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American Journal of Scientific Research

ISSN 1450-223X Issue 10 (2010), pp. 78-86© EuroJournals Publishing, Inc. 2010

http://www.eurojournals.com/ajsr.htm

Design of A Radio Telemetry Solar Radiation

Sensor Using Solar Cell

Sharif M. Raihan

Faculty of Engineering, International Islamic University Malaysia

Riza Muhida


M. Habib Ullah


E-mail: [email protected]

Lily Sulastri


Abstract

Solar radiation sensor is a device that is used to measure solar radiation in W/m2.

Determining the solar radiation and its interaction with the atmosphere and the earth's

surface is important because atmospheric circulation is driven by solar radiation. Moreover,

solar radiation accounts for almost all of the energy available to the earth. They are alsoused in meteorology to measure solar radiation. Meteorology is the scientific study of the

atmosphere that focuses on weather processes and forecasting. In this paper, the solarradiation sensor uses silicon solar cell or photovoltaic as sensor. Furthermore, wireless

measurement system using FM transmitter and FM radio receiver is also applied. There areseven steps to obtain the final graph of the solar radiation. Firstly, a solar radiation sensor

using solar cell needs to be designed. Than a photocurrent circuit is designed. The short

circuit current of the solar cell is directly proportional to the energy incident on the solarcell or the solar radiation. The solar cell is used as input and the photocurrent circuit

converts the current to voltage. Then signal conditioning needs to be designed so that it can

amplify the voltage from the photocurrent circuit which produces a voltage in a more easilyusable range. Next, a voltage-to-frequency converter is assembled that can convert

measured variable information voltage from the signal conditioning into a variable

frequency. Afterward, an FM Transmitter circuit is constructed that can transmit frequencyto an FM radio. The output of the FM radio is analyzed and simulated using LabVIEW.

Finally, after sampling and some calculation, the graph of the solar radiation is obtained.

Keywords: Radiation Sensor, Solar Cell, FM Transmitter, Photocurrent, FM Receiver.

1. IntroductionA pyranometer or also known as a solar radiation sensor is a type of actinometer used to measure

broadband solar irradiance on a planar surface. In other words, solar radiation sensor is a sensor that is

designed to measure the solar radiation flux density in watts per meter square (W/m2) from a field of

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79 Sharif M. Raihan, Riza Muhida, M. Habib Ullah and Lily Sulastri

view of 180 degrees. Pyranometers are frequently used in meteorology, climatology, solar energy

studies and building physics [1].

Solar radiation is radiant energy emitted by the sun, particularly electromagnetic energy. Thereare two ways solar radiation reaches the earth's surface. The first is direct solar radiation where the

solar radiation is directly transmitted through the atmosphere. The second is diffused solar radiation

where the incoming solar radiation is scattered or reflected to the earth's surface. About half of the

radiation is in the visible short wave part of the electromagnetic spectrum. The other half is mostly in

the near infrared part, with some in the ultraviolet part of the spectrum. The portion of this ultravioletradiation that is not absorbed by the atmosphere produces suntan or sunburn on people who have been

in sunlight for extended periods of time. Solar radiation is thermal radiation emitted from the surface of the sun, which is powered by nuclear fusion [3].

Because of the wide availability and importance as an alternative power source, it is tempting to

use silicon solar cell or photovoltaic as detector. In principle, a solar cell based instrument thatresponds to solar radiation is very simple. When solar energy falls on a solar cell, the cell produces

electrons. If a perfectly conducting wire is connected between the positive and negative terminals of

the solar cell, the flowing electrons produce a current, the magnitude of which is directly proportionalto the energy incident on the cell. This current is called the short circuit current.

Atmospheric circulation is driven by solar radiation. Determining the solar radiation and its

interaction with the atmosphere and the earth's surface is important, since solar radiation accounts foralmost all of the energy available to the earth [4].

As mentioned earlier, solar radiation sensor is a type of actinometer used to measure broadband

solar irradiance. Actinometers are actually instruments used to measure the heating power of radiation.

