[RE-wrenches] SolarEdge v Enphase

[Larry Crutcher, Starlight Solar Power Systems]

Once again Dan, you nail great information to this board. Key phrase: "used within its specification" 

Back in the '80's I replaced hundreds of small caps in very poorly designed 2-3 year old C-band satellite receivers, all damaged by excessive internal heat.

Thanks for your input.

Larry Crutcher
Starlight Solar Power Systems



On Jan 12, 2012, at 4:59 PM, Exeltech wrote:

Wrenches,

I wish this urban myth about electrolytic capacitors would
die, but it won't.  It's been a wonderful marketing ploy for
some time now.

Simply stated, existence of electrolytic capacitors in inverters
does NOT mean the inverters are less reliable.  Satellites
have been using electrolytic caps for decades, and look
how long THEY last!  (I know, because I've helped to design
power supplies for aerospace applications.)

What it boils down to is this: if a quality electrolytic capacitor
is used within its specifications, you can expect 60+ years
of life from it in an inverter application.  Conversely, if a
circuit is poorly designed, you can ruin any electronic part
in a very short time.

What defines capacitor "life"?  It's defined as the doubling
of the internal effective series resistance of the capacitor
from the value it had when it (the cap) was new.

This is energy lost.  It also causes the capacitor to operate
at a slightly higher internal temperature than when it was
new (all other factors being the same).

Result?  It all depends on how the circuit is designed.  In
our case, the inverter efficiency decreases approximately
a quarter to one half of a percent.   The waveform distortion
also increases, but it takes lab grade equipment to detect
the change.  If you're worried about a 1/2 percent drop in
the inverter efficiency, your concern is misplaced.  After all,
PV degrades over time much more than that!

So why the bad rap on capacitors?

Like tires, they DO wear out.  40 years ago, "premium"
tires were rated for 30,000 miles.  Could you wear them
out in less?  Absolutely!  Drive like a 16 year old kid with
a muscle car, and it's easy.  On the other hand, I just bought
a new set of tires.  The old ones still had tread, but at 88,000
miles, they'd seen their better days.  This is a far cry from 30k
mile tires.

Capacitors have progressed in the same manner.  A long time
ago, capacitors wore out in 5 to 10 years.  Today, it's an entirely
different story.

As long as the circuits in which the electrolytic capacitors are
used are well designed, you have nothing to worry about.
Electrolytic capacitors in a well-designed application will outlive
all of us.


Dan Lepinski
Senior Engineer
Exeltech


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