I agree with Willbe's comments, but a little more intuitive and simplistic approach is available.

The easiest way to evaluate panel power is, of course, to measure it directly with a wattmeter as you vary the load with a potentiometer or resistor load bank having sufficient power/current rating. Observe the load current or the load voltage or the load resistance at which the displayed power is maximized as you vary the power resistor.

Although I have been lucky enough to pick up a few wattmeters surplus from a local university, unfortunately very few of us have wattmeters, the passive, analog form of which are instruments with meters that resemble the familiar d'Arsonval (pointer) type analog meter except that the magnetic field is created not from a permanent magnet, but from a fixed coil that carries the load current. The moving coil is energized by the load voltage. The result is that the pointer displacement indicates the PRODUCT of the load voltage and the load current - i.e., the power. The scale will typically be very non-linear. There are also wattmeters that employ active analog or digital circuitry to compute and display the power.

Lacking a wattmeter, you can determine the peak power point by measuring the load voltage and the load current and plotting the product of the two vs. load resistance on a chart. At zero load resistance (short circuit) the current will be maximum, the voltage will be zero, and the product (power) will be zero. At infinite load resistance, the current will be zero, the voltage will be maximum, and the product (power) will again be zero. As you vary the load resistance and plot the product of voltage and current at several points, you will find a maximum in the power output curve somewhere near the mid point of voltage and current. Ideally you would let the panel reach steady state thermal conditions at each new point but getting data at nearly constant solar irradiance requires that you take data quickly.

One way to obtain a first-order correction factor for varying solar irradiance during your measurements would be to plot simultaneous readings of voltage or current from a properly loaded separate solar panel or even a tiny solar cell like you can (or used to be able to) buy at Radio Shack that is held at constant conditions and orientation.

Have fun.

awright

 

thanks awright that's a very good idea

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I am currently involved in project of Comparison study of Sensor and using Genetic Algorithm for Optimum Power for Solar Panel. I’ve developed a mini prototype, which includes a mini solar panel and PIC16f877a microcontroller and a motor as part of the tracking system.
For the first part of my project using sensors, the panel moves accordingly to the sensor values. (determine which is higher)

For the second part of my project using Genetic Algorithm, I would need a method to measure the voltage/power output so that the Genetic Algoritm could compute the accurate tilt of the panel, and move accordingly.

My problem now is, is there any method for me to measure the voltage/power output?
If P = V*I and
P=V2 / R

How could I measure voltage/power from mini panel? Let’s say we need 4 points from the panel. Is there any method?

 

Unless you have a very constant load resistance, your second formula will be of limited value in calculating power due to variations in load resistance. Measurement of both current and voltage and computation of the product will give you the instantaneous power, but that seems like a poor parameter upon which to make the decision of panel orientation. Variations in actual power output not due to orientation, but rather due fluctuations in loading or insolation, could lead to the wrong decision regarding optimum orientation.

I can't help you on microcontroller applications.

awright

 

Maybe the apparent internal resistance could be used as a Sun Seeking parameter. This resistance would appear to increase as the panel went off track.

This could be measured by rapidly changing the load applied to the panel, (switch in a known resistor value) and measure the new terminal voltage. The voltage difference could give an indication of the panel internal resistance.

Ron

 

A recent issue of Circuit Cellar had an article modelling solar cells. They used a light dependent current source shunted by a diode whose forward voltage was relatively insensitive to the incident light.

Same here.
Solar cell - Wikipedia, the free encyclopedia

So, it seems current delivered (to a varying load resistor, with varying illumination) is a better indicator of output power than output voltage. Since things with coils are current controlled, I 'spose solar cells should be connected to motors, or loads that act like motors.

And a motor spinning an optical disk is a current to freq. convertor, so a counter keeping track of the pulse count is an amp-hour meter. With constant cell voltage it becomes a watthour meter.

 

why not just have 2 light sensitive resistors pointing away from each other (not sure of angle but guess 90+ deg) that way the circuit knows which way the sun is so can return to start at sunrise and when the difference between the two falls below a certain amount it knows that its now night.

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www.simonsphotography.org.uk/ - My other hobby
www.rushdenrotaract.org.uk/ - make a difference and have fun !


Never buy "Trust" products, all mine broke !!!

 

Why not simply have the solar panel divide in two, with a vane standing between the halves. When the panel outputs are unequal, one is presumably being shaded by the vane and should be moved. Allowances should be made for the hopefully brief presence of clouds and birds.

 

why not just use solar panels for what they are meant and let sensors do their job ?

to do as you sa you will need to point the two panels in slightly different directions which will cause a powrr loss

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

www.simonsphotography.org.uk/ - My other hobby
www.rushdenrotaract.org.uk/ - make a difference and have fun !


Never buy "Trust" products, all mine broke !!!

 

Hi Friends,
There have a simple way to measuring the output power of solar panels.
You first measure an open circuit voltage of the solar panel (Voc), then you can calculate the maximum power point voltage (Vmp) from this approximate equation:
Vmp=(0.75-0.8)Voc.
(Don't forget that Voc is a temperature dependent parameter).
Then you can connect a proper load resistor to match the Vmp and after then measuring a maximum power point current (Imp).
Best Regards: Taner

 

So it's not <50% as I reasoned in another post, you're saying it's more like 80%.

 

Hi again Friends,
I tested two solar panels of Siemens, one for 12V batteries (Voc=21V) and one for 24V batteries (Voc=42V). I designed a scheme of my own maximum power point tracker (MPPT) with PIC MCU and connected it between PV and Grid-connected inverter. For the 24V PV panel reached Vmp=30-31V (Voc=42V) and for the 12V PV panel Vmp=16-17V (Voc=21V).
And the best way to supply maximum power from PV panels is to maintain a constant voltage near to Vmp with proper temperature compensation of the Vmp or Voc.
Best regards: Taner

 

Congratulations on your success, Taner!

How about showing us how you did it and how we can replicate it? Are you searching for the MPP dynamically or are you holding the output voltage of the panel at a fixed ratio of Voc?

What currents are you dealing with?

awright

 

Hi awright,
I checked and realized the two main methods and algorithms: Perturb and Observe (Hill-Climbing) agorithm and Constant Voltage algoritm.
And two methods gave very similar results.
The Dynamics of the MPPT algorithm depends on the dynamics of the whole system including: PV panels, Input filter capacitors and control algorithm of the Grid-connected Inverter (or other converter).
My opinion is that the better and stable of the two tested methods is Constant Voltage algorithm with proper temperature compensation of the PV Panel Voltage Voc.

 

Hi,

I want to find the Max power point of a 10W solar panel (Isc is 0.7 A and Voc is 19.2V). I am also charging a 12V dry battery with it thats running my circuit. I thought I would measure the current (with a shunt) and the voltage across the battery and calculate the max power, but I have now realized that the battery would draw different levels of current at different charging levels ..

I need some ideas... I think I need to vary the resistance (dont know how) and see the values of current and voltage(dropped across the resistor).. Im using a microcontroller btw. . .one idea that comes to mind is to short the terminals of the solar panel and use a mosfet in between , then vary the PWM to find the max current.


PS, I want to measure the Max point very accurately.. so need something thats very precise.