But after searching the web a bit it seems cheapest to buy individual cells
then tie them in series...No?

thanks,



My experience with tying together solar cells is that you'll probably
destroy a few along the way (the pads lift very easily when heated
with soldering iron), so either get extras or go with a solution which
does not require you to solder cells together (or be more careful than
I was, I guess).

On Mon, 12 Apr 2004 13:02:38 -0700, "Watson A.Name \"Watt Sun - the
Dark Remover\"" wrote:

Joerg wrote:

Another option might be to use a different voltage panel,
whatever has a good price, and then use a small switcher to run
the cells at their optimum load.

Regards, Joerg.

Seems foolhardy to me, to use a boost circuit, and waste a lot of power.
Just put more PV cells in series to increase the voltage.

The solar cell operates as a (badly) regulated power supply with
current limiting. At low load currents, the cell operates nearly as a
constant voltage source, but after a specific current (for a given
illumination) it operates nearly as a constant current source and
deliver approximately that current even into a short circuit.

The largest power from the cell (for a specific illumination) is
obtained at the point it switches from constant voltage to constant
current mode, in which both the voltage is quite close (within 30 %)
of both the maximum voltage (as measured at open circuit) and maximum
current (as measured at short circuit).

This maximum power point varies with illumination, but if the switcher
always loads the cell at this maximum power point, the largest
available energy at a specific time is extracted from the cell
independent of illumination.

Even if the losses in the maximum power point tracker is 10-20 %,
usually more energy can be obtained than running the module in some
non-optimal constant voltage or constant current mode.

Paul

On Mon, 12 Apr 2004 13:02:38 -0700, "Watson A.Name \"Watt Sun - the
Dark Remover\"" wrote:

Joerg wrote:

Another option might be to use a different voltage panel,
whatever has a good price, and then use a small switcher to run
the cells at their optimum load.

Regards, Joerg.

Seems foolhardy to me, to use a boost circuit, and waste a lot of power.
Just put more PV cells in series to increase the voltage.

The solar cell operates as a (badly) regulated power supply with
current limiting. At low load currents, the cell operates nearly as a
constant voltage source, but after a specific current (for a given
illumination) it operates nearly as a constant current source and
deliver approximately that current even into a short circuit.

The largest power from the cell (for a specific illumination) is
obtained at the point it switches from constant voltage to constant
current mode, in which both the voltage is quite close (within 30 %)
of both the maximum voltage (as measured at open circuit) and maximum
current (as measured at short circuit).

This maximum power point varies with illumination, but if the switcher
always loads the cell at this maximum power point, the largest
available energy at a specific time is extracted from the cell
independent of illumination.

Even if the losses in the maximum power point tracker is 10-20 %,
usually more energy can be obtained than running the module in some
non-optimal constant voltage or constant current mode.

Paul

On Mon, 12 Apr 2004 13:52:35 -0700, "Joel Kolstad"
wrote:

Watson A.Name "Watt Sun - the Dark Remover" wrote:
Also the currewnt outputdepends somewhat on the latitude you're at. You
won't get all that current at the arctic circle.

The difference for panels perpendicular to the sun on the equator and
the arctic circle in the summer noon is about 10-15 %, due to the
atmospheric absorbtion. The difference between the equator and pole is
about 30 % in the same conditions.

If the panel is tracking the sun, the panel on the pole during the
summer will produce electricity for 24 h each day, while the other
panel on the equator will produce for less than 12 h. On the arctic
circle about 18-20 h each day will give usable electric output.
Exactly at the arctic circle, the midnight sunlight is strongly
attenuated by the atmosphere, so you can look at it even with your
naked eyes or ordinary sunglasses, thus the electric output is also
minimal.

He might actually have a better chance there during the periods when the sun
never sets than at, e.g., the equator... solar cells are noticably more
efficient when they're keep cold, which is typically a lot earier to do in
the arctic than at the equator!

The silicon cell behaves quite in the same way as a silicon diode
which has a 0,7 V threshold voltage and -2 mV/C temperature constant,
thus the cell output voltage (and hence power) drops with temperature.

However, the cells are heated by solar radiation at nearly at constant
flux on the equator and arctic circle, thus, the main issue is how
well the heat will be removed from the cell to the environment. At the
arctic summer the air temperature can be well over 20 C for longer
periods of time, so this does not help a lot in keeping the cells
cool.

Paul

On Mon, 12 Apr 2004 13:52:35 -0700, "Joel Kolstad"
wrote:

Watson A.Name "Watt Sun - the Dark Remover" wrote:
Also the currewnt outputdepends somewhat on the latitude you're at. You
won't get all that current at the arctic circle.

The difference for panels perpendicular to the sun on the equator and
the arctic circle in the summer noon is about 10-15 %, due to the
atmospheric absorbtion. The difference between the equator and pole is
about 30 % in the same conditions.

If the panel is tracking the sun, the panel on the pole during the
summer will produce electricity for 24 h each day, while the other
panel on the equator will produce for less than 12 h. On the arctic
circle about 18-20 h each day will give usable electric output.
Exactly at the arctic circle, the midnight sunlight is strongly
attenuated by the atmosphere, so you can look at it even with your
naked eyes or ordinary sunglasses, thus the electric output is also
minimal.

He might actually have a better chance there during the periods when the sun
never sets than at, e.g., the equator... solar cells are noticably more
efficient when they're keep cold, which is typically a lot earier to do in
the arctic than at the equator!

The silicon cell behaves quite in the same way as a silicon diode
which has a 0,7 V threshold voltage and -2 mV/C temperature constant,
thus the cell output voltage (and hence power) drops with temperature.

