Pvdiesel Batter Doc

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ECONOMIC ANALYSIS AND

ENVIRONMENTAL IMPACTS OF A PV WITH

DIESEL-BATTERY SYSTEM FOR REMOTE AREAS

Abstract

This project discusses the economic analysis and environmental impacts of

integrating a photovoltaic (PV) array into diesel-electric power systems for remote

villages. MATLAB Simulink is used to match the load with the demand and apportion

the electrical production between the PV and diesel-electric generator. The economic part

of the model calculates the fuel consumed, the kilo watt hours obtained per gallon of fuel

supplied, and the total cost of fuel. The environmental part of the model calculates the 2,

particulate matters (PM), and the x emitted to the atmosphere. Simulations based on an

actual system in the remote Alaskan community of Lime Village were performed for

three cases:

1) Diesel only;

2) diesel-battery; and

3) PV with diesel-battery using a one-year time period.

The simulation results were utilized to calculate the energy payback, the simple

payback time for the PV module, and the avoided costs of 2, x, and PM. Post-simulation

analysis includes the comparison of results with those predicted by Hybrid Optimization

Model for Electric Renewables (HOMER). The life-cycle cost (LCC) and air emissions

results of our Simulink model were comparable to those predicted by HOMER.

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the model can be used to optimize the performance of the hybrid power system.

MATLAB Simulink is used to model the system and apportion the electrical production

between the PV array and diesel-electric generator. In general, the Simulink model can be

used to study the performance of any hybrid power system. Using Simulink, other

renewable energy sources, dynamic operation, and control system strategies can be easily

incorporated into the existing hybrid power system model to study the overall

performance of the system. Simulations are performed for three cases: 1) diesel only; 2)

diesel-battery; and 3) PV with diesel-battery using a one-year time period. The results of

the simulations are used to perform an economic analysis and predict the environmental

impacts of integrating a PV array into diesel-electric power systems for remote villages.

The economic part of the model calculates the fuel, consumed, the kilo watt hours

obtained per gallon of fuel supplied, and the total cost of fuel. The environmental part of

the model calculates the CO, particulate matter (PM), and the NO emitted to the

atmosphere. These results are then utilized to calculate the energy payback, the

simplepaybacktime for the PV module, and the avoided costs of CO, NO, and PM.

POWER SYSTEM MONITORING

Monitoring of power system operating status may include measurements of

analog signals, as well as measurements of CB contact status.

Monitoring of local events

The local events associated with operation of a substation include operation of digital

relays in the event of a fault or simple switching of a circuit breaker as a consequence of

operator action performed through SCADA. As a part of the monitoring of local events,

the required measurements may be either local or system-wide.

1. Use of local measurements.

Typical situation where local measurements are used for local monitoring function is the

case where a Digital Fault Recorder (DFR) is wired to monitor substation analog

measurements and contacts from circuit breakers. In this case the sampling of all the

measurements (signals) is synchronous across the entire substation. Detailed analysis of

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protective relay operations can be performed to accurately determine the fault type and

the timing in the switching sequences that include multiple circuit breaker operations.

2. Use of system-wide measurements.

System-wide measurements may be of interest in analyzing local events when the

information about system topology and sparse measurements across the network are used

to make conclusion about local events. The case in point is a new fault location algorithm

that relies on a fitting procedure where the signals obtained from short circuit studies are

compared to the signals recorded in the field. A fault is placed in the system model and

simulations are performed to generate fault signals at the points in the system where field

measurements with DFRs are made. By comparing the field-recorded and simulated

signals, an optimization of the match is performed while moving the fault location in the

model. An optimal match is obtained by minimizing the error between the field and

simulated signals. The fault location in the model that leads to the minimum of the cost

function is then taken as the actual fault location. Obviously, this method requires that

both the network topology and system-wide measurements are determined for the same

time instant.

Monitoring of system-wide events

Another monitoring situation is when the system wide events require the knowledge

of individual control actions performed at local substations. The case in point is ananalysis of a cascading event leading to a blackout. In this case, the impact of local events

causes broader impact at the system level.

1. Use of local measurements.

Local measurements of analog signals and contact status can contribute to the

understanding of system-wide events. An example is when the measurements are helping

in understanding actions from several protective relays. This is particularly important in

the case when N-2 contingency happens in the system. This type of contingency, while

still considered a local event, may significantly affect the operation of the entire power

system.

2. Use of system-wide measurements.

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This case is very common in any of the energy management system (EMS)

functions. Most of the EMS functions are system-wide and hence the measurements

required to execute the function are system-wide. Examples of such situations are the

state estimation and system stability monitoring functions.

As a summary of the discussion related to the monitoring background, Table I gives set

of examples where local and system-wide events may be monitored using either local or

system-wide measurements. While the mentioned examples are well known applications

in the power system, the specific use of the measurements given in Table 1 is a special

case of the application implementation that is not commonly used today but has distinct

benefits as described in the mentioned references.

Table. Monitoring and Measurements

Monitoring in real-time

This type of monitoring requires that both the analog measurements of current and

voltages, as well as measurements of CB status are taken. Depending on the events of

interest, different type of measurements may be required as summarized in Table 2 and

discussed in detail in the following text.

1. Measurements of currents and voltages

Currents and voltages may be measured to determine time-domain representation

or to reconstruct a phasor. Various applications require different forms of current and

voltages. In order to perform the measurements, samples of current and voltages need to

be taken. Two distinctly different approaches in sampling synchronization may be

implemented: a) synchronized sampling and b) unsynchronized sampling commonly

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called signal scanning. Further discussion is focused on synchronized sampling, which is

less common but yet more desirable from the applications stand-point.

1.1. Sampling synchronization.

When trying to implement synchronized sampling, two basic implementation

requirements are considered: a) location of the signals to be sampled and b) source of the

synchronization clock. Regarding the signal location, several options are possible: single

three phase circuit, circuits in the same substation, circuits in the adjacent substations, or

any circuits system wide. In this case the three phase circuit consists of three currents and

three voltage signals. As a source of synchronization, two types of sampling

synchronization clocks may be used, namely the local (relative) and system-wide

(absolute). The local clock may be derived from the data acquisition system and may be

used to strobe the sample and hold (S/H) circuits located on each signal that is being

sampled. If the sampling synchronization is to be performed on a wider basis than just the

single three-phase circuit, than a more effective way of synchronizing the sampling is to

use a reference clock that may be received from the Global Positioning System (GPS) of

satellites. The GPS synchronization signal may be transferred to the data acquisition

system located anywhere in the power system through a GPS receiver, which is a low

cost device that may serve several data acquisition systems in a given substation. This is

done through a special arrangement for the GPS clock distribution offered by some

vendors.

1.2. Phasor synchronization.

Many monitoring applications in power systems are based on tracking the phasor

measurements of currents and voltages. Phasor-based models of power systems are

commonly used to perform load-flow, short-circuit, and stability studies. In order to track

the phasors, quite often it is important to compare the phasors at different points in the

system. This leads to a need to measure phasors synchronously across the power system,

which is accomplished with commonly known Wide Area Measurement Systems

(WAMS) implemented using Phasor Measurement Units (PMUs) .

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2. Equipment switching status

While the measurements of analog signals are used by many power system

applications, it is inherently assumed that measurements of the equipment switching

status is also available since the analysis based on analog signals without knowing the

system topology is not feasible in many instances.

2.1. Status of single circuit breaker.

Many events in power systems, such as a fault, start on a single power system

element i.e. a transmission line, transformer, generator, etc. As a result, protective relays,

that are designed to disconnect the faulted power system components, will operate the

corresponding CB to disconnect the faulted element. In such cases, knowing the status of

the switching element during the switching sequence is a crucial part of the monitoring

task.

