Yet, Another RF Noise Question...

**SunEagle** · 06-29-2016, 06:58 PM

I guess we would need to know a little more about the solar hardware you plan on installing. I am not sure if #12 wire would be big enough to handle the current or voltage drop on 100 foot run.

So before you worry about RF I would first make sure your wiring is up to code and will do the job for a grid tie solar pv system.

**DanKegel** · 06-29-2016, 07:28 PM

Regardless of the answer to the conduit question, have your friend come over when they test the system, and have him bring a receiver; if he notices RFI, you can have the installer add chokes or other filtering that might help.

I didn't notice much RFI except right next to my inverter (SolarEdge), but I only looked with an old portable Sony shortwave radio.

I have a funny feeling an AC microinverter system like Enphase has more chances to generate RFI than a DC optimizer system like Solaredge, but I don't have any data to back that up.

**solarix** · 06-29-2016, 07:53 PM

Another reason not to do microinverters. While i'm sure they have the RF noise below any UL spec, you still have many little switching power supplies generating noise. I'm not sure it would be more or less total noise than a equivalent string inverter would generate, but at least on the DC side - a string inverter is absolutely quiet. All in all, our modern world is so full of power supplies with switching circuitry above 15kHz and harmonics that go way on up - that we are bombarded with RF already. It would be interesting to find out what you HAM guy can measure...

**DanKegel** · 06-29-2016, 08:42 PM

FWIW, at about 5pm in bright sunlight, I walked around the area with my shortwave receiver tuned to 5.000 MHz (WWV). The neighborhood is urban, lots of radio noise.
Away from the house, I could clearly hear the ticks and tones, and depending on where I was, even clearly understand the announcer giving the time.
In the house -- especially around the front porch, or right next to long wires or downspouts -- there was too much noise to hear any of that.
One LED floodlight made lots of noise, so I unscrewed it. (Bad Phillips, bad!) A dimmer made some noise, so I turned it off.
Killing the power to the entire house reduced the noise level enough so that I could even hear the ticks and tones in a few places inside the house.
Turning off the SolarEdge and throwing the DC disconnect didn't seem to change much.
Proximity to the panels didn't seem to do too much.
Proximity to the inverter did show some noise, even when it was off, probably because it's near lots of long wires and downspouts.
Being near one phone line was REALLY LOUD.

Our solaredge inverter came from the factory with big chokes on the inside near the bottom that aren't in pictures I've seen online, so they may have gotten more careful recently.

In short, found some noisy bits, but no smoking gun pointing to the solaredge inverters or optimizers, at least with my "drowns out WWV on a handheld shortwave reciever" test..

**sdold** · 06-29-2016, 08:45 PM

I think RF chokes near the inverters would be likely to attenuate the data going to the Envoy.

**Sunking** · 06-29-2016, 09:21 PM

You should ask a HAM radio operator instead of listening to Dan. I am KF5LJW, 73's.

The issue is not Radiated RF nose, or even generated on the DC side (panels) You are barking up the wrong tree. it is Induced and mitigated on the wiring of the output of the GT Inverter to utility that is the offender. No amount of shielding would be effective. The problem lies in the design of the Inverter end of story. So unless you are willing to spend the bucks on a Output Filter, don't bother with it or give it any thought.

If it offends any Ham Operator let them file a complaint with the FCC. Then in turn you pass the buck to the Installer and Manufacture for resolution at their expense.

**DanKegel** · 06-29-2016, 09:58 PM

Here's a picture showing the chokes: IMG_20160212_080151.jpg

**bcroe** · 06-29-2016, 10:07 PM

Some basics. First thing to understand is where the noise is generated. If you used a Pulse Width controller, the switching of the entire DC
output current would occur through the panels, the controller, and the battery. The whole system is an antenna. Not a lot can be done about
this, except try to control the rise and fall times of the switching.
With any kind of MPPT system, there is very noisy action in the controller/inverter, but a good product will shield and filter the input and
output leads to limit how much escapes or is conducted to be radiated by system wiring. For a very sensitive situation (HAM nearby), its
not outrageous to build a (well ventilated) metal cage (hardware cloth) around the inverter and add another level of filtering to power leads
to the inverter. My Fronius inverters had good internal filters which did not require this, even right next to my radio tower. Those doughnut
filters might get a product just under a gov reg, but they do so little as to useless to a HAM.
Finally if you use micro inverters, you have moved the radiation generator to a place where you can't treat radiation, and there are lots
of them instead of one. My expectation is that in order to keep the size and cost of individual micros down, they would not be shielded
and filtered as well as one big inverter. I recommend against them in a sensitive situation; putting the final cable in conduit isn't going
to buy you many DB (if any), and not much else is possible. Bruce Roe K9MQG since 1958

**SunEagle** · 06-30-2016, 08:50 AM

Going back to the OP original post I see that he is using Enphase micro inverters so it would be the AC lines that he is worried about being affected by RF.

