Max power from solar cells

In terms of using lasers to transmit power thru space to solar cells are the
following silly assumations on the right track or are the real life figures
way diffirent?

Most solar panels in use of Earth convert about 25% of the power over thier
useful life. I noticed that most solar panels I have seen are very dark in
colour, can I assume that the remaining 75% of light falling on them is
converted to heat.

Running with that assumation (a poor one I know) the average solar panel is
recieving about 1KW of sunlight per square meter, outputs 250 watts and dumps
out 750 watts of heat.

Since solar cells have a 50% output using lasers this suggest you can use a
flux of 1500 watts per square meter and get 750 watts power out and 750 watts
heat.

That is 3 times the power using lasers over sunlight.

Now the added problem, in space you don't have air to carry off the heat, is
it reasonable to radiate 750 watts per square meter in if the cells/radiator
are never raised over 35 degree C? It would seem that what present solar
arrays in space are doing or did I miss something?

Earl Colby Pottinger

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Earl Colby Pottinger wrote:

Now the added problem, in space you don't have air to carry off the heat, is
it reasonable to radiate 750 watts per square meter in if the cells/radiator
are never raised over 35 degree C? It would seem that what present solar
arrays in space are doing or did I miss something?

If you use a PV material with a higher bandgap, and use shorter wavelength
laser light, the PV cells should be able to operate at high temperature.

Even in sunlight, GaAs cells operate better at higher temperature than
do silicon cells.

Paul

"Paul F. Dietz" :

Earl Colby Pottinger wrote:

Now the added problem, in space you don't have air to carry off the heat,
is
it reasonable to radiate 750 watts per square meter in if the
cells/radiator
are never raised over 35 degree C? It would seem that what present solar
arrays in space are doing or did I miss something?

If you use a PV material with a higher bandgap, and use shorter wavelength
laser light, the PV cells should be able to operate at high temperature.

Even in sunlight, GaAs cells operate better at higher temperature than
do silicon cells.

Really? I thought all solar cells started to have degraded performance after
they past 45-50 degrees C.

Eal Colby Pottinger
--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
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In article , says...
Most solar panels in use of Earth convert about 25% of the power

I wouldn't say that most do. There certainly are PV cells that can
convert 25% or more of the incoming solar radiation they receive into
electricity.


over thier
useful life. I noticed that most solar panels I have seen are very dark in
colour, can I assume that the remaining 75% of light falling on them is
converted to heat.

Some gets reflected off the glazed surface and some gets converted to
low level heat. This heat can, in turn, degrade the efficiency of the
conversion process.



Running with that assumation (a poor one I know) the average solar panel is
recieving about 1KW of sunlight per square meter,

Yes, that's approximately true on the equator on earth. In earth orbit
the figure would be about 1350 W/m^2.

outputs 250 watts and dumps
out 750 watts of heat.

Since solar cells have a 50% output

They can have higher efficiency if optimal wavelengths are used that
match those for which the panel was designed to convert.


using lasers this suggest you can use a
flux of 1500 watts per square meter and get 750 watts power out and 750 watts
heat.

Yes, you can concentrate more power on the panels, to a degree, and they
will produce higher output. Of course, you can use passive
concentrators like mirrors and lenses as well.



That is 3 times the power using lasers over sunlight.

Now the added problem, in space you don't have air to carry off the heat, is
it reasonable to radiate 750 watts per square meter in if the cells/radiator
are never raised over 35 degree C?

I'm sure it can be done, with an appropriate radiator. Actually many
panels can tolerate a fair bit above this level of heat.


It would seem that what present solar
arrays in space are doing or did I miss something?

Indeed, many of them don't even require separate radiators, but radiate
heat away directly.

--
Quibbler (quibbler247atyahoo.com)
"It is fashionable to wax apocalyptic about the
threat to humanity posed by the AIDS virus, 'mad cow'
disease, and many others, but I think a case can be
made that faith is one of the world's great evils,
comparable to the smallpox virus but harder to
eradicate." -- Richard Dawkins

Earl Colby Pottinger wrote:
In terms of using lasers to transmit power thru space to solar cells are the
following silly assumations on the right track or are the real life figures
way diffirent?