2.2. Topology status.

In many other applications, the switching status of the entire power system needs

to be know, which places a requirement for monitoring the network topology with very

accurate time synchronization.

Table. Monitoring location and time Synchronization

Monitoring of Circuit Breaker Status

System wide real-time monitoring of circuit breaker operation and statuses

currently is implemented using RTUs of SCADA system. Based on detected voltage

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levels on circuit breaker contacts, these units are providing information on final status of

the circuit breakers such as OPEN or CLOSE. The transitions in time of control

signals, such as Trip or Close Initiate, X and Y coil currents, Control and Yard DC

voltages, Closing Coil and others, used by protection and maintenance engineers for

evaluation of CB performance cannot be monitored using RTU and SCADA approach.

Table 3 lists the CB control circuit signals that an alternative approach, proposed in this

paper, aims to monitor.

1. Architecture

The proposed solution is based on a new CB Monitor (CBM) which would be

permanently connected to the substation CBs. CBM captures detailed information about

each CB operation in real time, regardless of whether the operation is initiated manually

by the operator or automatically by the protection and control equipment and stores them

in COMTRADE file format. As shown in Fig.1, the relevant CB control circuit signals

are recorded and transmitted by wireless link to the concentrator PC, which automatically

performs the analysis.

Table 3. Signals of circuit breaker control circuit monitored by CBMA

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Figure CB monitoring system architecture

1.1. Multiple uses of CB Status.

The CB status information can be used at the local substation level as well as thesystem level. At the substation level, the monitored signals can provide information about

the state of circuit breaker and whether it needs maintenance. At the system level, the

status information can be used to verify network topology and make topology data more

robust. As a result, different groups of utility staff may be involved in accessing the

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information and analyzing it, as suggested in Figure 1. In order to make the information

accessible to a wide range of users, an automated system for analysis of data coming

from the CB called Circuit Breaker Monitoring Analysis System. (CBMAS) has been

developed. Such system uses Data Acquisition Unit (DAU) to collect data from various

CBs. After the data is collected it is automatically processed to extract the information of

interest, which is then distributed to various users.

1.2. Client Server Solution.

The CBMA system supports client/server architecture. The client part resides in

substation. It consists of the DAUs attached to the CBs and software running on

concentrator PC, both permanently installed in the substation, as shown in Figure.

Figure Client server solution

When breaker operates, recorded files are wirelessly transmitted to the

concentrator PC. The client application automatically performs the analysis of recorded

signals. For more efficient data manipulation, IEEE file naming convention is used for

naming the recordings files. The signal processing module of the analysis software

extracts various parameters from recorded signal samples and expert system evaluates

them against empirically obtained values and tolerances selected for specific type of

circuit breaker.

The resulting report describes detected abnormalities and possible causes of the

problem. If discovered problem presents serious threat to the reliability of future circuit

breaker operation, programmable notification is sent to the server located in the central

office. The notification is then processed and a warning is sent via email or pager to the

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maintenance and protection personal. Reporting is provided for both local and

geographically dislocated users through implementation of local database and web server

supporting information exchange through dynamic HTML pages. Recorded files and

reports can be downloaded to the server via Ethernet network relying on standard, fast

and reliable TCP/IP protocol. In the central office or control center, the server part of

CBMAS consisting of the analysis module, a central database and master web server is

running. The central database allows for easy archiving and retrieving of the records and

analysis reports from all system substations. Master web application allows remote users

to search for the records and/or analysis reports from anywhere on the corporate network

(Intranet).

2. Hardware, software and communications

The system hardware in substation consists of DAUs located on each breaker in

the switch yard and a concentrator PC, used for gathering data, placed in the control

room.

2.1. DAU for CB monitoring. The data acquisition unit (DAU) has three main tasks:

Perform data acquisition of signals from the CB control circuit and record sequences of

tripping and closing

Convert captured signals into files according to COMTRADE file specifications

Transmit files wirelessly to the concentrator device.

Figure Circuit Breaker Control Circuit

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The DAU captures 15 electrical signals, listed earlier, from the circuit breaker

control circuit shown in Figure 3. The signals are generated during either tripping or

closing of the breaker. Of these 15 signals, 11 are analog and four are status signals. The

system is shown in Figure 4. It consists of:

Signal conditioning. The signal conditioning boards provide conditioning, galvanic

isolation and convert the signals to appropriate voltage levels for data acquisition. The

voltage levels of signals at circuit breaker are either 130VDC or 1 VDC. The signal

conditioning module scales the input signals to be in the [-5V, +5V] range as required at

the input of the A/D converter module.

Analog to digital converter.

The A/D converter takes the input from signal conditioning board and converts it

to digital form. All signals are sampled synchronously to get accurate signal

reproduction.

Microprocessor. A microprocessor is used for controlling the data acquisition and

running the communication protocols.

Wireless Transmitter.

A wireless transmission system, which employs commonly available Frequency

Hopping Spread Spectrum technology, is capable of transmitting data to distances over

300m is used for transmitting the recorded data to the concentrator PC.

Figure Functional block diagram of DAU

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2.2. Master-Slave data transfer.

The master unit communicates with the slave units using a wireless link. When an

event occurs, the slave unit records the electrical signals and upon completion of

recording sends a request to master unit for accepting data. If the master unit is ready to

accept data it sends a begin transfer message to slave. The slave then transmits the

header, configuration and data files in COMTRADE format to the master. A protocol for

data transfer is established and the receiving software is set up appropriately. The master

unit receives the COMTRADE files and stores them in a database. Figure 5 shows the

master-slave system diagram.

Figure Master-slave communication

5. Application benefits

The ability to closely monitor CB status has multiple benefits. They relate to

different application functions that involve information about combined analog signal and

contact status measurements where the status is either taken from a single CB or from the

entire population of CBs in the network topology. To illustrate the benefits, two

important applications, namely fault analysis and state estimation, are described next. In

each case, due to a close monitoring of CBs, together with accurate measurements of

analog signals, new implementation algorithms for the mentioned functions are feasible.

1. Fault Analysis

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Fault analysis includes an accurate determination of fault clearing sequence, as

well as calculation of the fault location. The applications are improved with better CB

monitoring and better measurements of analog signals.

1.1. Sequence of events.

One aspect of fault analysis is to determine, as precisely as possible, a detailed

sequence of events involved in a fault clearing sequence. This involves fault detection,

fault classification, relay communication channel actions, relay trip decision, circuit

breaker operation, interruption of fault currents, auto-reclosing sequence, etc. An

automated analysis of field recordings of currents and voltages, as well as contact statuses

from circuit breakers and communication channels is possible if synchronous sampling of

all the mentioned signals is performed across the substation. This is typically available if

all the signals are wired to a single instrument such as DFR. If recordings from Digital

Protective Relays (DPRs) are used to implement the automated analysis, then there may

be some difficulty in performing an automated analysis if some of the signals needed in

the analysis come from multiple relays. The problem is the signal sampling

synchronization, which would only be provided for the signals related to one relay but

will not in general be available for the signals that involve multiple relays since the

sampling synchronization across the relays is not readily available today.

The analysis capabilities coming from CB monitoring improvements are multiple.

The existing analysis depends on the reliability of CB a and b contacts, while the

new CB monitoring expands the number of signals to verify the opening and closing

sequence for CB. In addition, the new monitoring scheme monitors CB currents allowing

for confirmation of the final status of the CB by verifying the existence of the CB

currents. Finally, if the signal sampling for CB monitoring is synchronized with the

sampling of other signals available for other IEDs, a powerful correlation between signals

coming from different IEDs observing the same event, such as DFRs, DPRs and CBMs,

can be performed to enhance the analysis of the switching sequence.

