NATIONAL UNIVERSITY OF COMPUTER & EMERGING SCIENCES, FASTDEPARTMENT OF ELECTRICAL ENGINEERING

Solar Thermal Power System

PROJECT REPORTSUBMITTED BYFaiq Ahmed (10-6313) Shoaib Ahmed Khan (10-6317) Ammar Masood (10-6304) Bachelors in Electrical EngineeringYear 2013PROJECT SUPERVISORSir, Mr. Rehmatullah KundiDEPARTMENT OF ELECTRICAL ENGINEERING160-Industrial Estate Jamrud Road, Peshawar

ACKNOWLEDGEMENTS

We are humbly grateful to ALMIGHTY ALLAH that with His will and help we were able to successfully achieve our project and then to our parents that with their prayers and support in thin and thick time of life we were able to achieve our goal.

We will like to give special credit to our supervisor Mr. Rehmatullah Kundi that with his advice, intellectual abilities and full time support at each building step we never got wrong footed and pursued the right direction for successfully achieving our goal.

DECLARATION

We hereby declare that no portion of the work referred to in this Project Thesis has been submitted in support of an application for another degree or qualification of this of any other university or other institute of learning. If any act of plagiarism found, we are fully responsible for every disciplinary action taken against us depending upon the seriousness of the proven offence.

COPYRIGHT STATEMENT

Copyright in text of this thesis rests with the student author. Copies (by any process) either in full, or of extracts, may be made only in accordance with instructions given by the author and lodged in the Library of NUCES-FAST (Peshawar) department of EE. Details may be obtained by the Librarian. This page must form part of any such copies made. Further copies (by any process) of copies made in accordance with such instructions may not be made without the permission (in writing) of the author.The ownership of any intellectual property rights which may be described in this thesis is vested in NUCES-FAST (Peshawar) department of EE, subject to any prior agreement to the contrary, and may not be made available for use by third parties without the written permission of the department of EE, which will prescribe the terms and conditions of any such agreement.Further information on the conditions under which disclosures and exploitation may take place is available from the Library of NUCES-FAST (Peshawar) department of EE.Group Members: Shoaib Ahmed Ammar Masood Faiq Ahmed

Project Supervisor Prof. Mr. Rehmatullah Kundi

Signature ___________

FYP Coordinator Prof. Mr. Ahmad Saeed Qazi

Signature__________

Verified By: Prof. Mr. Ahmed Saeed Qazi Head of Department Of Electrical Engineering

Signature_________________________ABSTRACTThe motivation behind the designing of solar thermal power system was to get familiar to each aspect of the voltage generation though a parabolic trough design because of the extraordinary increasing demand of fuel energy in our country. In our project we tried our level best design the complete project of solar thermal power system based on the layouts of leading Solar energy Institutes such as NREL(National Renewable Energy Laboratory) ,SANDIA National laboratory, SUN labs. We successfully simulated our solar tracking device in FYP-1 and when simulation results were worth to be implemented on hardware , we generated the layout on Proteaus for those components that were to be fabricated on PCB. After the fabrication on PCB, the hardware results were analyzed, and implemented on mini level project which provided successful results. In FYP-2 we implemented all of the theory which was presented in FYP-1 on a complete hardware project which though could not generate electricity due to less parabolic troughs and its applicability on a small level, yet provided the concept of complete solar thermal power system through a parabolic trough design.

Table of contentsAcknowledgements .2Declaration.3Copyright statement4Abstract.5Table of contents6List of figures.7Chapter 1.8Introduction

LIST OF FIGURES

figure 1.1 principle of photovoltaic cells based on photoelectric principle 9

Figure 1.2 Principle of CSP based on heating fluid and generating electricity through its steam by a turbine10Figure 1.3 The back structure of an LS-2 parabolic trough solar collector assembly at Kramer Junction, California. 13Figure 1.4 The back structure of an LS-3 parabolic trough solar collector assembly at Kramer Junction, California. 13figure 1.5 The back structure of Euro parabolic trough solar collector assembly at Kramer Junction, California.14

