Energy for Sustainability 2015 Sustainable Cities: Designing for People and the Planet Coimbra, 14-15 May, 2015
COMPARISON BETWEEN TWO LOW COST DESIGNED PYRANOMETERS IN ORDER TO ESTIMATE SOLAR IRRADIANCE Mehran Dehghan 1*, M.H.Ghodsirad 2 and Seyedmasoud Taheri 2 1: Faculty of Technology Telemark University College Kjolnes 3914, Porsgrunn , Norway E-mail:
[email protected] 2: Faculty of Mechanical Engineering University of Coimbra Polo II, Coimbra, Portugal E-mail:
[email protected],
[email protected]
Keywords: Solar Radiation, Solar Cell, Calibration, Pyranometer Abstract there are several instruments which are able to measure and estimate solar radiation in different climates and locations. But when it comes to the cost, most of these equipments are expensive. Another parameter which should be considered to use solar radiation meters is size of them. The main goal of this research is designing a cheap and small sensor in order to estimate and measuring sun radiation in different latitudes . Two different methods have been used in order to estimate and measure solar radiation. An electronic circuit and a solar cell are used to capture solar irradiance and produce an electrical signal based on that. In order to find a convert coefficient, a calibration method is used to convert electrical signals to the standard unit (Watt per square meter (W/m 2 )) which usually used for measuring sun radiation. Calibration is done by using a reliable Pyranometer DT-1037 to find accuracies of sensors and compare them with each other. A calibration Constant of 2004.5 ± 30W/m2 for the electronic circuit and 424.5± 1 W/m2 for the solar cell is obtained. An experimental test has been done to capture sun radiation within 6 days which consists of sunny days and partly cloudy days. All of experiences have been done in Porsgrunn City in Norway in March and April of 2014 and under supervision of Telemark University of College.
M.Dehghan, M.H. Ghodsirad and S.M Taheri
1. INTRODUCTION As solar radiation is becoming increasingly important factor which is considered in solar projects ,estimating and measuring of solar radiation cannot be neglected in order to modelling and designing of solar systems such as photovoltaic (PV) systems or solar heating systems or even weather forecasting usages[1]. There are several methods to estimate and predict solar irradiance in different locations based on latitude and time. an acceptable method for estimating solar radiation was achieved by using atmospheric transmittance model [2] while some scientist have used diffuse fraction and clearness index models[3]. Those models give an accurate solar radiation with having less possible error and also there are several instruments which are able to capture and measure solar radiations. in this research by designing and testing a sky instruments (instruments which is able to measure radiation from the entire sky [4]), it is tried to develop a practical method to estimate and measure solar radiation regardless the location. In this research, two designed low cost Pyranometers are compared in order to estimate solar radiation. The first designed Pyranometer is a simple solar cell which is able to capture solar irradiance and produce an output voltage based on them amount of the radiation[5], and the second Pyranometer is an electronic circuit which has been designed as a reliable Pyranometer in term of measuring and estimating solar radiation[4]. 2. SOLAR LED LIGHTING A solar LED lighting is a tiny instrument which has been designed for beauty usages in the houses or gardens. It consists of a solar cell, battery, LED and ending terminal in order to locate it in the ground. This instrument works based on a simple principle. During daytime, solar cell absorbs the sun radiation and produces voltage. The battery is rechargeable which is charged by produced voltage of the solar cell. When there is no sun, battery start discharging through a LED and it causes to turn it on during the night time or when there is no light. Figure 1 shows a solar LED lighting. In order to use this instrument for measuring the sun radiation, it is needed to separate solar cell from the other parts[5].
Figure 1. Solar LED Lighting 2
M.Dehghan, M.H. Ghodsirad and S.M Taheri
3. ELECTRONIC CIRCUIT An electronic circuit is designed and tested for measuring sun radiation. Here a method which has been applied in Mubi Adamawa state of Nigeria is used in order to design an electronic circuit. In this model it is tried to construct a reliable model Pyranometer to irradiance measurements [4]. The most important part of this circuit is a silicon diode which is responsible to receive the radiation or the sun intensity. The developed sensor generates an electrical signal proportional to the revived irradiance and converts the small output current of sensor to the voltage and amplifies it to the voltmeter. Photoelectric sensors are normally used to short-wave radiation. Figure 2 illustrates a schematic diagram of this sensor.
