2.0 Introduction

In EME 810, you learned about the difference between optoelectronic and optocaloric solar energy conversion. As you may remember, optoelectronic refers to the photovoltaic effect of photons (radiation) being converted to electrons (electricity) while optocaloric refers to photons being converted to heat (thermal energy). In order to maximize solar energy gain and the subsequent conversion to useful thermal energy, it is necessary to understand how different materials interact with the sun’s electromagnetic radiation (photons) at different wavelengths. There are three key pieces to gaining a useful understanding of what is going on during the optocaloric conversion process:

1. A basic understanding of radiation heat transfer (D&B Chapter 3) is useful in light of the fact that solar energy, which passes through the atmosphere and reaches your collector surface, is trasferred via the process of radiation (not conduction or convection, though those heat transfer mechanisms can also play a part depending on the system configuration).

2. To convert photons to heat, the photons must be absorbed by the collector. This process requires opaque materials as opposed to reflective or transparent materials which would not absorb the energy but transfer it elsewhere. As such, an understanding of the radiation characteristics of opaque materials (D&B Chapter 4) is especially useful.

3. Many solar thermal energy conversion systems utilize a cover-absorber system to increase efficiency. Covers are typically glass, but can be made out of any material that transmit radiation while reducing losses from convection to the surroundings. As such, an understanding of the transmission of radiation through glazing (D&B Chapter 5) is useful.

These three main topics together provide important background for selection and use of materials in solar thermal energy conversion systems.

Lesson Objectives

• Identify materials best suited as components of solar thermal collectors.
• Apply selective surface characteristics in calculations.
• Calculate transmittance, reflectance, absorptance, and tau-alpha for various scenarios.

What is due for Lesson 2?

This lesson will take us one week to complete. Please refer to the Course Calendar in Canvas for specific time frames and due dates. A brief list of the lesson assignments is provided in the table below. More specific directions can be found on the pages of this lesson and in Canvas.

Questions?

If you have any questions, please post them to our Questions and Answers discussion forum, located under the Modules tab in Canvas. I will check that discussion forum regularly will do my best to respond. While you are on the forum, please feel free to post your own responses if you are able to help out a classmate.