[RFI] RFI when solar array is switched off?

[nlsa at nlsa.com]

Dear Michael,

Thank you for your clear and specific reply to my question.

I will investigate whether residual RFI continues when microinverters are
shut down.

Best regards,

Michael, W9IP

 

From: Michael Carter <Mike.Carter at unh.edu> 
Sent: Tuesday, January 03, 2023 1:26 PM
To: RFI at contesting.com; nlsa at nlsa.com
Subject: Re: [RFI] RFI when solar array is switched off?

 

Hi Michael,

 

All inverters, whether centralized or distributed (microinverters

on each module of the PV array) have an accepted input

voltage range over which they will perform the DC to AC conversion.

If the inverter's input DC voltage falls below the low end

of the range, it will shut down.  However, the PV module

I-V curve exhibits only moderate changes in terminal voltage

with large changes in irradiance of the module, and the

inverter(s) may not shut down even with low irradiance

levels (think early morning and late afternoon when sun

angles are shallow relative to array inclination).  Both 

centralized and distributed inverters with Maximum Power

Point Tracking (MPPT) have an additional constraint on the

range over which MPPT is possible.  In that sense, the array being

'off' is not defined by the PV module terminal voltage

but by the inverter's design specifications.

 

The RFI potential of various inverters/microinverters has been

discussed at length on this forum - it's important to 

discuss with your prospective PV system installer which

system architecture (centralized vs. distributed inverter)

and equipment brands they customarily use before committing

to purchase.

 

Can one shut off inverters?  For a central inverter, certainly via

the array disconnect switch.  For distributed inverters - maybe.

Some microinverters are compliant with the Rapid Shutdown

requirement (for UL listing of such equipment as well as 

NEC 2020) and both AC and DC sides of the microinverter

can be disconnected remotely.  Whether there is any 

residual RFI generation in that state is an open question.

A mains disconnect switch is a requirement for any

PV system, but as others on this forum have noted the

primary mode of inverter RFI is via radiation from the PV

array wiring rather than the AC mains.

 

In short, discuss your concerns with prospective PV 

system installers and bring the installers' responses

back to this forum.

 

73,

Mike, K8CN

  _____  

From: RFI <rfi-bounces+mike.carter=unh.edu at contesting.com
<mailto:rfi-bounces+mike.carter=unh.edu at contesting.com> > on behalf of
nlsa at nlsa.com <mailto:nlsa at nlsa.com>  <nlsa at nlsa.com <mailto:nlsa at nlsa.com>
>
Sent: Tuesday, January 3, 2023 12:19 PM
To: RFI at contesting.com <mailto:RFI at contesting.com>  <RFI at contesting.com
<mailto:RFI at contesting.com> >
Subject: [RFI] RFI when solar array is switched off? 

 

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Dear friends,

I have a question about the "off" state of PV arrays.  If a solar array
generates RFI when it is on, does it stop when the array is turned off?

I suppose that the answer depends on several factors:

*       type of array (string inverter vs microinverter)
*       definition of "off"
*       mains disconnect status

I'm asking because my family is considering a pretty big array.  I don't
know in advance whether its RF emissions will be troublesome to my 2m EME
system but I assume the worst.  However, if I can throw a switch that
RF-silences the solar array while I'm operating, then the problem
disappears..

Thanks -

Michael, W9IP

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