measuring power of solar panels

[duffy]

ummm, duffy, you might want to be a little more diplomatic about using terms like, "dumb."

...it is usually done simply using a variable resistor with suitable power rating and resistance range. There is some unique combination of voltage and current out of the panel for any given set of conditions...

Get a reference voltage off a fixed resistor and get the loading off a lookup table. Swapping power resistors around in a production unit is [insert diplomatic term here].

Thank you for "insolation".

 

[umer27]

you talking to me .. what about my idea ?

PS ROFLMAO !

 

[duffy]

Sounds like you're on the right track. I wouldn't bother with an instrumentation amp, just an opamp, maybe an LM6132, which is fast and can do near-ground sensing. You would set the gain based on 5V/max volts across resistor, which is your maximum solar-cell current times the .1Ω resistor.

 

[Mr RB]

Hi Umer27, I read some of your other thread too.

I designed a commercial high-efficiency switchmode solar MPPT a few years back, and if you really want to deliver maximum power into a 12v battery the ONLY factor you need to optimise is the CURRENT delivered into the battery itself. So you need to think of it as a "maximum current point tracker". This in effect gives you the greatest power into the battery itself, no need to complicate things trying to measure or control "power".

Of course if you want to measure voltage too, then your AVR can do a multiply calc and show "power" on the display to entertain the user.

Re the mechanics, in your other post you mentioned trying to make it as efficient as possible, I would suggest doing the sensing optically to determine solar position using 2 light sensors and one lens. Then close-loop the error output through the AVR to control your actuator. Your AVR can maximise efficiency by running the motor and leadscrew infrequently and leaving the entire actuator system in a zero power state for 90+% of the time, leadscrews are good for that because they are resistant to being backdriven by the wind.

For cloud conditions etc the AVR can guess solar posiiton based on previous days and its 24hour clock, an average of where the sun was at that time on previous days.

I think on the PIClist years ago someone had a mechanical tracker system where the PIC actually was able to realign its own 24hour clock based on solar zenith (noon) averaging, so it kept flawless time all year round and used that time to control the mechanical position of the solar panels. One of the benefits was it only needed one light sensor (noon detector) and dirt problems etc of the sensor were much more easily addressed than dual sensors (like when a bird craps on ONE of the 2 sensors).

 

[smanches]

if you really want to deliver maximum power into a 12v battery the ONLY factor you need to optimise is the CURRENT delivered into the battery itself. So you need to think of it as a "maximum current point tracker". This in effect gives you the greatest power into the battery itself, no need to complicate things trying to measure or control "power".

Just to clarify, this is the current after the switcher, not before it, right? So is the MPP on the IV curve both before and after the switcher directly proportional? EDIT: Answered my own question. IV curve IS a power curve, so of course they would both be directly proportional.

Before the switcher, both voltage and current fluctuate with sun, so you would have to track both to find the MPP. After the switcher, the voltage is usually being held at a steady level, so you only have to track the current to the load.

That makes it a lot easier.

 

[KMoffett]

umer27,

This is a circuit that I built for a Physicist to determine MPP of some small 12V/65W research solar panels. The control and outputs are interfaced to a LABVIEW program through National Instruments AD/DA boards. The Datel DTL-24A is a voltage controlled electronic load.
https://www.murata-ps.jp/products/power/ds/dtl24a.pdf
The program periodically sweeps the load from Vo to Is.
According to him, the MPP is Vo x Is x K.
K =~0.5 to 0.7, depending on the panel type.

Ken

Oh, by the way they aren't cheap: DTL24A They were $250 when I bought them.

 

[Mr RB]

..... After the switcher, the voltage is usually being held at a steady level, so you only have to track the current to the load.

That makes it a lot easier.

I'm sure I said that.

 

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[Mr RB]

Did we just get SPAMMED????

I feel so dirty....

 

[KMoffett]

Now this is real spam: YouTube - Monty Python - Spam

Ken