Chapter 1IntroductionIn recent decades, the search for alternative energies has become increasingly important to the average citizen. Whether its due to concerns for the environment or worries about shortages in fuel or rising prices, most people agree that other options need to be found. Considering the amazing amount of energy that is showered down upon us every day from the sun, its no wonder that a lot of research and development is focused on improving our capabilities of capturing this source for electricity generation. As a major bonus solar power is also a renewable energy source that produces no polluting emissions or safety concernsAt present there are two main methods used to capture solar energy and convert it to electricity. One way is by using photovoltaic power and the other is with solar thermal power. When most people think of solar power, they are usually thinking of photovoltaic power, also known as PV for short. PV panels are able to directly convert sunlight into energy . These are the sort of solar panels that you often see on peoples homes and can buy at hardware stores. Unlike photovoltaic power cells, solar thermal power (also known as concentrated solar power) does not directly produce electric power. Instead, it produces heat. However, this heat can be captured and changed into electricity. In most solar thermal power plants, sunlight is concentrated to heat a fluid, such as oil or liquid salt, which is then used to heat water to create steam. The steam is then used to turn a turbine which generates electricity. Photovoltaic power has many advantages, such as the ability to operate on a very small scale or unattended, which has likely led to its vast popularity. However, when it comes to large scale productions of electricity, PV is much more expensive than solar thermal power. Thus, this Report will review the ways in which solar thermal energy is used for power generation. 1.1 Basic Principle of operationThere are basically two types of producing power out of solar energy photovoltaic normaly known as solar panels and solar thermal energy (upon which our project is based).

1.2 Photovoltaic cells or solar panels:Solar cells, also called photovoltaic (PV) cells by scientists, convert sunlight directly into electricity. PV gets its name from the process of converting light (photons) to electricity (voltage), which is called the PV effect. The PV effect was discovered in 1954, when scientists at Bell Telephone discovered that silicon (an element found in sand) created an electric charge when exposed to sunlight. Soon solar cells were being used to power space satellites and smaller items like calculators and watches. Today, thousands of people power their homes and businesses with individual solar PV systems. Utility companies are also using PV technology for large power stations.Solar panels used to power homes and businesses are typically made from solar cells combined into modules that hold about 40 cells. A typical home will use about 10 to 20 solar panels to power the home. The panels are mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight. Many solar panels combined together to create one system is called a solar array. For large electric utility or industrial applications, hundreds of solar arrays are interconnected to form a large utility-scale PV system.Traditional solar cells are made from silicon, are usually flat-plate, and generally are the most efficient. Second-generation solar cells are called thin-film solar cells because they are made from amorphous silicon or nonsilicon materials such as cadmium telluride. Thin film solar cells use layers of semiconductor materials only a few micrometers thick. Because of their flexibility, thin film solar cells can double as rooftop shingles and tiles, building facades, or the glazing for skylights.Third-generation solar cells are being made from variety of new materials besides silicon, including solar inks using conventional printing press technologies, solar dyes, and conductive plastics. Some new solar cells use plastic lenses or mirrors to concentrate sunlight onto a very small piece of high efficiency PV material. The PV material is more expensive, but because so little is needed, these systems are becoming cost effective for use by utilities and industry. However, because the lenses must be pointed at the sun, the use of concentrating collectors is limited to the sunniest parts of the country.

figure 1.1 principle of photovoltaic cells based on photoelectric principle1.3 Photothermic cells or solar thermal power systems:In solar thermal power system we trap the sunrays to heat some fluid and convert its steam into electricity through turbinesflat panel PV is not the way solar energy will be harnessed in the near term for large scale power generation. While it is the most visible of all solar technologies and for that reason attracts the attention and support of the public and policy makers, concentrating solar power(CSP) is positioned to be the true leader in solar power generation technology today. In CSP, mirrors or lenses first focus and amplify the suns energy. The concentrated sunlight is then converted to electricity through the photovoltaic process or a thermodynamic heat cycle, which uses a motor or turbine. In all CSP technologies, mirrors or lenses follow the trajectory of the sun through the sky and thus optimize energy collection. The four prominent CSP technologies are concentrating, parabolic trough, dish Stirling, and power tower; the latterthree use a heat cycle to produce energy. Currently, CSP is the most efficient and cost-effective way to generate electricity from the sun.In addition, hundreds of megawatts of CSP generating capacity could be brought on-line within a few years and make a meaningful contribution to our energy needs. Exhibit 18 provides an overview of solar power cost of flat panel PV and CSP technologies.

