The aim of this project is to design, calibrate, and validate a simple low-cost sun radiometer. We follow the method proposed by Forrest Mims [1] which consists of using a light-emitting diode (LED) as a low-cost detector and optical filter. The LED acts as a photovoltaic (PV) detector whose short-circuit current (photocurrent) is proportional to the Sun’s irradiance. This current and, thus, the voltage it generates are amplified by a transimpedace amplifier as shown below [2]:
Fig. 1.
The architecture of the proposed system was designed in Solidworks and consists of two degrees of freedom, as shown in Fig. 2. The tube of this system is designed to house an LED diode that is used as our sensor. The length of the tube allows the sensor to have a narrow aperture angle of 3° approximately in order to measure direct radiation only and avoid the interference of diffused radiation [3]. The LED acts as a PV detector and its short- circuit current is amplified by an operational amplifier (LM324) using a feedback resistor Rf = 4M Ω. The amplified signal (voltage) is automatically read by an Arduino UNO. The amplifier circuit uses a voltage source of ±9V while the servomotors are powered with a separate voltage source of 5V . The implemented device is shown in Fig. 3. Note that Fig. 3 shows that a red LED was used for initial experiments; however, a green LED (520nm) was used to collect the data used in this report.
Fig. 2.
Fig. 3.
Fig. 4.
The position of the tube is controlled by two servomotors, whose angles are calculated by the Arduino. More specifically, the purpose of the Arduino program is to align the tube with the position of the Sun thorough the day; that is, it calculates the Sun’s azimuth and zenith angles constantly.
An example of the data collected is shown in Fig. 5. From this, we obtained the Langley plot shown in Fig. 6.
Fig. 5.
This repository contains the following folders and scripts:
Read_Solar.py: Python script that reads the collected data (.CSV files from thedatafolder) and generates the Langley plots (Fig. 5 and 6).utils.py: Python script that contains the functions used to calculate the zenith angle, distance from Sun to Earth, air mass correction, etc.Arduino\SolarRadiometer.ino: Arduino program that controls the servomotors and stores the data automatically thorough the day.Hardware_Solidworks\: Folder that contains the Solidworks files of the structure of the device. The subfolderFiles ready for printingcontains the files that can be directly 3D-printed. The design of the moving base was adapted from https://github.com/BrownDogGadgets/SolarTracker
[1] Forrest M. Mims. Sun photometer with light-emitting diodes as spectrally selective de- tectors. Appl. Opt., 31(33):6965–6967, Nov 1992
[2] Joseph Shaw. Lecture notes in remote sensing systems, EELE 583 - Spring 2022, Montana State University.
[3] Glenn E. Shaw. Sun photometry. Bulletin of the American Meteorological Society, 64(1):4 – 10, 1983