[aprssig] FW: Solar Ham Radio Interference

Robert Bruninga bruninga at usna.edu
Sat Nov 19 10:31:55 CST 2016


> You can't use string inverters on an array that receives
> partial shade otherwise your array efficiency will be lower.

This is a common sales tactic to sell more expensive microinverters and
optimizers than are actually needed.  Remember, 60% of the US economy is
based on selling us things we do not need (we all heard that after 9/11
when people stopped buying)....  And it is not really the salesmen's
fault.  They are just repeating what they have been taught under some
conditions and then applying it to ALL conditions.

Series strings perform identically to microinvertters and optimizers in the
presence of shading except under two conditions.

Condition 1:  Once the series string has all panels shaded except for a
remaining 6 or so, then the voltage has dropped so far in the string that
the inverers drop out.  But when it gets to that point in the day,  either
1) it is only a few minutes from sun down or total shade, or 2) at such
oblique angles that the lost few hundred watts for 15 minutes is
insignificant, or 3) one needs to invest in a chain saw.

Condition 2.  The structure is such that one cannot place the panels in
groups of 10 to 14 panels all facing the same way.  If one can only have
smaller bunches of panels all facing different angles, then  yes,
micorinverters can collect those smaller increments of power and sum them..

But in all other cases, each panel reacts virtually the same way to shading
whether it is in a series string or in a microinverter.  Here is why...

Every panel typically has an operating voltage of about 30 volts.  But
since silicon cells cannot tolerate any reverse voltage over 10 volts, the
panels are all wired internally as three 10 volts strings in series.  And
there are THREE reverse-protection diodes inside the little connection box
on the back of the panel.  Thus, not only is the entire panel reverse
protected, but in fact each third of the panel is reverse protected.

So when you get partial shading on ANY SINGLE CELL, yes, the output of that
10v string falls, and gets reversed biased, and so the 1/3rd of the panel
(with one cell shaded) gets bypassed.

* But there is no impact on the other 13 panels in the string nor of even
the other two 10v strings in the same panel.  Salesmen make all their money
convincing people that the entire array suffers.  Not true one single bit.

* AND, this loss of that 1/3rd (10v) string occurs exactly the same with a
microinverter,. Since the microinverter is connected at the 30v panel
output, and not three microinverters operating at only 10v input.  When a
single cell is shaded, that 1/3rd of the panel is lost for the
microinverter too!

Another reason they like to sell microinverters, is that it makes their job
easier.  They dont have to use metal conduit to route the HV dc down to
your utility closet and find room to hang a large DC string inverter.
Their job is easier and one pays more for it.

And finally, the temperature extremes on the roof of a house from -30F to
+150F is the last palce (and most inaccessible place) one would want to put
their expensive RFI generating electronics.

It is easy for a salesman to use the XMAS string analogy of a shaded panel
taking out them all,  But is simply not true since every panel must already
have (by the laws of physics) bypass diodes.

Solar panels only produce 95% of their power during the middle 4 to 6 hours
of the day.  Spending lots more, creating sources of RFI, and introducing a
maintenance nightmare to recover the final few perecnt is not worth it.

But again, microinverers ARE required when one cannot place solar panels at
least 10 or more in groups all facing the same way.

Hope that helps.
Bob, WB4aPR




> On 2016-11-18 17:11, Robert Bruninga wrote:
> > NEW ISSUE:
> >
> > Previously QST and my emails discussed the rise in the noise floor from
> home
> > solar and my suggestions to avoid purchasing a system with
> micro-invrters or
> > elecronic "optimizers" on every panel on the roof, and stick with the
> > wuieter or easier-to-fix all DC wiring and central inverters.
> >
> > THAT’S NOT ALL!   It was pointed out at the ARISS meeting this weekend
> that
> > one must also watch out for their NEIGHBORS!  That is, if you want to
> keep
> > your clean noise floor for your own hamming and your own solar, you must
> > also be vigilant of your surrounding neighbors.
> >
> > The time to make friends so you can guide their future investment is NOW,
> > well in advance before they make an irreversible decision.
> >
> > Ill try to remember to go out and see how far the noise radiates from
> some
> > of the other solar panels in my neighborhood.  Although my DC system with
> > central inverters is much quieter, I should go out and see how far beyond
> > these houses, the various system's interference can be detected.
> >
> > Bob, Wb4APR
> >
> > -----Original Message-----
> > From: Robert Bruninga [mailto:bruninga at usna.edu]
> > Sent: Sunday, October 23, 2016 12:55 PM
> > To: Amsat BB
> > Cc: bruninga at usna.edu
> > Subject: Solar Ham Radio Interference
> >
> > Not Satellite related, but people often ask about any RFI from my solar
> > arrays at home.  Interest stems from an RFI issue in April QST and my
> letter
> > in Sept 2016 QST.
> >
> > Well, FINALLY, the jury is in.  For the first time since installing
> solar, I
> > finally got all my full-sized dipoles up in the air again. And listened
> with
> > the arrays on and off.
> >
> > Yes, I have inverter noise about 12 dB above the noise floor every 38
> kHz on
> > 80 meters,. But couldn't really find anything on 20 meters.  I did not
> do a
> > thorough search, but enough to finally say, "yes, there is some noise..."
> >
> > I post this because my 16kw of arrays are conventional series string
> arrays
> > and much quieter than the  "optimizers" on every panel all over the roof
> > noted in the April QST article.  I always thought my string array was
> quiet,
> > but now I have some data noted above.  This could easily be fixed with
> some
> > clamp-on ferrites down in the basement on the wires going into the
> > inverters...
> >
> > But for my rare HF operating, the solar AC disconnect switch is about 3
> feet
> > from the kitchen door.  Easy enough to pull if I want HF silence.  I
> could
> > also install a 40 amp disconnect relay from a switch in the shack...  But
> > with my rare operating style, I'll probably do nothing.  Of course it is
> > perfectly quiet at night ;-)
> >
> > It took me 6 years to get around to this test, so don't hold your breath
> > waiting for me to add some clamp-on filters to the inverter wires and see
> > what that does.
> >
> > For those into solar, come join us on SolarDIY at yahoogroups.com Bob,
> WB4APR
>
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