Most solar panels in use of Earth convert about 25% of the power over thier
useful life. I noticed that most solar panels I have seen are very dark in
colour, can I assume that the remaining 75% of light falling on them is
converted to heat.

25% is rather high. Certainly way too high for silicon based ones.


Running with that assumation (a poor one I know) the average solar panel is
recieving about 1KW of sunlight per square meter, outputs 250 watts and dumps
out 750 watts of heat.

Since solar cells have a 50% output using lasers this suggest you can use a
flux of 1500 watts per square meter and get 750 watts power out and 750 watts
heat.

That is 3 times the power using lasers over sunlight.

but why do it at only 3 times the power?


Now the added problem, in space you don't have air to carry off the heat, is
it reasonable to radiate 750 watts per square meter in if the cells/radiator
are never raised over 35 degree C? It would seem that what present solar
arrays in space are doing or did I miss something?

the other side of teh solar panel is probably facing very cold space.


Earl Colby Pottinger


--
Sander

+++ Out of cheese error +++

quibbler wrote:
In article , says...
Most solar panels in use of Earth convert about 25% of the power

I wouldn't say that most do. There certainly are PV cells that can
convert 25% or more of the incoming solar radiation they receive into
electricity.


Lab top is 30% - but these are not "simple" silicon ones.


--
Sander

+++ Out of cheese error +++

In article ,
Sander Vesik wrote:

That is 3 times the power using lasers over sunlight.

but why do it at only 3 times the power?

Increasing the incident flux will not linearly increase generated power,
and may damage the cells. There is an optimal brightness...doubling that
will less than double your power, and will probably drastically reduce
the lifetime of the cells. Of course, what this is depends on the type
of the cell, operating temperature, etc.


the other side of teh solar panel is probably facing very cold space.

Which is about as good as you can get for radiating heat away, but it
can still be difficult to dispose of enough heat by radiation alone,
without air to carry excess heat away. A cooling system that lets you
use higher intensity light on smaller PV cells might give you an overall
reduction in weight...but PV cells can be thin and pretty light, it'd
probably be better to run a larger array at lower intensity if heating
is a problem.

I wonder if a heat engine would be better for supplying large amounts of
power...use high intensity microwave or laser beams to run a turbine or
Stirling engine. No need to drag a bulky, fragile, difficult to orient
PV array around, which would be a plus for something that has to
accelerate. (big arrays in freefall are one thing, big arrays under
acceleration would very difficult to manage)
A rectenna would probably be more efficient, and far less failure prone.

Are you the same Sander from the POV-Ray newsgroups?

--
Christopher James Huff
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG:
http://tag.povray.org/

Sander Vesik :

25% is rather high. Certainly way too high for silicon based ones.

Is 15% more reasonable?

So this time assume an input 1KW
of sunlight per square meter, outputs 150 watts and dumps out 850 watts of
heat. Thus at a 50% output using lasers this suggest you can use a flux of
1700 watts per square meter and get 850 watts power out and 850 watts heat.

That is 5.66.. times the power using lasers over sunlight. This just sounds
better and better.

Earl Colby Pottinger

--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp

Christopher James Huff :

I wonder if a heat engine would be better for supplying large amounts of
power...use high intensity microwave or laser beams to run a turbine or
Stirling engine.

Why has no-one suggested it before, seems like a good idea to me.

Earl Colby Pottinger

--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp

In article ,
says...
quibbler wrote:
In article , says...
Most solar panels in use of Earth convert about 25% of the power

I wouldn't say that most do. There certainly are PV cells that can
convert 25% or more of the incoming solar radiation they receive into
electricity.


Lab top is 30% - but these are not "simple" silicon ones.

There have been higher results, especially with multiband gap materials
-- but they are somewhat exotic materials and can require elaborate
manufacturing procedures compared to normal silicon. FWIW, maximum
photovoltaic efficiency is estimated to be somewhere in the 60% range.
That's one reason that people have long explored alternatives, from
solar thermal concentrators to optical rectennas. Thermal diode
efficiency also appears to be on an uptick.


--
Quibbler (quibbler247atyahoo.com)
"It is fashionable to wax apocalyptic about the
threat to humanity posed by the AIDS virus, 'mad cow'
disease, and many others, but I think a case can be
made that faith is one of the world's great evils,
comparable to the smallpox virus but harder to
eradicate." -- Richard Dawkins