Total Solar Energy –What You Need to Understand

Ok, so what is this term that we hear about called “Total Solar Energy Rejected?” Often times we see some untrained window film dealers implying that this is temperature reduction percentage. Well, not really… while the measurement does translate indirectly to temperature reduction it should never be confused with it. Why is this so?

Heat and Temperature –What is the Difference?

When we measure temperature we are measuring the intensity of molecular motion. If you were to measure the temperature of the flame created by a lighter versus the flames of a forest fire they would be similar, however, the forest fire would generate much more heat than the lighter. Heat is a unit of energy. So even though the temperature of the flames are the same the far greater volume of mass of a forest burning will result in much more energy (heat) being produced.

The energy that makes up the solar spectrum is divided into three areas, Ultraviolet Radiation, Visible Light, and Infrared. Their intensities vary depending on their wavelength size and each one accounts for varying percentages of heat as indicated in the following diagram. (Note: See Updated Understanding of Energy Distribution.)

Total Solar Energy Pie Chart

As you can see 53% of the sun’s energy comes to us in the Infrared Spectrum, 44% from the Visible Light Spectrum, and 3% from the Ultra Violet Spectrum. All of these three areas make up what is known as the Solar Spectrum and their combined energy is what we are referring too when we use the term “Total Solar Energy.” Window Films act as a filter reducing varying percentages of each part of the Solar Spectrum. Darker films will filter out more visible light resulting in energy reduction whereas lighter films have to filter out more infrared in order to reject large amounts of energy. Films can be designed to work on either one part of the Solar Spectrum or all three. Clearly then when we read the specification called “Total Solar Energy Rejection”, we can now see that it is not referring to temperature reduction percentage, but rather, it is the percentage of incident solar energy rejected. The Total Solar Energy (TSER) specification along with another specification that is commonly used in the glass industry called the “Solar Heat Gain Coefficient” (SHGC) are two excellent ways for a consumer to compare the performance of one window film to another.

Window films alone cannot lower the temperature of a room but they can reduce the rate that energy enters a room which helps reduce the load placed air conditioning systems. The greater the glass area, the greater the impact window film can have on heat transfer into or out of a room. This makes window films an essential component to creating a more energy efficient building or home.



1 Response to “Total Solar Energy –What You Need to Understand”

  1. 1 Mike Feldman July 3, 2008 at 6:34 am

    Terrific Blog!

    Educational and timely.

    This should be required reading for all window film industry people.

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