However, the cells are heated by solar radiation at nearly at constant
flux on the equator and arctic circle, thus, the main issue is how
well the heat will be removed from the cell to the environment. At the
arctic summer the air temperature can be well over 20 C for longer
periods of time, so this does not help a lot in keeping the cells
cool.

Paul

Paul Keinanen wrote:
At the
arctic summer the air temperature can be well over 20 C for longer
periods of time, so this does not help a lot in keeping the cells
cool.

....and the windchill is also reasonably comparable? I didn't realize the
arctic could be so 'balmy!' Thanks for the info.

I suppose that if you wanted to push the issue, a heat pipe stuck in the ice
going back to a metal layer on the back of the panel would be quite
effective in cooling the panel...

Paul Keinanen wrote:
At the
arctic summer the air temperature can be well over 20 C for longer
periods of time, so this does not help a lot in keeping the cells
cool.

....and the windchill is also reasonably comparable? I didn't realize the
arctic could be so 'balmy!' Thanks for the info.

I suppose that if you wanted to push the issue, a heat pipe stuck in the ice
going back to a metal layer on the back of the panel would be quite
effective in cooling the panel...

"Paul Keinanen" wrote in message
...
On Mon, 12 Apr 2004 13:02:38 -0700, "Watson A.Name \"Watt Sun - the
Dark Remover\"" wrote:

Joerg wrote:

Another option might be to use a different voltage panel,
whatever has a good price, and then use a small switcher to run
the cells at their optimum load.

Regards, Joerg.

Seems foolhardy to me, to use a boost circuit, and waste a lot of
power.
Just put more PV cells in series to increase the voltage.

The solar cell operates as a (badly) regulated power supply with
current limiting. At low load currents, the cell operates nearly as a
constant voltage source, but after a specific current (for a given
illumination) it operates nearly as a constant current source and
deliver approximately that current even into a short circuit.

The largest power from the cell (for a specific illumination) is
obtained at the point it switches from constant voltage to constant
current mode, in which both the voltage is quite close (within 30 %)
of both the maximum voltage (as measured at open circuit) and maximum
current (as measured at short circuit).

This maximum power point varies with illumination, but if the switcher
always loads the cell at this maximum power point, the largest
available energy at a specific time is extracted from the cell
independent of illumination.

Even if the losses in the maximum power point tracker is 10-20 %,
usually more energy can be obtained than running the module in some
non-optimal constant voltage or constant current mode.

Paul

Yeah, I see what you mean, sort of like an impedance match, but at DC.
But at the beginning or end of the day, or cloudy day, you can't pull
any more energy out of the cells than there is there. What it looks to
me is that you're adding circuitry to give a better match at the ends of
the day or a cloudy day, and in return sacrificing a few percent
overall.

My attitude is that rather than try to do this (and in the process lose
reliability), it's better to go supersize on the cells, add more area
and overall capacity to get you thru the cloudy days, and have a higher
capacity overall.

"Paul Keinanen" wrote in message
...
On Mon, 12 Apr 2004 13:02:38 -0700, "Watson A.Name \"Watt Sun - the
Dark Remover\"" wrote:

Joerg wrote:

Another option might be to use a different voltage panel,
whatever has a good price, and then use a small switcher to run
the cells at their optimum load.

Regards, Joerg.

Seems foolhardy to me, to use a boost circuit, and waste a lot of
power.
Just put more PV cells in series to increase the voltage.

The solar cell operates as a (badly) regulated power supply with
current limiting. At low load currents, the cell operates nearly as a
constant voltage source, but after a specific current (for a given
illumination) it operates nearly as a constant current source and
deliver approximately that current even into a short circuit.

The largest power from the cell (for a specific illumination) is
obtained at the point it switches from constant voltage to constant
current mode, in which both the voltage is quite close (within 30 %)
of both the maximum voltage (as measured at open circuit) and maximum
current (as measured at short circuit).

This maximum power point varies with illumination, but if the switcher
always loads the cell at this maximum power point, the largest
available energy at a specific time is extracted from the cell
independent of illumination.

Even if the losses in the maximum power point tracker is 10-20 %,
usually more energy can be obtained than running the module in some
non-optimal constant voltage or constant current mode.

Paul

Yeah, I see what you mean, sort of like an impedance match, but at DC.
But at the beginning or end of the day, or cloudy day, you can't pull
any more energy out of the cells than there is there. What it looks to
me is that you're adding circuitry to give a better match at the ends of
the day or a cloudy day, and in return sacrificing a few percent
overall.

My attitude is that rather than try to do this (and in the process lose
reliability), it's better to go supersize on the cells, add more area
and overall capacity to get you thru the cloudy days, and have a higher
capacity overall.

On Tue, 13 Apr 2004 09:18:00 +0300, Paul Keinanen
wrote:


The solar cell operates as a (badly) regulated power supply with
current limiting. At low load currents, the cell operates nearly as a
constant voltage source, but after a specific current (for a given
illumination) it operates nearly as a constant current source and
deliver approximately that current even into a short circuit.

The largest power from the cell (for a specific illumination) is
obtained at the point it switches from constant voltage to constant
current mode, in which both the voltage is quite close (within 30 %)
of both the maximum voltage (as measured at open circuit) and maximum
current (as measured at short circuit).

This maximum power point varies with illumination, but if the switcher
always loads the cell at this maximum power point, the largest
available energy at a specific time is extracted from the cell
independent of illumination.

Even if the losses in the maximum power point tracker is 10-20 %,
usually more energy can be obtained than running the module in some
non-optimal constant voltage or constant current mode.

Paul

I have seen elegant ckts where a simple switcher was used, regulating
the *input* voltage coming from the solar cell, keeping it in max
efficiency mode at all loads. This obviously only works with flexible
loads such as slow chargers or such.

--
- René