Maximum Power Point Problem

[davidegrima]

Dear people,

I am currently attending my diploma in electrical/electronics engineering and as an end of year project I decided to compare the efficiencies of different models of solar panels. To do this, I am taking the readings for the voltage and current.

Now, I know that in order to take out the maximum power out of a solar panel, you need to determine the maximum power point. I have seen how typical graphs should come out when doing the test, however I do not know why my graph is not coming out as it should be.

To construct the particular model, I have purchased about 14 small solar panels (45mm x 26mm x 2.5mm) having 0.45V and 100mA output each and 4 mid sized panels (75mm x 45mm x 2.5mm) having 0.45V and 400mA output each and connected all of them in series.

Can anyone suggest what the problem might be?

I know that at 0 load resistance, the voltage should be 0V where as the current should be at maximum. On the other hand at infinite load resistance, the voltage should be at maximum and the current should be 0A.

[Sunking]

What are you using to determine current and voltage? Al I see is a current graph.

[davidegrima]

What are you using to determine current and voltage? Al I see is a current graph.

I am vary a load resistance, from 500Ohms up to 10kOhms and using a multimeter to read the voltage and current.

I am attaching the readings I obtained

[Sunking]

I am vary a load resistance, from 500 Ohms up to 10kOhms and using a multimeter to read the voltage and current.

I am attaching the readings I obtained

Well you need to run a few hundred Ohm's Law equation drills so you fully understand the LAW.

• Your load resistance needs to be 0 to about 100 Ohms.
• Next problem you have is you are only using 2-axis of the graph and missing the 3rd axis.

[Sunking]

To construct the particular model, I have purchased about 14 small solar panels (45mm x 26mm x 2.5mm) having 0.45V and 100mA output each and 4 mid sized panels (75mm x 45mm x 2.5mm) having 0.45V and 400mA output each and connected all of them in series.

Here is one of your many problems. If you series connect 100 ma cells in series with 400 ma cells, your max current is going to be 100 ma short circuit. You do not understand Ohm's Law.

Try this take your smaller 14 cells rated at .45 volts @ 100 ma and connect them in series. With a ZERO Ohm Load (Just the meter acting as a short circuit) In bright sun noon sun you should measure around 100 ma. Then measure the voltage with open circuit (infinite resistance) and you should measure about 7 volts.

Then with a adjustable resistance go from ZERO Ohms up to 100 Ohm's (1 watt). At around 62 Ohm's you should see about 6.3 volt @ 100 ma or .6 watts MPP

[davidegrima]

Here is one of your many problems. If you series connect 100 ma cells in series with 400 ma cells, your max current is going to be 100 ma short circuit. You do not understand Ohm's Law.

I know that the maximum short circuit current will be 100mA and that is how I want it to be.

[davidegrima]

Well you need to run a few hundred Ohm's Law equation drills so you fully understand the LAW.

• Your load resistance needs to be 0 to about 15 Ohms.
• Next problem you have is you are only using 2-axis of the graph and missing the 3rd axis.

I will try to carry out the experiment using a load from 0 to 15Ohms and see what happens.

Why do I need a third axis if I am determining the optimal load resistance based on current and voltage? xs... every other graph I saw only had two axis as is mine.

[Sunking]

Why do I need a third axis if I am determining the optimal load resistance based on current and voltage? xs... every other graph I saw only had two axis as is mine.

No every graph you have seen has an input axis of Irradiance Input expressed as w/m2 like this one

There is no way to know how much current it should output if you do not know the input irradiance. The graph should look like a bent knee and leg. You will only be able to make 3 points on the graph:

Voc = voltage open circuit
Isc = current short circuit
Mpp = maximum power point (voltage and current at some unkown resistance between 0 and 100 Ohms.) You are looking at 500 to 10K. WRONG BALL PARK 1 watt @ 500 Ohm's is how much current and voltage Mr. Ohm? Could it possibly be 500 volts @ 2 ma?

[Mike90250]

here's an IV curve

[davidegrima]

Correct me if I am wrong... lets say that I have a normal solar panel having an output of 0.45V and current of 100mA...

If I connect a 0Ohm resistor, the Voltage will be zero and short circuit current will come out.

Putting a very high resistance will output the maximum voltage (open circuit voltage) and no current will be seen.

Right?

[Mike90250]

Correct me if I am wrong... lets say that I have a normal solar panel having an output of 0.45V and current of 100mA...

If I connect a 0Ohm resistor, the Voltage will be zero and short circuit current will come out.

Putting a very high resistance will output the maximum voltage (open circuit voltage) and no current will be seen.

Right?

right

[davidegrima]

right

Than how come when I short the circuit (do not connect a load just measure the terminal of the solar panel) I get the the max voltage and max current?

And then, when I put a variable resistor and lower the resistance to 0Ohms, I get not voltage and no current, than as I start increasing the load, the voltage starts to increase and so does the current until I reach 10kOhms and the voltage output will be at max and so is the current?

[Sunking]

Than how come when I short the circuit (do not connect a load just measure the terminal of the solar panel) I get the the max voltage and max current?

Because you are making the measurement incorrectly, measuring Voltage open circuit, and do not know how to use your meter. Set the dial to amps, and use the appropriate input on your meter for amps. YOUR METER CANNOT MEASURE VOLTAGE AND CURRENT AT THE SAME TIME

[Sunking]

Take your meter and solar panel. DO NOT CONNECT ANY RESISTOR TO THE PANEL ONLYTHE METER. Configure the meter to read voltage and Read the OPEN CIRCUIT VOLTAGE. THEN SWITCH THE METER TO AMPS and read the Current Short Circuit.

[davidegrima]

Take your meter and solar panel. DO NOT CONNECT ANY RESISTOR TO THE PANEL ONLYTHE METER. Configure the meter to read voltage and Read the OPEN CIRCUIT VOLTAGE. THEN SWITCH THE METER TO AMPS and read the Current Short Circuit.

I did that and the voltage came out as 5.86V and the current 8.1mA