1.2. Fault location.

It is well known that fault location can be quite accurate if phasors of voltages and

currents area available from both ends of the transmission line, and if both phasor sets are

synchronized. What is not as widely known is that fault location can be significantly

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possible to determine the switching state of the entire network very accurately, which in

turn would provide a state estimator with a topology processor that is indeed reliable.

This feature is not presently available for any state estimator implementation, but can be

easily added by performing the topology analysis at the substation level and uploading

the information to the SCADA database.

2.2. Two-stage estimator.

This approach requires a re-formulation of the state estimator for the case when

the estimator indicates an error at a suspect substation. Since it is not easy to determine if

the error is caused by a wrong topology or measurement, this approach allows expansion

of the system model to include a precise topology of the substation. By doing this a

possible cause of error associated with the topology is eliminated and further analysis

may be focused on the measurement errors. Determining the substation topology and

maintaining dynamic changes is a task that can significantly be improved through the

new CB monitoring system. If signal sampling on all the CBM DAUs is synchronized

through GPS receiver, than the topology analysis is much easier to perform.

Future needs

Based on the discussion of the real time approach for CB monitoring, changes in

the present practice will be desirable. The changes bring significant benefits, theimplementation requirements for the changes are rather simple and the involved cost is

reasonable. Further discussion is focused on some of the immediate needs for the

improvements that may be met by development of the new approach.

1. Change in measurement architecture

The architecture for making measurements of analog current and voltage signals,

as well as digital contact statuses is quite inadequate today if one wants to make the

improvements discussed in this paper. If one relies on SCADA to perform the

measurements, the analog signals are scanned and reported by exception if the values of

RMS exceed a threshold. The contact signals are also scanned and reported by exception

where the entire conclusion about the CB status depends on how reliable the a and b

contacts and related communications are. Further discussion indicates how the

measurements may be improved through introduction of the CBMAS and an expansion

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of the measurement points through the use of other substation IEDs. The focus of the

improvements are the introduction of synchronized sampling through the use of GPS

receivers and the ability to correlate measurements from the Circuit Breaker Monitoring

Analysis System (CBMAS) and a Wide Area Measurement System (WAMS) that uses

Phasor Measurement Units (PMUs).

1.1. Synchronized sampling.

While many different techniques were used in the past to synchronize signal

sampling across different IEDs, the prevailing method in use today is to perform the

synchronization using a reference time signal from the Global Positioning System (GPS)

of satellites [19]. The systems that are designed to perform precise measurement of

voltage phasors are the WAMS systems that rely on the use of PMUs. The problem that

we are addressing in this paper, namely the topology determination in real time, does not

seem to be related to the WAMS system when in fact a close correlation between the

measurements from the two systems can indeed be beneficial. To make sure the

correlation is meaningful, both systems need to be synchronized through a common or

separate GPS receiver. The CBM system may be synchronized to GPS time reference

signal by introducing a GPS synchronization input at the DAU level. Once the CBM

system is GPS synchronized, further benefits of correlating changes in the voltage

phasors detecting by the WAMS to the to the changes in the status signal and

corresponding current signals detected by the CBM system can be explored.

1.2. Correlation between analog and status measurements.

One obvious benefit of the correlation between the analog and CB status signals is

an ability to precisely define the sequence of events related to fault clearing. This is not

only improving the analysis of operation of a single breaker, but enables analysis of

operation of multiple breakers, including the case when two breakers need to be operated

to clear a fault on a transmission line terminating in a substation with a breaker and a half

bus arrangement.

Another situation where the correlation helps is when a dynamic change in the

substation topology needs to be verified using analog measurements. This can be

significantly facilitated if both the CB contact changes and phasor changes are measured

with a common time reference, which assures that a given measurement scan is aligned

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in time avoiding possible confusions about the sequence of events. Some techniques for

fault location mentioned earlier can also benefit from the alignment between the phasor

and status measurements across the entire power system network. The measurements are

used to match simulations in the system, which can be accomplished if all the

measurements are taken using the same time reference.

2 Change in data processing

To achieve the correlation between the analog and status measurements across

different measurement infrastructures, a new approach to data integration and

information exchange is needed. Further discussion concentrates on the data integration

at the substation level where the data from different IEDs is collected in a common

database and process to extract the relevant information, which can be then shared among

a variety of applications.

2.1. Data integration

To perform data integration, one has to design a corresponding substation

database which will be interfaced to different substation IEDs. The data base may reside

on a separate substation PC or may be integrated in an expanded RTU. Creation of the

database enables merger of the data coming from different infrastructures such as WAMS

and CBM system. Through such integration, correlation between accurate measurements

of phasors and CB contact statuses may be achieved. To illustrate this concept, Figure 6

and Figure 7 are showing an existing and future monitoring infrastructure respectively.

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A- Analogue inputs S- Status (contact) inputs

SC-substation computer MS-master station

CFL-centralized fault loc. EM-energy management

PE-protection engineer IS- integrated systems

DFR-Digital fault recorder FL-Fault locator

IED-Intelligent Electronic Device

RTU-Remote terminal unit

SER-Sequence of events recorder

DPR-Digital protective relay

Figure Legacy infrastructure

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DDR- Digital Disturbance Recorder

Figure Future infrastructure

2.2 Information exchange

Once the mentioned data integration infrastructure is available, it becomes

straight forward to process the data to extract information of interest. As the information

about local substation events is extracted, the next step is to share the information with

the appropriate users, including EMS. This may be represented with the functional

diagram shown in Figure 8. The information exchange concept allows the information

about substation topology to be exchanged among different applications that may reside

at other substations or at the centralized level. The utility groups that may be interest in

the topology status are, besides operations, protection, substation control, maintenance

and planning.

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PLC-Programmable logic controller

PQM-Power Quality Monitor

CBM-Circuit Breaker Monitor

Figure Information Exchange Concept

Diesel engine systems

Diesel engines comprise the vast majority of prime movers for standby power

generators because of their reliability, durability and performance under load. Diesel

powered generators are depended on for back-up power systems in the most critical

locations: hospitals, airports, government buildings, telecommunications facilities, and

even nuclear power plants. In standby power applications, diesel generators can start and

assume full-rated load in less than 10 seconds, and they typically can go 30,000 hours or

more between major overhauls.

This remarkable set of credentials is unique to diesel engines, but like any

mechanical device, maintenance is critical for ensuring that a diesel powered standby

generator will start and run when needed. Facilities with qualified in-house technical

personnel can often perform required preventive maintenance on diesel generators. Other

facility managers prefer to contract with a local service provider or power system

distributor for regular maintenance serviceespecially if they have generators in

multiple locations. (For unplanned maintenance, engine repairs or overhauls, it is always

best to use qualified diesel service technicians.)

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A well-planned maintenance program is essential to the operation of any power

generation system.

Preventive maintenance

Because of the durability of diesel engines, most maintenance is preventive in

nature. Preventive diesel engine maintenance consists of the following operations:

General inspection

Lubrication service

Cooling system service

Fuel system service

Servicing and testing starting batteries

Regular engine exercise

It is generally a good idea to establish and adhere to a schedule of maintenance and

service based on the specific power application and the severity of the environment. For

example, if the generator set will be used frequently or subjected to extreme operating

conditions, the recommended service intervals should be reduced accordingly. Some of

the factors that can affect the maintenance schedule include:

Using the diesel generator set for continuous duty (prime power)

Extreme ambient temperatures

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Exposure to weather

Exposure to salt water

Exposure to dust, sand or other airborne contaminates

If the generator set will be subjected to some or all of these extreme operating

conditions, it is best to consult with the engine manufacturer to develop an appropriate

maintenance schedule. The best way to keep track of maintenance intervals is to use the

running time meter on the generator set to keep an accurate log of all service performed.

This log will also be important for warranty support. FIGURE shows a typical diesel

engine maintenance schedule for generator sets.

