Can you focus sunlight onto PV cells

[Pom-pom-pom]

It occurs to me that I could cover 100 square meters in PV cells, or cover
it in mirrors/lenses and reflect/focus all that sun onto a smaller bunch of
PV cells which would then receive 10x/20x/100x (whatever) the normal amount
of energy.

Would this "higher density" arrangement work? If it would only work in part,
how much could it be pushed to (2x or 5x the normal output levels??)

Any inf appreciated

Try http://www.entechsolar.com
they seem to be leaders in this field

or google witth 'entech photovoltaic concentrator' to find various papers

 

[Kate]

It occurs to me that I could cover 100 square meters in PV cells, or cover
it in mirrors/lenses and reflect/focus all that sun onto a smaller bunch of
PV cells which would then receive 10x/20x/100x (whatever) the normal amount
of energy.

Would this "higher density" arrangement work? If it would only work in part,
how much could it be pushed to (2x or 5x the normal output levels??)

Any inf appreciated

 

[Anthony Matonak]

It occurs to me that I could cover 100 square meters in PV cells, or cover
it in mirrors/lenses and reflect/focus all that sun onto a smaller bunch of
PV cells which would then receive 10x/20x/100x (whatever) the normal amount
of energy.

Would this "higher density" arrangement work? If it would only work in part,
how much could it be pushed to (2x or 5x the normal output levels??)

You could try to solar concentrator archive.
http://sol.crest.org/renewables/solar-concentrator-list-archive/

I think the basic concept works but there are issues. Most PV cells
become less efficient the warmer they get so cooling is important.
Typical panels use ordinary solder and a potting material that can't
withstand extremely high temperatures. 2X is considered possible
without major problems in an air cooled setup and normal panels but
if you want more then your setup becomes more complex and prone to
failures.

Anthony

 

[Honka Honka Burnin' Love]

Sure it will work. It's usually just cheaper to add more PV cells and
forget about concentrating the sunlight, however.

 

[Steve Spence]

5x sun would greatly degrade the lifespan of the cells. 2x might have little
affect on lifespan, but might be near as expensive as doubling the number of
panels, depending on method used.


--
Steve Spence
Renewable energy and sustainable living
http://www.green-trust.org
Discuss vegetable oil and biodiesel
powered diesels at
http://www.veggievan.org/discuss/

 

[Steve Spence]

That wouldn't be very concentrating, so no issue there.

--
Steve Spence
Renewable energy and sustainable living
http://www.green-trust.org
Discuss vegetable oil and biodiesel
powered diesels at
http://www.veggievan.org/discuss/

 

[Anthony Matonak]

Just wanted to be sure. Now, the next question. Will the reflection
increase the efficiency(?) of the panels? The site is actually in a swamp
situated on a small bluff looking over a small creek, we simply marked off
the footprint of the cabin and built the cabin in the trees. We'll only
have maybe an hour+ (maybe 3 hours total) of good sunshine on either side of
solar noon that will get to the cabin so any enhancement for the panels is
welcomed.

More light does not mean more efficiency but it does mean more power.
For instance, an amorphous panel at roughly 6% efficiency is going
to produce half the power of a crystalline panel exactly the same
size at 12% efficiency. Double the amount of sunlight striking each
panel and the 6% one will produce twice the power it did before but
still only half of what the 12% one will.

To be more precise, the panels will decrease in efficiency the
warmer they get so more sunlight can actually decrease efficiency.

You could look at mounting the panels somewhere else that gets more
sunlight. This might be some distance away or up a tower or pole.
You might also want to explore using the creek for hydropower if
possible. Even a very small turbine can produce a significant amount
of electricity over time.

Anthony

 

[ddwyer]

Hi Ed;



Yes, depending on the specifics this can achieve
a 2X concentration factor. With the out being a bit
under 2 times the 1X output.


Possibly. It depends on how hot the PV panels get.

Many say the manufactures won't warrantee panels
with concentration. I have asked them and most
actually say they won't warrantee panels that have
been over heated.

Just be careful about getting to hot.

Snow and heat reflecting white shingles also impart
some concentration, although not 2X.

I contend that more energy per day will be gotten
by solar tracking and it's safer as the temperatures
can be less.



Duane

Seems to me that there are benefits if panels are cooled by incoming
water that's due to be heated anyway.

