[TowerTalk] Solar Panel RFI/Microinverters

[Howard Hoyt]

Hi all,

When I was researching for my 6 KW system in 2011, I used a small 
portable Eton emergency radio tuned to static above the AM BCB to listen 
for RFI when visiting sites.  There was a large difference between 
manufacturers, and I did hear some RFI from the (at the time) new 
Enphase microinverters, so I discounted using them, perhaps they are 
different now.  I know the exact wire routing and grounding can make a 
large difference in both conducted and radiated RFI, so I also thought 
if RFI should it occur, it would be easier to address just one or two 
sources as opposed to 20 (the number of microinverters I'd need).

Among the large string inverters I originally wanted to purchase 
Schneider, but the RFI was quite a bit higher than the quietest brand I 
found, SMA.  I ended up purchasing two German manufactured SMA SunnyBoy 
4000 units and split my PV string in half.  The system is monitored 
using a SMA WebBox and I can see the data  in real-time online.  When I 
did the install I made all above-ground AC and DC wiring in steel EMT, 
and twisted the current carrying pairs before pulling.  I did not choke 
any DC input lines or AC outputs, and using a Tek 2712 SA on my 235' 
dipole which is 130' away from the PV array I cannot see any hash or 
noise floor increase when the system is on or off from 1.8 MHz up.  
Below that BCB signals swamp everything.

Given the large number of variables between each PV install I can only 
state that in my particular situation using SMA inverters and twisted 
pair wiring in steel conduit there is an acceptably low level of 
conducted and radiated RFI.  There are much cheaper inverters available, 
but the SMA units have given 100% uptime for over five years so far with 
effectively zero RFI, so I feel it was worth it.  Just my $0.02.

Cheers & 73,

Howie - WA4PSC