[Aggotrom]

Hi There,

Cool thread!
I am about to assemble my meter for a university thesis project, but I have some doubts about Rsh.
My highest reading of my solar panel (from a ALDI garden light) in Portugal over the last 3 days was today, with Isc = 72 mA.
If I look back at what Werk_AG did in the beginning, he said this would approximately refer to 1300 W/m2. Since I am also in PT, this would result in 1.81 ohm for my Rsh to get a voltage drop of 1mV per 10 W/m2.

However, this is a very rough approximation since I have no clue if at the measured second the value actually refered to 1300 W/m2. Personally, I think it more likely refered to 1400 W/m2, as according to ALDI the panel is a 50mA panel. Considering that ALDI uses the standard of 1000W/m2 at 25°C for this value, 72 mA would correspond to 1440 W/m2, not taking into account temperature deviations. This would result in a Rsh of 2 Ohm.

Now, nevertheless what I take for my Rsh, Werk_AG, wrote that later, one would be able to see if this value made sense and actually calibrate the meter to better match the real Irradiance.

My question is, how to calibrate the meter afterwards as the resistor cannot be changed? Would you change the relationship of 1 mV to 10 W/m2? 

Thanks heaps for your help and sorry if this has been answered somewhere but I cannot find it

Axel

[hornychz]

Not properly a schematic, but is something like this:



Forget the greyed part of this circuit. R1 value will deppend of characteristics of solar cell used.

 

Hi There,

Cool thread!
I am about to assemble my meter for a university thesis project, but I have some doubts about Rsh.
My highest reading of my solar panel (from a ALDI garden light) in Portugal over the last 3 days was today, with Isc = 72 mA.
If I look back at what Werk_AG did in the beginning, he said this would approximately refer to 1300 W/m2. Since I am also in PT, this would result in 1.81 ohm for my Rsh to get a voltage drop of 1mV per 10 W/m2.

However, this is a very rough approximation since I have no clue if at the measured second the value actually refered to 1300 W/m2. Personally, I think it more likely refered to 1400 W/m2, as according to ALDI the panel is a 50mA panel. Considering that ALDI uses the standard of 1000W/m2 at 25°C for this value, 72 mA would correspond to 1440 W/m2, not taking into account temperature deviations. This would result in a Rsh of 2 Ohm.

Now, nevertheless what I take for my Rsh, Werk_AG, wrote that later, one would be able to see if this value made sense and actually calibrate the meter to better match the real Irradiance.

My question is, how to calibrate the meter afterwards as the resistor cannot be changed? Would you change the relationship of 1 mV to 10 W/m2? 

Thanks heaps for your help and sorry if this has been answered somewhere but I cannot find it

Axel

Hallo Axel,

You can change boost of operational amplifier as is on the picture from Werk_AG in this thread and fine-tune the error by inaccurate determination of resistance.
I used to do very similarly when using the SP440 pyranometer - the principle is always the same:
   

[Aggotrom]

Not properly a schematic, but is something like this:



Forget the greyed part of this circuit. R1 value will deppend of characteristics of solar cell used.

 

Hi There,

Cool thread!
I am about to assemble my meter for a university thesis project, but I have some doubts about Rsh.
My highest reading of my solar panel (from a ALDI garden light) in Portugal over the last 3 days was today, with Isc = 72 mA.
If I look back at what Werk_AG did in the beginning, he said this would approximately refer to 1300 W/m2. Since I am also in PT, this would result in 1.81 ohm for my Rsh to get a voltage drop of 1mV per 10 W/m2.

However, this is a very rough approximation since I have no clue if at the measured second the value actually refered to 1300 W/m2. Personally, I think it more likely refered to 1400 W/m2, as according to ALDI the panel is a 50mA panel. Considering that ALDI uses the standard of 1000W/m2 at 25°C for this value, 72 mA would correspond to 1440 W/m2, not taking into account temperature deviations. This would result in a Rsh of 2 Ohm.

Now, nevertheless what I take for my Rsh, Werk_AG, wrote that later, one would be able to see if this value made sense and actually calibrate the meter to better match the real Irradiance.