Figure 1.2 Principle of CSP based on heating fluid and generating electricity through its steam by a turbine.Advantages Of Solar thermal Power systems Over other Plants:1.4 Storage System in Solar thermal power systemsA distinct advantage of power tower and parabolic trough solar thermal power plants is the availability of a relatively inexpensive way of storing energy in the form of heat, especially compared with other intermittent renewable energies, such as PV and wind. Solar power plants with heat storage collect thermal energy during the day by increasing the temperature of a large heat reservoir. At one of the parabolic trough plants near Kramer Junction, California, heat storage utilized oil (see The 354-MW SEGS Power Plants). However, the power tower demonstration project, Solar Two, used a more effective and safer molten-salt storage system. In future applications, the heat reservoir will, therefore, likely be a large tank of molten salt rather than oil. The heat capacity of these storage systems is very large. For example, six-hour full-load heat storage of a 100-MW parabolic trough contains enough energy to power a home for nearly 70 years.Molten-salt heat storage is technologically ready, safe, and the most economic of all thermal energy storage technologies. It allows thermal energy to be collected during the day and to be saved for use at night or it can be used to keep the plant at full output when clouds pass over the plant location. The effectiveness of heat storage increases with the operating temperature of the thermal solar power plant. The high temperatures of the power cycle in power towers make this technology particular attractive for heat energy storageIn a competitive market, energy storage also allows the operator to maximize profits. For example, during periods of low hourly power prices, the operator could forgo generation and dump heat into storage. At times of high prices, the plant could run at full capacity even if the solar field was not receiving full sun, or no sun at all. Many of the high load/high price periods in the Desert Southwest occur in the three to four hours after darka time period the operator could target for dispatch. Therefore, additional revenues from the energy market may justify the cost of adding storage. Additional flexibility in the operation of a thermal solar plant with storage comes from oversizing the solar field, that is, the collectors generate more heat than required by the steam turbine of the plant. For example, a 100-MW thermal solar plant could have a solar field that has a nominal

NREL and Solar thermal Power systems:Flat panel PV is not the way solar energy will be harnessed in the near term for large scale power generation.[1.1]Sandia Laboratories and Solar thermal Power systems Currently, CSP is the most efficient and cost-effective way to generate electricity from the sun.[1.2]

1.5 Capital Cost Of CSP in comparison with other power Plantsone unit of electricity production cost is as less then as 13.4 cents/kwhr capital cost of coal plant is 900-1200 $/kwhr capital cost of combustion turbine 325-450 $/kwhr capital cost of combine cycle is 525-625 $/kwhr capital cost of wind turbine is 850 $/kwhr capital cost of nuclear energy is 2100$/kwhr[1.3]

1.6 Co2 Emission Of CSP in comparison with other Power PlantsCsp emits zero percent of C02. coal plants emits 1930 lbs/MWhr c02 gas boiler emits 1230 lbs/MWhr c02 combustion turbine emits 1345 lbs/MWhr co2 no co2 emission in nuclear and wind plants takes place[1.4]1.7 Abundance of sun energy:Sun emits 4.3 *10^20j in on hour while the energy consumed on planet in a whole year is 4.1*10^20j [1.5]

1.8 Green House Effects:In a world pushing for green products, an obvious benefit of solar thermal power stations is the fact that they could help reduce greenhouse gas emissions1.9 Concentrating Mirrors or collectors: Different type of collectors are used worldwide, each have their own pros and cons. Concentrator StructureThe structural skeleton of the parabolic trough solar collector is the concentrator structure. The concentrator structure: Supports the mirrors and receivers, maintaining them in optical alignment Withstands external forces, such as wind Allows the collector to rotate, so the mirrors and receiver can track the sun.Types of collectors include: Luz system Eurotrough Solargenix

1.10 Luz System Collectors

Figure 1.3 The back structure of an LS-2 parabolic trough solar collector assembly at Kramer Junction, California.

Figure 1.4 The back structure of an LS-3 parabolic trough solar collector assembly at Kramer Junction, California.Luz system collectors represent the standard by which all other collectors are compared. The industrial nature of these collectorsmade from galvanized steelmakes them suitable for commercial power plant applications. And they have proven to be highly reliable. For example, most of the SEGS (solar electric generation system) power plants used Luz system collectors.There are two types of Luz system collectors: LS-2 and LS-3.The LS-2 collector features a very accurate design. Its torque-tube structure is simple to erect and provides torsional stiffness. It has six torque-tube collector modules, three on either side of the drive. And each torque tube has two 4-meter-long receivers. Unfortunately, the torque tube uses a lot of steel and requires precise manufacturing to build.For reducing manufacturing costs, Luz designed the larger LS-3 to lower manufacturing tolerance and require less steel. It proved to be a very reliable design. The LS-3 uses a bridge truss structure in place of the torque-tube. Luz's LS-3 collector has truss assemblies on either side of the drive. Each LS-3 truss assembly has three, 4-meter-long receivers.The LS-3 truss design didn't lower manufacturing costs as much as expected. It also suffered from insufficient torsional stiffness, which led to lower than expected optical and thermal performance.