General inspection

When the generator set is running, operators need to be alert for mechanical

problems that could create unsafe or hazardous conditions. Following are several areas

that should be inspected frequently to maintain safe and reliable operation.

Exhaust system: With the generator set operating, inspect the entire exhaust system

including the exhaust manifold, muffler and exhaust pipe. Check for leaks at all

connections, welds, gaskets and joints, and make sure that the exhaust pipes are not

heating surrounding areas excessively. Repair any leaks immediately.

Fuel system: With the generator set operating, inspect the fuel supply lines, return

lines, filters and fittings for cracks or abrasions. Make sure the lines are not rubbing

against anything that could cause an eventual breakage. Repair any leaks or alter line

routing to eliminate wear immediately.

DC electrical system: Check the terminals on the starting batteries for clean and tight

connections. Loose or corroded connections create resistance which can hinder starting.

Engine: Monitor fluid levels, oil pressure and coolant temperatures frequently. Most

engine problems give an early warning. Look and listen for changes in engine

performance, sound, or appearance that will indicate that service or repair is needed. Be

alert for misfires, vibration, excessive exhaust smoke, and loss of power or increases in

oil or fuel consumption.

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FIGURE Typical diesel maintenance schedule.

Lubrication service

Check the engine oil level when the engine is shut down at the interval specified

in FIGURE 1. For accurate readings on the engines dipstick, shut off the engine and wait

approximately 10 minutes to allow the oil in the upper portions of the engine to drain

back into the crankcase. Follow the engine manufacturers recommendations for API oil

classification and oil viscosity.

Keep the oil level as near as possible to the full mark on the dipstick by adding

the same quality and brand of oil.

Change the oil and filter at the intervals recommended in FIGURE 1. Check with

the engine manufacturer for procedures for draining the oil and replacing the oil filter.

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Used oil and filters must be disposed of properly to avoid environmental damage or

liability cooling system service

Check the coolant level during shutdown periods at the interval specified in

FIGURE 1. Remove the radiator cap after allowing the engine to cool and, if necessary,

add coolant until the level is about 3/4-inch below the radiator cap lower sealing surface.

Heavy duty diesel engines require a balanced coolant mixture of water, antifreeze and

coolant additives. Use a coolant solution as recommended by the engine manufacturer.

Inspect the exterior of the radiator for obstructions and remove all dirt or foreign material

with a soft brush or cloth. Use care to avoid damaging the fins. If available, use low

pressure compressed air or a stream of water in the opposite direction of normal air flow

to clean the radiator. Check the operation of the coolant heater by verifying that hot

coolant is being discharged from the outlet hose.

Fuel system service

Diesel fuel is subject to contamination and deterioration over time, and one reason

for regular generator set exercise is to use up stored fuel over the course of a year before

it degrades. In additional to other fuel system service recommended by the engine

manufacturer, the fuel filters should be drained at the interval indicated in FIGURE

Water vapor accumulates and condenses in the fuel tank and must also be periodically

drained from the tank along with any sediment present. The charge-air piping and hoses

should be inspected daily for leaks, holes, cracks or loose connections. Tighten the hose

clamps as necessary. Also, inspect the charge-air cooler for dirt and debris that may be

blocking the fins. Check for cracks, holes or other damage.

The engine air intake components should be checked at the interval indicated in FIGURE.

The frequency of cleaning or replacing air cleaner filter elements is primarily determined

by the conditions in which the generator set operates. Air cleaners typically contain a

paper cartridge filter element which can be cleaned and reused if not damaged.

Starting batteries

Weak or undercharged starting batteries are the most common cause of standby

power system failures. Even when kept fully charged and maintained, lead-acid starting

batteries are subject to deterioration over time and must be periodically replaced when

they no longer hold a proper charge. Only a regular schedule of inspection and testing

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under load can prevent generator starting problems. See FIGURE for the recommended

inspection interval for the batteries and charging system.

Testing batteries: Merely checking the output voltage of the batteries is not indicative

of their ability to deliver adequate starting power. As batteries age, their internal

resistance to current flow goes up, and the only accurate measure of terminal voltage

must be done under load. This test is performed automatically every time the generator is

started on Cummins Power Generation generator sets equipped with Power command. On

other generators, use a manual battery load tester to verify the condition of each starting

battery.

Cleaning batteries: Keep the batteries clean by wiping them with a damp cloth

whenever dirt appears excessive. If corrosion is present around the terminals, remove the

battery cables and wash the terminals with a solution of baking soda and water (1/4-

pound baking soda to one quart of water). Be careful to prevent the solution from

entering the battery cells, and flush the batteries with clean water when done. After

replacing the connections, coat the terminals with a light application of petroleum jelly.

Checking specific gravity: Use a battery hydrometer to check the specific gravity of

the electrolyte in each battery cell. A fully charged battery will have a specific gravity of

1.260. Charge the battery if the specific gravity reading is below

Checking electrolyte level: Check the level of the electrolyte in the batteries at least

every 200 hours of operation. If low, fill the battery cells to the bottom of the filler neck

with distilled water.

Generator set exercise

Generator sets on continuous standby must be able to go from a cold start to being

fully operational in a matter of seconds. This can impose a severe burden on engine parts.

However, regular exercising keeps engine parts lubricated, prevents oxidation of

electrical contacts, uses up fuel before it deteriorates, and, in general, helps provide

reliable engine starting. Exercise the generator set at least once a month for a minimum of

30 minutes loaded to no less than one-third of the nameplate rating. Periods of no-load

operation should be held to a minimum, because unburned fuel tends to accumulate in the

exhaust system. If connecting to the normal load is not convenient for test purposes, the

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best engine performance and longevity will be obtained by connecting it to a load bank of

at least one-third the nameplate rating.

> White paper_ By Timothy A.

HYBRID POWER SYSTEMS

Introduction

Electrical energy requirements for many remote applications are too large to

allow the cost-effective use of stand-alone or autonomous PV systems. In these cases, it

may prove more feasible to combine several different types of power sources to form

what is known as a "hybrid" system. To date, PV has been effectively combined with

other types of power generators such as wind, hydro, thermoelectric, petroleum-fueled

and even hydrogen. The selection process for hybrid power source types at a given site

can include a combination of many factors including site topography, seasonal

availability of energy sources, cost of source implementation, cost of energy storage and

delivery, total site energy requirements, etc.

Hybrid power systems use local renewable resource to provide power.

Village hybrid power systems can range in size from small household systems (100

Wh/day) to ones supplying a whole area (10s MWh/day).

They combine many technologies to provide reliable power that is tailored to the local

resources and community.

Potential components include: PV, wind, micro-hydro, river-run hydro, biomass,

batteries and conventional generators.

A. Configuration of hybrid system

Figure shows the basic configuration of hybrid system discussed in this study.

The hybrid system was consisted of reduction gear, main-motor (EM1), sub- motor

(EM2), engine, power controller and battery. It was supposed that a double-motor system

was prepared for the driving system discussed in this study. At first, acceleration was

assisted by was applied only by main motor when the driving speed was low, while the

corporation by two motors was often achieved to drive the system.

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If the SOC (state of charge) of battery was decreased below the specific threshold,

the battery was charged by sub-motor. This operation was priority to over other actions.

Figure 2 shows the modified configuration of hybrid system proposed in this study. In the

modified system, CVT was utilized to keep constant revolution numbers of the sub-motor

when the sub-motor contributed to assist the system.

Schematic view of double motor hybrid system with CVT

Petroleum-fueled engine generators (Gensets)

Petroleum-fueled gensets (operating continuously in many cases) are presently the

most common method of supplying power at sites remote from the utility grid such as

villages, lodges, resorts, cottages and a variety of industrial sites including

telecommunications, mining and logging camps, and military and other government

operated locations. Although gensets are relatively inexpensive in initial cost, they are not

inexpensive to operate. Costs for fuel and maintenance can increase exponentially when

these needs must be met in a remote location. Environmental factors such as noise,

carbon oxide emissions, transport and storage of fuel must also be considered.

