always, the devil is the details, and the large print 
giveth while the small print taketh away. :)


73, Jim K9YC

On Mon,7/18/2016 1:42 PM, Joe Subich, W4TV wrote:

When I looked into solar a
few years ago, the quote specifically excluded building permit(s).
By the time the necessary PE reports, building permits, mortgage holder
sign-off, etc (regulatory crap) were added and the benefit of the
federal tax credit reduced because it is not a "refundable" credit,
the payback period was so long the ROI was not competitive with US
Government bonds! 



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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Joe Subich, W4TV]

I figure it should save about $1000/year in electricity bills and
they are quoting me $17.5 k for the system. That's a 5.7% return on
investment, or 8.3% ROI after the federal tax credit.


Make sure they are quoting *everything.*  When I looked into solar a
few years ago, the quote specifically excluded building permit(s).
By the time the necessary PE reports, building permits, mortgage holder
sign-off, etc (regulatory crap) were added and the benefit of the
federal tax credit reduced because it is not a "refundable" credit,
the payback period was so long the ROI was not competitive with US
Government bonds!

73,

   ... Joe, W4TV


On 7/18/2016 1:22 PM, Alan Bloom wrote:

Thanks for the pointer.  I was already aware that their "0% down" lease
arrangement is not a very good deal, so I am looking at buying the
system outright.  I figure it should save about $1000/year in
electricity bills and they are quoting me $17.5 k for the system. That's
a 5.7% return on investment, or 8.3% ROI after the federal tax credit.

http://energy.gov/savings/residential-renewable-energy-tax-credit

Alan N1AL


On 07/18/2016 05:54 AM, Wes Stewart wrote:

I would not be interested in working with Solar City.

http://watchdog.org/191409/congress-probes-solarcity/

On 7/18/2016 12:05 AM, Alan Bloom wrote:

I am contemplating having a solar photovoltaic power system installed
on my roof.



Solar City is not interested in working with me on this -



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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[RIchard Williams via Elecraft]

I installed solar panels on my roof last year, and have had no problems with 
noise from them. 

On the subject of Solar City, I will agee with Wes to stay away from that 
company.    Initially, I contacted Solar City for a bid, and have to say I was 
extremely disappointed with them.  First, they send out a young chick with a 
sales pitch to beat the band, and to "evaluate" an installation.  She came up 
with a plan of 31 panels, at a cost that I felt was on the high side (to say 
the least) and a 20 year loan with a higher interest rate than I expected!!!
She submitted her findings to the company, and several days later a 
'technician" arrived to check out the roof and verify what the chick told me 
they could do.  I went up on the roof with him, and he told me I wasn't suppose 
to be up there with him!!!  Told him it was my damn roof, and if I wanted to be 
up there, that was my prerogative.  He relented, but told me to stay out of the 
pictures he was going to take (fair enough - I'm not that photogenic anyway).   
 First thing he told me was a section of the roof where I wanted 3 panels was 
too steep for their employees to work on (scratch three panels).  When he was 
finished, he told me he would submit his plan to the engineering dept for their 
final approval.
The next thing I got was a call from the sales chick who came out the first 
time; sad news, scratch the 11 panels on the garage because (get this),  their 
"ace professional engineer" (must have graduated last in his class at Podunk 
Univ) said the roof on the garage would not hold the weight of the solar panels 
because  the additional weight of the Glen Martin Engineering 8 Foot  RT-832 
roof mounted tower weighing a whopping 32 POUNDS, the Yaesu G-5400 AZ- EL rotor 
(20 Pounds), the M2 2MCP14 (6 Pounds, M2 436CP30 (5 Pounds), and the weight of 
a 5 ft aluminum mast and 10 ft fiberglass cross boom (weight - at most 15 
Pounds - probably less).   So, he was telling me the additional 80 POUNDS on 
the roof was going to be too much weight on the roof!!!   O well, maybe it 
was the weight of the coax (that I didn't add in) was the final blow?
I told the chick exactly what I thought of there PE Dept; and the idiots must 
not have any idea of what was on the roof (80 lbs of aluminum!).   She did get 
back a few days later and told me the PE Dept agreed with my assessment (not 
they were a bunch of idiots, but at least the part where the roof would have no 
problem holding an additional 80 lbs).  I put them on hold until I looked at 
more estimates, and eventually cancelled out with them. 
I found a local company, and they had no problem with 30 panels (he dropped one 
because of too much shade), and no problem with the three on the one section of 
roof.So, I have solar (30 panels producing 8.25 KW) with micro inverters on 
each panel.  Am using SolarWorld SW275 panels and Enphase M250-60-2LL-S22 
inverters. 
Total price was just under $29,000 divided into two loans.  The first was 
$8,100 interest free loan for the first year; to be payed off with the income 
tax refund of 30% of the cost of the system.  The remain loan was a 12 year 
long just under $29,000 at 2.99%.  This is/was a much better deal than what 
Solar City offered!

