Solar concentrating - does it work?

Does the concept of reflecting the sun onto a panel equate to an proportional increase of Wattage? (NOTE: none of that Ampere talk in this thread, we are talking about Watts LOL)

Saw on ebay a 190W concentrator from a 95W setup i assume. My first thoughts are - Isn't the cell effiency the limiting factor here? Second thoughts are - if it works, why doesn't everyone with low V:temp coeffient panels do the same thing?

What are the limiting factors? irradiance levels (W/m2), panel efficiency (%), or something else in this case?

Is this just a gimmick as i feel it may be?

Andrew
(ps: looks like i used my yearly quota of question marks lol)
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Reply By: Battery Value Pty Ltd - Monday, Apr 12, 2010 at 09:10

Monday, Apr 12, 2010 at 09:10
Hello Andrew,

haven't researched concentrators yet myself.

First questions spring to mind:
how much will this raise the cell temperature which impacts on output power,
how uniformly can a solar concentrator insolate the panel? I expect cells with the least amount of light on them to become the spanner in the works, similar to a partially shaded panel.
If the panel/concentrator aren't mounted on a tracker, then there will most likely be irregular insolation on the panel with similar results.

Maybe someone else has looked into this more deeply.

Best regards, Peter
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Reply By: GerryP - Monday, Apr 12, 2010 at 09:45

Monday, Apr 12, 2010 at 09:45
Hi Andrew,

The maximum solar energy available per square metre obviously cannot change, therefore the overall "capture" area would need to be similar to a normal panel. However, where the savings come in is the reduction of silicon needed, due to concentrating the rays onto a smaller cell area.

As Peter has mentioned, the temperature does rise quite markedly. While this does not pose a huge problem in colder climates like Europe, it can have quite adverse effects on the cells themselves in the hotter parts of our country. I do recall an overseas entry in the World Solar Challenge last year who 'cooked' a bunch of their cells with concentrators.

Depending on the design of the concentrator, if they are of a parabolic type shape, they can work quite well within a range of sun angles.

Cheers
Gerry
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Follow Up By: oldtrack123 - Monday, Apr 12, 2010 at 10:31

Monday, Apr 12, 2010 at 10:31
Hi
An interesting concept , no doubt based on the well recognised fact that within limits the solar panel output increases with higher irradiation levels
This can be readily seen with days when there are highly reflective clouds.
I have seen an output increase of about 10%

However that is dispersed light intensity ,
Not sure how a concentrator would achieve such an even distribution
Peter
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Reply By: Pete Jackman (SA) - Monday, Apr 12, 2010 at 10:21

Monday, Apr 12, 2010 at 10:21
I am tempted to get a big mirror out and have a play in the back yard this weekend to see what happens.

Pete
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Follow Up By: Member - Andrew (QLD) - Monday, Apr 12, 2010 at 10:35

Monday, Apr 12, 2010 at 10:35
good idea :)

My question was based somewhat on this design i've seen:

Image Could Not Be Found
source: http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=260579171197

Andrew
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Reply By: pop2jocem - Monday, Apr 12, 2010 at 10:36

Monday, Apr 12, 2010 at 10:36
Strange that a solar panel that by definition needs the sun to generate power becomes less efficient if the panel's cells overheat.
I wonder if anyone can or has come up with an effective way of reducing the cell temperature in the same way that a cooling system controls the engine temperature in our vehicles???
Maybe some type of heat sink such as some electronic components use.
I guess using a fan which would consume some power may absorb more power than it helps produce.
Just a thought or has this already been done

Cheers
Pop
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Follow Up By: Member - Alan H (QLD) - Tuesday, Apr 13, 2010 at 08:03

Tuesday, Apr 13, 2010 at 08:03
Most stats seem to be for an air temp of 20 degrees. The heat quickly decreases output and this is why panels should be freestanding (air all around) or if mounted should be raised above the surface to allow airflow.

Alan
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Follow Up By: guzzi - Tuesday, Apr 13, 2010 at 14:02

Tuesday, Apr 13, 2010 at 14:02
Everything I've read mentions 25deg C.
With every 10deg C rise in temp above 25 deg you get a 5% decrease in output.
Which is why you will only get around 58W out of a 80 W panel in real conditions.

