Monitoring with Effect
Performance Evaluation of Stand Alone, PV Systems
Keith Presnell1 and Dave Turcotte2
1. Deputy Director, Northern Territory Centre for Energy Research
Phone: 61-8-8946 6883, Facsimile : 61-8-8946 6993
AUSTRALIA
keith.presnell@ntu.edu.au
2. CANMET-Energy Diversification Research Laboratory
Phone: +1 450-652-5572, Facsimile: +1 450-652-5177
CANADA
dave.turcotte@nrcan.gc.ca
Abstract
Equitable assessment of the performance of "Stand Alone Systems" is complicated by configuration
options, application possibilities, and cultural variables. Task III of the International Energy
Agency’s Photovoltaic Power Systems sub-committee (IEA PVPS) is developing a monitoring manual,
designed to facilitate fair comparison of system performances. The Manual,
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provides a system classification that is based on an amalgam of system configuration and system
application,
recommends individual sets of performance monitoring parameters that reflect the use for which
the data might be intended, and
introduces quality management procedures for monitoring case study performances.
Used correctly, the Manual will serve to improve computed data quality, simplify performance
analyses and raise the level of confidence in the conclusions inferred from the data, especially for
third parties.
It is proposed that the guidelines be tested in the current Five Year Work Plan for Task III, via a series
of case studies representing the system categories identified by the process.
1.
Motivation and Background
Prospective users of sustainable energy based systems usually require advice about which technology
best suits their needs. More often than not, different system architectures, monitoring procedures and
application specifics, so complicate comparisons between the performance of “isolated or stand
alone” systems that they utterly confuse the technology capability issue. Third parties, interested in
“sustainable energy” solutions, face claims and counterclaims about proprietary products, and are
plied with an assortment of performance data, some derived from the maker’s specification, some
measured in the field, but nearly all collected on a piecemeal basis without any form of quality control.
The solution is to introduce sensible quality procedures and establish monitoring guidelines that
provide for equitable comparison of system performance.
The International Energy Agency, Photovoltaic Power Systems (IEA PVPS) latest Task III Work Plan
registers the problem, and allocates substantial effort to minimising the difficulty. It provides that a
monitoring manual be prepared with guidelines setting out how to equitably monitor system
performance for a range of “stand alone” PV systems. The Guidelines effectively prescribe quality
“entrance levels” for registering a case study on the IEA PVPS data-base, and in doing so they raise
the level of confidence in the conclusions inferred from the data, especially for third parties.
Monitoring with Effect: Performance Evaluation of Stand Alone, PV Systems
Presenell & Turcotte
Task III’s motivation is the need to be able to analyse the performance of a series of case studies to
determine what comprises a successful, or conversely an unsuccessful, installation. To do this it
requires a monitoring environment that is conducive to equitable comparison of system performance.
It can then disseminate the information to industry and in doing so accelerate development of product
improvements.
2.
Objective
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Task III’s objective with this initiative is to help establish a data-base from which the performance
characteristics of “stand-alone” PV systems for different applications and operating environments
can be equitably evaluated.
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It is intended that analyses derived from the data will serve to guide potential investors in their
choice of PV system, and help to ensure that available finance is used to best effect.
3. Approach Taken
The approach taken was to categorise the types of stand alone systems that might be used, and in
parallel generate monitoring guidelines designed to introduce industry quality procedures for acquiring
performance data and there from extracting meaningful performance indicators.
3.1 System Categories:
An amalgam of system application and system architecture was used to establish “stand alone” system
categories. The primary objective was to limit the categories to the minimum number possible, given
the need to ensure that performance assessments still provide for realistic comparison of system
capabilities.
A copy of the adopted categories is provided in Figure 1. They range from a simple Photovoltaic (PV)
array delivering dc electricity directly to load, through to hybrid system configurations delivering ac
electricity to load. A straight diesel generator category is also included to provide a datum against
which the performance of various PV systems can be measured.
