About Solar Radiation Intensity Measurements
and Data Processing
GORDAN Ioan Mircea
1, MICH-VANCEA Claudiu
21
University of Oradea, Romania
Electrical Engineering Department, Faculty of Electrical Engineering and Information Technology 1, University st., 410087 Oradea, Romania mgordan@uoradea.ro
2
University of Oradea, Romania
Electrical Engineering Department, Faculty of Electrical Engineering and Information Technology 1, University st., 410087 Oradea, Romania cmich@uoradea.ro
Abstract - Measuring the intensity of solar radiation is one of the directions of investigation necessary for the implementation of photovoltaic systems in a particular geographical area. This can be done by using specific measuring equipment (pyranometer) sensors based on thermal or photovoltaic principle. In this paper it is presented a method for measuring solar radiation (which has two main components - direct radiation and diffuse radiation) with sensors based on photovoltaic principle. Such data are processed for positioning solar panels, in order their efficiency to be maximized.
Keywords: solar radiation; virtual instrument; solar radiation sensor; database.
I. INTRODUCTION
Sun is the oldest source of heat (about 4 ... 5 billion a year) to maintain a temperature of planet Earth so it is possible to develop life as we know it today. This source is found in interplanetary space and it is an inexhaustible source of energy. Sun came to the attention of researchers as an energy source only a few decades ago, after several attempts to find a local energy sources to
meet energy needs necessary to technological
development.
Solar power is consumed by its absorption by some gases in the atmosphere and by clouds and is influenced by some geometric factors, which must be taken into consideration when the surface, where the solar radiation falls, is not the same with the incident one. The mechanisms, by which the solar radiation intensity is charged, while crossing the atmosphere, are absorption and scattering. However, while the total solar radiation is huge, the area where this radiation can be captured is very large and the energy is diffuse. So, the capture devices must have large areas with solar panels in order to collect the desired solar power. [4] [6].
For the study of solar radiation is important to share some important parameters such as the solar constant, which is the heat flow per unit received from the sun and
solar radiant energy flow. The atmosphere absorbs (retains, filters) X radiation almost completely and part of the ultraviolet radiation. Water vapor, carbon dioxide and other gases from the atmosphere, contribute to the absorption of solar radiation by the atmosphere. Absorbed radiation is converted into heat in general and diffused radiation obtained is returned in all directions in the atmosphere. Global radiation obtained from the sun, on a horizontal surface at ground level, in a clear day, is the sum of direct radiation and diffuse radiation. Diffuse solar radiation can be considered the same, regardless of the orientation of the receiving surface, even if in reality there are slight differences. Direct solar radiation depends on the orientation of the receiving surface.
II. MEASUREMENT AND DATA PROCESSING
Direct solar radiation intensity depends on the atmospheric condition and position in the world, with daily and annual variations depending on the movement of the terrestrial globe. It also depends on in temperature from day to night and from season to season. In the context of continuous development and growing consumption of energy that reduce pollution, the international scientific community, reconsiders all approaches on renewable energies. Among these, solar energy has one of the most important potential all over the world, because for a very long time, sun was considered a huge source of free energy. As noted previously, the intensity of solar radiation, outside the limits of the atmosphere, is relatively constant and this value was determined experimentally by measurements with specific technology satellites. The obtained values
are of approx. 1350 ... 1366 W/m2 [1]. From the limit of
atmosphere to land surfaces, solar radiation intensity is reduced because of the above effects (reflection, absorption, etc.) and the value of solar radiation intensity at ground level, have different values, depending on geographical location (latitude, longitude, altitude), weather conditions and the presence or absence of pollution, etc. [5].
Thus, in circumstances in which somebody wants to implement a solar power system for energy production it is necessary to measure solar radiation as a necessity for the design and implementation of solar panels to choose positions in space where their effectiveness will be maximized.
Scheme for measuring solar radiation is shown in Figure 1, where for measuring total and diffuse solar radiation intensity were used a photovoltaic transducer, whose properties are shown in Table 1. Solar radiation
FIGURE 1. System for measuring solar radiation.
