Author Topic: One simple mirror it can offer 40% more performance at the solar cell.  (Read 6718 times)

Kiriakos GR

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I do not know how many are aware that a simple mirror it can offer 40% more performance at the solar cell,
when it is placed flat down and in front of solar cell it self.

Beware I am not talking about a complete panel !!

What I did was to add one small scale solar cell on a multimeter and by adding one mirror flat and in front of them I got 40% more current from it.
I am not saying 40% more voltage as its one cell haves it own max voltage output.
What probably happened in my case is that the mirror managed to double the light in a way, and the cell received the max solar energy for it size.
 
In the bellow picture imagine instead of wood this meter to be placed on a mirror !! ( The magic gets in to play after that)  ;)
Complete link of my finished project if you care to see it.
http://www.ittsb.eu/forum/index.php?topic=91.0

Every comment about this trick that causes so much extra gain is welcome.



SeanB

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #1 on: December 02, 2012, 12:40:12 AM »
More light means more current up to a point where the cell saturates. If you use a parabolic mirrir to focus on a cell you can get a lot out of a cell, provided you can keep it cool so it has a higher open circuit voltage.

Kiriakos GR

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #2 on: December 02, 2012, 07:22:03 AM »
you can keep it cool so it has a higher open circuit voltage.

My first thought after watching this effect was some videos  about making an solar oven.  ;D

In my test, the multimeter inner temperature stabilize to 32C  and the solar cell temperature raised close to 42C.
The special automotive dual side tape that I have use, has some serious thickness which block the heat transfer.
The environmental temperature this day was up to 25C.


   
up to a point where the cell saturates.

Yes I think that this is the point that I did reached, by feeding the cell with light from any vertical angle.
In my test after adding the mirror the actual horizontal positioning at facing the sun become less important.
An better description could be, that the horizontal degrees range, about getting the most of it, become wider. 

The sum of my thoughts leads me to believe that every solar cell with out active positioning it can benefit allot by the mirror. 

SeanB

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #3 on: December 02, 2012, 08:29:44 AM »
Using a reflector means either building in basic tracking to keep the reflection on the cell, or using a parabolic or other shape such that there is a large portion of the day that a reflection is on the cell in addition to the sun direct. If going to high power you would probably have to use a water cooling system on the cells. A plus is that you can use high efficiency cells and fewer of them, and the power gain in the conversion will probably offset the cost and complexity of the water system and the tracking system.

MJLorton

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #4 on: December 03, 2012, 03:53:30 AM »
I do not know how many are aware that a simple mirror it can offer 40% more performance at the solar cell,
when it is placed flat down and in front of solar cell it self.

Beware I am not talking about a complete panel !!

What I did was to add one small scale solar cell on a multimeter and by adding one mirror flat and in front of them I got 40% more current from it.
I am not saying 40% more voltage as its one cell haves it own max voltage output.
What probably happened in my case is that the mirror managed to double the light in a way, and the cell received the max solar energy for it size.
 
In the bellow picture imagine instead of wood this meter to be placed on a mirror !! ( The magic gets in to play after that)  ;)
Complete link of my finished project if you care to see it.
http://www.ittsb.eu/forum/index.php?topic=91.0

Every comment about this trick that causes so much extra gain is welcome.
Great to see the end result and all your testing you posted Kiriakos. I've had similar issues using diodes with small solar cells charging AA batteries. The losses / voltage drop was an issue and in many of my projects I just left out the diode. There's obviously the loss / leakage back through the solar cell to consider but in many cases this has not been a problem i.e. losses including a diode vs not.

I have an LED sensor light (scary old YT video...goto 10:47 - http://www.youtube.com/watch?v=WWqiiXrgC-E) that I originally setup in the States...now used here in South Africa daily. It's been working for 3 years with no problem...original Duracell rechargeable batteries...which I thought would have been "cooked" by now.

The thoughts on using a mirror to enhance performance are interesting. Good input from Sean.

I still want to play with the cooling side of larger PV panels. I can certainly see how the performance of our array (2250 watt) is affected on a "normal" hot summer day down here in Cape Town. On a clear cool day at the peak (12-1pm) it will produce 2300 + Watts...I've seen it sustain 2500 watts at times and even hit 3000 watts for short durations. On a clear hot summer day it will only sustain 1700-1800 watts at midday.

