Variation of Solar Absorptance of CNT Coating with Incident AngleZijuan Lai, Dr. Forrest Schultz

University of Wisconsin-Stout, Menomonie, WI 54751

Introduction

With the explosive development of science and technology, solar energy, as a form of alternative energy sources, is becoming increasingly important! However, capturing this energy is still a science and engineering challenge that has not yet been solved. At UW-Stout, a carbon nanotube and ceramic nanoparticle based black coating for solar panels has been developed. The goal of this research project is to explore the variation of solar absorptance of UW-Stout coating and commercially available coating at different incident angles by using an integrating sphere attachment with UV-VIS-NIR spectroscopy.

Instruments

UV-VIS-NIR spectroscopy can use light in the ultraviolet, visible and near infrared ranges to determine the absorbance of liquids. However, using an integrating sphere attachment allows the instrument to measure the percent of light reflected away from a sample. Additionally, an absolute reflectometry attachment is used to change the incident angle.

Materials

Six samples, including both of UW-Stout coatings and commercially available coatings, have been measured at incident angles of 5 degrees, 12 degrees and direct normal angle. Our experimental data indicates that the UW-Stout coating exhibits variation based on formulation parameters.

Measurement and Calculation

Eq (1) %A = 1 - %REq (2) Rs= Σ (ES * %A)/ Σ ES

Equation 1 and 2, derived from ASTM G 173-03, are used to calculate the solar absorptance of the samples.

A Get the data of sample reflectance with UVProbe softwareB Calculate the absorptance (%A) of the sample by using Equation 1C Get the data of solar irradiance (Es) from ASTM G 173-03 ReferenceD Calculate the solar absorptance (Rs) of the sample by using Equation 2

Conclusion: Our experimental data indicates that the UW-Stout coating exhibits variation based on formulation parameters.

1. Effect of Incident Angle

Measure each sample respectively at incident angles of 5 degrees, 12 degrees and direct normal angle, and then we can get all samples’ overlaid spectrum of different angles.Conclusion: Our experimental data indicates that the smaller the incident angles is, the less the sample reflects, the more the sample absorbs.

2. Compare the performance of UW-Stout coating and commercially available coating

Generally, the performance of the UW-Stout coating is similar to that of commercially available coatings at incident angles of 5 degrees, 12 degrees and direct normal angle, but a closer look at Figure 2 and Figure 3 shows that the Mirotherm sample surpasses the UW-Stout sample. Figure 3 indicates that the highest solar irradiation occurs between 300nm with 1500 nm and Figure 2 indicates that when scanning between 300nm with 1500nm the reflectance of Mirotherm is lower than that of Sample 6, which performs best during all the UW-Stout samples. Therefore, in order to improve the efficiency of CNT Coatings, we need to increase its solar absorptance in the range where there is much solar irradiation.

Discussion

For Further InformationFor more information please contact Zijuan Lai laiz4264@my.uwstout.edu

Figure 3.) Solar Radiation Spectrum

Figure 1.) Reflectance of Mirotherm at 5 degrees, 10 degrees and normal angle

Figure 2.) Reflectance of Mirotherm and Sample 6 at direct normal angle

Instrument SettingsInstrument MPC-3100 UV-3600

Measuring Mode ReflectanceScan Speed Fast

Scan Range (nm) 200-2500Slit Width (nm) 32

Sampling Interval (nm) 2

Sample 1 2 3 4 5 6

Formation

Aluminum

Mirotherm

CNT CoatingNO.53

CNT CoatingNO.56

CNT CoatingNO.64

CNT CoatingNO.82

Sample 1 2 3 4 5 6

Solar Absorpt

ance0.173 0.714 0.696 0.680 0.642 0.705