IEC TS 62257-2:2015

IEC TS 62257-2 ®
Edition 2.0 2015-12
TECHNICAL
SPECIFICATION
Recommendations for renewable energy and hybrid systems for rural
electrification –
Part 2: From requirements to a range of electrification systems
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IEC TS 62257-2 ®
Edition 2.0 2015-12
TECHNICAL
SPECIFICATION
Recommendations for renewable energy and hybrid systems for rural

electrification –
Part 2: From requirements to a range of electrification systems

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-3064-0

– 2 – IEC TS 62257-2:2015 © IEC 2015
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Methodology for non-technical preliminary studies . 10
4.1 Place and role of preliminary studies in a decentralized rural electrification
project . 10
4.2 Specifications of the preliminary study . 10
4.2.1 General . 10
4.2.2 Data for a better understanding of the project environment . 11
4.2.3 Necessary data for the techno-economic study . 12
4.2.4 Necessary data for the financial analysis . 14
4.2.5 Necessary data for the organizational study . 15
4.3 The stages of a socio-economic study . 16
5 Classification of electrification systems . 16
5.1 Introduction to a range of systems . 16
5.2 Users requirements . 16
5.3 Typology of qualitative requirements . 16
5.3.1 Type of desired use . 16
5.3.2 Availability . 16
5.3.3 Quality of the supply . 17
5.4 Typology of quantitative requirements . 17
5.5 Classification for electricity services provided . 18
5.6 Assisted selection of production subsystem . 18
5.7 Typology of decentralized electrification systems . 19
5.7.1 General . 19
5.7.2 Selection process . 19
5.7.3 From user needs to electrification system – Summary for a range of
electrification systems . 20
6 Electrification systems architecture . 21
6.1 General . 21
6.2 General presentation of isolated electrification systems . 22
6.2.1 General . 22
6.2.2 Production subsystem. 22
6.2.3 Distribution subsystem . 22
6.2.4 User or application subsystem or demand subsystem . 22
6.3 Combining subsystems . 23
6.4 Functional diagrams . 25
6.5 Related references. 25
6.6 Limits between production, distribution and demand/application subsystems . 26
6.7 Summary of the different electrification system types . 26
Annex A (informative) Stages of a socio-economic study . 27
A.1 General . 27
A.2 Preparation phase. 27

A.3 Drawing up of the questionnaires – choice of surveyors and choice of
sample . 28
A.4 Conducting the survey – Analysis of the results . 28
A.5 Extrapolation of the results . 28
Annex B (informative) Analysis of the type of receivers installed versus types of use
and demonstrating seasonable variability (where applicable) . 29
B.1 Domestic use . 29
B.1.1 General . 29
B.1.2 Utilisation – Example 1 . 30
B.1.3 Utilisation – Example 2 . 31
B.2 Analysis of the type of receivers versus usage types . 32
B.2.1 General . 32
B.2.2 Health and care centre . 32
B.2.3 Worship places . 32
B.2.4 Community centre . 32
B.2.5 School . 33
B.2.6 Administrative premises . 33
B.2.7 Communication system . 33
B.2.8 Public lighting . 33
B.2.9 Pumping . 33
B.2.10 Battery charging station . 34
Annex C (informative) Supply quality indicators for isolated electrification systems . 35
Annex D (informative) Assisted selection of production subsystem . 36
D.1 Characteristics of possible production subsystems . 36
D.2 Assisted selection of a decentralized production system suited to the
requirement . 36
Annex E (informative) Functional diagrams . 38
E.1 Glossary of symbols . 38
E.2 Architectures of systems . 39
E.2.1 Type T I: REN Systems operating with no storage (in sync with solar,
wind or water energy sources) – REN production . 39
E.2.2 Type T I: Individual electrification systems – REN production with
energy storage . 43
E.2.3 Type T I: Individual electrification systems: (REN + diesel) production
without energy storage . 46
E.2.4 Type T I: Individual electrification systems: (RE + diesel) production
with energy storage . 49
E.2.5 Type T I: Individual electrification systems: genset only without storage . 51
E.2.6 Type T I: Individual electrification systems: genset only with storage . 52
E.2.7 Type T C: Collective electrification systems: REN only without storage . 53
E.2.8 Type T C: Collective electrification systems: REN Micropower plant
supplying a microgrid . 53
E.2.9 Type T C: Collective electrification systems: Multi sources micropower
plant (RE + diesel) without energy storage, supplying a microgrid . 56
E.2.10 Type T C: Collective electrification systems: Multi sources micropower
plant (RE + diesel) with energy storage supplying a microgrid . 59
E.2.11 Type T C: Collective electrification systems: Diesel micropower plant
supplying a microgrid . 62
E.2.12 Type T C: Collective electrification systems: Diesel micropower plant
with energy storage supplying a microgrid . 64