The participating members of Task III have been asked to nominate case studies for any category
where they believe they can “showcase” a technology. This does not preclude other agencies
nominating a case study, but if they do, they will be required to nominate what level of monitoring
would be undertaken, and to guarantee that quality monitoring procedures would be used in
accordance with the draft Manual.
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Figure 1. Classification for Stand-alone PV Systems
System Configuration
PV generator /dc load
PV/Storage/
PV/storage/
Inverter
Conventional
appliances and tools
PV/ engine ac hybrids
(Restricted supply)
(conventional
demand)
Other Hybrid
configurations
eg dc engine generators
and/or other RE’s
Engine generator sets
(conventional
demand)
Notes:
Typical Application
Water pumping &
treatment. Eutectic
refrigerators
Code
Primary demand
Battery charging
Back up provision
PV1
PV generation
supply of dc electricity
PV2
Stored energy
PV Generation
Stored energy
Additional battery capacity
invert electricity from
storage to ac
PV3
Stored energy
PV generation
Stored energy
Additional battery capacity
Primary ac electricity
from generator
PV4
PV Generation
Excess PV Generation
Stored energy
Additional battery capacity
Stored energy
PV generation
Stored energy
Engine generator set
Stored energy
Engine generator set
ac electricity from
storage
NA
Peaking power
NA
Case Study reference
C/kWh
% user satisfaction
NA
PVH1
Primary ac electricity
from RE generation
PVH2
PV generation
Excess PV Generation
Battery storage &
Primary ac electricity
from diesel gen-set.
PVH3
Gen set
Gen set
Parallel variations as
above
PV1a,
PVH1a
etc
All electricity
generated as ac.
D1
All electricity
generated as ac.
D2
N/A
Engine generator set or
multiple sets
Gen set
NA
Covered by set sizing
Nil, or portable emergency
engine generator, or tractor
mounted welder etc
Gen set
NA
Multiple sets
Multiple sets
Primary demand is the electricity dispatched to the user but not including battery recharging.
Peaking power is the electricity required to meet daily peak demands.
Backup provision is the provision made for maintaining the service during periods when there is insufficient output from the renewable energy components of the system to meet demand.
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NOTES ACCOMPANYING FIGURE 1
It was found necessary to include system application as well as configuration as a basis for the categorisation. This resulted in eight typical categories and two atypical
categories. Of the two atypical categories, one covers straight diesel generators and was included to provide a performance base line to work from. The other provides the
classification system with the flexibility needed to accommodate the range of possible hybrid configurations where the PV is hybridised with other renewable energy
resources.
PV1:
This is the simplest of systems, where PV output goes directly to a dc load. For example water pumping.
PV2:
Take PV1 and add the facility for storing electricity (battery and regulator) to arrive at category PV2. The storage component is used to provide electricity on
a 24h/day basis, which is why it warrants a separate category. Solar home systems are an example of PV2
.
PV3:
This category, which includes an inverter, facilitates performance measurement to determine the differences between systems supplying a dc load and systems
that supply ac power. The system is configured to meet demand via the battery storage system. Under normal operating circumstances this configuration
would only be used for smaller demands.
PV4:
With this configuration, PV input is dispatched directly to load via the inverter. Output from the PV in excess of the demand, is used to charge the batteries.
This configuration is more typical of large PV systems where efficient use of the PV power is a significant consideration.
PVH1:
The next category steps up to a hybrid configuration. Again demand is met by power from the batteries. The typical application for this configuration is a
small remote site where the variable load impacts negatively on diesel set maintenance costs and fuel transport is expensive. The battery storage plus PV
capacity needs to be sufficient to meet daytime demands ideally leaving the diesel to charge the batteries in a few hours coinciding with peak demand, ideally
placing a steady, 80% load on the diesel over that period.
PVH2:
As demand increases, the configuration outlined for PVH1 becomes less attractive due to battery power leading to excessive system efficiency losses. Under
these circumstances the PV, is configured to feed directly to load, and in conjunction with battery charging duties for the diesel generator when it would
otherwise be lightly loaded, it serves to reduce the load fluctuations that otherwise cause a problem with diesel maintenance. The diesel set can then be down
sized to better match the base load. At night when demand falls, the diesel can be closed down so that it is not operating under-loaded, and the smaller
demand is able to be carried via the batteries.