My question is, how to calibrate the meter afterwards as the resistor cannot be changed? Would you change the relationship of 1 mV to 10 W/m2? 

Thanks heaps for your help and sorry if this has been answered somewhere but I cannot find it

Axel

Hallo Axel,

You can change boost of operational amplifier as is on the picture from Werk_AG in this thread and fine-tune the error by inaccurate determination of resistance.
I used to do very similarly when using the SP440 pyranometer - the principle is always the same:

Hey Zdenek,

thanks a lot for your answer
Since I have no ability to test the meter against a calibrated pyranometer here in Portugal I would do it later, somewhere else. Thus, it would be easier for me to change the code. Would you agree that I could just also change the linear relationship? For example I said my 72mA refered to 1350 W/m2 and I chose a 1.875 resistance. Later when I would have access to a pyranometer I would for example see that when my meter shows 1000 W/m2 (100 mV) it is actually 900 W/m2 on a calibrated pyranometer. Thus, I could change the relationship to 1mV - 9 W/m2?

Cheers for your help 

[hornychz]

Hello,

Now I'm not able to look into the code, but personally I'm convinced that no nonlinearity counts - so, in my opinion, yes, you can ...
(The theory is based on the assumption of "work in a short circuit" - that is, in a linear area of characteristic.)

[Aggotrom]

Hello,

Now I'm not able to look into the code, but personally I'm convinced that no nonlinearity counts - so, in my opinion, yes, you can ...
(The theory is based on the assumption of "work in a short circuit" - that is, in a linear area of characteristic.)

Thanks a lot!
Don't worry about the code, as I am actually writing my own code. My weak area is electronics .

Thanks for your help

[Aggotrom]

Thanks for your help peps!! This forum made it possible for me to build my pv-cell pyranometer based on an ALDI garden light (attached) with a friend of mine! It will be used to validate machine learning GHI predictions of my master thesis in rural Kenya to improve the efficiency of rural electrification  .
It logs the data on a micro SD card to be independent of potentially lacking IT infrastructure and is powered by a battery to be independent of missing power supply. The best feature is probably the fancy cord handle, hence its potentially the most haute couture pyranometer ever build  .

[uncle_bob]

Fantastic! Best wishes towards the PHD!

[Aggotrom]

Fantastic! Best wishes towards the PHD!

Thanks @uncle_bob 

Let's see if a PhD is gonna be happening but I applied for one haha 

[hornychz]

Thanks for your help peps!! This forum made it possible for me to build my pv-cell pyranometer based on an ALDI garden light (attached) with a friend of mine! It will be used to validate machine learning GHI predictions of my master thesis in rural Kenya to improve the efficiency of rural electrification.
It logs the data on a micro SD card to be independent of potentially lacking IT infrastructure and is powered by a battery to be independent of missing power supply. The best feature is probably the fancy cord handle, hence its potentially the most haute couture pyranometer ever build.

Congratulations! Good job. 

(Just remember that a solar cell is likely to last for one, at most, two seasons. Then it needs to be replaced - it will be completely gray ...)

I keep my fingers crossed while you working on the PhD! 

[Aggotrom]

Thanks for your help peps!! This forum made it possible for me to build my pv-cell pyranometer based on an ALDI garden light (attached) with a friend of mine! It will be used to validate machine learning GHI predictions of my master thesis in rural Kenya to improve the efficiency of rural electrification.
It logs the data on a micro SD card to be independent of potentially lacking IT infrastructure and is powered by a battery to be independent of missing power supply. The best feature is probably the fancy cord handle, hence its potentially the most haute couture pyranometer ever build.

Congratulations! Good job. 

(Just remember that a solar cell is likely to last for one, at most, two seasons. Then it needs to be replaced - it will be completely gray ...)

I keep my fingers crossed while you working on the PhD! 

Thanks Zdenek 

I'll keep the degradation in mind
Not a PhD yet   . It's my master thesis, but let's see what the future brings haha

Cheers