Figure 2. Sensor diagram with different elements[4]
4. CALIBRATION In order to convert electrical voltage from the designed electronic circuit and solar cell to readily quantifiable units, a calibration method must be used. The Standard unit for the solar irradiance is W/m2 and it is expected to find a convert coefficient to obtain values with this unit. Since calibrating must be done with high accuracy, and different parameters like temperature, humidity and even wind speed might affects on it, here all experience is done under a clear sky. A reference Pyranometer DT-1037 is used for calibration. The Pyranometer is located next to the sensors horizontally, and data is collected based on the time table for each of the instruments. Table 1 shows received data for a sunny day within 6 hours. Table 1. Received data by solar cell, Electronic circuit and Pyranometer Time 9:00 am 10:00 am 11:00 am 12:00 pm 13:00 pm 14:00 pm
Pyranometer W/m2 1030 1056 1075 1136 1260 1058
Electronic Circuit mV 522 523 542 542 542 518 3
Solar Cell V 2.43 2.48 2.54 2.54 2.54 2.49
M.Dehghan, M.H. Ghodsirad and S.M Taheri
In order to do calibrating based on the recorded data, 1Volt is considered as a constant voltage to obtain conversion coefficient. By obtaining a convert coefficient for every hour and calculating mean of them, below values are achieved: Convert Coefficient for Electronic Circuit ≈ 2004.5 ± 30W/m2 for 1 V 2
Convert Coefficient for Solar Cell ≈ 424.5± 1 W/m for 1V
(1) (2)
5. TEST OF SENSORS AND MEASURING RADIATION In order to test sensors and measure sun radiation, a test method has been considered. Sensors are located horizontally in the North direction and data are captured for six days continuously. The captured days consist of sunny days and partly cloudy days in the spring. Figure 3 shows captured variation of solar radiation by solar cell in different days in March.
Figure 3. captured sun radiation by Solar Cell for 6 days (Vertical axis unit: W/m2 – Horizontal axis unit: Time)
As it is seen in figure 3, data has been capture between 9:00 am until 18:30 pm, where sun radiation has the maximum amount and it is possible to use this amount of radiation for heating usages or producing electricity. In order to test designed electronic sensor it is needed to capture sun radiation with it. Figure 4 shows captured data by electronic circuit within 6 days. There were complete sunny days from day 1 (20th March) until day4 (23rd of March) and radiation has a high level, and day 5 (24th March) until day 6 (25th March) were partly cloudy days and as it is seen in the figures, radiation has the lower level.
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M.Dehghan, M.H. Ghodsirad and S.M Taheri
Figure 4. Captured sun radiation by electronic circuit for 6 days (Vertical axis unit: W/m2 – Horizontal axis unit: Time)
6. CONCLUSION By studying and comparing the results of these two sensors under actual environmental conditions of Porsgrunn, Telemark state of Norway, it can be seen that the both sensors are able to measure the sun radiation with an acceptable accuracy; however the solar cell has the less error in comparison with electronic circuit. The maximum radiation reaches the outer limit of the earth's atmosphere is approximately 1360 W/m2 [5] and as it is seen in table 1, designed sensors are able to capture maximum 1075 W/m2 of solar radiation which cover the major fraction of received irradiance on the earth. Based on the calibrating data, by using solar cell and electronic circuit in a sunny weather or even a partly cloudy weather, the sun radiation can be estimated with low percent of error, however still temperature, humidity and the location can affect on the measurements. REFERENCES [1] D. F. A. Riza, "Hourly Solar Radiation Estimation Using Ambient Temperature and Relative Humidity Data," International Journal of Environmental Science and Development, June 2011. [2] G. S. Campbell, “Introduction to Environmental Biophysics, 2nd ed. New York: Springer-Verlag., 1998. [3] R. DT, "Diffuse fraction correlations," Solar Energy, vol. 45, pp. 1-7, 1990. [4] D. W. Medugu, Burari, F. W. Bello, A. A., "Experimental comparative study of the performances of constructed reliable model and standard pyranometers,"Ozean Journal of Applied Sciences, 2010. [5] M. Dehghan, M.H Ghodsirad, "Possibility of Designing and Implementing of a low cost and small sensor in order to measure and estimate solar radiaition," Submitted in The first national conference on Renewable Energy and Sustainable Development, Iran, 2015. 5