 

[Chuck Yerkes]

It occurs to me that I could cover 100 square meters in PV cells, or cover
it in mirrors/lenses and reflect/focus all that sun onto a smaller bunch of
PV cells which would then receive 10x/20x/100x (whatever) the normal amount
of energy.

Would this "higher density" arrangement work? If it would only work in part,
how much could it be pushed to (2x or 5x the normal output levels??)

At PEAK sunlight, the issues are that you don't want to "overfill"
your inverter.

With (say) 3kw of panels, THAT"S when you max out your 3kw inverter.

But MOST of the time, outside of that "golden hour" or two, you're
not generating CLOSE to the peak because of sun angle.

In THEORY, that would seem to be the time it would seem that I'd want
(on a flush roof mount system) perhaps a mirror on east and west to
catch the rising or falling sun and give it an extra 10 percent.

All that said, my nearer neighbors would hate me.

A neighbor downhill just put 8 panels on up my side of his roof and
4 hrs after sunrise, it seems I get most of his sun from his roof

 

[[email protected]]

More light does not mean more efficiency...

I seem to recall a slight efficiency increase.

To be more precise, the panels will decrease in efficiency the
warmer they get so more sunlight can actually decrease efficiency.

Perhaps not, if they are cooled.

Nick

 

[Anthony Matonak]

intheswamp00 wrote:
....

The river has had my mind spinning for quiet some time now. It's a fair
sized river, probably 25' wide and probably 8' deep in front of the cabin.
But, no head. Not a very fast river...definitely not whitewater or
anything. I've tinkered with the idea of building a small dam across it or
at least a venturi(sic?). The trick here is that this river rises and falls
pretty fast with heavy rains...from the small bluff where the cabin is you
can watch the river flood most of the swamp. I don't know if I have the
ability to build a dam substantial enough to keep from being torn apart from
the current during these floods. I've looked at the Jackrabbit generator
which sounds more likely to work for me.

....

The power you get out of hydro depends on speed (or pressure) and
volume both. A place with a high head and therefor lots of pressure
can generate lots of power with very little volume of water. The
less head (pressure, or speed) the more volume of water you need
to make the same power. A 25' wide river 8' deep contains a large
volume of water so it likewise can probably produce a lot of power
even at slow speeds. You won't be able to use a small device to
tap into that power though. Likely you are going to need something
like an undershot water wheel mounted on a barge. Might wind up
looking something like a riverboat.

Anthony

 

[John Beardmore]

Re the water: is it possible to make a very small dam? Only need be
something little to turn a water wheel.

Any good info on type of alternator / generator to use to get a few
watts to tens of watts out of a 2'6" wheel ?


Cheers, J/.

 

[Anthony Matonak]

Any good info on type of alternator / generator to use to get a few
watts to tens of watts out of a 2'6" wheel ?

You might look into some of those websites that show how to build
your own permanent magnet generator or simply purchase a suitable
electric permanent magnet motor or stepper motor.

For example, find a DC electric motor with permanent magnets inside
that takes 50 watts to run at XX rpm. Spin it with your wheel at
XX rpm and it should generate a little less than 50 watts.

Anthony

 

[John Beardmore]

John Beardmore wrote:

You might look into some of those websites that show how to build
your own permanent magnet generator or simply purchase a suitable
electric permanent magnet motor or stepper motor.

Stepper motors seem to hive significant problems with starting torque
when accessed through the velocity ration required to get a decent
output voltage.

We are looking at making something with NIB magnets, but it's
frustrating that getting a few watts of educational project to work well
is nearly as much effort as getting a domestic scale system designed and
constructed.

Part of the problem is that the input speed from the wheel is order 15
rpm, and our limited experiments suggest that most motors need order of
900 rpm to generate the 16 or more volts that we need for battery
charging.

1:60 is quite a big jump for conventional generators, and I suspect 15
rpm is too slow for any direct driver generation even with NIB magnets.

For example, find a DC electric motor with permanent magnets inside
that takes 50 watts to run at XX rpm. Spin it with your wheel at
XX rpm and it should generate a little less than 50 watts.

It all sounds so easy.

Certainly in the UK, I haven't found any cheap sources of DC PM motors
in that power range at a sensible price, but I'd be pleased to hear from
anybody who can point me in the right direction !


