Experiment to Measure Solar Radiation Using Pyranometer on Tilted Surface at Different Angles of Inclination

The measurement of solar radiation is crucial in solar energy applications, as it provides an understanding of the amount of solar energy available for converting into electricity. A Pyranometer is a scientific instrument used to measure solar radiation, specifically the total solar irradiance incident on a surface. This experiment focuses on measuring the solar radiation using a pyranometer mounted on a tilted surface at different angles of inclination and plotting the radiation versus time characteristics.

Objective:

To measure the solar radiation using a pyranometer mounted on a tilted surface at different angles of inclination and plot the radiation vs. time characteristics for a certain duration.

Equipment/Materials Required:

  1. Pyranometer (to measure solar radiation)
  2. Tilted Surface (for mounting the pyranometer at different angles)
  3. Protractor (to adjust and measure the angle of inclination)
  4. Data Logger (for recording the measurements of solar radiation over time)
  5. Mounting Stand (to securely hold the pyranometer on the tilted surface)
  6. Solar Radiation Data Logging Software (optional, if available, for real-time data capture)
  7. Stopwatch/Timer (for manual timing of the data collection period)
  8. Thermometer (optional, for noting temperature conditions)
  9. Compass (optional, to ensure the orientation of the pyranometer is in the correct direction)

Theory of Operation:

Solar radiation is the energy emitted by the sun, and it can be measured in terms of irradiance (W/m²), which represents the power per unit area received from the Sun. A pyranometer measures this incident radiation on a surface, which includes both direct and diffuse solar radiation.

The amount of radiation received by the pyranometer is influenced by various factors, including:

  • The tilt angle of the surface (which affects the effective surface area that receives sunlight).
  • The time of day (due to the change in the solar angle).
  • The weather conditions (cloud cover, atmospheric dust, etc.).
  • The geographical location (latitude).

The tilt angle of the pyranometer significantly affects the measurement of solar radiation. At certain times of the day, when the sun is at a higher angle in the sky, the radiation is more intense on a horizontal surface. However, when the pyranometer is tilted at an angle (for example, to face the sun more directly), it may capture more or less radiation, depending on the angle and time of day.

Procedure:

1. Setting Up the Pyranometer:

  1. Mount the Pyranometer: Attach the pyranometer to a mounting stand or a platform that allows you to tilt it at different angles. Make sure the pyranometer is securely positioned.

  2. Angle of Inclination:

    • Choose a range of angles for the experiment, for example, 0° (horizontal surface), 15°, 30°, 45°, and 60°.
    • Use a protractor to accurately measure and adjust the tilt angle.
    • The orientation should ideally face the sun directly for maximum exposure, which can be determined using a compass to ensure the surface faces south (in the Northern Hemisphere) or north (in the Southern Hemisphere).

2. Calibration and Pre-Check:

  1. Check Pyranometer Calibration: Before proceeding with the measurements, ensure that the pyranometer is calibrated and functioning properly. If a data logger is used, check its settings and make sure it’s recording at the correct time intervals.

  2. Ensure Clear Weather Conditions: The experiment should be carried out on a clear sunny day for accurate measurement of solar radiation. Cloud cover will significantly affect the readings.

3. Measure Solar Radiation at Different Angles:

  1. Set the Pyranometer at the First Tilt Angle (e.g., 0° for a horizontal surface).

  2. Record the Solar Radiation:

    • Start the data logger or manually record the solar radiation in watts per square meter (W/m²).
    • Measure solar radiation at regular intervals (e.g., every minute) over a certain time period (e.g., 1 hour).
    • Ensure that the pyranometer is exposed to direct sunlight during the measurements.

  3. Repeat the Process for Other Tilt Angles:

    • Adjust the pyranometer to the next tilt angle (e.g., 15°), ensuring proper orientation.
    • Repeat the radiation measurements at the same time intervals for the next tilt angle.
    • Perform the same for other angles (e.g., 30°, 45°, and 60°).

  4. Record Data for Each Angle:

    • For each tilt angle, record the solar radiation values and the corresponding time.

4. Analyze and Plot Radiation vs. Time Characteristics:

  1. Organize the Data:

    • Prepare a table where you list the time intervals (X-axis) and the corresponding solar radiation values (Y-axis) for each tilt angle.
    • For example, columns would include: "Time", "Radiation at 0°", "Radiation at 15°", "Radiation at 30°", etc.

  2. Plot the Graph:

    • Using graphing software (Excel, Google Sheets, or a plotting tool), create a line graph with:
      • X-axis: Time of day (e.g., in minutes).
      • Y-axis: Solar radiation (W/m²).
    • Plot the curves for each tilt angle on the same graph for comparison.

  3. Analyze the Results:


    • Observe the trend of solar radiation over time for each tilt angle.
    • You will typically observe that the radiation increases during midday (when the sun is highest) and decreases in the morning and afternoon.
    • Compare how the radiation changes as the tilt angle is varied. At certain times, a tilted surface might receive more radiation than a horizontal surface, and at other times, it might receive less.

Precautions:

  1. Ensure Proper Orientation: The pyranometer must be oriented correctly to measure the correct amount of solar radiation. The sensor should face directly towards the Sun, or the platform must be adjusted accordingly.
  2. Calibration: Verify the calibration of the pyranometer to ensure accurate readings.
  3. Weather Conditions: Solar radiation readings can be affected by clouds, dust, or atmospheric conditions. Perform the test on a clear day to reduce these effects.
  4. Safety: Avoid direct exposure to the Sun for prolonged periods while setting up or handling the equipment to prevent eye strain or damage.

Results and Discussion:

  • Plot the Radiation vs. Time for different tilt angles (e.g., 0°, 15°, 30°, 45°, 60°).
  • Discuss how the solar radiation changes throughout the day and how it varies with different tilt angles.
  • Typically, you will see that the highest solar radiation is captured when the pyranometer is tilted optimally towards the Sun (i.e., angles that match the position of the Sun in the sky).
  • The horizontal surface (0°) may receive less radiation during non-peak sunlight hours (e.g., early morning and late afternoon).
  • The tilted surfaces may receive more direct radiation during specific times of the day, especially if the tilt matches the sun’s path.

Conclusion:

This experiment helps to understand the relationship between solar radiation and the tilt angle of the surface. By measuring solar radiation using a pyranometer at different tilt angles and times, we can determine the optimal tilt angle for maximizing solar energy absorption throughout the day. The results can be used to optimize solar panel installations for better efficiency based on geographic location and the time of year.