Solar Power Charting Tool

Figure 2. Current-To-Voltage Converter to Measure Current from the Solar Cell

Charting the Sun with .NET

The charting program consists of a User Control that plots data points on an XY Plotter. (See my previous article, An XY Plotter User Control in GDI+) a timer control, and the ActiveX control that talks to the GP-3 board. The program also has buttons that allow you to start and stop charting and a calibration check box to allow you to speed up data collection to test the program. Normally sampling takes place once every minute. In calibration mode, sampling is once every second. Figure 3 shows the solar charting form in calibration mode. The output you see was caused by varying the position of the solar cell:

Figure 3 . Charting solar power in calibration mode.

To chart the sun's power, it is more practical to take data every 1 minute or every 5 minutes because the sun doesn't change intensity that drastically every second. So when you are through in calibration mode, switch back to normal mode by clicking the checkbox again and hit the Clear button. Place your solar cell outside (make sure your serial cable reaches far enough!) and hit the start button to check the power potential in your area.

The code for capturing data is shown in Listing 1. The program reads A/D Channel #0 on the GP-3 board every time it enters the timer's event handler. The handler also adjusts the A/D reading to a voltage and converts the voltage back to a current using ohms law (current = voltage/resistance). The current is then multiplied by the voltage of the solar cell (.5V) to get a power measurement.

Listing 1. Measuring Power with the GP-3 and Displaying it in the Windows Form.

private float SimulatedHour = 0.0f;
private long StartClock = DateTime.Now.Ticks;
private void timer1_Tick(object sender, System.EventArgs e)
{
    // Take a reading every minute
    long tmp1 = this.axGP3IO2.a2d(0);
    // Convert the A/D reading from voltage to current using Ohm's law
    float current1 = ((float)tmp1 * 5.0f / 1024.0f) / 110;
    // Voltage is about 1/2 a volt in the solar cell
    float voltage1 = 0.50f;
    // Compute power using current X voltage
    float power = current1 * voltage1 * 1000;
    // Get the current time of day for the X axis
    float time = (float)DateTime.Now.Hour + (float)DateTime.Now.Minute / 60.0f;
    // Check for calibration mode
    if (checkBox1.Checked)
    {
        // In calibration mode, simulate the time increase
        SimulatedHour += 0.20f;
        time = SimulatedHour;
        // Stop the timer after 24 simulated hours
        if (SimulatedHour > 24)
            timer1.Stop();
    }
    else
    {
        // Stop the charting after 24 hours.
        if (DateTime.Now.Ticks - StartClock > (24 * 3600 * 1000))
        {
            timer1.Stop();
        }
    }
    // Add a point to the xy plot user control
    xyGraphControl1.AddPoint(time, power);
}

Conclusion

One easy improvement that could also be added to this project is to sum the total power produced over the course of a day. This way, you would have a number that is represented in mW-hours which, in essence, is a total energy measurement for that day.

If you want to try this experiment yourself, you can get a hold of the GP-3 board at the AWC website. The cost of the kit is $39.95. The other parts for the experiment (the op-amps, resistors, and solar cells) can all be purchased at Radio Shack.

Solar power is definitely viable in the near future. If you want to see some cool stuff being done with solar power, check out the SERC website. They have developed a solar/fuel cell car and are experimenting with using solar energy to create storable, clean hydrogen fuel. Also, check out the National Renewable Energy Laboratory Website for more information on renewable energy.

Previous Articles using .NET and the GP-3 Board

A Virtual Storage Oscilloscope in .NET

A Virtual VoltMeter in .NET