1.11 EuroTrough CollectorFollowing the demise of Luz, a European consortiumEuroTroughinitiated the development of a new collector design intended to build on the advantages of the LS-2 and the LS-3. The EuroTrough collector utilized a torque-box design to integrate the torsional stiffness of a torque tube and the lower steel content of a truss design.

figure 1.5 The back structure of Euro parabolic trough solar collector assembly at Kramer Junction, California.1.12 Solargenix CollectorThe Solargenix collector is made from extruded aluminum. It uses a unique organic hubbing structure, which Gossamer Spaceframes initially developed for buildings and bridges. The new design: Weighs less than steel designs Requires very few fasteners Requires no welding or specialized manufacturing Assembles easily Requires no field alignment.The 64-MWe Nevada Solar One parabolic trough project features the Solargenix SGX-1 collector.

Thermal portion

Block Digram

Heat Exchanger:Aheat exchangeris a piece of equipment built for efficientheat transferfrom one medium to another. The media may be separated by a solid wall to prevent mixing or they may be in direct contact.They are widely used inspace heating,refrigeration,air conditioning,power plants,chemical plants,petrochemical plants,petroleum refineries,natural gas processing, andsewage treatment. The classic example of a heat exchanger is found in aninternal combustion enginein which a circulating fluid known asengine coolantflows throughradiatorcoils andairflows past the coils, which cools the coolant and heats the incomingair.Shell and tube heat exchanger:Shell and tube heat exchangers consist of series of tubes. One set of these tubes contains the fluid that must be either heated or cooled. The second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required. A set of tubes is called the tube bundle and can be made up of several types of tubes: plain, longitudinally finned, etc. Shell and tube heat exchangers are typically used for high-pressure applications (with pressures greater than 30 bar and temperatures greater than 260C)..This is because the shell and tube heat exchangers are robust due to their shape.Several thermal design features must be considered when designing the tubes in the shell and tube heat exchangers: There can be many variations on the shell and tube design. Typically, the ends of each tube are connected to plenums (sometimes called water boxes) through holes in tubesheets. The tubes may be straight or bent in the shape of a U,called U-tubes. Tube diameter: Using a small tube diameter makes the heat exchanger both economical and compact. However, it is more likely for the heat exchanger to foul up faster and the small size makes mechanical cleaning of the fouling difficult. To prevail over the fouling and cleaning problems, larger tube diameters can be used. Thus to determine the tube diameter, the available space, cost and the fouling nature of the fluids must be considered. Tube thickness: The thickness of the wall of the tubes is usually determined to ensure: There is enough room for corrosion That flow-induced vibration has resistance Axial strength Availability of spare parts Hoop strength (to withstand internal tube pressure) Buckling strength (to withstand overpressure in the shell)

Steam Turbine: Asteamturbineis a device that extractsthermal energyfrom pressurizedsteamand uses it to domechanical workon a rotating output shaft.Because the turbine generatesrotary motion, it is particularly suited to be used to drive anelectrical generator about 90% of all electricity generation in the United States is by use of steam turbines.The steam turbine is a form ofheat enginethat derives much of its improvement inthermodynamic efficiencyfrom the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible expansion process.Process:An ideal steam turbine is considered to be anisentropic process, or constant entropy process, in which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving the turbine. No steam turbine is truly isentropic, however, with typical isentropic efficiencies ranging from 2090% based on the application of the turbine. The interior of a turbine comprises several sets of blades, orbucketsas they are more commonly referred to. One set of stationary blades is connected to the casing and one set of rotating blades is connected to the shaft. The sets intermesh with certain minimum clearances, with the size and configuration of sets varying to efficiently exploit the expansion of steam at each stage.