They are used in meteorology to measure solar radiation [2]. Meteorology is the scientific study of theatmosphere that focuses on weather processes and forecasting. Meteorological phenomena are

observable weather events which illuminate and are explained by the science of meteorology. Those

events are bound by the variables that exist in earth's atmosphere. They are temperature, pressure,water vapor and the gradients and interactions of each variable and how they change in time. The

majority of earth's observed weather is located in the troposphere [3].

The most important factors influencing how much shortwave radiation reaches the earth's

surface and how much is absorbed in a day of year, cloud cover, and albedo. The intensity of solarradiation varies significantly over the course of a year ranging from no solar radiation during the polar

winter to a maximum of 350 to 400 W/m2

in the summer. Over the course of a day, the sun's angle

above the horizon (solar altitude) influences the intensity of solar radiation. The noon sun is moreintense than the rising or setting sun. The maximum altitude of the sun depends on time of year and

latitude. Of course, during the polar winter the sun is below the horizon for 24 hours, and there is no

solar radiation, while at midsummer the sun changes little in altitude over the course of a day.Clouds reflect some incoming radiation back to space, thereby reducing the amount of radiation

that reaches the earth's surface. However, clouds also reradiate infrared energy back toward the earth's

surface, thereby moderating the temperature of the lower atmosphere. Globally, clouds have a cooling

effect on the earth atmosphere system, because of their high albedos. In polar region, however, clouds

seem to have a net warming effect as the reduction in solar radiation is outweighed by the effect of clouds in increasing long wave radiation to the surface [5].

Incoming solar radiation that strikes the earth's surface is partially reflected and partiallyabsorbed, in proportion to surface reflectivity (albedo). Darker surfaces have a lower albedo and absorb

more solar energy than do lighter surfaces. The albedo of a surface is also a function of the incidence

angle of solar radiation, i.e., the amount of solar energy a surface absorbs depends on the solar altitude[4].

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Design of A Radio Telemetry Solar Radiation Sensor Using Solar Cell 80

Figure 1: Solar radiation sensor block diagram.

The main objective of this paper is to design a solar radiation sensor using solar cell. The aim is

to obtain the final output graph of the solar radiation. Basically the objectives are:

1. To use solar cell as sensor in building the solar radiation sensor.2. To design a solar radiation sensor that powered from a power supply.

3. To apply wireless measurement system using FM transmitter and FM radio receiver.

1.1. Solar Cell

The dimension of the solar cell that is used to build the solar radiation sensor is 0.65 cm wide and 2.7cm height. The voltage across the solar cell in the room under room light is 156.1 mV and in sunlight is

602 mV.

1.2. Photocurrent

The short circuit current of the solar cell is directly proportional to the energy incident on the solar cellor the solar radiation. The solar cell is used as input and the photocurrent circuit will converts the

current to voltage. The value of resistor, Rf = 508 is used in experiment. An experiment is done using

the photocurrent circuit and also the solar cell and the results are as follows:

• Voltage in sun light = 9.61 V

• Voltage in dark (sun light) = 0.0012 V

Figure 2: Photocurrent circuit diagram.

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Figure 2 demonstrates the circuit diagram of photo current. From the results, graph and the

transfer function can be obtained. So the experimental transfer function is Vout = 525.41 Isc, where Vout

is output voltage and Isc is short circuit current.

1.3. Signal Conditioning

This signal conditioning circuit can amplify the voltage from the photocurrent circuit so that it

produces a voltage in a more easily usable range [7]. The solar cell itself can produce voltage in therange of 0.0012V to 9.61V as mentioned earlier. Each day the intensity of the sun is different so it isassumed that the solar cell can produce voltage in the range of 0.0012V to12.53V. From the test the

V/F converter circuit connected to the FM transmitter circuit and find the frequency on FM radio when

varied the input voltage from the V/F converter. Only when the voltage is from 0.422V to 1.582V, thewaveform of the FM radio can get a square wave that is shown through the oscilloscope in Figure 3. It

is assumed that the range of voltage is from 0.422V to 2V to make it in a wider range. From this

experimental result of the FM radio, the signal conditioning needs to be designed so that the solarradiation sensor produces range of voltage from 0.422V until 2V.

Vout = (m) Vin + Vo is used to develop the signal conditioning that produces output voltage in

the range of 0.422V to 2V.

