Incident Angle Modifier

Introduction

Photovoltaic module efficiencies continue to develop due to enhancing solar cell design structures as well as module manufacturing capabilities. These advancements include Passivated Emitter Rear Contact (PERC) cells, bifacial cells and true bifacial modules, half-cells, shingling, etc. However, a pivotal focus in PV design is module/array orientation. The spectrum and incident angle of sunlight will continuously vary, affecting the module performance as a function of its tilt, orientation and placement. This effect is quantified by the incident angle modifier (IAM), which needs to be calculated for each type of module. The IAM is also a very important input parameter in software packages such as PVsyst, System Advisory Model (SAM), and Homer, which are used to estimate annual system performance. SunSolve is one of the most accurate tools to model IAM and is currently used for this purpose by many large companies.

Learning Objectives

  • Understand the effects of module orientation on PV performance
  • Be able to perform single factor response experiments to observe the effects of module orientation on PV performance
  • Be able to perform experiments to observe how IAM changes the optical losses observed on PV modules
  • Understand the importance of a module’s IAM response
  • Understand the importance and utility of axis tracking technology

Tutorial Exercise

In this tutorial, you will determine the IAM of a PV module. The zenith and azimuth angle inputs are defined as the angle of the light source from the normal of the PV module. The template for the module under investigation can be found under Modules -> 72 Cell monofacial module. Please refer to the appropriate SunSolve about pages for further information and reading.

REMINDER

Make sure to save and organise any templates/simulations as you proceed throughout this tutorial; any unsaved progress will be lost if the SunSolve page is closed/changed/refreshed.

Part One – Effect of IAM on PV Performance

You will be conducting a simple sweep experiment to observe the effect of the zenith angle on the IAM of a PV module. By sweeping the zenith angle, you change the angle of the incident photon current density reaching the module and, hence, observe the changing performance of the module. You will then be able to plot the IAM losses normalised to the value at zenith = 0º. The responses that you will need to record are listed below.

Responses to be observed in Part One
ResponseUnits
Incident photon current density (Jinc)mA/cm2
Front reflected photon current density (JR,Front)mA/cm2 &
% of Jinc
Absorbed solar cell bulk photon current density (JBulk)mA/cm2
Maximum Power Output (Pmp)W

Conducting the Experiment

  1. Open a new 72 Cell Monofacial Module template
  2. Using the sweep function, sweep the zenith angle from 0º-80º with 10º  intervals
  3. Record the 5 responses listed in Table 1. Note that the absolute value and % of front reflection is required
  4. Sketch an X-Y scatter plot for each response (y-axis) versus the zenith angle (x-axis)
  5. Describe the relationships between the zenith angle and each response
  6. Calculate the IAM response by dividing the absorbed bulk photon current density by the incident photon current density. Normalise your results to the value at zenith = 0º and plot the response vs zenith angle.

Questions

  1. Are the relationships found above as expected, if not, why?
  2. When observing optical losses at different layers, i.e. parasitic reflection, absorption and transmission, is the absolute value or percentage a better metric for this experiment? Why?
  3. What does the IAM response tell you about PV module performance under changing incident angle of light? Therefore, why might this response be important for a module’s datasheet?

Part Two – IAM Throughout the Day

You will be conducting simulations to observe the changes in the optical losses that occur due to IAM. By sweeping the zenith angle at different azimuth angles, you can change the incident light reaching the module, and the breakdown of optical losses are provided. Different hours of the day on the June winter solstice or December summer solstice will be simulated. The expected zenith and azimuth angles of the sun to a flat and tilted panel can be collected from the PV lighthouse Solar Path Calculator. Furthermore, in a realistic experiment, diffuse light would have to be accounted for in the measurements but that will not be the case for these SunSolve simulations.

As you tilt the light source, the incident intensity will drop, affecting module current, therefore when observing the changes in optical losses, refer to the “Fraction of  Jinc” to read the % of reflection and absorption losses. You will also plot the IAM response, normalising the values to zenith = 0º. The responses you will observe are listed below.

Responses to be observed in Part Two
ResponseUnits
Incident photon current density (Jinc)mA/cm2
Absorbed solar cell bulk photon current density (JBulk)mA/cm2
Front reflected photon current density (JR,Front) % of Jinc
Parasitic absorption in the Glass layer % of Jinc
Parasitic absorption in the EVA layer % of Jinc

Conducting the Experiment

  1. Open the Solar Path Calculator and ensure the latitude and longitude is set for UNSW TETB i.e. -33.9176, 151.2269
  2. Input the date for either the June or December solstice in 2020 i.e. 21st of June/ December, 2020. (You may work with a partner to do one solstice each)
  3. Set the module installation to 0º tilt and azimuth
  4. Sweep through the mean solar time from 09:00 to 17:00 with 1 hour intervals and record the incident and azimuth angles provided by the calculator
  5. Open a new 72 Cell Monofacial Module template
  6. Using the sweep function, sweep the zenith and azimuth angle according to the angles provided by the solar path calculator. This can be done by clicking the fix icons for each sweep
  7. Record the responses listed in Table 3 above. You can use the sweep inputs run summary to keep track of the different settings and run number
  8. Sketch line curves of the responses and the incident angle (y-axis) to the mean solar time (x-axis)
  9. Plot the IAM response for this experiment, normalising your values to the zenith = 0º value in Part One.
  10. Repeat the experiment with a 30º tilt on the module orientation in the solar path calculator

Questions

  1. For the tilt used this experiment, would the winter or summer solstice present better results? You can compare your results with someone who did this experiment on a different solstice to you.
  2. Looking back at the Solar Path Calculator, the air mass also changes throughout the day. How would this affect the PV module performance?
  3. Compare these results to the same module under standard test conditions (i.e. run no. 1 of your experiment in Part One). Describe the changes to the optical losses and resulting photon current absorbed in the bulk.
  4. Have you saved and organised your simulations?

Part Three – Further Understanding of IAM Losses

The tutors will ask you the following questions on IAM losses. Make sure that you understand the concepts involved and prepare your answers while completing the above tasks

  1. From the above experiments, why would you consider applying a tilt to a PV array at TETB?
  2. In Part Two, which module orientation performs better in summer and which orientation performs better in winter at TETB?
  3. A large percentage of Jinc is often lost to front reflection. List the layers of the module or cell design that can be optimised to reduce these losses.
  4. Describe how single-axis tracking for PV arrays works, how would this be beneficial for PV performance?
  5. Dual-axis tracking will further improve the PV performance of an array, but what other factors may deter installers from using this technology?