Optimal String Sizing for PV Systems
by mark on Apr.23, 2010, under Solar
Optimal string sizing for a given inverter can improve your return on investment.
As an example, I will use my system as an example. The PVI-5000-OUTD-AU efficiency plot is given below.
Aurora Efficiency Plot
The important panel parameters are:
Panel: TH175M24
Pmax: 175watts
Vmp: 36.2V
Imp: 4.85A
Voc: 43.9V
Isc: 5.30A
It can be seen from the inverter efficiency diagram that the sweet spot is at 50% full power and 345V string voltage. Note that it has 2 MPPTs. These may be independently specified.
Now the 28 panels for 4.9kW need to be split between the MPPTs such that the Pmax string voltages are near the optimal 345V. This gives us 2 optimal and a symterical choices:
- 2 x 9 Panels in parallel + 1 x 10 panels. This gives string voltages of 325.8V and 362V.
- 2 x 10 panels in parallel + 1 x 8 panels. This gives string voltages of 362V and 289.6V.
- 2 x 7 panels in parallel + 2 x 7 panels in parallel. This gives string voltages of 253.4V
The open circuit string voltage for this inverter must be less than 600V. This is 439V for 10 panels, so this parameter is ok.
By inspection of the efficiency plot, configuration 1 is the best. In fact is it 0.3% better than the symmetrical configuration, which would result in about $10 per year more income/power at 68c/kWh.
The MPPT which has 2 strings in parallel has a greater weight attributed when choosing panel configuration as it supplies more power.
PV System Install Phase1
by mark on Apr.23, 2010, under Solar
The panels are up but the Aurora inverter is still coming due to supply issues in mid May.
I have opted not to obtain an alternative GCI due to the excellent efficiency of the powerone aurora. It is generally 2% or more better than others currently able to be supplied at short notice so worth waiting. 2% is worth 98W at full power, and derated, works out to about $100 per year.
All things going well, we should be generating power and income in June some time, fingers crossed. Hopefully AGL wont stuff us around like others I know when we apply for the premium rate tarrif too.
4.9kW PV Panel Install with 28 x 175W Mono
Mapping special names to multiple USB serial adapters
by mark on Apr.17, 2010, under Solar, linux
The watts clever envi has a USB serial adapter which is a Prolific pl2303. When inserted it is assigned /dev/ttyUSB0 by udev, among a few other symlinks. I have now obtained an RS485 serial adapter on ebay for A$13.98 delivered which uses the exact same chip, which makes it indistiguishable from the envi’s port. What I needed was a way to guarantee uniqueness regardless of the enumeration order on boot or random hot plugin. Naturally, this is for the Aurora GCI which will be installed when they become available in May.
Researching udev a bit, I found /lib/udev/rules.d/60-persistent-serial.rules (mine is a debian system). This file shows how the standard symlinks are done. Since each USB port is unique, I should be able to use that uniqueness to map another symlink to the device.
Firstly plug in the device in the chosen USB port and issue
udevadm info --query=all --name=/dev/ttyUSB1
This shows a heap of stuff but mainly we are interested in
P: /devices/pci0000:00/0000:00:1a.0/usb2/2-1/2-1:1.0/ttyUSB1/tty/ttyUSB1
Create a file in /etc/udev/rules.d/70-persistent-serial.rules which contains
#see /lib/udev/rules.d/60-persistent-serial.rules
ACTION!=”add|change”, GOTO=”persistent_serial_end”
SUBSYSTEM!=”tty”, GOTO=”persistent_serial_end”
KERNEL!=”ttyUSB[0-9]*|ttyACM[0-9]*”, GOTO=”persistent_serial_end”IMPORT=”usb_id –export %p”
#IMPORT=”path_id %p”ENV{ID_SERIAL}==”", GOTO=”persistent_serial_end”
# usb nearest ethernet connector
ENV{DEVPATH}==”*usb2/2-2/2-2:1.0*”, SYMLINK+=”serial/by-name/envi”
#bottom front connector
ENV{DEVPATH}==”*usb7/7-1/7-1:1.0*”, SYMLINK+=”serial/by-name/rs485″
# usb below nearest ethernet connector
ENV{DEVPATH}==”*usb2/2-1/2-1:1.0*”, SYMLINK+=”serial/by-name/rs485″LABEL=”persistent_serial_end”
Replug and voila you get /dev/serial/by-name/rs485 which will always be the correct device.
Now I just have to run the wire to where the GCI will be installed.
Funny Characters for gcc/g++ errors and warnings
by mark on Apr.01, 2010, under linux
I have found that on some linux systems when you compile with gcc and g++ the error messages have funny characters like
test.c: In function â:
test.c:6: warning: unused variable â
This is due to the default locale being set to something other than the default.
in /etc/default/locale you will have a line like
LANG="en_AU.UTF-8"
add
LC_CTYPE=C
Restart the shell and compile again and the errors are now meaningful.
test.c: In function 'main':
test.c:6: warning: unused variable 'x'
Naturally you could set it in the local shell for the session, but then you would have to do it every time.
Alternative Fridge-Freezer Anomaly Explanation
by mark on Mar.27, 2010, under Solar
This explanation is probably wrong because you would expect a deadzone in the power/current quantization levels to stay the same. However, what Ive observed is that the anomaly remains even when the base power varies by -50W to at least +2kW. I believe this precludes the previous explanation because this scale invariance should not exist under these circumstances if the dynamic range switching premise holds, which I still believe to be the case.