The last time I had my panels out it was around 32deg C ambient, at the end of 1 hour the panels were over 60 deg C, I needed gloves on to handle them.
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Reply By: Member - KC (TAS) - Monday, Apr 12, 2010 at 10:59

Monday, Apr 12, 2010 at 10:59
A south Aussie bloke, here, has it covered I think. Minimum cells maximum output. Have a look at his site. If you haven't seen him on New Inventors. Google " sun ball "
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Follow Up By: Member - Jeremy W (SA) - Monday, Apr 12, 2010 at 14:58

Monday, Apr 12, 2010 at 14:58
Solar concentrating seems a logical way to go but seems to cause more problems than answers!!

Before we consider efficiencies, materials, construction etc.

Please consider:


1. The sun puts out about 900W per sq. metre and if we raised this to 1800W/m**2 then the collector dimensions (l & b) increase by 42% - not a great deal bigger than a single flat panel - 2 panels = 2x power.

2. The mirror must be curved so that the light is concentrated on the whole panel. This is a problem in itself. We may use fancy optics instead of a mirror - got to get it first!! - mechanical mounting of the mirror and panel must be looked at.

3. The mirror/solar panel must track the sun.

Points 2 and 3 can be a major headache and for all this effort what is to be gained ?

I'd place my bets on doubling the number of panels - 1 to 2.



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Reply By: Member - Boobook - Monday, Apr 12, 2010 at 17:04

Monday, Apr 12, 2010 at 17:04
I did it with a mirror I had handy. They work in overcast or cloudy conditions but as mentioned previously can raise the temp in full sun and make the system worse. Also you have to keep moving the mirrors, more than the panel it's self.

Not really worth it.
AnswerID: 412659

Reply By: trainslux - Wednesday, Apr 14, 2010 at 10:29

Wednesday, Apr 14, 2010 at 10:29
Using a silver window shade, I leaned it against the panels so the reflection landed on the panel, and it did increase the panels output by a few amps.
Rekon it would be well worth it if you were chasing amps on a cloudy day, or early morning, or late evening.

Give it a go, and see for yourself.
cheap, easy, and always good to see for yourself.

Trains
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Reply By: Alloy c/t - Wednesday, Apr 14, 2010 at 10:37

Wednesday, Apr 14, 2010 at 10:37
What you need to look at is the solar farm at Windorah , hundreds of mirrors reflecting the sunlight onto the solar panel , costs squillions to set up and still requiring diesel backup for when the sun don't shine.
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Follow Up By: Member - Andrew (QLD) - Wednesday, Apr 14, 2010 at 15:54

Wednesday, Apr 14, 2010 at 15:54
Reference: http://ecogeneration.com.au/news/windorah_solar_farm/011780/

Wow, 26kW generated from a panel around 1m square (or less) by a rough comparison of sizing. Does that sound right?

Thanks for the headsup on this system, it seems to be possible, albeit with a parabolic arrangement to gain 500 X concentrating, though i'm not sure of the doubling on a simple system. ;)

Andrew
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Follow Up By: oldtrack123 - Wednesday, Apr 14, 2010 at 21:24

Wednesday, Apr 14, 2010 at 21:24
Hi Andrew
You should not get too carried away. A lot of detail is missing from that link to make any comparision
But can you image that a standard say 100w panel capable of approx 5.6amps max in normal conditions could put out 5.6x500 = 2800 amps
& 2800amps x 14.3v =4004o watts ???
I think not so
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Follow Up By: Member - Andrew (QLD) - Wednesday, Apr 14, 2010 at 21:52

Wednesday, Apr 14, 2010 at 21:52
yeh, you are right that there is not much detail. ;) I'm open to suggestions as to how the numbers appear to add up, as long as we stick to watts. LOL

It is an interesting twist though to the concentrated solar discussion that i was originally considering. I was only looking at a 2 X multiplication, not the much greater benefits that seem to be generated in that real world environment.

It seems to ask more questions than solving. :)

Andrew
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