Cheers, J/.

 

[John Beardmore]

Doesn't that just mean you need a gearbox to turn 15 RPM in 900 RPM?

Yes, but that isn't cheap or efficient.

Even doing it with toothed and v belts uses about 150 UKP of parts, and
still needs a frame etc welding.


Cheers, J/.

 

[John Beardmore]

Home made motors are mostly very bad performers, so I would definitely
look for efficiency figures before building.

Yes. Before the advent of cheap NIB magnets I wouldn't have even
considered self build.

One way to run steppers is to connect them via a clockwork spring, so
they dont turn at all initially, then when the spring is wound up
enough the motor gets going, running off the spring wind, then it all
stops and the spring recharges. You can effectively get huge gear
ratios that way.

That's very interesting. Does anybody make a tidy module that includes
this kind of spring mechanism.

Maybe couple wheel to motor at rim rather than at shaft.

Yes, we tried that. Trouble is, because of the type of site, (protected
national park), the wheel has been made of wood, and the wood warps.

Chain drive
would itself give a nice big gear ratio.

But would rust if not oiled, and no release of oil is acceptable in this
stream.

I'd be leary of belt drive
though. The gearing ratio would be dia of waterwheel to dia of motor
pulley/cogwheel.

Needs to go via an intermediate shaft anyway I think.

What power rating are car radiator fan motors? With belt drive you
might drive 2 of them on one belt, or as many as you want on a chain.
I've not tried them, its just a thought.

It's an interesting one. I'll see if we've got any lying around.


Cheers, J/.

 

[Anthony Matonak]

Home made motors are mostly very bad performers, so I would definitely
look for efficiency figures before building.

Electric generators operate slightly differently than electric motors.
A device which might make a highly inefficient electric motor can
operate very efficiently as an electric generator.

These sites have some interesting information on building home made
low speed generators.

http://www.picoturbine.com/
http://homepages.enterprise.net/hugh0piggott/
http://homepages.enterprise.net/hugh0piggott/pmgbooklet/index.htm

Anthony

 

[Fred B. McGalliard]

....

Electric generators operate slightly differently than electric motors.
A device which might make a highly inefficient electric motor can
operate very efficiently as an electric generator.

I have heard that the Wimshurst generator (a variable capacitance high
voltage generator) can be an efficient generator. You would have to step the
voltage down for practical use, but you would already have the high voltage
DC for a long transmission line. Also, the materials are easy to work in a
home shop.

 

[John Beardmore]

I have heard that the Wimshurst generator (a variable capacitance high
voltage generator) can be an efficient generator. You would have to step the
voltage down for practical use, but you would already have the high voltage
DC for a long transmission line. Also, the materials are easy to work in a
home shop.

Did anybody say that water wheels are usually in damp locations ?


Cheers, J/.

 

[[email protected]]

Richard J Komp <sunwattaattjunoddoottcom> writes:

Dear Duane, Nick and others,

Amazing that they are still throwing away the valuable heat. When we
make the calculation of the dollar value of the energy extracted, the
heat from our PV/thermal hybrid (where we extract the heat as either hot
water or hot air, or both) is actually worth more than the electricity.

My friend in Florida has paid for his PV/hybrid installation more than
three times over over the 18 years of its life time so far, and he
doesn't count the electricity since he only uses that for a backup system
when the power goes off. We use a 2 to 1 concentration ratio to keep the
finger series resistance within bounds, and also so that the collector
modules can be mounted in a fixed position without need for tracking or
seasonal adjustment (which makes the plumbing connections easier to deal
with). I can send more information if you are interested, but a lot of
this is in my book: PRACTICAL PHOTOVOLTAICS.

By the way, MESEA will be doing a PV/Hybrid installation workshop on
the weekend of the 31st of July and the 1st of August. We will be
installing a the usual 110 watt Hybrid on a house trailer for a local
family. The workshop costs $60 for the entire weekend, which includes
lunch (a cheap weekend in Downeast Maine) We can do this at this price
with the help of a small grant from the Maine Public Utility Comission.

Rich

Richard Komp PhD. President
Maine Solar Energy Association
17 Rockwell Rd SE, Jonesport ME 04649
207-497-2204 [email protected]
www.mainesolar.org