Turbine efficiency:To maximize turbine efficiency the steam is expanded, doing work, in a number of stages. These stages are characterized by how the energy is extracted from them and are known as either impulse or reaction turbines. Most steam turbines use a mixture of the reaction and impulse designs: each stage behaves as either one or the other, but the overall turbine uses both. Typically, higher pressure sections are reaction type and lower pressure stages are impulse type.Impulse turbines:An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain significant kinetic energy, which is converted into shaft rotation by the bucket-like shaped rotor blades, as the steam jet changes direction. A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage. As the steam flows through the nozzle its pressure falls from inlet pressure to the exit pressure (atmospheric pressure, or more usually, the condenser vacuum). Due to this high ratio of expansion of steam, the steam leaves the nozzle with a very high velocity. The steam leaving the moving blades has a large portion of the maximum velocity of the steam when leaving the nozzle. The loss of energy due to this higher exit velocity is commonly called the carry over velocity or leaving loss.

Dynamo(Generator):Adynamois anelectrical generatorthat producesdirect currentwith the use of acommutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including theelectric motor, the alternating-currentalternator, and therotary converter. Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons. A dynamo has the disadvantages of a mechanical commutator. Also, converting alternating to direct current using power rectification devices (vacuum tube or more recentlysolid state) is effective and usually economic.The dynamo uses rotating coils of wire and magnetic fields to convert mechanical rotation into a pulsing direct electriccurrentthroughFaraday's law of induction. A dynamo machine consists of a stationary structure, called thestator, which provides a constantmagnetic field, and a set of rotating windings called thearmaturewhich turn within that field. The motion of the wire within the magnetic field causes the field to push on the electrons in the metal, creating an electric current in the wire. On small machines the constant magnetic field may be provided by one or morepermanent magnets; larger machines have the constant magnetic field provided by one or moreelectromagnets, which are usually calledfield coils.Commutation: Thecommutatoris needed to producedirect current. When a loop of wire rotates in a magnetic field, the potential induced in it reverses with each half turn, generating an alternating current. However, in the early days of electric experimentation,alternating currentgenerally had no known use. The few uses for electricity, such aselectroplating, used direct current provided by messy liquidbatteries. Dynamos were invented as a replacement for batteries. The commutator is essentially a rotaryswitch. It consists of a set of contacts mounted on the machine's shaft, combined with graphite-block stationary contacts, called "brushes", because the earliest such fixed contacts were metal brushes. The commutator reverses the connection of the windings to the external circuit when the potential reverses, so instead of alternating current, a pulsing direct current is produced.Excitation: The earliest dynamos usedpermanent magnetsto create the magnetic field. These were referred to as "magneto-electric machines" ormagnetos.However, researchers found that stronger magnetic fields, and so more power, could be produced by usingelectromagnets(field coils) on the stator.These were called "dynamo-electric machines" or dynamos.The field coils of the stator were originallyseparately excitedby a separate, smaller, dynamo or magneto. An important development byWildeandSiemenswas the discovery that a dynamo could alsobootstrapitself to beself-excited, using current generated by the dynamo itself. This allowed the growth of a much more powerful field, thus far greater output power.

Dynamo

Chapter 22.1 Solar tracker:Figure 1.6 Block Diagram of Solar tracking system

A solar tracker is a device that orients a payload toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices.In flat-panel photovoltaic (PV) applications, trackers are used to minimize the angle of incidence between the incoming sunlight and a photovoltaic panel. This increases the amount of energy produced from a fixed amount of installed power generating capacity. In standard photovoltaic applications, it was predicted in 2008-2009 that trackers could be used in at least 85% of commercial installations greater than 1MW from 2009 to 2012.However, as of April 2014, there is not any data support these predictions.In concentrated photovoltaic (CPV) and concentrated solar thermal (CSP) applications, trackers are used to enable the optical components in the CPV and CSP systems. The optics in concentrated solar applications accept the direct component of sunlight light and therefore must be oriented appropriately to collect energy. Tracking systems are found in all concentrator applications because such systems do not produce energy unless pointed at the sun.