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Figure Hybrid PV/Generator System Example; Courtesy Photron Canada Inc., Location:

Sheep Mountain Interpretive Centre, Parks Canada Kluone National Park, Yukon

Territories, Canada, 63 North Latitude; Components shown include: generator (120/240

V), battery (deep cycle industrial rated @ 10 kWh capacity), DC to AC stand-alone

inverter (2500 W @ 120 V output), miscellaneous safety + control equipment including

PV array disconnect, PV control/regulator, automatic generator start/-stop control,

DC/AC system metering etc.; -Components not shown: PV array (800 W peak).

Fuel to power conversion efficiencies may be as high as 25% (for a diesel fueled

unit operating at rated capacity). Under part load conditions, however, efficiencies may

decline to a few percent. Considerable waste heat is therefore available and may be

utilized for other requirements such as space and/or water heating.

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Figure: Genset fuel efficiency vs. capacity utilized.

Why a PV/genset hybrid?

PV and genset systems do not have much in common. It is precisely for this

reason that they can be mated to form a hybrid system that goes far in overcoming the

drawbacks to each technology. Table 10.1 lists the respective advantages and

disadvantages. As the sun is a variable energy source, PV system designs are increased in

size (and therefore cost) to allow for a degree of system autonomy. Autonomy is requiredto allow for provision of reliable power during "worst case" situations, which are usually

periods of adverse weather, seasonally low solar isolation values or an unpredicted

increased demand for power. The addition of autonomy to the system is accomplished by

increasing the size of the PV array and its requisite energy storage system (the battery).

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When a genset is added, additional battery charging and direct AC load supply

capabilities are provided. The need to build in system autonomy is therefore greatly

reduced. When energy demands cannot be met by the PV portion of the system for any

reason, the genset is brought on line to provide the required backup power. Substantial

cost savings can be achieved and overall system reliability is enhanced.

PV/genset hybrid systems have been utilized at sites with daily energy

requirements ranging from as low as 1 kWh per day to as high as 1 MWh per day, which

illustrates their extreme flexibility. They are a proven and reliable method for efficient

and cost-effective power supply at remote sites.

PV/genset hybrid system description

The PV/genset hybrid utilizes two diverse energy sources to power a site's loads.

The PV array is employed to generate DC energy that is consumed by any existing DC

loads, with the balance (if any) being used to charge the system's DC energy storage

battery. The PV array is automatically on line and feeding power into the system

whenever solar insulation is available and continues to produce system power during

daylight hours until its rate of production exceeds what all existing DC loads and the

storage battery can absorb. Should this occur, the array is inhibited by the system

controller from feeding any further energy into the loads or battery? A genset is

employed to generate AC energy that is consumed by any existing AC loads, with the

balance (if any) being used by the battery charger to generate DC energy that is used in

the identical fashion to that described for the PV array above.

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Figure Block diagram of a hybrid PV-Genset system.

At times when the genset is not running, all site AC power is derived from the

system's power conditioner or inverter, which automatically converts system DCenergy

into AC energy whenever AC loads are being operated. The genset is operated cyclically

in direct response to the need for maintaining a suitable state of charge level in the

system's battery storage bank.

Figure Hybrid PV/Generator System Example. Courtesy Photron Inc., Location:

Caples Lake, California, USA; 65 kVA 3 0 @ 480 V generator which includes co-

generation equipment (i.e. heat exchangers to utilize the thermal energy created by unit

operation).

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Other PV/hybrid types

Certain specific site locations may offer access to other forms of power

generation. Access to flowing water presents the potential for hydro power. Access to

consistent wind at sufficient velocity presents the potential for wind power. PV/hydro and

PV/wind hybrid systems have been utilized at sites with daily energy requirement ranges

similar to those described for PV/genset hybrids. Their use, however, is much more site

dependent, as their energy source is a factor of that locations' topography.

PV/Thermoelectric generator hybrid systems have been used effectively at sites

whose daily energy requirement is relatively low, ranging from 1 to 20 kWh per day.

Propane is the fuel source for the thermoelectric process, and conversion efficiencies of

up to 8% can be achieved. Considerable waste heat is therefore available which may be

utilized for other requirements. In cold climates, this heat is often used to maintain the

battery storage system at desired temperature levels. Table 10.1 Relative Advantages of

Energy Sources: Genset vs. PV

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Architectural Integration

Motivation

The last two decades have brought significant changes to the design profession. In

the wake of traumatic escalations in energy prices, shortages, embargoes and war alongwith heightened concerns over pollution, environmental degradation and resource

depletion, awareness of the environmental impact of our work as design professionals has

dramatically increased. In the process, the shortcomings of yesterday's buildings have

also become increasingly clear: inefficient electrical and climate conditioning systems

squander great amounts of energy. Combustion of fossil fuels on-site and at power plants

adds greenhouse gases, acid rain and other pollutants to the environment. Inside, many

building materials, furnishings and finishes give off toxic by-products contributing to

indoor air pollution. Poorly designed lighting and ventilation systems can induce

headaches and fatigue.

Architects with vision have come to understand it is no longer the goal of good

design to simply create a building that is aesthetically pleasing - buildings of the future

must be environmentally responsive as well. They have responded by specifying

increased levels of thermal insulation, healthier interiors, higher-efficiency lighting,

better glazing and HVAC (heating, ventilation and air conditioning) equipment, air-to-air

heat exchangers and heat-recovery ventilation systems. Significant advances have been

made and this progress is a very important first step in the right direction. However, it is

not enough. For the developed countries to continue to enjoy the comforts of the late

twentieth century and for the developing world to ever hope to attain them, sustainability

must become the cornerstone of our design philosophy. Rather than merely using less

non-renewable fuels and creating less pollution, we must come to design sustainable

buildings that rely on renewable resources to produce some or all of their own energy and

create no pollution. One of the most promising renewable energy technologies is

photovoltaics. Photovoltaics (PV) are a truly elegant means of producing electricity on

site, directly from the sun, without concern for energy supply or environmental harm.

These solid-state devices simply make electricity out of sunlight, silently with no

maintenance, no pollution and no depletion of materials. Photovoltaics are also

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exceedingly versatile - the same technology that can pump water, grind grain and provide

communications and village electrification in the developing world can produce

electricity for the buildings and distribution grids of the industrialized countries.

Figure HEW, Hamburg, Germany: 16.8 kWp facade-integrated PV system. The

polycrystalline PV modules are installed as fixed shading devices.

There is a growing consensus that distributed photovoltaic systems which provide

electricity at the point of use will be the first to reach widespread commercialization.

Chief among these distributed applications are PV power systems for individual

buildings. Interest in the building integration of photovoltaics, where the PV elements

actually become an integral part of the building, often serving as the exterior weathering

skin, is growing world-wide. PV specialists from some 15 countries are working within

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the International Energy Agency's Task 16 on a 5-year effort to optimize these systems

and architects are now beginning to explore innovative ways of incorporating solar

electricity into their building designs.

Figure SOS Kinderdorf, Zwickau, Germany: 2.9 kWp roof-integrated PV system.

Frameless architectural laminated glass with amorphous silicon cells.

Planning context of an energy conscious design project

The possibilities of an active and passive solar energy use in buildings are greatly

influenced by the form, design, and construction and manufacturing process of the

building envelope. A promising possibility of active solar energy use is the production of

electricity with photovoltaics. This technology can be adapted to existing buildings as

well as to new buildings. It can be integrated into the roof, into the facade or into

different building components, such as a Photovoltaic roof tile. Such integration makes

sense for various reasons:

The solar irradiation is a distributed energy source; the energy demand is distributed as

well.The building envelopes supply sufficient area for PV generators and therefore

additional land use is avoided as well as costs for mounting structures and energy

transport.

