Paul wrote:
A question about bypass diodes:
....

Do most panels have the bypass diodes (to allow current flow through shaded
cells)? The specs for my Shell 100W panels do not mention them. I'm not
talking about the series reverse-current blocking diodes, but the per-cell
bypass. I am considering an MPPT controller, and if the panels have these
diodes, it should be better to connect the panels in series, rather than in
parallel. My installation has three panels, and does have issues with panel
shading. Currently I have the panels in parallel, and use a non-MPPT
controller.

I will probably do some V/I curves for the panels with varying types and
degrees of shading, which should answer the bypass diode question, but until
then any advice would be appreciated.

I may be wrong but I don't think most panels come with diodes - mine
don't. In fact, diodes aren't really the right thing to use. The
Blue Sky (and I'm guessing the Outback) comes with a relay that closes
when appropriate and opens to prevent reverse current flow. This is a
much more efficient way to do it.

Goofball_star_dot_etal wrote in
:

http://www.jaycar.com.au/images_uploaded/impmatch.pdf



The schematic and chart on page 1 of this pdf is also valid for any DC
circuit, like the inefficient solar panel, where source
resistance/impedance is a good part of the circuit. Even a lead acid
battery has some, mostly insignificant, source resistance, that rises as
it discharges quite rapidly. The point where load resistance equals
source resistance shown on the graph is what I was describing. If you
can operate the solar panel at that point with that load, you get more
power than at any other point.

As to this "measuring voltage" charge controller, I still don't see how
that's possible. ANY load, whatsoever, causes a drastic drop in solar
panel output voltage from its open circuit, natural voltage due to the
large series natural resistance that makes the cells get hot as hell.
They might be able to interrupt the load current, measure the voltage,
then reload the cell during a pulse width. That would work, I suppose.
Cell temperature varies cell resistance an awful lot.

http://www.mrs.org/s_mrs/bin.asp?CID...1&DOC=FILE.PDF
http://www.emcore.com/assets/photovo...SC%20Aiken.pdf

http://quantum.soe.ucsc.edu/research...r%20Thesis.pdf
Look at the graphs and information on pp 23-28 of this thesis paper.

Of course, you will need the powerpoint slides in pdf format:
http://www.ipcrystalclear.info/Share...0workshop%204%
20Nov%202005-%20IMEC/Presentations%20SiNx%20workshop/Carnel.pdf
and
http://www.smn.uio.no/pdf/Wadahl-Seminar/Ulyashin.pdf

Obviously, any discussion on a boat newsgroup is an oversimplification of
a very complex subject...solar cells. We'll need a few million dollars
of government grant funding from NIST to further our education and
experimentation at sea. (www.nist.gov)

See your tax dollars at work. Sign up to get NIST grant and symposium
announcements sent to your post office address. I still get them all 10
years after I signed up. They BEG you to take the money...try it.

Larry
--
VIRUS ALERT! VISTA has been released!
NOONE will be spared!

Paul wrote:

A question about bypass diodes:

snip

Do most panels have the bypass diodes (to allow current flow through shaded
cells)? The specs for my Shell 100W panels do not mention them. I'm not
talking about the series reverse-current blocking diodes, but the per-cell
bypass. I am considering an MPPT controller, and if the panels have these
diodes, it should be better to connect the panels in series, rather than in
parallel. My installation has three panels, and does have issues with panel
shading. Currently I have the panels in parallel, and use a non-MPPT
controller.

I will probably do some V/I curves for the panels with varying types and
degrees of shading, which should answer the bypass diode question, but until
then any advice would be appreciated.

Thanks,
Paul



IIRC once you are over a fairly low reverse voltage on an individual
cell (I belive somewhere around 5V), if any significant current is
available, long term damage tends to occur. Sources indicate that this
isnt a significant problem in simple 12V battery charging setups but
becomes an issue once the difference between the flat battery voltage
and the array OC output excedes this. Check with the supplier if the
cells are rated for series connection in 24V chaging applications as
they should have shunt diodes or better yet just ask them directly.
Also watch out that you dont exceed the maximum input rating of the MPPT
controller, even in direct normally incident sunlight with additional
light being reflected onto the panels and remember that a supply as low
as 32 volts in a wet envirioment can be a lethal shock hazard.

