Solar cell modules

[maxfoo]

Anyone know of any solar cell vendors that sell
solar cell modules that put out 6-9volt @ 100mA?


TIA,









Remove "HeadFromButt", before replying by email.

 

[Johnboy]

I think Harbor Freight had something.
Lots of stuff from places like Electronic Goldmine,
and others, real cheap.

 

[John Popelish]

Anyone know of any solar cell vendors that sell
solar cell modules that put out 6-9volt @ 100mA?

TIA,

Remove "HeadFromButt", before replying by email.

JC Whitney sells 12 volt panels competitively. These are not as
efficient when loaded to 6-9 volts, but they put out at least as much
current as when run with a 12 volt load.
http://www.jcwhitney.com/webapp/wcs...-1&productId=218359&mediaCode=ZX&appId=385939

 

[Joerg]

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.

 

[Bill Bowden]

Anyone know of any solar cell vendors that sell
solar cell modules that put out 6-9volt @ 100mA?


TIA,

Lots of solar panels for sale on ebay. Here's a 12 volt 200mA
unit for 11 dollars.

Http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=41981&item=3187173830&rd=1


-Bill

 

[Roy Lewallen]

You've asked for a module that puts out 6-9 volts @ 100 mA. A more
accurate description of a solar panel would be that it puts out 100 mA
at 6-9 volts. Solar cells act a lot more like a current source than a
voltage source. So a panel that's rated at 100 mA at 12 volts will also
put out about 100 mA at 6 or 9 volts. (It'll be a bit more than 100 mA,
but not a whole lot more.) The open circuit voltage of a "12 volt" solar
panel (one intended to deliver current to a 12-14 volt load) will be
somewhere around 18 or 20 volts, and one specifically designed to work
at 6 volts will be about half that, 9 or 10 volts. So if you have a 6 -
9 volt device that you want to power with solar cells, you'll have to
float the panel across a battery, or use a voltage regulator to limit
the voltage. (A properly sized zener diode would be adequate for the
power level you're dealing with.) A 12 volt panel will be physically
larger than you need, but it might be easier to find and less expensive.

If you're looking for a module that includes a built in voltage
regulator to limit the voltage to 6 - 9 volts, you need to make it
clear. Most of the responses seem to be referring to 12 volt panels,
which will be fine if you limit the voltage, but won't be suitable if
you need voltage regulation to be included in the external module.

Roy Lewallen, W7EL

 

[[email protected]]

Hi;
I must say that this last responce was well writen and informitive, it
was a pleasure to read.

Thank you Mr. Lewallen

 

[maxfoo]

If you're looking for a module that includes a built in voltage
regulator to limit the voltage to 6 - 9 volts, you need to make it
clear. Most of the responses seem to be referring to 12 volt panels,
which will be fine if you limit the voltage, but won't be suitable if
you need voltage regulation to be included in the external module.

my pcb has a Linear Tech LT1117-5 LDO regulator on board, regulates 5volts with
a min input Voltage of 6 volts, so I'm currently using 4 AA batteries in a
battery pack with a 9v type clip. Wanted to be able to charge the batteries with
solar cells basically.

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

thanks,







Remove "HeadFromButt", before replying by email.

 

[Watson A.Name \Watt Sun - the Dark Remover\]

Anyone know of any solar cell vendors that sell
solar cell modules that put out 6-9volt @ 100mA?

Try All ELectronics. www.allcorp.com.

 

[Watson A.Name \Watt Sun - the Dark Remover\]

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.

 

[Watson A.Name \Watt Sun - the Dark Remover\]

You've asked for a module that puts out 6-9 volts @ 100 mA. A more
accurate description of a solar panel would be that it puts out 100 mA
at 6-9 volts.

Also the currewnt outputdepends somewhat on the latitude you're at. You
won't get all that current at the arctic circle.

 

[Joel Kolstad]

Also the currewnt outputdepends somewhat on the latitude you're at. You
won't get all that current at the arctic circle.

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!

 

[Watson A.Name \Watt Sun - the Dark Remover\]

my pcb has a Linear Tech LT1117-5 LDO regulator on board, regulates 5volts with
a min input Voltage of 6 volts, so I'm currently using 4 AA batteries in a
battery pack with a 9v type clip. Wanted to be able to charge the batteries with
solar cells basically.

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

For 6V, I would put two of these in series, along with a 1N5817 schottky
diode to prevent reverse current. Each cell is encapsulated with epoxy
and the wires can be soldered to the pads on the back. Each puts out an
honest 30 mA, or more in bright sunlight. Price is reasonable too.

http://www.allelectronics.com/cgi-bin/category.cgi?category=565&item=SPL-60&type=store

You can also put two pairs in parallel to get a faster charge.

 

[Seth Koster]

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).

 

[Paul Keinanen]

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

 

[Paul Keinanen]

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

 

[Joel Kolstad]

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...

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

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.

 

[René]

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.

 

[Joel Kolstad]

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.

The argument usually goes that getting, say, 10-20% more power from a better
charge controller (one of these so-called 'maximum power point controllers')
can be cheaper (in additional expenditures) than getting 10-20% larger
panels. It's sometimes difficult to show, though, particularly on small
systems -- but MPPT controllers have been getting cheaper for awhile, now,
and I expect that eventually all but the cheapest/smallest will have this
functionality.


---Joel Kolstad