Another thing to think about when the system is oversized for the
inverter being used (or charge controller)
and it clips all the time (I call it current limiting), is that the
input voltage will rise to reduce the output
power (to keep it limited) which will usually make the inverter or
charge controller heat up more.
boB
On 1/28/2013 9:40 AM, John Berdner wrote:
In a grid tied system the question becomes how much clipping and how often.
Intuitively we all know little clipping is probably ok but a lot of clipping is
a bad thing. How much is ok is the question.
Ultimately we should all be concerned with economics (LCOE / ROI). The clipping
experienced by one system design may or may not have a negative influence on LCOE
compared to an alternative system designs. We run LCOE analysis frequently and have a
field in the spreadsheet for clipping losses. For now we just use a fixed percentage but
time of day metering makes this much more complicated. With TOD metering the value of
energy varies both by time of day and seasonally so the energy lost to clipping can have
a different value than the increased energy "on the shoulders".
Ideally one would look at the irradiance over a year and then do a distribution
of the hours per year at various insolation levels. In places other than
Hawaii you need to correlate irradiance to temperature since module power is
varies with temperature (typically -0.5%/degree C), i.e. high irradiance on a
hot summer day is less likely to cause clipping than high irradiance on a cold
winter day.
@ Marco: does your weather data source have a database of insolation and
temperature over the year ?
Best Regards,
John Berdner
General Manager, North America
SolarEdge Technologies, Inc.
3347 Gateway Boulevard, Fremont CA 94538 USA (*Please note of our new address.)
T: 510.498.3200, X 747
M: 530.277.4894
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of William Miller
Sent: Sunday, January 27, 2013 8:05 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] high insolation value and inverter undersizing
Jesse:
Do you have any way to compare the total harvest for the day for a given module in a
"clipping" scenario versus an unclipping? The question I want to answer is: Do
we improve production enough on the shoulders of the clip to justify the loss on the peak?
Thanks,
William Miller
At 06:25 PM 1/27/2013, you wrote:
A while back (3 years)I installed a system (bid spec) for a school that
used 215W RECs and D380s on a dual axis tracker. With the ability to
monitor the array, I see constant clipping. The modules will usually
produce 199Ws regularly. A few days ago we had temps of -34F and clear
skies. My array at home had one of its best days this winter. I have
Tigos on so I can monitor watts, current, temp and voltage. I was
seeing anywhere from 215W to 223W from my modules between 11:30am and
1pm. The modules on the tracker were still producing 199W. I didn't
get an irradiance reading that day but my Tigos showed above IMP
readings and way above VMP reading that day.
I've only been doing this for 6 years, so I don't have the experience
that some people on this list have, but it seems foolish to me to waste
that production. It's kinda site specific, but where I live the cold
temps and snow reflection seem like something we should be utilizing.
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