PVH3:
In large diesel systems with a demand curve that exhibit a temperature related peak, PV capacity can be added to meet that peak, In this configuration, the
diesel set/s carry the base load 24 hours a day. This configuration does not require a storage battery, and strategically, it is the most commercially prospective
of all PV power generation configurations.
PVa:
This is the first of the atypical categories. It is included to cover the range of hybrid configurations that may develop as other renewable energy sources such
as wind are used in conjunction with PV’s.
D1 & D2:
Straight diesel generators are the second atypical category. There are two configurations, the single diesel or “lighting plant” system, and the multiple-set
diesel power station.
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3.2 Preparation of the Monitoring Guidelines:
A review of existing data-bases holding data from “stand-alone” PV systems, quickly established that
in the main, performance capability is usually taken directly from the system manufacturer’s
specification, and cases where system performance had been measured in a scientific manner over
time, are rare. The review also confirmed that the scope and form of data provided in a
manufacturer’s specification varied between products and brand names, frustrating comparisons
thereof.
Planning for the Activities included in the Task III Workplan soon highlighted the need for reliable
performance data. However, the logistics of monitoring a case studies for the range of data that might
be needed, while maintaining consistent quality throughout the exercise, is daunting.
The solution was to prepare a set of monitoring guidelines arranged so that the data needs of the
various end users was prescribed as a series of discrete data sets. This enables the Project Manager to
nominate the type of monitoring that they considered relevant for their purposes up front, and in the
process eliminate any parameters extraneous to their needs.
Thus, the concept of monitoring Guidelines evolved to include seven discrete data sets:
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4.
5.
6.
7.
General.
Quality measures.
Commercial performance indicators.
System performance modelling/analysis.
Battery storage performance.
Appliance performance evaluation..
User adaptation to technology
In addition to providing guidelines for collecting data, the Manual will:
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Include valuable information about methodology and the techniques of quality monitoring.
Provide a description of the different types of sensors, data acquisition systems and associated
hardware to help guide those planning to monitor a new system.
Provide tips and tricks to help avoid common pitfalls associated with monitoring.
Address reporting procedure to minimise it as a source of interpretive error and loss of valuable
information.
Provide a system “Key” to link third party needs with the classification system
3.3 The Key:
Section 3 of the Manual includes a key that can be used to determine which of the identified PV
system categories is most appropriate for a given situation.
Once a prospective user is aware of the category that best suits their needs, they can refer to the
appropriate case study/s to determine what performance they might expect. The performance of each
case study listed will have been monitored in accordance with one or more sets of monitoring
parameters. These sets are described in section 2 of the Manual. The person/company nominating a
case study for the data base will, up front, be required to nominate which of the data sets they intend
using for their performance monitoring. This process is intended to simplify comparison of the
performance of different systems.
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4.
Presenell & Turcotte
Conclusions
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Although the Monitoring Manual is primarily oriented to the needs of Task III for a coherent
framework for its activities, it will also be useful for external bodies. Essentially, the “attraction”
for a Project Manager considering whether or not to offer a case study as an IEA reference project,
is that prospective investors will demand access to quality-managed data as soon as they realise it
is available. This means that a case study that has qualified for inclusion on the database will be
exposed in a positive manner to those considering investing in sustainable energy technology.
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Provision of a commercial electricity supply using renewables is a recent advance. Being new,
there is a need to convince the “establishment” of its performance capabilities. To date, most
demonstrations in Developing Countries have been less than impressive, with the process being
characterised by parallel lessons in perpetuity. The answer is to accumulate experience and use it
as a springboard to better performance.
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The Task III Monitoring Manual is the first step in this direction. I urge you all to support the
initiative and commit to the second step, which is capacity building
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Introducing quality measures to performance monitoring will help to establish international
performance benchmarks for the industry. In turn, this will help focus efforts to mature the
competencies and depth of industry capabilities needed to position renewable energy comfortably
in the mainstream of international commerce.
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