2.2 C code:

#include "main.h"enum{on=0,off=1};#definebase_1RD2#definebase_2RD3

#define m_base_left{base_1=on;base_2=off;}#define m_base_right {base_1=off;base_2=on;}#define m_base_stop{base_1=on;base_2=on;}

#define up_ldrRC4#define down_ldrRC5//===================Variable's========================================================unsigned long soler_adc,soler_volt;

unsigned int temp1;

unsigned int adc0;//==============================================================================

void main(void){init_ic();init_lcd();init_adc(all_analog);lcd_text("Concentrated ",_1st);lcd_text("Soler Power(CSP)",_2nd);__delay_ms(2000);lcd_text("Supervisor Sir ",_1st);lcd_text("Rehmatulah Kundi",_2nd);__delay_ms(2000);lcd_text("Group ",_1st); lcd_text("Members ",_2nd);__delay_ms(2000);lcd_text("Faiq Ahmed ",_1st);lcd_text("P10-6313 ",_2nd);__delay_ms(2000);lcd_text("Ammar Masood ",_1st);lcd_text("P10-6304 ",_2nd);__delay_ms(2000);lcd_text("shoaib Ahmed Khan ",_1st);lcd_text("P10-6317 ",_2nd);__delay_ms(2000);lcd_clear;while(1){///-Soler Volt-///////////////soler_adc=adc_read(ch4);soler_volt=((soler_adc)*500/1023);digit_convert(soler_volt,4);lcd_text("V=",_1st);lcd_data(decimal[2]);lcd_data(decimal[3]);lcd_data('.');lcd_data(decimal[4]);lcd_data('V');lcd_data(' ');

///////////-Temp-///////////-Soler Volt-///////////////adc0=adc_read(ch1);temp1=(float)(adc0)*(4.882);lcd_text("T=");digit_convert(temp1,4);lcd_data(decimal[2]);lcd_data(decimal[3]);lcd_data('.');lcd_data(decimal[4]);lcd_data('C');lcd_data(' ');///////////////////////////////if(up_ldr==0 && down_ldr==0){m_base_stop;lcd_text("MOTOR No Action ",_2nd);__delay_ms(100);}if(up_ldr==1 && down_ldr==1){m_base_stop;lcd_text("MOTOR No Action ",_2nd);__delay_ms(100);}if(up_ldr==0 && down_ldr==1){lcd_text("MOTOR_Move F ",_2nd);m_base_right;__delay_ms(50);m_base_stop;}///////////////////////////////////////////if(down_ldr==0 && up_ldr==1){lcd_text("MOTOR_Move R ",_2nd);m_base_left;__delay_ms(50);m_base_stop;}

}

void init_ic(void){// Set the I/O direction.TRISA= 0x0f;// Configure PORTA I/O direction.TRISB= 0x00;// Configure PORTB I/O direction.TRISC= 0b00110000;// Configure PORTC I/O direction.TRISD= 0x00;// Initialize the ports.PORTB = 0x00;PORTC = 0x00;PORTD = 0x00;}

Components Used:

LDR:Aphotoresistororlight-dependent resistor(LDR) orphotocellis a light-controlled variableresistor. Theresistanceof a photoresistor decreases with increasing incident light intensity; in other words, it exhibitsphotoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits.A photoresistor is made of a high resistancesemiconductor. In the dark, a photoresistor can have a resistance as high as a few megaohms (M), while in the light, a photoresistor can have a resistance as low as a few hundred ohms. If incident light on a photoresistor exceeds a certainfrequency,photonsabsorbed by the semiconductor give boundelectronsenough energy to jump into theconduction band. The resulting free electrons (and theirholepartners) conduct electricity, thereby loweringresistance. The resistance range and sensitivity of a photoresistor can substantially differ among dissimilar devices. Moreover, unique photoresistors may react substantially differently to photons within certain wavelength bands.

Symbol

Comparator: A comparator is the simplest circuit that moves signals between the analog and digital worlds. Simply put, a comparator compares two analog signals and produces a one bit digital signal. The symbol for a comparator is shown below.

The comparator output satisfies the following rules: When V+is larger than V-the output bit is 1. When V+is smaller than V-the output bit is 0Just to give you an idea of how a comparator works, here is a simulation of using a comparator. Set the voltages on the control panel to adjust the voltage inputs to the comparator.

Simulation

Real comparators may work like the one in the simulation, but there are sometimes other considerations. For example, a common comparator is the LM339, which come on a chip with four comparators. The four comparators are all open collector outputs. We need to discuss that. Here's a diagram of the output circuitry showing how the comparator is connected to the output transistor, and how the collector of the transistor is connected to the output terminal on the chip.