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Active and Passive Solar Design Principles ( Ingo Hagemann

In order to use PV together with other available techniques of active and passive

solar energy, it must be considered that some techniques fit well together and others

exclude each other. For example: As a kind of a "passive cooling system", creepers are

used for covering the south facade of building. The leaves evaporate water and provide

shade on the facade. This helps to avoid penetration of direct sunlight and reduces the

temperature in the rooms behind the facade. At the same time the leaves create shading

on PV modules that may be mounted on the facade resulting in a far lower electricity

production. To avoid such design faults it is necessary to compare and evaluate the

different techniques that are available for creating an energy conscious building. An

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overall energy concept for a building should be made at the beginning of the design

process. Therefore, the architect and the other experts involved in the design and

planning process need to work together right from the beginning of the design and

planning process. All together they have to search right from the beginning for the best

design for a building project.

Photovoltaics and Architecture

Photovoltaics and Architecture are a challenge for a new generation of buildings.

Installations fulfilling a number of technical approaches do not automatically represent

aesthetical solutions. Collaboration between engineers and architects is essential to create

outstanding overall designs. This again will support the wide use of PV. These systems

will acquire a new image, ceasing to be a toy or a solar module reserved for a mountain

chalet but becoming a modern building unit, integrated into the design of roofs and

facades. The architects, together with the engineers involved are asked to integrate PV at

least on four levels during the planning and realization of a building:

Design of a building (shape, size, orientation, color)

Mechanical integration (multi functionality of a PV element)

Electrical integration (grid connection and/or direct use of the power)

Maintenance and operation control of the PV system must be integrated into the usualbuilding maintenance and control.

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Planning Responsibilities and Lay Down of Energy Consumption.

THE PHOTOVOLTAIC ARRAY

A PV array consists of a number of PV modules, mounted in the same plane and

electrically connected to give the required electrical output for the application. The PV

array can be of any size from a few hundred watts to hundreds of kilowatts, although the

larger systems are often divided into several electrically independent sub arrays each

feeding into their own power conditioning system.

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PHOTOVOLTAIC TECHNOLOGY

Photovoltaics is the field of technology and research related to the devices which

directly convert sunlight into electricity using semiconductors that exhibit thephotovoltaic effect. Photovoltaic effect involves the creation of voltage in a material upon

exposure to electro magnetic radiation.

The photovoltaic effect was first noted by a French physicist, Edmund Bequerel,

in 1839, who found that certain materials would produce small amounts of electric

current when exposed to light. In 1905, Albert Einstein described the nature of light and

the photoelectric effect on which photovoltaic technology is based, for which he later

won a Nobel prize in physics. The first photovoltaic module was built by Bell

Laboratories in 1954. It was billed as a solar battery and was mostly just a curiosity as it

was too expensive to gain widespread use. In the 1960s, the space industry began to make

the first serious use of the technology to provide power aboard spacecraft. Through the

space programs, the technology advanced, its reliability was established, and the cost

began to decline. During the energy crisis in the 1970s, photovoltaic technology gained

recognition as a source of power for non-space applications.

The solar cell is the elementary building block of the photovoltaic technology.

Solar cells are made of semiconductor materials, such as silicon. One of the properties of

semiconductors that makes them most useful is that their conductivity may easily be

modified by introducing impurities into their crystal lattice. For instance, in the

fabrication of a photovoltaic solar cell, silicon, which has four valence electrons, is

treated to increase its conductivity. On one side of the cell, the impurities, which are

phosphorus atoms with five valence electrons (n-donor), donate weakly bound valence

electrons to the silicon material, creating excess negative charge carriers. On the other

side, atoms of boron with three valence electrons (p-donor) create a greater affinity than

silicon to attract electrons. Because the p-type silicon is in intimate contact with the n-

type silicon a p-n junction is established and a diffusion of electrons occurs from the

region of high electron concentration (the n-type side) into the region of low electron

concentration (p-type side). When the electrons diffuse across the p-n junction, they

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recombine with holes on the p-type side. However, the diffusion of carriers does not

occur indefinitely, because the imbalance of charge immediately on either sides of the

junction originates an electric field. This electric field forms a diode that promotes

current to flow in only one direction.

Ohmic metal-semiconductor contacts are made to both the n-type and p-type sides

of the solar cell, and the electrodes are ready to be connected to an external load. When

photons of light fall on the cell, they transfer their energy to the charge carriers. The

electric field across the junction separates photo-generated positive charge carriers

(holes) from their negative counterpart (electrons). In this way an electrical current is

extracted once the circuit is closed on an external load.

SOLAR CELL

The photovoltaic effect was first reported by Edmund Bequerel in 1839 when he

observed that the action of light on a silver coated platinum electrode immersed in

electrolyte produced an electric current. Forty years later the _rst solid state photovoltaic

devices were constructed by workers investigating the recently discovered

photoconductivity of selenium. In 1876 William Adams and Richard Day found that a

photocurrent could be produced in a sample of selenium when contacted by two heated

platinum contacts. The photovoltaic action of the selenium di_ered from its

photoconductive action in that a current was produced spontaneously by the action of

light. No external power supply was needed. In this early photovoltaic device, a

rectifying junction had been formed between the semiconductor and the metal contact. In

1894, Charles Fritts prepared what was probably the _rst large area solar cell by pressing

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a layer of selenium between gold and another metal. In the following years photovoltaic

e_ects were observed in copper {copper oxide thin _lm structures, in lead sulphide and

thallium sulphide. These early cells were thin _lm Schottky barrier devices, where a

semitransparent layer of metal deposited on top of the semiconductor provided both the

asymmetric electronic junction, which is necessary for photovoltaic action and access to

the junction for the incident light. The photovoltaic eject of structures like this was

related to the existence of a barrier to current ow at one of the semiconductor {metal

interfaces (i.e., rectifying action) by Goldman and Brodsky in 1914. Later, during the

1930s, the theory of metal {semiconductor barrier layers was developed by Walter

Schottky, Neville Mott and others.

However, it was not the photovoltaic properties of materials like selenium which

excited researchers, but the photoconductivity. The fact that the current produced was

proportional to the intensity of the incident light, and related to the wavelength in a

definite way meant that photoconductive materials were ideal for photographic light

meters. The photovoltaic effect in barrier structures was an added benefit, meaning that

the light meter could operate without a power supply. It was not until the 1950s, with the

development of good quality silicon wafers for applications in the new solid state

electronics, that potentially useful quantities of power were produced by photovoltaic

devices in crystalline silicon.

In the 1950s, the development of silicon electronics followed the discovery of a

way to manufacture p{n junctions in silicon. Naturally n type silicon wafers developed a

p type skin when exposed to the gas boron trichloride. Part of the skin could be etched

away to give access to the n type layer beneath. These p {n junction structures produced

much better rectifying action than Schottky barriers, and better photovoltaic behaviour.

The first silicon solar cell was reported by Chapin, Fuller and Pearson in 1954 and

converted sunlight with an efficiency of 6%, six times higher than the best previous

attempt. That _figure was to rise significantly over the following years and decades but,

at an estimated production cost of some $200 per Watt, these cells were not seriously

considered for power generation for several decades. Nevertheless, the early silicon solar

cell did introduce the possibility of power generation in remote locations where fuel

could not easily be delivered. The obvious application was to satellites where the

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requirement of reliability and low weight made the cost of the cells unimportant and

during the 1950s and 60s, silicon solar cells were widely developed for applications in

space.