 
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

Kiriakos GR

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #5 on: December 03, 2012, 04:35:48 AM »

Great to see the end result and all your testing you posted Kiriakos. I've had similar issues using diodes with small solar cells charging AA batteries. The losses / voltage drop was an issue and in many of my projects I just left out the diode. There's obviously the loss / leakage back through the solar cell to consider but in many cases this has not been a problem i.e. losses including a diode vs not.

Your comment made me to realize that I have skip two measurements.
a) The solar cell internal resistance at the dark.
b) The returning / leakage back current ( No diode).

The solar cell even with no direct light it produces 3.5V minimum in to a bright room = it can compensate the leakage back current.
Personally I have the bad habit to keep anything is soft bags when is out of use.  ;)

If the inner resistance of the cell is high enough it could minimize the loss completely.  (speculating here)
I will explore the details about this scenario.




Kiriakos GR

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #6 on: December 03, 2012, 05:35:41 AM »
Extra measurements are taken.   :)

No diode = 10mA leakage back current (Dark room)
With Diode = 1uA   leakage back current (Fluke 28II REL out uA range)

Panel inner resistance.
Only the Agilent U1272A and U1273A & (AX) can do such a measurement world wide, due their smart Ohm function,
which can measure resistor under voltage.
The panel even is a very dark place it produces mV,  the measurement shown 320K Ohm and 20mV ,
as soon the light gets in, the inner resistance drops down.
Unfortunately this Smart Ohm function has a limit at 640mV and above.
Even so it did worked nicely at my measurement.     

The diode is a killer mostly for for the current, by bypassing it I got almost double mA output,
but the batteries are fully charged and from 30mA with diode the current jumped to 50mA. ( No diode = higher top up which is normal).
I did the crazy thing to add two diodes in parallel to see if their inner resistance has any influence, but nothing happened.

Sum up, No diode is no good for a circuitry that is not charge / discharge daily.

Thank you Martin , now I have the complete picture.
And luckily you have the U1272A to confirm the solar cell resistance. ( Get a good dark room )  ;D   
« Last Edit: December 03, 2012, 05:49:47 AM by Kiriakos GR »

SeanB

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #7 on: December 03, 2012, 10:16:12 AM »
Kiriakos, what diode are you using? Low drop shottky diodes or ordinary run of the mill silicon. This is the one area where germanium diodes are still a usable item. I have however seen a method that uses a little of the panel power to drive a DC-Dc converter to generate gate voltage for a mosfet that acts as a synchronous rectifier, so that on state only millivolts are dropped while current flow can be 100A or more.

Kiriakos GR

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #8 on: December 03, 2012, 11:57:50 AM »
I am using Schottky IN5819  which causes 300mV drop at 5,9V input, and so I get 5.6V as peak after the diode. 

MJLorton

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #9 on: December 04, 2012, 03:15:17 AM »

Thank you Martin , now I have the complete picture.
And luckily you have the U1272A to confirm the solar cell resistance. ( Get a good dark room )  ;D
Interesting feedback.....but if I start heading into dark rooms with my multimeters.... :o
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

Kiriakos GR

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #10 on: December 04, 2012, 05:31:04 PM »
I have too interesting news.

1) My measurement about the blocked current on the diode is valid.
In the specifications sheet it called as ..  Maximum DC reverse current. (and it is measured in uA)

2) I got congratulations by Agilent EMEA (Europe) about this project on Tweeter.  8)

I have to admit that the word from @SeanB about the Germanium diodes, it did trigger my interest,
but I am not willing to spent time about searching random specifications so to accidentally discover the perfect germanium diode with the less losses.   

I have retest the small mirror and the gain looks to be really there, and it does contribute even far more that what a ideal low loss diode can do.
This is a fact.  ;) 

SeanB

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Re: One simple mirror it can offer 40% more performance at the solar cell.
« Reply #11 on: December 04, 2012, 11:34:49 PM »
Ge diodes are not going to be available with high currents though, you might look at using Ge transistors.