Solar cell: 0.0012V 12.53V

Signal conditioning: 0.422V 2V

Instrumentation amplifier is used as the signal conditioning. Instrumentation amplifier isactually differential amplifier with high input impedance and low output impedance. Voltage follower

is connected to the instrumentation amplifier for isolation. So the transfer function is Vout = 0.1259 Vin

+ 0.4218 or Vout = 0.1259 (Vin + 3.3503).

Figure 3: Graph of Frequency_Radio (kHz) vs Voltage (V).

1.4. Voltage-Frequency Converter

V/F converter undergoes an analog to digital conversions with the aim of converting measured variable

information, Vin from the signal conditioning into a variable frequency. The IC used is LM331.

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Figure 4: V/F converter circuit diagram.

The input voltage need to be varied in order to obtain the value of frequency and the results are

graphed. From the graph, the experimental transfer function is obtained as ƒout = 1847 Vin. The graph

of Frequency versus Voltage is illustrated in Figure 5.

Figure 5: Graph of Frequency (kHz) vs Voltage (V).

1.5. FM Transmitter and FM Radio

The FM transmitter can transmit on any FM radio station from 88-108 MHz. Basically, both FMtransmitter and FM radio have the same frequency. FM transmitter transmits the frequency to FM radio

and FM radio acts as the receiver of the wireless measurement system.

2. Design SpecificationThe result from the FM radio is then being transferred to the computer for analysis or doing experiment

by using National Instruments LabVIEW 7.1. The data acquisition card (DAQ) is connected to the

computer. In this paper, PCI 6014 with BNC 2021 is used for data acquisition between the FM radio

and the computer. A cable for the headphone is connected to the FM radio. The other end of the cableis connected to the BNC 2120 at channel 0. In order to obtain the final output graph of the solar

radiation, the solar radiation sensor needs to be sampled for one day. The programming language of the

LabVIEW needs to be designed including both block diagram and front panel. Fourier transforms are

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used to convert from time domain into the frequency domain. The output of the solar radiation sensor

is sampled in certain duration of time and the value of voltage is obtained. From the value of voltage,

the value of current is obtained by inserting the value of voltage to V in = 66.1491 Isc + 0.418. Figure 6shows the front panel in LabVIEW for experiment.

2.1. Testing the Whole Circuit

The whole circuits that are the solar cell itself connected to photocurrent circuit and then connect it tothe signal conditioning circuit, V/F converter circuit and finally connect it to the FM transmitter circuitis tested including the FM radio. The solar cell is exposed to the spotlight instead of sunlight. It is hard

to control the sunlight to produce required output voltage of the solar cell. The input voltage from the

spot light is varied and the value of frequency of FM radio is obtained. Figure 6 shows the front panelwaveform and Figure 7 presents the Graph of Whole Radio Frequency vs. Voltage.

Figure 6: Front panel waveform for experiment.

Figure 7: Graph of Frequency_Radio_Whole (kHz) vs Voltage (V).

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3. Experimental ResultThe results are graphed and the experimental transfer function is obtained. The experimental transfer

function of FM radio is ƒout = 2074.95 Vin. As mentioned earlier, the experimental transfer function of photocurrent is Vout = 525.41 Isc. The experimental transfer function of signal conditioning is Vout =

0.1259 (Vin + 3.3503). The transfer function is Vout = 66.1491 Isc + 0.4218. The experimental transfer

function of the whole circuit is ƒout = 2074.95 Vin. Integrating the earlier transfer function with thewhole circuit transfer function, the transfer function is ƒout = 2074.95 (66.1491 Isc + 0.4218). The

overall transfer function is then Vin = 66.1491 Isc + 0.418. Figure 8 shows the front panel viewexperiment.

Figure 8: Front panel for experiment.

Experiment is done every 5 seconds. The final graph of voltage and current versus time

obtained.

Table 1: Experimental Results.

