IEA PVPS Task 3 has published three new reports aimed at improving the operational performance selection and use of Stand Alone PV (SAPV) systems. The reports address testing of batteries, appliance selection and load matching, and guidelines for selecting an appropriate system for a given application.
Testing of batteries
The battery bank is often the weakest component of an SAPV system and a major contributor to the system’s overall life-cycle
cost. Insight into the likely field performance of different batteries is therefore of major concern to system designers, suppliers and managers of technology dissemination projects. A variety of accelerated battery cycling procedures simulating field operating conditions are used to evaluate
battery lifetime. These invariably aim to induce ageing of the battery including sulphation, corrosion, stratification and
softening of the battery grid and the active
mass.
The new report, IEA-PVPS T3-11:2002, assesses seven cycling test procedures and the performance of more than 40 different batteries. One of the key findings of the study is that none of the test procedures alone actually induce a significantly high level of degradation. This implies that choosers of batteries should apply several of the procedures to ascertain which of the degradation patterns is most likely to match their application before deciding on the correct battery. This is particularly true for flat plate
solar batteries where lifetime is very dependent upon the test procedure adopted.
In terms of battery technology, the results
show a wide variation in efficiency and life
between batteries of the same technology. This is due to differences in the type of grid alloy, the active mass composition, the manufacturing process or the cell geometry.
One clear conclusion from the analysis is
that it confirms the longer and better service of tubular batteries.
Use of appliances
While batteries are the most common failure point, inappropriate loads are very often the origin of PV system malfunction or
failure. Start-up power peaks, or reactive
power and harmonic distortion can cause
system signal instability with the result that
protective devices will close the system
down.
A well-matched load together with a carefully selected choice of appliances can lead to significant savings in terms of reduced PV
and electricity storage capacity. Conversely,
inefficient appliances and processes,
standby loads and inappropriate loads will
increase the requirement for expensive PV
and storage capacity.
This new report, IEA-PVPS T3-09:2002, presents a survey of real cases from around the world with load related problems for a
range of applications and the effects on
quality and cost of the service. The study
goes on to present the solutions that were
adopted together with suggested alterna-
tive solutions.
One of the main conclusions of the work is the importance of integrating the choice of appliance into the total SAPV system design.
Guidelines for selecting SAPV systems
With such a variety of system architectures,
components of varying performance and a barrage of claims to compare, choosing a system to service a specific stand-alone
power need within realistic budget constraints can be a daunting task. The new guidelines from Task 3, Report IEA-PVPS T3-12:2002, are not intended to replace competent professional design, but were developed to help those seeking to invest in a PV
power supply to identify features of an appropriate system and also to appreciate the role of the different components in that system.
The guidelines aim to simplify the range of
system design options into a manageable number of categories within three main groups: systems with or without batteries and inverter; PV hybrids; and conventional generation technologies including the diesel generator set against which PV might be competing. A ‘Key’ is also used to filter the user of the guidelines through four simple options – is technical support for the application difficult to access; does the application require AC or DC power; is intermittent supply acceptable; and what is the daily demand on site in kilowatt-hours.
Armed with this tool, the user is helped to identify component requirements from which they can make an informed decision
of SAPV investment options.
All reports are available for download from
the publications' section.
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