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'[EE]:: Solar MPPT Tracker'
2008\04\26@093258 by Apptech

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Horrendously complex MPPT solar panel controller.(Maximum
Power Point Tracking)

Enough related stuff to make it worth looking at.
Uses a PIC :-)

       http://www.drgw.net/workshop/MPPT/mppt.html




       Russell



2008\04\26@101916 by Bob Axtell

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Apptech wrote:
> Horrendously complex MPPT solar panel controller.(Maximum
> Power Point Tracking)
>
> Enough related stuff to make it worth looking at.
> Uses a PIC :-)
>
>         http://www.drgw.net/workshop/MPPT/mppt.html
>
>
>
>
>         Russell
>
>
>
>  
Russell, this design is 10 years old. Somewhere in the stone age.
But the write-up is nice, aside from the misspelled words.

How ya been? Did you figure out after all that hoopla last week that
we loved 'ya anyway? Have a great day!

--Bob A

2008\04\26@110941 by Apptech

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>> Horrendously complex MPPT solar panel controller.(Maximum
>> Power Point Tracking)
>> Enough related stuff to make it worth looking at.
>> Uses a PIC :-)
>>
>>         http://www.drgw.net/workshop/MPPT/mppt.html

> Russell, this design is 10 years old. Somewhere in the
> stone age.

Yep.
Sunraycer 99 I think they said.

I post that sort of thing for the useful content.
MPPT is largely not practiced by amateurs and even the
discussion about it can be worthwhile.
There is often nothing magic about MPPT hardware (although I
do have some magic ideas).

> How ya been? Did you figure out after all that hoopla last
> week that
> we loved 'ya anyway? Have a great day!

I don't think that I figured out that any loved me more or
less than before. But, I'm always very happy to be loved
:-).




       Russell





2008\04\26@150444 by Matthew Miller

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On Sun, Apr 27, 2008 at 01:32:41AM +1200, Apptech wrote:
> Horrendously complex MPPT solar panel controller.(Maximum
> Power Point Tracking)
>
> Enough related stuff to make it worth looking at.
> Uses a PIC :-)
>
>         http://www.drgw.net/workshop/MPPT/mppt.html

Hi Russell, thanks for posting this. I'm trying to learn as much as I can
about MPPT right now. For my project though, I'm short on time and I decided
to go with a plain boost converter using a LT1680. Please more info if you
have it!

Matthew

--
...those who search for, or imagine they have found, the perpetual motion,
are always men to whom the most certain and invariable truths in mechanics
are unknown.  -- Jacques Ozanam (1640-1717)

2008\04\26@204446 by Apptech

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>> Horrendously complex MPPT solar panel controller.(Maximum
>> Power Point Tracking)

>>         http://www.drgw.net/workshop/MPPT/mppt.html

> Hi Russell, thanks for posting this. I'm trying to learn
> as much as I can
> about MPPT right now. For my project though, I'm short on
> time and I decided
> to go with a plain boost converter using a LT1680. Please
> more info if you
> have it!


LT1680 looks like a good choice.

MPPT is nice but not essential for your project.

A good and easy approach to MPPT is to use a PV pilot cell
to decide what voltage the main PV panel should be loaded to
for a given level of insolation. While there are issues with
aging and matching the results can be very good. Maybe best
called QGPPT [tm] :-).


Here is a low power MPPT tracker that works without a uP
using a pilot cell. As it drives a boost converter and will
run with almost zero main PV panel voltage it can extract
energy when other systems provide nothing at all. To do this
they run the MPPT hardware from its own supply and minimise
power used to allow the overall result to be efficient
overall.

       http://others.servebeer.com/misc/MPPTsolar.pdf



       Russell McMahon






2008\04\27@052824 by Apptech

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>>> Horrendously complex MPPT solar panel
>>> controller.(Maximum
>>> Power Point Tracking)
>>>         http://www.drgw.net/workshop/MPPT/mppt.html


> A good and easy approach to MPPT is to use a PV pilot cell
> to decide what voltage the main PV panel should be loaded
> to
> for a given level of insolation. ...
> Here is a low power MPPT tracker that works without a uP
> using a pilot cell.

>        http://others.servebeer.com/misc/MPPTsolar.pdf

Another method of "Good enough" (perhaps) MPPT is to load
the PV panel to 75% to 80% of its open circuit voltage.

You could do this using a pilot cell as above to establish
what the Voc of the main panel would be in a given situation
OR you can occasionally O/C the main PV panel briefly and
test. This can be very brief so interrupt the power only a
little. This makes the MPPT system independent of any
current measurements.



           Russell

2008\04\27@085306 by rlistas

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Hi Russel,

Using a different brand or size of  PV pilot cell  than
the ones used in the main solar array will give different
maximum power points, because each solar panel
has its owm power curve, right ?

Best regards,

Rubens

At 21:44 26/4/2008, you wrote:
{Quote hidden}

>

2008\04\27@163721 by Apptech

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> Using a different brand or size of  PV pilot cell  than
> the ones used in the main solar array will give different
> maximum power points, because each solar panel
> has its owm power curve, right ?

That's discussed in the article.
The match will not be perfect - as I noted , there are
issues with aging and matching (and more). But he tested the
pilot cell against the main cell and found a good match
between the two.

What he is really doing is measuring the insolation (light
level) with the small cell and using it to set a target
voltage level for the main cell.  You could decide to use a
completely different sort of pilot cell or light measurement
system and then make decisions on that basis using a lookup
table or algorithm. He provides a table in his paper for
Vmpp/Voc for the main cell and gets a figure of about 0.75 -
0.80 acros the range (see paper for actual figures). The
pilot cell is then used to set the main cell to this figure.

If the two cells start off tracking OK but one ages more
rapidly, or the glass on one is dirtier or degrades with UV
or temperature or ... then errors may occur with time. An
alternative is to use the main PV panel as its own sensor.
"Occasionally" open circuit the panel, measure its OC
voltage  and then load it again to a suitable level. A PV
panel by itself will change voltage extremely rapidly - they
will actually follow changing light in the sub millisecond
range with ease (close to microsecond range response is used
for panel characterisation by some systems). So eg taking
the system off load for a few milliseconds once a second is
probably viable with a suitable circuit. This at a minimum
seems to need a "switch" controlling the main panel so it
adds significant cost and effort in a large system. In a
large system a pilot cell or other method is more liable to
be used and in a small system a FET to switch the main panel
is not a major cost issue overall so main panel switching is
probably viable.

Note that by having a seperate supply for his simple
hardware tracker he can run at panel voltages approaching
zero and still get some power output. Systems that rely on
the panel itself to power the system do not work at such low
voltage levels. This is not a major issue with multiple PV
cells in series, but his system will actually work on a
single PV cell (about 0.5V in full sun).



       Russell

For interest: 10 people downloaded the paper in about 20
hours.



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