Hello,

I am trying to measure and compare the total daily output of two identical solar panels: one is stationary and the other tracks the sun. I know how to measure the voltage acorss a load and determine the power but what is the best way to measure the total power produced, from sunrise till sunset, on these panels?

Thanks.

 

Total energy. . .?

Assuming a resistive load:
.....you could make an amp-hour meter from an IC Voltage-Frequency Convertor
http://www.national.com/mpf/LM/LM331.html
and a shunt resistor. The Freq. increments a counter. Total count + total time = total amp-hours.
.....You also need a voltmeter that displays average voltage. Use another V-F convertor and counter and divide the voltage count by the hours.
.....Then you have average V and total amp-hours, and so total watt-hours.

 

hi,
Are you planning to record every day or just a day or so.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Sorry for the late reply. I am just planning to record a day or so. Any suggestions?

Willbe - thanks for your suggestion. Is that the only method to do so?

Thanks.

 

Do you have an 'identical' charger and storage battery for each solar panel? Just charge both batteries and then discharge each one under identical conditions (Same inverter powering the same load. Inverter should have a low-battery cutoff. Measure time to cutoff for each battery. Swap batteries and repeat the next day.)

 

Well if you are only going to compare a couple of days differences you might consider the following lower cost but more math solution.

If you wire both panels to identical load resistors and place each resistor in identical size oil baths you could trend the temperature rise of both baths over time. After you acquire the raw data you can use excel to calculate the power generated by each panel over time. I'm sure a little searching could find the proper temp/BTU/Calories/watts relationship. Again this would require more math but the hardware cost should be lower.

Lefty

__________________
Measurement changes behavior

 

I guess you could add charge in chunks to two capacitors using sampling and the final "volt-hours" and amp-hours would correspond to the capacitor voltages. Then you multiply once.
Exactly how to do this with rising and falling voltages doesn't exactly jump out at me. One of these, maybe. . .?
http://en.wikipedia.org/wiki/Charge_pump
but I've never designed one.

Or
a voltage controlled current source (an FET or vacuum tube) feeding the cap, with ΔV across the cap = IΔT/C. 1v cell voltage means 1 mA into the cap, 10v means 10 mA, and for a 1000 µF cap you apply the 1 mA current for 10 mS and you get 10 mV.
Adjust the current and its duration to avoid voltages higher than the cap's rating by the end of the day.
You'll need low-leakage caps.

 

for watts:
put some resistance on the output of each panel, and measure the voltage across the resistor.

P = V²/R
power = voltage²/resistance

 

hi,
As its only a few days I would suggest the following.
Interface a MCP3204 , 4 channel 12bit ADC to the parallel port of a PC.
Use two of the channels to monitor panel voltage and the other two channels for current.

This would give W1 = V1*I1 and W2 = V2*I2 which could be plotted on the PC.

If you decide on this method I could help out with the PC interface details and a simple log program.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

I am aware of that. The question is how do you keep track of the power through out the day, and how do you record it and add it up?

 

Was my suggestion of any use.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Hello,

Another approach would be to log the solar irradiance from sensors placed next to each panel. Assuming the panels are identical, this would tell you how much energy you are getting for each configuration. The comparison will vary depending on the cloud conditions and angle of the sun and panels. A clear day would be a good starting point for comparison.

You can check out the following link for a "solar data logger" kit that logs solar irradiance and cummulative incident energy.

Micro Circuit Labs SDL-1

The kit manual describes how to compute cumulative solar energy in kWh from logged irradiance data as well as some other background on solar power.

Hope that helps.
Jeff Fedison
Micro Circuit Labs