Need advice on Solar design with regards to interference

[fresnoboy]

Hi - we're building a new house here in the SF Bay area. It's a 2 story craftsman style home, so the roof has some facets to it, sort of like this house: https://cdn.houseplans.com/product/r.../w1024.jpg?v=7, but larger overall. The front of the house is south by southwest, which means the panels mostly should be on the front and right side of the house, and there is a detached garage as well that faces the same way that can host panels as well.

Due to rates here in PG&E land, getting a lot of power out of the array is important to me. The solar contractor my GC has recommended wants to use Solaredge gear, as the optimizers would help deal with panels that are at different angles. Th problem with that is that I am a ham radio operator, and the Solaredge optimizers (not the inverters) use DC-DC converters that have been poorly designed from a radio interference point of view.

Even if the main inverter is off, they put out a ton of RF in the shortwave bands, wiping out most of the signals I'd like to be able to receive. This has been validated in a couple articles by hams who had been saddled with these and so I'd need to avoid Solaredge because of it.

There is some anecdotal evidence that some of the string inverter companies like SMA do not have such problems, but I am told the roof design means its going to take a efficiency hit without the use of some type of optimizer.

I was wondering if folks here had any experience with the Tigo optimizers, as they don't seem to have DC-DC converters in their designs, or the new Maxim integrated optimizers that as far as I can tell are only in Chinese panels so far, and not in the highest wattage panels at that.

The first sets of Enphase inverters were TERRIBLE as well in the interference department, but newer units are supposed to be better, but radio operators tend to stay away from them so I can't find anyone who has them and can say they aren't a problem.

And also some have heard that Solaredge has newer optimizer designs that are better, but again I can't find anyone who can verify that or tell me the various versions they have shipped and their differences.

My GC's solar guy looks at me strangely when I bring all this up, as I don't think he's ever dealt with this issue.

Has anyone here experienced a lot of interference to your AM radios and such, or general RF interference and can guide me away from or to designs that would serve my home well and not interference with radio signals?

This is a real problem in an emergency where this type of communication is important, and provides links when the normal networks have problems.


thanks!
mike

[cebury]

IIRC Sunking has the experience and maybe a possible workaround (dont recall if it was financially reasonable) for this issue. He is out in Texas disaster so has been missing for a bit. You might try finding the posts using google site searches for this forum, his name, and the ham intereference until he gets back.

[fresnoboy]

IIRC Sunking has the experience and maybe a possible workaround (dont recall if it was financially reasonable) for this issue. He is out in Texas disaster so has been missing for a bit. You might try finding the posts using google site searches for this forum, his name, and the ham intereference until he gets back.

Indeed! I didn't know there were threads about this topic here! Funny, Google didn't lead me here...

I look forward to Sunking's return!

Thanks,
mike

[cebury]

I didnt mean to imply he was the only one with HAM experience, but I do remember this topic discussed and some of his reply.

[Mike90250]

So, if your roof does not have shade issues, till late in the afternoon (minimal impact) groups of panels that have the same illumination angle (and no shade) won't benefit from optimizers.
If you use a string inverter, and intelligently group panels to individual MPPT inputs, you will be OK. (staying within the MPPT specs)
Beware - some inverters work from 200 - 550Vdc but the MPPT works 280-490Vdc - dig into the fine print when grouping the strings.

[bcroe]

I didnt mean to imply he was the only one with HAM experience, but I do remember
this topic discussed and some of his reply.

HAMs aren't the only ones with interference issues. Interference from one central inverter can be contained by
the usual filtering and shielding methods. Using micro inverters or optimizers will multiply the sources to every
panel. Dealing with every single one would not be out of the question here, but the communication optimizers
need operationally might be affected.

There are a pair of 7.5KW grid tie inverters here. The first operational test was to check how much filtering
they would require. These Fronius were very well behaved; no external filter was needed. A peek inside
revealed use of a standard EMI filter. String inverters win.

You might study the problem and try to organize your panels into groups having similar orientation and shading.
If some groups are strings of the same length, they may be directly paralleled. If some are different lengths,
they might take advantage of a multiple MPPT input inverter. Panels don't have to have the same orientation
as the roof; maybe some could be braced up to match a group. I wouldn't be above putting a couple on the
ground for a solution. good luck, Bruce Roe K9MQG since 1958

[fresnoboy]

Thanks folks. I saw in the other thread that wb8erj had great results using the enphase M215 microinverters, which was surprising to me. Do their newer units perform well RFI wise as well?

As for string inverters, that's my current guidance to the solar guy, but he doesn't install many of them these days, and doesn't have experience with Fronius. I've asked him for a design using a string and we'll see what he comes back with.

If you look at the photo I linked in the original post, the house is craftsman style, so the facets on the roof would seem to call out for an optimizer design of some sort, but we'll see what the hit is from the planning software when he plans it out.

Does anyone have experience withe maxim integrated parts in the panels from an RFI POV? There are some scattered reports of lots of TV interference from Australia, but nothing solid on HF or VHF.

thx
mike

[bcroe]

I doubt any installer will actually have the knowledge and experience to deal with EMI from solar. Best to make
your measurements from an operational system. Bruce Roe

[idnominal]

I doubt any installer will actually have the knowledge and experience to deal with EMI from solar. Best to make
your measurements from an operational system. Bruce Roe

I agree, for example, consider finding a ham with a mobile HF installation and drive close to enphase installations and see what radiated noise you can detect.