Additionally, I had to move the Glen Martin tower to the edge of the garage to 
make room for all the panels;  and the guy helped me move the system to the 
place where it would not interfer with the installation of the panels!!
System has been in for a year, and producing 93% of what was calculated 
(calculations based on weather data).
Bottom line, I would check out local small companies that are not bound by all 
kinds of nit picky rules and restrictions, numerous levels of management and 
depts that all up the price they must charge to pay all the worker bees.
Dick, K8ZTT. 



  From: Wes Stewart <wes_n...@triconet.org>
 To: elecraft@mailman.qth.net 
 Sent: Monday, July 18, 2016 6:54 AM
 Subject: Re: [Elecraft] OT: RF noise in solar photovoltaic system
   
I would not be interested in working with Solar City.

http://watchdog.org/191409/congress-probes-solarcity/

On 7/18/2016 12:05 AM, Alan Bloom wrote:
> I am contemplating having a solar photovoltaic power system installed on my 
> roof.

> Solar City is not interested in working with me on this -

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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Alan Bloom]

Thanks for the pointer.  I was already aware that their "0% down" lease 
arrangement is not a very good deal, so I am looking at buying the 
system outright.  I figure it should save about $1000/year in 
electricity bills and they are quoting me $17.5 k for the system. 
That's a 5.7% return on investment, or 8.3% ROI after the federal tax 
credit.


http://energy.gov/savings/residential-renewable-energy-tax-credit

Alan N1AL


On 07/18/2016 05:54 AM, Wes Stewart wrote:

I would not be interested in working with Solar City.

http://watchdog.org/191409/congress-probes-solarcity/

On 7/18/2016 12:05 AM, Alan Bloom wrote:

I am contemplating having a solar photovoltaic power system installed
on my roof.



Solar City is not interested in working with me on this -



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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Clay Autery]

My local solar companies look at me like I'm an alien when I try to
explain to them what I want  They have ZERO actual knowledge... they
are building from a standard recipe...

I'm going to build my own...  Do NOT discount the AC conversion at the
panel approach...  it has MANY advantages, and probably the quietest
system you can build IF you do it right.

Jim, K9YC wrote a response to that article with some good info...

That article was basically what one guy did to band-aid a flawed design
and poorly chosen parts by a willing but uninformed vendor.

Follow the guidance in Jim's many papers and design the system
yourself...  Put it in yourself, and find a Master Electrician to
sign-off on your work and do the cross-connection to the grid.

73,

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Clay Autery, KY5G
MONTAC Enterprises

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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[KD6QZX]

Alan I have information on the SOLAR install as I have done this and have a big 
noise issue that I am combating still.  I think this email will just go to you 
please confirm and I will provide more information.
Scott AK6Q
 

On Monday, July 18, 2016 12:06 AM, Alan Bloom [via Elecraft] 
 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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Re: [Elecraft] OT: RF noise in solar photovoltaic system

[Wes Stewart]

I would not be interested in working with Solar City.

http://watchdog.org/191409/congress-probes-solarcity/

On 7/18/2016 12:05 AM, Alan Bloom wrote:

I am contemplating having a solar photovoltaic power system installed on my 
roof.



Solar City is not interested in working with me on this -


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Re: [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
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