In this situation, you don't need to know a lot about transistors (although it's a good idea to learn that if you don't know it!). What you need to know is that, in this situation, the transistor acts like a switch. A transistor doesn't always act that way, but it does in this situation. When the output of the comparator is a 1, current flows from the comparator through the base of the transistor, out the emitter to ground, as shown. When that current flows, the transistor acts like a switch that permits current to flow from the collect to the emitter to ground.

The way you connect the comparator is to put your load between five volts and the collector connection on the chip - like this

Microcontroller:

PIC16F877A

Features

Special Microcontroller Features - 100,000 erase/write cycle Enhanced Flash Program Memory Typical - Self-reprogrammable under software control - Single-supply 5V In-Circuit Serial Programming - Watchdog Timer (WDT) with its own on-chip RC oscillator - Programmable Code Protection - Power-Saving Sleeping ModePeripheral Features - Two 8-bit (TMR0, TMR2)timer/counter with Pre scalar - One 16-bit timer/counter - Brown-out detection circuitry - Parallel Slave Port (PSP): 40/44 pin-device onlyHigh-Performance RISC CPU - Only 35 single-word instructions to learn - DC-20MHz clock input - Up to 8K x 14 words of Flash Program Memory - Pin out Compatible to other 28-pin or 40/44-pinAnalog Features - 10-bit, up to 8-channel Analog-to-Digital Converter (A/D) - Brown-out Reset(BOR) - Two Analog Comparators - Programmable on-chip voltage reference (VREF) moduleCMOS Technology - Low-power, high-speed Flash/EEPROM technology - Fully Static Design - Wide Operating Voltage Range (2.0V to 5.5V) - Low-power Consumption

Pin Layout:

PIC16F877A

Pin Description

Pin NumberDescription

1MCLR/VPP

2RA0/AN0

3RA1/AN1

4RA2/AN2/VREF-/CVREF

5RA3/AN3/VREF+

6RA4/T0CKI/C1OUT

7RA5/AN4/SS/C2OUT

8RE0/RD/AN5

9RE1/WR/AN6

10RE2/CS/AN7

11VDD

12VSS

13OSC1/CLKI

14OSC2/CLKO

15RC0/T1OSO/T1CKI

16RC1/T1OSI/CCP2

17RC2/CCP1

18RC3/SCK/SCL

19RD0/PSP0

20RD1/PSP1

21RD2/PSP2

22RD3/PSP3

23RC4/SDI/SDA

24RC5/SDO

25RC6/TX/CK

26RC7/RX/DT

27RD4/PSP4

28RD5/PSP5

29RD6/PSP6

30RD7/PSP7

31VSS

32VDD

33RB0/INT

34RB1

35RB2

36RB3/PGM

37RB4

38RB5

39RB6/PGC

40RB7/PGD

H Bridge:AnH bridgeis anelectronic circuitthat enables a voltage to be applied across a load in either direction. These circuits are often used inroboticsand other applications to allow DC motors to run forwards and backwards. Most DC-to-AC converters (power inverters), mostAC/AC converters, the DC-to-DCpushpull converter, mostmotor controllers, and many other kinds ofpower electronicsuse H bridges. In particular, abipolar stepper motoris almost invariably driven by a motor controller containing two H bridges.

20 Ampare H Bridge IC

DC Gear Motor:A DC motoris an internallycommutatedelectric motordesigned to be run from adirect currentpower source. Brushed motors were the first commercially important application of electric power to driving mechanical loads, and DC distribution systems were used for more than 100 years to operate motors in commercial and industrial buildings. Brushed DC motors can be varied in speed by changing the operating voltage or the strength of the magnetic field. Depending on the connections of the field to the power supply, the speed and torque characteristics of a brushed motor can be altered to provide steady speed or speed inversely proportional to the mechanical load. Brushed motors continue to be used for electrical propulsion, cranes, paper machines and steel rolling mills. Since the brushes wear down and require replacement,brushless DC motorsusingpower electronic deviceshave displaced brushed motors from many applications.

References[1.1] http://www.nrel.gov/learning/re_csp.html.[1.2] http://energy.sandia.gov/?page_id=907 (SANDIA NATIONAL LABORATORIES) [1.3] Fuel from the sky [july 2002, NREL/ SR 550-32160] by Dr, Arnold Leitner Senior Consultant, RDI Consultant.[1.4] Fuel from the sky [july 2002, NREL/ SR 550-32160] by Dr, Arnold Leitner Senior Consultant, RDI Consultant.