As to direct AC line coupled noise, my feeling is that the enphase power line comms signal should be isolated at a dedicated PV AC panel by an industrial filter. It takes more time, costs a few hundred extra (more if done by an installer), however this solution isolates the power line comms signals to the envoy, PV AC panel, and microinverters. This solution will not help with any HF radiation from microinverters themselves (if that is an issue).

I explained it here: https://www.solarpaneltalk.com/forum...-from-pv-panel

[bcroe]

It appears to me that after a lot of research, someone could write a book on removing the EMI while
attempting to retain all the forms of internal communication these systems are using. Here its no
issue; any EMI goes, other solar communications are not necessary. Bruce Roe

[fresnoboy]

It appears to me that after a lot of research, someone could write a book on removing the EMI while
attempting to retain all the forms of internal communication these systems are using. Here its no
issue; any EMI goes, other solar communications are not necessary. Bruce Roe

I agree that choosing PLC for the solar comms is not the best choice to reduce RFI. I think the Tigo gear uses 2.4 GHz mesh communications, which at least wouldn't be in a band that would be a problem.

I will make sure the solar gets terminated in its own panel, but I am also trying to feed the station with it's own separately grounded feed, though an isolation transformer from the main panel, and then grounding everything through it's own stub from the house foundation ground. I am hoping that will decouple the station from internal building noise (I have a rack of servers in the basement, which will have their own isolation transformer feeding that circuit).

Is it the consensus that the RFI from these solar systems propagates through the power wiring in the house as opposed to radiating from the roof and getting into the antennas that way?

Thx
mike

[bcroe]

Mike, every situation is different. Certainly the wiring conducts noise, but unless its in metal
conduit (with well grounded ends) wiring is also an antenna. Your arrangement, the frequencies,
background radiation there are all factors.

My experience is, halfway measures might get you a few db, but that isn't much in over-the-air
communications. Really big improvements mean attacking the source big time, no exposed
radiating wires. The "perfect" containment doesn't really exist, how good is "good enough"
for you? Bruce Roe

[idnominal]

... Is it the consensus that the RFI from these solar systems propagates through the power wiring in the house as opposed to radiating from the roof and getting into the antennas that way? ...

For a robust enphase plc system with minimal plc RFI in the home, it is best to not intentionally (and needlessly) inject the enphase plc signals into the entire home electrical system. There are many successful alternative filtering schemes and solutions. However, a good first step is to strongly isolate the enphase PV plc system, preferably by a dedicated separate PV AC panel, then add additional remedies (if needed).

The more common wisdom seems to be to save money by installing the branch AC PV breakers in the home's main panel. Once that approach is taken, there is no other option than to try filter individual circuits (load up on ferrites) and/or individual gear (e.g. AC line filters). One reason it is so hard to filter out the enhpase plc from there, is that each of the PV branch breakers from the enphase micros couple the enphase plc signals directly into the main home panel heavy bus bars.

The huge advantage of a separate dedicated AC PV panel for an enphase system is that you can strongly filter once between the enphase system and the home's electrical panel. The reason it is such a robust solution is that now there is only one AC line from the PV panel to the home's main panel, and a suitable filter can be placed in L1/L2 of that single line (but, not in the neutral line). This solution does take an extra panel (it can be a relatively inexpensive panel from a home store or electrical supplier) and a $100 to $300 relatively high current industrial inline filter, plus an appropriately sized cable between the PV AC panel and the home's main panel.

[sdold]

The other important part of the sub-panel method of isolation is to use an outlet on that sub panel for the Envoy, so that the 144 KHz signal from the inverters to the envoy is not attenuated, but they are both isolated from the main panel. It worked really well for me using a couple of toroids on the two hot legs between the main panel and sub panel. They were around 1.5 inch diameter, maybe 2", and I'm not sure what the mix was. It was probably 43, I don't know if that's optimum but it's probably what was in my box.

I just measured the effect of my 16 M215s at 1:30 pm in full sun on a 2m radio with the antenna about 20 feet from the array, there was no interference. In ham lingo, the effective sensitivity was about 118 dBm with the inverters on or off, they made less than a dB difference. I've never looked at them on HF though.

Mike, have you searched around on qrz.com to see if there is anything? There's a good chance this has come up. You're smart to think of this before selecting an inverter, for some reason it never crossed my mind when I was picking equipment.

Steve

[idnominal]

The other important part of the sub-panel method of isolation is to use an outlet on that sub panel for the Envoy ...

yes, thank you, I came back to add that. The envoy is direct connected (either outlet or hard wired) to the PV AC panel.

plc's only purpose is to make communications between the micros on one or more branch circuits and the envoy. The envoy gets directly connected to the isolated part, the PV AC panel. Ideally, the envoy would not work at all anywhere on the home side of the single filter, because plc is sufficiently attenuated everywhere outside the isolated PV comms system. But, on the PV AC panel side of the AC plc filter, 5 solid bars!

Another advantage of a separate PV AC panel isolated by a good quality industrial filter (including some DIY filter implementations) is that once installed, the system is relatively insensitive to any changes in the home's wiring or loads. When there is no isolation (enphase branch circuit and envoy both connected to the main panel), a "fix" by ferrites and/or line filters may stop working if something new is plugged in, or even if only minor changes are made later in any of the home circuits.