Author Topic: Design and simulation of electronic Instruments for Solar Energy measurement sys  (Read 2665 times)

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Author : Shachi Awasthi, Anupam Dubey, Dr. J.M.Kellar, Dr. P.Mor
International Journal of Scientific & Engineering Research Volume 3, Issue 1, January-2012
ISSN 2229-5518
Download Full Paper : PDF

1   INTRODUCTION                                                                     
WITH expansion of urbanization and population the energy requirement is increasing day by day which leads to extraction of renewable resources of energy, like sun and wind among these sun energy has a vast potential to fulfill the energy needs.
The terrestrial solar radiation is very important data for evaluating the performance of solar energy conversion system. One can use the electronic integrator for total radia-tion measurement. The principle of the electronic integrator is based on the use of voltage and current consumption of  solar cell . A typical solar radiation measuring station usually installs the pyranometer quite far from the integrator. Since the EMF output signal from the pyranometer is very small. The signal is in microvolt level ,which results more noise coupling. The insolation value is also printed out locally. To make the insolation data base for wide area, we have to install many stations. This makes  difficulty to collect data. The proposed work describes the alternative method by connecting the Solar cell to the high-resolution analog to digital converter and the use of computer software along with the memory card  for computing the insolation including the use of internet server for sending the everyday data to the receiver.
From the latest researches it would appear that solar, wind or biomass would be sufficient to supply all of our energy needs, however, the increased use of biomass has had a negative effect on global warming and dramatically increased food prices by diverting forests and crops into biofuel production. As intermittent resources, solar and wind raise other issues.

Development of suitable solar irradiance measurement system with additional features such as remote monitoring , real time capture  and facility to backup and store the data is thus essential.

2.1 Overview
As seen from the figure above our measurement unit consist of PIN photodiode as a SENSOR whose readings are converted digitally using a 10 bit delta to sigma analog to digital converter unit which is inbuilt in AVR ATMega16 microcontroller, unit takes the sample and convert the digital data into energy per  unit distance from the formulae as describe  in section 2.3.3, energy unit is then passed to tcp/ip stack by ENC28j60 Ethernet module. Microcontroller unit here acts as a data acquisition device which is converting the analog reading into meaning data to be transferred to the Ethernet gateway.

2.2  Microcontroller unit as a DAQ (Data acquisition System)
Transducers, a common component of any data acquisition system, convert physical phenomena, such as strain or pres-sure, into electrical signals that can be acquired by a data acquisition (DAQ) device. Common examples of transducers include microphones, thermometers, thermocouples, and strain gauges. When selecting a transducer for use with a DAQ device, it is important to consider the input and output range of the transducer and whether it outputs voltage or current. Often, the sensor and DAQ device require signal conditioning components to be added to the system to acquire a signal from the sensor or to take full advantage of the resolution of the DAQ device. However, the transducer's output impedance is commonly overlooked as a vital consideration when building a DAQ system.
Impedance is a combination of resistance, inductance, and capacitance across the input or output terminals of a circuit. Figure 1 models the resistive output impedance of a transducer and the resistive input impedance of a DAQ device. Realistically, capacitance and inductance are also present in all DAQ systems. It is important that the input impendence of the DAQ device is much higher relative to the output impedance of the selected transducer. In general, the higher the input impedance of the DAQ device the less the measured signal will be disturbed by the DAQ device. It is also important to select a transducer with as low an output impedance as possible to achieve the most accurate analog input (AI) readings by the DAQ device. The following sections address how high output (source) impedance affects a measurement system and how to use a unity gain buffer or voltage follower to decrease the output impedance of a sensor.
Figure 1.-Model of a Typical Transducer and DAQ Device

2.3 Using a Unity Gain Buffer to Decrease Source Impedance
When you can neither use a transducer with a low output impedance nor reduce the sampling rate of the DAQ device, you must use a voltage follower that employs operational amplifiers (op-amps) with unity gain (gain = 1) for each high-impedance source before connecting to the DAQ device. This configuration is commonly referred to as a unity gain buffer, and it decreases the impedance of the source connected to the DAQ device. A power supply is required to provide +/- 5 V to the op-amp, and the power supply should be referenced to the analog input ground (AIGND) of the DAQ device.
Figure: Unity gain Buffer for the ADC  to decrease the source impedance here LM358 is used as a unity gain buffer , PIN photodiode BPW34  solar irradiance sensor, R1 as shunt resistor

3   Measurement And Readings
Silicon PIN photodiode is used as a irradiance transducer .Photodiode used has a photosensitive area of 7.5mm2. Below is the characteristics’ table of BPW34 photodiode. Readings taken by a standard ammeter
Photodiode 3.337 +/- 0.116 mA at an ambient temperature of 25ºC when exposed to a solar irradiance of 1000 W/m2.In order to keep the readings in a voltage range a shunt resistance is used to calibrate the circuit . Our goal is to make full sunlight give a 100 mvolts reading on the digital meter (full sunlight is about 1000 watts per square meter), so our meter will read 1 mvolts per 10 Watts/m2.

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