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Understood. Thank you.
So that would mean on what's about your best production day your array(s) are producing something like 155 kWh from 34.95 STC kW of PV ?
If I might test your forbearance for questions a bit more: How about a SWAG for total annual output for all the installed PV you have in terms of kWh/yr. per installed STC kW ?Comment
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You could say that, yes. The way I see it, 15KW inverters produced 155KWH mid May, because
my limiting factor is the size of the inverter plant. All the commercial applications seen here
recently state the inverter AC output capacity, with a DC/AC ratio, and I am following that approach.
Not included in that statement, is the cloudy sky performance, hard to put precise numbers on. What
I see is for clear skies, 15KW output for more than 8 hours. For rather slight clouds, output remains
saturated much of the day. For clouds starting to eliminate hard shadow lines, output is 80%. In days
the sun is not seen output may run 40 to 50% of capacity. In a rain storm output is usually in the range
of 10 to 25%. Here is my daily output curve recently. Annual output depends on the weather and
upgrades, latest is 28,500 KWH.
PV15May19.png
For a 15KW system installed here at Zip 61084, 42 deg lat, never ending clouds of varying weight, I claim other
systems will not do as well as mine. My system is not optimized for the SW desert, and designs from there perform
poorly here. Arrays I have seen:
FIXED ARRAY.
Less optimum annual angle
Huge snow removal effort required more than a dozen times each winter
Limited day hours near peak output.
Output severely limited under less than optimum sun.
DUAL AXIS TRACKER: Never used on sizable arrays.
SINGLE AXIS TRACKER, E-W Scan.
The shaft on this oft used commercial setup is parallel to the ground. At 42 deg Lat
the incident angle drops output to about 0.7. This means the DC/AC ratio
must be increased accordingly, this while keeping tracker complexity.
No compensation for weaker sun at day extremes.
Good snow rejection ONLY when used with enough ground clearance.
FIXED ARRAY WITH MULTIPLE PANEL ORIENTATION, EASY summer/winter tilt change,
snow gaps, and high ground clearance. Inverters will tolerate a high DC/AC ratio
because only some of the panels are at a most favorable sun angle at any given time.
High snow rejection, most snow would clear without manual intervention shortly.
Careful selection of tilt will provide near level output under a day of best sun,
partly compensating for weakness of day extremes.
Inverters are kept at peak output most of the day under good sun.
Under medium clouds, high DC/AC ratio produces considerably more
than a tracker, perhaps double that of a fixed array.
There are harder questions to ask. I have a lot more money in 6061 aluminum, SS hardware,
concrete, wire, Rbar, and tools, than in PV panels. Adding EASY seasonal tilt change does
increase production, at considerable cost. Combining that with easy snow control adds
some more cost. I am glad to trade initial cost, for very little snow removal efforts.
On the other side, DIY efforts provide huge savings. This is partly enhanced by scaled
down DIY tools (backhoe, trencher) available when convenient, not on a preset schedule.
Small tools help avoid erosion problems. On site materials may be repurposed for new
construction. Arrays following my land (10% grade) are way simpler than attempting a
perfectly level construction.
Bruce RoeLast edited by bcroe; 05-18-2019, 10:40 AM.Comment
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Thanks for the comprehensive answer. My take away is that your DC to AC ratio is accomplishing your goals.9 kW solar, 42kWh LFP storage. EV owner since 2012Comment
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Right, when combined with multiple panel orientations.
Regarding DIY, I discovered long ago that most tools would pay for themselves the first
time you used them (avoiding hired labor). Recent example, for my first PV panel
experiment I paid $1K to have a full scale backhoe dig the 10 holes. Good work, but
the heavy machinery so messed up my grass (on a 10% grade) that by spring there was
a very serious erosion problem. I paid a landscaper $2.3K to get my grass restored.
On the latest array I used my own $3.3K mini backhoe, no erosion problem, and no
BIG DAY schedule issues. Bruce RoeComment
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Did a little snow clearing today, couple inches of light wind blown stuff. Blowing north
to south this time, it did manage to stick to my near vertical E, W facing panels. I found
that just driving by with the snow blower blowing a bit again the top surfaces, almost
all the snow on the panels just fell off.
For my earliest (not yet updated) panels at summer angle, the scraper was used to
clear snow. This is the latest version, a couple earlier types were failing. Remembering
I will not use a conductive pole, this is a telescoping fiberglass flagpole. The potential
16 foot was collapsed to 10.5 feet for more strength, the 2.5 foot increase over the old
pusher meant I did not need to lean over the panels anymore. The previous wood
poles were too short and did not splice together well. I may eventually sub some
lighter materials at the far end. Bruce Roe
SnowPusher.jpgComment
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Nice to see some creative panel orientations. While I generally agree South facing is often the most efficient, there are always circumstances where other orientations make sense for the owner. I recently saw a many examples of that on a drive from San Francisco to LA.9 kW solar, 42kWh LFP storage. EV owner since 2012Comment
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It looks like excellent ground clearance (for snow) as well. Bruce RoeComment
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It was sunny in the morning and sunny in the late afternoon, but partly cloudy mid day......you get the picture. Shoulder array working to perfection......
2020-02-14 (2).pngComment
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