Spectral response from 400 to 1100 nm
Nominal calibration coefficient 100mv for 1000W/m2
Coefficient in temperature +0.1%/°C
Operating temperature from -30°C to +60°C
Humidity dependence 100% HR
Mode photovoltaic
Surface active 1 cm2
Material Polycrystalline silicon
Front face Translucent PMMA
TABLE 1. Properties of the solar radiation sensor.
data, converted as an electrically analog signal, are transmitted to a data acquisition system (ADS), which, after the conversion into a digital format, will send the data to a data processing unit, in order to build a database (DB). Data processing units were characterized by an important development in last years, both in terms of hardware and software. Today on the technological market exist equipments with data processing units or only with memory environments, witch will be downloaded in a PC for a processing process, developed by a specialist in a virtual tool. [2].
The data visualization and analysis by user are developed by a virtual tool, which can be created by LabVIEW program, which is a graphical programming
environment that has revolutionized application
development testing, measurement and control. Through this program, regardless of experience, engineers and scientists can rapidly and effectively interface with the acquisition and control hardware, analyze data and can design distributed systems. The graphical programming environment offered by LabVIEW virtual instrument defines a software module (program), which consists of a user interface front panel (which provides an intuitive picture of a classical instrument) and a type-scheme
program block (a chart, available for repairs and maintenance). [3] [7].
In database terms, this can be created and updated automatically or on request of the user. For each measurement will be generated a unique identification and registration which will contain measured solar radiation, the sensor position in space, time and date when the measurement was developed. Organizational insertion/ extraction of data and the database are shown in figure 2.
!
"
!FIGURE 2. Organizational read / write database.
III. RESULTS AND CONCLUSIONS
The program performs two measurements made per second and records in the database the average result for 60 seconds (one minute). Data on the solar radiation obtained after the measurement are stored for every minute, over 24 hours (one day). Data are given as graphs or numerically.
During 24 hours was measured the intensity of solar radiation and the radiant exposure or global irradiation. The data obtained can determine the maximum amount of solar radiation intensity and the average values for day light (east - sunset) or for 24 hours.
Depending on the results obtained can be designed the solar energy conversion equipment required.
Measurements take place at the University of Oradea Gaudeamus Didactic Base from Stâna de Vale (Apuseni mountains, approx. 90 km S-SE of Oradea) and in the campus of University of Oradea. The sensor is placed horizontally in areas of freedom degrees of the horizon
3600.
April 18 to 24, 2012. Figure 5 presents the measurements developed over 24 hours on 26 April 2012, very serene day.
REFERENCES
[1] Cristian Oprea, RadiaĠia solară. Aspecte teoretice úi practice, Bucureúti 2005, ISBN 973 – 03915 -1.
FIGURE 3 . Measurements during April 11 to 21 in Stâna de Vale. FIGURE 4. Measurements between 18 to 24 April 2012 in Oradea.
[2] Petru COTFAS, Daniel COTFAS, Doru URSUTIU, Instrument virtual pentru măsurarea radiaĠiei solare, ConferinĠa internaĠională de instrumentaĠie virtuală, EdiĠia a III-a, Bucureúti, 29 Mai 2006.
[3] *** - LabVIEW course manual 2011.
[4] Ioan Mircea GORDAN – Măsurări electrice în electrotehnică, Ed. UniversităĠii din Oradea, 2003, ISBN 973-613-260-9.
[5] S.X. Chu, L.H. Liu - Analysis of terrestrial solar radiation exergy, Solar Energy, Volume 83, Issue 8, August 2009, Pages 1390–1404,
[6] Gayathri Vijayakumar, Michaël Kummert, Sanford A. Klein, William A. Beckman - Analysis of short-term solar radiation data, Solar Energy, Volume 79, Issue 5, November 2005, Pages 495–504;
[7] Claudiu MICH-VANCEA, Ioan Mircea GORDAN – Traductoare, interfeĠe úi AchiziĠii de date, note de curs, 2010
FIGURE 5. Measurements on April 26, 2012 in Oradea.
