This paper present the development of a handheld solarimeter which is integrated with temperature sensor modules by using the application of Microcontroller PIC16F877A. The solarimeter employs a reference solar cell which is calibrated to measure the solar irradiance. Besides the solarimeter, two temperature sensor modules will also be introduced to measure ambient temperature and photovoltaic module temperature respectively. All measurements from the solarimeter and temperature modules will be controlled by a Microprocessor PIC16F877A which provides programming strategy through basic C language. The designed algorithm is based on the calibration of the used solar cell and the temperature sensor modules. All the measurements of the solarimeter and temperature modules will be displayed on a LCD display. The results show that the developed integrated pyranometer device is accurate and cost effective as compared to the commercial pyranometer devices.
Keywords-solar irradiance, ambient temperature, module temperature, solar cell, temperature sensor, microcontroller.
INTRODUCTION
Nowadays, there is a global need for a renewable energy sources which can provide a green energy that is safe to the environment and will last forever. One of the renewable energy is solar energy and now has been used in our daily life . Solar energy actually has been harnessed by humans since ancient times which are using the technologies keep changing and evolving by time to time. This solar energy can be obtained directly from the sunlight that reaching the earth.
Recently, there are a lot of researches related to solar irradiance measurement due to the increasing need of photovoltaic system. Thus many technologies are developed to produce methods or devices that can measure the solar irradiance. In photovoltaic system, solar irradiance is the measure incident of total amount of solar radiation transmitted to the surface of the solar cell in a given unit of time. It varies throughout the day with the movement of the sun and the clouds. This measurement is normally done in the units of watts per square meter (W/m2) . The measurements of solar irradiance are the important thing for estimating power generation from the photovoltaic (PV) systems and determining the correlations to the electric system loads .
Solar irradiance is usually measured by pyranometers, solarimeters, or actinoraphy. Based on of all the devices, pyranometer is suitable and can be integrating with other devices so that it can be used for photovoltaic system application. Pyranometer is a type of device that used to measure solar irradiance or the radiation flux density .
Temperature
A solar cell is a device that generates electricity directly from the visible light especially from the sunlight. There are several factors that affect the solar cell efficiency such as effects of cell temperature, MPPT (maximum power point tracking) and energy conversion efficiency [2]. An efficient type of solar cell is due to reduced recombination in solar cell itself. Recombination is a limiting factor for current in a solar cell. Using polycrystalline silicon cell as hat can absorb the solar irradiance from the sunlight.
This project also will provide the data such as the solar irradiance (W/m2), module temperature (oC) and ambient temperature (oC) which can help when evaluating the performance of photovoltaic (PV) solar energy systems.
METHODOLOGY
Callibration of Solar Cell
A polycrystalline solar cell (6V/100mA) is connected to a resistor 100Ω used to measure the solar irradiance. This solar cell supposed to feed the resistor by a certain current and voltage under a certain solar irradiance and ambient temperature. However, the solar cell current can be relatively measured by measuring the resistor terminal voltage.
Hardware Development
In this project, there are five main parts consisting solar cell, digital thermometer sensor, ambient temperature sensor, Microcontroller and LCD as a display. Polycrystalline solar cell been used in this project because solar irradiance is the most influenced parameter on the performance of polycrystalline solar cell in Malaysian climate .
Figure 1
Figure 1 shows the hardware design of this integrated pyranometer project.PIC16F877A is a microcontroller operated based on program created by using MPlab software and it interfaces with a solar cell and two temperature sensors. The solar cell is used to measure the solar irradiance based on the terminal voltage of the resistor which is connected to the solar cell itself. The LM35 temperature sensor is used to measure the ambient temperature using analog-to-digital (ADC). The precision of the LM35 sensor is precision temperature sensor which the output voltage is linearly proportional to the Celscius (Centigrade) temperature.
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