Voltage (V) Current (A) Voltage (V) Current (A) Voltage (V) Current (A)

0.82 0.006020 1.45 0.015544 1.18 0.011462

0.86 0.006624 1.44 0.015392 1.29 0.013125

0.90 0.007229 1.44 0.015392 1.45 0.015544

0.93 0.007683 1.44 0.015392 1.45 0.015544

0.98 0.008439 1.44 0.015392 1.44 0.015392

1.21 0.011916 1.45 0.015544 1.44 0.015392

1.39 0.014637 1.45 0.015544 1.44 0.0153921.44 0.015392 1.45 0.015544 1.44 0.015392

1.46 0.015695 1.45 0.015544 1.44 0.015392

1.46 0.015695 1.45 0.015544 1.44 0.015392

1.46 0.015695 1.44 0.015392 1.30 0.013276

1.38 0.014485 1.45 0.015544 0.86 0.006624

1.15 0.011008 1.45 0.015544 0.69 0.004054

1.14 0.010857 1.44 0.015392 0.56 0.002089

1.28 0.012974 1.44 0.015392 1.45 0.015544

1.46 0.015695 1.44 0.015392 1.45 0.015544

1.46 0.015695 1.44 0.015392 1.45 0.015544

1.45 0.015544 1.44 0.015392 1.45 0.015544

1.45 0.015544 1.44 0.015392 1.45 0.015544

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1.45 0.015544 1.44 0.015392 1.45 0.015544

1.45 0.015544 1.44 0.015392 1.45 0.015544

1.45 0.015544 1.44 0.015392 1.45 0.015544

1.45 0.015544 1.16 0.011160 1.45 0.015544

1.45 0.015544 1.45 0.015544

Figure 9: Graph of Voltage (V) vs Time.

Graph of Voltage (V) vs Time

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

12:00:00 AM 2:24:00 AM 4:48:00 AM 7:12:00 AM 9:36:00 AM 12:00:00 PM 2:24:00 PM 4:48:00 PM

Time

Voltage (V)

Moreover from the sampling, the value of voltage is obtained and the results are tabulated inTable 1. The value of current, Isc is obtained by inserting the value of voltage and is also recorded in

Table 1. The final graph of solar radiation in terms of voltage and current are obtained as shown in

Figures 9 and 10. The voltage versus time graph is shown in Figure 9 and the current versus time graphis shown in Figure 10.

Figure 10: Graph of Current (A) vs Time.

Graph of Current (A) vs Time

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

12:00:00 AM 2:24:00 AM 4:48:00 AM 7:12:00 AM 9:36:00 AM 12:00:00 PM 2:24:00 PM 4:48:00 PM Time

Current (A)

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4. ConclusionThe solar radiation sensor using solar cell has been constructed. All the circuits required to design this

solar cell have also been constructed and tested. The circuit used to design this solar radiation sensor ispowered from a ±15V power supply. This power supply has also been constructed. Moreover, the

mechanical part of the solar radiation sensor has been built. After integrating the FM transmitter part

and FM radio receiver part of the solar radiation sensor, the experiment using LabVIEW 7.1 is done.After sampling and some calculation of the results from LabVIEW, the final graph of the solar

radiation is obtained.

References[1] Castaner, L. & Silvestre, S. (2002). Modelling Photovoltaic Systems using PSpice. England:

John Wiley & Sons.

[2] Sharp. Photodiode/Phototransistor Application Circuit . (n.d.). Retrieved January 12, 2006.

[3] Johnson, C. D. (2003). Process Control Instrumentation Technology (7th

Ed). United States:Prentice Hall, p. 151.

[4] Marchand Electronics Inc. Dual 15V Regulated Power Supply Model PS10. (n.d.). Retrieved

November 11, 2006.

[5] Castaner, L. & Silvestre, S. (2002). Modelling Photovoltaic Systems using PSpice. England:John Wiley & Sons.

[6] Johnson, C. D. (2003). Process Control Instrumentation Technology (7th

Ed). United States:

Prentice Hall, pp. 150-152.[7] Supit, I; van Kappel, R.R. (1998). A simple method to estimate global radiation. Solar Energy.

No. 63, pp.147-160.

[8] Marion, W.; George, R. (2001). Calculation of Solar Radiation Using a Methodology withWorldwide Potential. Solar Energy, No. 71, pp. 275-283.

[9] Safi, S.; Zeroual, A.; Hassani, M. (2002). Prediction of global daily solar radiation using higher

order statistics. Renewable Energy No. 27 , pp. 647-656.

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