Also in 1954, a cadmium sulphide p{n junction was produced with an efficiency

of 6%, and in the following years studies of p{n junction photovoltaic devices in gallium

arsenide, indium phosphide and cadmium telluride were stimulated by theoretical work

indicating that these materials would over a higher effciency. However, silicon remained

and remains the foremost photovoltaic material, benethting from the advances of silicon

technology for the microelectronics industry. Short histories of the solar cell are given

elsewhere [Shive, 1959; Wolf, 1972; Green, 1990].

In the 1970s the crisis in energy supply experienced by the oil-dependent western

world led to a sudden growth of interest in alternative sources of energy, and funding for

research and development in those areas. Photovoltaics were a subject of intense interest

during this period, and a range of strategies for producing photovoltaic devices and

materials more cheaply and for improving device efficiency were explored. Routes to

lower cost included photo electrochemical junctions, and alternative materials such as

polycrystalline silicon, amorphous silicon, other `thin _lm' materials and organic

conductors. Strategies for higher efficiency included tandem and other multiple band gap

designs. Although none of these led to widespread commercial development, our

understanding of the science of photovoltaics is mainly rooted in this period.

During the 1990s, interest in photovoltaics expanded, along with growing

awareness of the need to secure sources of electricity alternative to fossil fuels. The trend

coincides with the widespread deregulation of the electricity markets and growing

recognition of the viability of decentralized power. During this period, the economics of

photovoltaics improved primarily through economies of scale. In the late 1990s the

photovoltaic production expanded at a rate of 15{25% per annum, driving a reduction in

cost. Photovoltaics first became competitive in contexts where conventional electricity

supply is most expensive, for instance, for remote low power applications such as

navigation, telecommunications, and rural electri_cation and for enhancement of supply

in grid-connected loads at peak use. As prices fall, new markets are opened up. An

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ELECTRICAL CONNECTION OF THE CELLS

The electrical output of a single cell is dependent on the design of the device and

the Semi-conductor material(s) chosen, but is usually insufficient for most applications.

In order to provide the appropriate quantity of electrical power, a number of cells must beelectrically connected. There are two basic connection methods: series connection, in

which the top contact of each cell is connected to the back contact of the next cell in the

sequence, and parallel connection, in which all the top contacts are connected together, as

are all the bottom contacts. In both cases, this results in just two electrical connection

points for the group of cells.

Series connection:

Figure shows the series connection of three individual cells as an example and the

resultant group of connected cells is commonly referred to as a series string. The current

output of the string is equivalent to the current of a single cell, but the voltage output is

increased, being an addition of the voltages from all the cells in the string (i.e. in this

case, the voltage output is equal to 3Vcell).

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Fig. Series connection of cells, with resulting currentvoltage characteristic.

It is important to have well matched cells in the series string, particularly with

respect to current. If one cell produces a significantly lower current than the other cells

(under the same illumination conditions), then the string will operate at that lower current

level and the remaining cells will not be operating at their maximum power points. Parallel connection

Figure shows the parallel connection of three individual cells as an example. In this

case, the current from the cell group is equivalent to the addition of the current from each

cell (in this case, 3 Icell), but the voltage remains equivalent to that of a single cell.

As before, it is important to have the cells well matched in order to gain

maximum output, but this time the voltage is the important parameter since all cells must

be at the same operating voltage. If the voltage at the maximum power point is

substantially different for one of the cells, then this will force all the cells to operate off

their maximum power point, with the poorer cell being pushed towards its open-circuit

voltage value and the better cells to voltages below the maximum power point voltage. In

all cases, the power level will be reduced below the optimum.

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Fig. Parallel connection of cells, with resulting currentvoltage characteristic.

MOUNTING STRUCTURE

The main purpose of the mounting structure is to hold the modules in the required

position without undue stress. The structure may also provide a route for the electrical

wiring and may be free standing or part of another structure (e.g. a building). At itssimplest, the mounting structure is a metal framework, securely fixed into the ground. It

must be capable of withstanding appropriate environmental stresses, such as wind

loading, for the location. As well as the mechanical issues, the mounting has an influence

on the operating temperature of the system, depending on how easily heat can be

dissipated by the module.

TILT ANGLE AND ORIENTATION

The orientation of the module with respect to the direction of the Sun determines

the intensity of the sunlight falling on the module surface. Two main parameters are

defined to describe this. The first is the tilt angle, which is the angle between the plane of

the module and the horizontal. The second parameter is the azimuth angle, which is the

angle between the plane of the module and due south (or sometimes due north depending

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on the definition used). Correction of the direct normal irradiance to that on any surface

can be determined using the cosine of the angle between the normal to the Sun and the

module plane.

The optimum array orientation will depend on the latitude of the site, prevailing

weather conditions and the loads to be met. It is generally accepted that, for low latitudes,

the maximum annual output is obtained when the array tilt angle is roughly equal to the

latitude angle and the array faces due south (in the northern hemisphere) or due north (for

the southern hemisphere). For higher latitudes, such as those in northern Europe, the

maximum output is usually obtained for tilt angles of approximately the latitude angle

minus 1015 degrees. The optimum tilt angle is also affected by the proportion of diffuse

radiation in the sunlight, since diffuse light is only weakly directional. Therefore, for

locations with a high proportion of diffuse sunlight, the effect of tilt angle is reduced.

However, although this condition will give the maximum output over the year,

there can be considerable variation in output with season. This is particularly true in high-

latitude locations where the day length varies significantly between summer and winter.

Therefore, if a constant or reasonably constant load is to be met or, particularly, if the

winter load is higher than the summer load, then the best tilt angle may be higher in order

to boost winter output. Prevailing weather conditions can influence the optimisation of

the array orientation if they affect the sunlight levels available at certain times of the day.

Alternatively, the load to be met may also vary during the day and the array can be

designed to match the output with this variable demand by varying the azimuth angle.

Notwithstanding the ability to tailor the output profile by altering the tilt and azimuth

angles, the overall array performance does not vary substantially for small differences in

array orientation. Figure shows the percentage variation in annual insolation levels for

the location of London as tilt angle is varied between 0 and 90 degrees and azimuth angle

is varied between 45o (south east) and +45o (south west). The maximum insolation

level is obtained for a south-facing surface at a tilt angle of about 35 degrees, as would be

expected for latitude of about 51oN. However, the insolation level varies by less than

10% with changing azimuth angle at this tilt angle. A similarly low variation is observed

for south facing surfaces for a variation of +/- 30 degrees from the optimum tilt angle.

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Fig. Percentage variation of annual sunlight levels as a function of tilt angle and azimuth

angle.

The calculations were carried out for the location of London using Meteonorm

Version 3.0. The final aspect to consider when deciding on array orientation is the

incorporation in the support structure. For building-integrated applications, the system

orientation is also dictated by the nature of the roof or faade in which it is to be

incorporated. It may be necessary to trade off the additional output from the optimum

orientation against any additional costs that might be incurred to accomplish this. The

aesthetic issues must also be considered.

SUN-TRACKING/CONCENTRATOR SYSTEMS

The previous section has assumed a fixed array with no change of orientation

during operation. This is the usual configuration for a flat-plate array. However, somearrays are designed to track the path of the Sun. This can account fully for the suns

movements by tracking in two axes or can account partially by tracking only in one axis,

from east to west. For a flat-plate array, single-axis tracking, where the array follows the

east-west movement of the Sun, has been shown to increase the output by up to 30% for a

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location with predominantly clear sky conditions. Two-axis tracking, where the array

follows both the daily east-west and north-south movement of the sun, could provide a

further increase of about 20% (Lepley, 1990). For locations where there are frequent

overcast conditions, such as northern Europe, the benefits of tracking are considerably

less. It is usually more economical to install a larger panel for locations with less than

about 3000 hours of direct sunshine per annum. For each case, the additional output from

the system must be compared to the additional cost of including the tracking system,

which includes both the control system and the mechanism for moving the array. For

concentrator systems, the system must track the Sun to maintain the concentrated light

falling on the cell. The accuracy of tracking, and hence the cost of the tracking system,

increases as the concentration ratio increases.