A better but not intuitive explanation is that the mechanical vibration of each unit alters the behaviour of the other, increasing the total VA (since that’s what the current sensor measures). The 2 units are located next to each other so are mechanically coupled through the floor.
Of course this explanation could be wrong too but I can’t think of another ATM.
Migrating Windows User Ids
by mark on Mar.12, 2010, under Windows
There are times when domains on windows change and thus your user id changes. However, you may have lots of files owned by you that are not in your user dir. Migrating these user ids to you new one, I’ve found, is not too difficult after all.
All you need is a tool from microsoft called subinacl.
Download and install the msi. Install path is
C:\Program Files\Windows Resource Kits\Tools\subinacl.exe
So use this for the command name below.
First find your old userid. Use a file you know you used to own. E.g. the projects directory.
Subinacl /file c:\projects /display
Copy and paste yours for use in the commands below
Now for the commands. Do for all drives if you have multiple disks.
The lines below are for me of course so sub in your cut S-xxx and new user id
Subinacl /subdir c:\ /accountmig=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx=newdomain\username
also the primary group, which can be found up the top of the display dump.
Subinacl /subdir c:\ "/accountmig=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx=newdomain\Domain Users"
all registry keys
Subinacl /subkeyreg HKEY_CURRENT_USER /accountmig=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx=newdomain\username
Subinacl /subkeyreg HKEY_LOCAL_MACHINE /accountmig=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx=newdomain\username
Subinacl /subkeyreg HKEY_CLASSES_ROOT /accountmig=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx=newdomain\username
(none found, so optional)
and the groups
Subinacl /subkeyreg HKEY_CURRENT_USER "/accountmig=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx=newdomain\Domain Users"
Subinacl /subkeyreg HKEY_LOCAL_MACHINE "/accountmig=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx=newdomain\Domain Users"
Subinacl /subkeyreg HKEY_CLASSES_ROOT "/accountmig=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx=newdomain\Domain Users"
After you are happy
Subinacl /subdir c:\ /suppresssid=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx
Subinacl /subkeyreg HKEY_CURRENT_USER /suppresssid=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx
Subinacl /subkeyreg HKEY_LOCAL_MACHINE /suppresssid=S-x-x-xx-xxxxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxx
When you are finished, everything you used to own you will own again.
Fridge/Freezer Anomaly Explained (Probably)
by mark on Mar.10, 2010, under Solar
I had some more thoughts on the fridge/freezer anomaly previously detailed.
I had read about the 144 Bug. I suspect it is related to this.
This has to do with the way that the transmitter samples the current sensor. I have noticed that the resolution is much better at lower power than higher power. I suspect this is because the ADC reference in the PIC is connected to a PWM output (smoothed of course) to provide a variable dynamic range sampling system. As you would expect, there would be quite a few range change points in the sampling algorithm. The 144 bug details one at 3kW. I suspect there is also one at somewhere between 450W and 600W which is not calibrated correctly. There are probably others too.
If these range change points are known, it would be easy enough to add fudge factors during datalogging to correct for this. Alternatively I could disassemble the transmitter PIC code and just fix it.
No time for this now.
Another possibility is that the sampling system is non-linear, increasing apparent measurements. Not enough calibrated sample points to prove. Anyhow the former is more likely.
Watts Clever Fridge + Freezer Power Anomaly
by mark on Mar.07, 2010, under Solar
I have noticed what appears to be an anomaly in the power presented by my fridge and freezer as measured by the watts clever mains power monitor.
Fridge + Freezer Power Usage
As can be seen, the base load is about 320W which consists of 2 PCs and incidental standbys. The fridge cycles more frequently than the freezer. The fridge power alone is about 75W and the freezer alone is about 100W. You would thus expect their combined power to be 175W. However, this is not so! Measured combined power is about 250W.
Given that the mains power monitor is power factor insensitive, and the compressors of both devices have inductive power factor, this result is unexpected. I’m also assuming that the power factor of the baseload is 1.0, which I think is reasonable as using another power meter showed a power factor of 1 for the PCs and these predominate the baseload.
I would expect the vector sum of fridge+freeze+baseload to be less than the sum of their magnitudes.
Wordpress Install Direct Filesystem Hack
by mark on Mar.05, 2010, under Wordpress
I use
chgrp -R www-data wp-content
chown -R g+w wp-content
To make this work with wordpress, edit wp-admin/includes/file.php in function get_filesystem_method() and comment out
if ( getmyuid() == fileowner($temp_file) )
to
#if ( getmyuid() == fileowner($temp_file) )
If the test file can be written, who cares if it is not owned by the webserver.
You will have to reapply this edit every time wordpress core is updated.
PV Panel Orientation Effectiveness
by mark on Mar.05, 2010, under Solar
This site has a nice image showing PV panel orientation and the expected output as a percentage of optimal orientation at latitude 35°S.
A fully west or east facing panel will still achieve over 80% of the output of an optimally north facing system. This indicates orientation, whilst critical is not a reason to not install them if no available north facing roof space is available.
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Hi
Hopefully there is some useful info here in my documentation effort on things I'm interested in.
Local Weather
Sunday, Aug 1
Mostly Cloudy
Currently: 10˚C
Feels Like: 8˚ C
Hi: 12˚, Lo: 8˚
Wind: 14, Gust: N/A MPH
Wind Direction: NNW (330)
Monday, Aug 2
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Wind: 13, Gust: N/A MPH
Wind Direction: SSW (200)
Tuesday, Aug 3
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Wind: 5, Gust: N/A MPH
Wind Direction: SW (222)
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