No doubt Mr G. Ball will be along shortly to point out my mistakes.


--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL:
'Stingo' Albacore #1554 - 15' Early 60's, Uffa Fox designed,
All varnished hot moulded wooden racing dinghy.

"Paul" wrote in message
...
A question about bypass diodes:
Do most panels have the bypass diodes (to allow current flow through
shaded cells)? The specs for my Shell 100W panels do not mention them.
I'm not talking about the series reverse-current blocking diodes, but the
per-cell bypass. I am considering an MPPT controller, and if the panels
have these diodes, it should be better to connect the panels in series,
rather than in parallel. My installation has three panels, and does have
issues with panel shading. Currently I have the panels in parallel, and
use a non-MPPT controller.

I will probably do some V/I curves for the panels with varying types and
degrees of shading, which should answer the bypass diode question, but
until then any advice would be appreciated.

Thanks,
Paul



Can't speak for "most," but Unisolar flexible 35's will continue to operate
partially shaded, at reduced output.

On Fri, 09 Feb 2007 20:52:23 -0500, Larry wrote:

Goofball_star_dot_etal wrote in
:

http://www.jaycar.com.au/images_uploaded/impmatch.pdf



The schematic and chart on page 1 of this pdf is also valid for any DC
circuit, like the inefficient solar panel, where source
resistance/impedance is a good part of the circuit.

It is not
a)A constant voltage source.
b)A linear circuit

"An ideal solar cell may be modelled by a current source in parallel
with a diode"

Even a lead acid
battery has some, mostly insignificant, source resistance, that rises as
it discharges quite rapidly. The point where load resistance equals
source resistance shown on the graph is what I was describing. If you
can operate the solar panel at that point with that load, you get more
power than at any other point.

As to this "measuring voltage" charge controller, I still don't see how
that's possible. ANY load, whatsoever, causes a drastic drop in solar
panel output voltage from its open circuit, natural voltage due to the
large series natural resistance that makes the cells get hot as hell.
They might be able to interrupt the load current, measure the voltage,
then reload the cell during a pulse width. That would work, I suppose.
Cell temperature varies cell resistance an awful lot.

From the linked patent for the device:

"As shown in FIG. 2, an approximation of the open circuit voltage of
array 2 is measured every eight seconds by sample and hold circuit 22
based on a 15 ms signal from oscillator 24. PWM controller 10 reduces
the duty cycle on Q1 transistor to zero for the 15 ms sample period to
obtain the open circuit voltage approximation. During this 15 ms
period the charge on C1 increases to approximately open circuit
voltage and the voltage reading is stored by sample and hold circuit
22. After the 15 ms period, PWM controller 10 returns to normal
operation"



http://www.mrs.org/s_mrs/bin.asp?CID...1&DOC=FILE.PDF
http://www.emcore.com/assets/photovo...SC%20Aiken.pdf

http://quantum.soe.ucsc.edu/research...r%20Thesis.pdf
Look at the graphs and information on pp 23-28 of this thesis paper.

Of course, you will need the powerpoint slides in pdf format:
http://www.ipcrystalclear.info/Share...0workshop%204%
20Nov%202005-%20IMEC/Presentations%20SiNx%20workshop/Carnel.pdf
and
http://www.smn.uio.no/pdf/Wadahl-Seminar/Ulyashin.pdf

Obviously, any discussion on a boat newsgroup is an oversimplification of
a very complex subject...solar cells. We'll need a few million dollars
of government grant funding from NIST to further our education and
experimentation at sea. (www.nist.gov)

See your tax dollars at work. Sign up to get NIST grant and symposium
announcements sent to your post office address. I still get them all 10
years after I signed up. They BEG you to take the money...try it.

Larry