I am not sure how to install chokes on the micro inverters ouputs but maybe it can be done.

I still wouldn't worry about the RF since my concern is that #12 wire runs of 100 foot length which might cause even an AC voltage drop and might not have a high enough amp rating depending on the number of micro inverters per string..

**Engineer** · 06-30-2016, 09:22 AM

I work in RF test and have a 100k SA/NA in my house (I work from home part time) I could take some measurements with. Deciding outright that micros are a problem as solarix did above is stupid, RF signals and interference is extremely tricky - i.e. there's NO way to decide a-priori whether there is an issue or not and doing so is being ignorant, you have to measure a particular system. And recognize that another 'identical' system may not have the same interference characteristics (all it takes is for one 'rusty bolt' to cause some intermod distortion).

I definitely wouldn't enclose in conduit as, supposing you have some interference, that wouldn't necessarily fix the problem (and probably wouldn't anyhow). RF has a way of sneaking around simple brute force approaches like that.

Anyhow I can talk more about it later. I'm on vacation so don't feel like playing the RF engineer, but maybe I'll do some tests.

**Engineer** · 06-30-2016, 09:38 AM

Here's a story for you. At work we have a large 1MW tracking solar array which is a beauty to see. We also have electric car stations, and having a lot of engineers we have a number of electric cars including a bunch of home brews. Anyhow these engineers noticed difficulties charging their cars, and being engineers went about finding why with using lots of really expensive test equipment we have there at work. Turns out RF interference wasn't an issue (we are a RF facility with a large state of the art anechoic chamber) but it was the noisy power coming off the inverters. You see because they couldn't figure out what department to charge for the power for the cars, they just put the car charging on the inverter side of the system (AC directly from the inverters), not the load side which for reasons unclear to me would have resulted in cleaner AC. Anyhow the dirty power coming off the inverters was causing trouble with the cars charging systems. Then we got a new CEO who is into electric cars (he has a BMW i8), so the problem got fixed by putting them on the other side of the circuit (and dealing with the costs somehow).

What kind of system do we have? Big old fatty string inverters.

**SunEagle** · 06-30-2016, 10:27 AM

Originally posted by Engineer

Here's a story for you. At work we have a large 1MW tracking solar array which is a beauty to see. We also have electric car stations, and having a lot of engineers we have a number of electric cars including a bunch of home brews. Anyhow these engineers noticed difficulties charging their cars, and being engineers went about finding why with using lots of really expensive test equipment we have there at work. Turns out RF interference wasn't an issue (we are a RF facility with a large state of the art anechoic chamber) but it was the noisy power coming off the inverters. You see because they couldn't figure out what department to charge for the power for the cars, they just put the car charging on the inverter side of the system (AC directly from the inverters), not the load side which for reasons unclear to me would have resulted in cleaner AC. Anyhow the dirty power coming off the inverters was causing trouble with the cars charging systems. Then we got a new CEO who is into electric cars (he has a BMW i8), so the problem got fixed by putting them on the other side of the circuit (and dealing with the costs somehow).

What kind of system do we have? Big old fatty string inverters.

They probably should have installed HMT transformers to reduce the harmonic distortion and clean up the power quality. Those HMT's would also be more efficient and probably reduce electric costs.

**bcroe** · 06-30-2016, 07:21 PM

Originally posted by SunEagle

Going back to the OP original post I see that he is using Enphase micro inverters so it would be the AC lines that he is worried about being affected by RF.

I am not sure how to install chokes on the micro inverters ouputs but maybe it can be done.

I thought he said "I am planning"; I suggest that going that route means you are stuck with whatever radiation happens. Bruce Roe

**Sunking** · 06-30-2016, 07:27 PM

Enclosing the Wires will do nothing. The noise is generated in Differential Mode, not Common Mode. Any Engineer would know that.

It requires an In-Line Filter that cost you money. One for each Micro Inverter.

Yet, Another RF Noise Question...

Yet, Another RF Noise Question...

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