SHADING

Shading of any part of the array will reduce its output, but this reduction will vary

in magnitude depending on the electrical configuration of the array. Clearly, the output of

any cell or module which is shaded will be reduced according to the reduction of light

intensity falling on it. However, if this shaded cell or module is electrically connected to

other cells and modules which are unshaded, their performance may also be reduced

since this is essentially a mismatch situation.

For example, if a single module of a series string is partially shaded, its current

output will be reduced and this will then dictate the operating point of the whole string. If

several modules are shaded, the string voltage may be reduced to the point where the

open-circuit voltage of that string is below the operating point of the rest of the array, and

then that string will not contribute to the array output. If this is likely to occur, it is often

useful to include a blocking diode for string protection, as discussed earlier.

Thus, the reduction in output from shading of an array can be significantly greater

than the reduction in illuminated area, since it results from

The loss of output from shaded cells and modules;

The loss of output from illuminated modules in any severely shaded strings that cannot

maintain operating voltage; and

The loss of output from the remainder of the array because the strings are not operating

at their individual maximum power points.

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For some systems, such as those in a city environment, it may be impossible to

avoid all shading without severely restricting the size of the array and hence losing output

at other times. In these cases, good system design, including the optimum interconnection

of modules, the use of string or module inverters and, where appropriate, the use of

protection devices such as blocking diodes, can minimize the reduction in system output

for the most prevalent shading conditions.

THE PHOTOVOLTAIC SYSTEM

A PV system consists of a number of interconnected components designed to

accomplish a desired task, which may be to feed electricity into the main distribution

grid, to pump water from a well, to power a small calculator or one of many more

possible uses of solar-generated electricity. The design of the system depends on the task

it must perform and the location and other site conditions under which it must operate.

This section will consider the components of a PV system, variations in design according

to the purpose of the system, system sizing and aspects of system operation and

maintenance.

System design

There are two main system configurations stand-alone and grid-connected. As

its name implies, the stand-alone PV system operates independently of any other power

supply and it usually supplies electricity to a dedicated load or loads. It may include a

storage facility (e.g. battery bank) to allow electricity to be provided during the night or

at times of poor sunlight levels. Stand-alone systems are also often referred to as

autonomous systems since their operation is independent of other power sources. By

contrast, the grid-connected PV system operates in parallel with the conventional

electricity distribution system. It can be used to feed electricity into the grid distribution

system or to power loads which can also be fed from the grid.

It is also possible to add one or more alternative power supplies (e.g. diesel

generator, wind turbine) to the system to meet some of the load requirements. These

systems are then known as hybrid systems. Hybrid systems can be used in both stand-

alone and grid-connected applications but are more common in the former because,

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provided the power supplies have been chosen to be complementary, they allow

reduction of the storage requirement without increased loss of load probability. Figures

below illustrate the schematic diagrams of the three main system types.

Fig. Schematic diagram of a stand-alone photovoltaic system.

Fig. Schematic diagram of grid-connected photovoltaic system.

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Fig. Schematic diagram of hybrid system incorporating a photovoltaic array and a motor

generator (e.g. diesel or wind).

GREENHOUSE GAS EMISSIONS

THE rising concentrations of greenhouse gases (GHGs) of anthropogenic origin

in the atmosphere such as carbon dioxide (CO2), methane (CH4) and nitrous oxide

(N2O) have increased, since the late 19th century. According to the Third Assessment

Report (TAR) of the Intergovernmental Panel on Climate Change1, because of the

increase in concentration of greenhouse gases in the atmosphere (for e.g., CO2 by 29 per

cent, CH4 by 150 per cent and N2O by 15 per cent) in the last 100 years, the mean

surface temperature has risen by 0.40.8C globally. The precipitation has become

spatially variable and the intensity and frequency of extreme events has increased. The

sea level also has risen at an average annual rate of 12 mm during this period. The

continued increase in concentration of GHG in the atmosphere is likely to lead to climate

change resulting in large changes in ecosystems, leading to possible catastrophic

disruptions of livelihoods, economic activity, living conditions, and human health2.

The United Nations Framework Convention on Climate Change3 requires the

parties to protect the climate system in accordance with their common but differentiated

responsibilities and respective capabilities. It enjoins upon developed countries to take

the lead role for combating climate change and the adverse effects thereof, considering

their historically higher contribution to the total anthropogenic load of greenhouse gases

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in the atmosphere. In the year 1990, the developed world (Australia, Canada, USA,

Europe, former USSR and Japan) emitted around 66 per cent of the total global GHG

emissions, which though has reduced to 54 per cent in 2000, mainly offset by the rise in

Chinese emissions (see Figure 1). The South Asian region, including three-fourths

emission share of India, contributed only 3 per cent of the total global GHG emissions in

1990 and the share of emissions from South Asia has grown merely by 4 per cent in

2000. In accordance with the Article 12 of the climate convention, the parties are required

to report on a continuous basis an information on implementation of the convention inter

alia an inventory of greenhouse gases by sources and removals by sinks (see note 1) and

also the steps taken to address climate change. Towards the fulfillment of the obligations

under the convention, India submitted its Initial National Communication to the

UNFCCC on 22 June 2004.

This analyses the improvements made in GHG inventory estimation reported

therein with respect to earlier published estimates and highlights the strengths, the gaps

that still exist and the future challenges for its refinement. Further, the paper examines the

key sources where efforts are needed to develop a more refined inventory with attendant

reduction in uncertainties. The also makes an assessment of the current and projected

trends of GHG emission from India and some selected countries.

Figure Regionwise GHG emissions in (a) 1990 and (b) 2000

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Summary of greenhouse gas emissions in Gg (thousand tonnes) from India in

1994 by sources and sinks

Greenhouse gas inventory estimation

Estimations of anthropogenic GHG emission inventories in India, began in a

limited scale in 1991, which were enlarged and revised and the first definitive report for

the base year 1990 was published4 in 1992. Since then, several papers and reports have

been published which have upgraded the methodologies for estimation, included country-

specific emission factors (see note 2) and activity data (see note 3)5, accounted for new

sources of emissions and new gases or pollutants610. A comprehensive inventory of the

Indian emissions from all energy, industrial processes, agriculture activities, land use,

land use change and forestry and waste management practices has recently been reported

in Indias Initial National Communication to the UNFCCC11 for the base year 1994. All

these emission estimates reported have been made using the IPCC guidelines for

preparing national greenhouse gas inventories, either by Tier I, Tier II or Tier III. The use

of any of these tiers depended upon the level of disaggregated activity data available for a

particular source of GHG emissions and its relative importance as a GHG emission

source with respect to the total emissions from the country. Table 1 summarizes the GHG

inventory estimates reported under the aegis of Indias initial national communication11.

In 1994, 1228 million tonnes of CO2 equivalent (see note 7) emissions took place

from all anthropogenic activities in India, accounting for 3 per cent of the total globalemissions. About 794 million tonnes, i.e. about 63 per cent of the total CO2 equivalent

emissions was emitted as CO2, while 33 per cent of the total emissions (18 million

tonnes) was CH4, and the rest 4 per cent (178 thousand tonnes) was N2O. The CO2

emissions were dominated by emissions due to fuel combustion in the energy and

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transformation activities, road transport, cement and steel production. The CH4 emissions

were dominated by emissions from enteric fermentation in ruminant livestock and rice

cultivation.The major contribution to the total N2O emissions came from the agricultural

soils due to fertilizer applications. At a sectoral l

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