– 4 – IEC TS 62257-2:2015 © IEC 2015
Figure 1 – Example of the content of a non-technical preliminary study . 11
Figure 2 – Systems architecture and dispatchable energy . 20
Figure 3 – General configuration of an electrification system . 24
Figure A.1 – Flowchart of the stages of a socio economic study . 27
Figure D.1 – Better adequacy of production subsystems solutions with supply
availability and daily duration of service . 37
Figure E.1 – Type T I-a system . 40
Figure E.2 – Type T I-b system . 41
Figure E.3 – Type T I-c system . 42
Figure E.4 – Type T I-d system . 43
Figure E.5 – Type T I system . 45
Figure E.6 – Type T I-a system . 47
Figure E.7 – Type T I-b system . 48
Figure E.8 – Type T I system . 50
Figure E.9 – Type T I system . 51
Figure E.10 – Type T I system . 52
Figure E.11 – General architecture of a micropower plant supplying a microgrid . 54
Figure E.12 – Type T C system . 55
Figure E.13 – Type T C-a system . 57
Figure E.14 – Type T C-b system . 58
Figure E.15 – Type T C-a system . 60
Figure E.16 – Type T C-b system . 61
Figure E.17 – Type T C system . 63
Figure E.18 – Type T C system . 65
Table 1 – Application types and types of uses . 16
Table 2 – Expected quality of the supply . 17
Table 3 – Synthesis of quantitative requirements/category – Examples of type of user
and use. 18
Table 4 – Typology of decentralized electrification systems . 19
Table 5 – Preliminary range of relevant (as a minimum) decentralized electrification
systems . 21
Table 6 – Recapitulation of characteristics of different types of isolated electrification
systems . 26
Table C.1 – Combined categorization . 35
Table C.2 – Service specification (example) . 35
Table D.1 – Principles and characteristics of production subsystems . 36
Table E.1 – Glossary of symbols . 38
Table E.2 – List of cases, type T I . 39
Table E.3 – List of cases, type T I . 46
Table E.4 – List of cases, type T C . 56
Table E.5 – List of cases, type T C . 59
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
RECOMMENDATIONS FOR RENEWABLE ENERGY
AND HYBRID SYSTEMS FOR RURAL ELECTRIFICATION –

Part 2: From requirements to a range of electrification systems

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62257-2, which is a technical specification, has been prepared by IEC technical
committee 82: Solar photovoltaic energy systems.

– 6 – IEC TS 62257-2:2015 © IEC 2015
This second edition cancels and replaces the first edition issued in 2004. It constitutes a
technical revision.
The main technical changes with regard to the previous edition are as follows:
• redefine the maximum AC voltage from 500 V to 1 000 V, the maximum DC voltage from
750 V to 1 500 V;
• removal of the limitation of 100 kVA system size. Hence the removal of the word “small” in
the title and related references in this technical specification.
This technical specification is to be used in conjunction with the other documents of the
IEC 62257 series.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
82/947/DTS 82/998A/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62257 series, published under the general title Recommendations
for renewable energy and hybrid systems for rural electrification, can be found on the IEC
website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

INTRODUCTION
The IEC 62257 series intends to provide to different players involved in rural electrification
projects (such as project implementers, project contractors, project supervisors, installers,
etc.) documents for the setting up of renewable energy and hybrid systems with AC voltage
below 1 000 V and DC voltage below 1 500 V.
These documents are recommendations:
a) to choose the right system for the right place;
b) to design the system;
c) to operate and maintain the system.
These documents are focused only on rural electrification concentrating on but not specific to
developing countries. They should not be considered as all inclusive to rural electrification.
The documents try to promote the use of renewable energies in rural electrification; they do
not deal with clean mechanisms development at this time (CO emission, carbon credit, etc.).
Further developments in this field could be introduced in future steps.
This consistent set of documents is best considered as a whole with different parts
corresponding to items for safety, sustainability of systems aiming at the lowest life cycle cost
as possible. One of the main objectives is to provide the minimum sufficient requirements,
relevant to the field of application that is: renewable energy and hybrid off-grid systems.
The purpose of this part of the IEC 62257 series is to propose a range of renewable energy
based electrification systems able to meet the requirements of customers identified in the field
of decentralized rural electrification projects.
This technical specification was developed in cooperation with other IEC technical committees
and subcommittees dealing with renewable energies and related matters, namely technical
committee 21 ("Secondary cells and batteries"), subcommittee 21A ("Secondary cells and
batteries containing alkaline or other non-acid electrolytes"), technical committee 64
("Electrical installations and protection against electric shock"), technical committee 88 ("Wind
turbines"), and others.
– 8 – IEC TS 62257-2:2015 © IEC 2015
RECOMMENDATIONS FOR RENEWABLE ENERGY
AND HYBRID SYSTEMS FOR RURAL ELECTRIFICATION –

Part 2: From requirements to a range of electrification systems

1 Scope
This part of IEC 62257 proposes a methodological approach for the setting up and carrying
out of socio-economic studies as part of the framework of decentralized rural electrification
projects. It is addressed to project teams and in particular to experts in charge of socio-
economic studies in international projects.
The amount of detail gathered and the requisite number of experts needed would depend on
the scale of the proposed project. For large projects involving many households, a detailed
study would be required, for a project which involves a single or few households, the study
could be truncated.
The information coming from such preliminary studies could be used for several purposes,
such as more complete economic and financial studies of the electrification project.
This technical specification also provides some structures as technical solutions that could be
recommended, depending on the qualitative and quantitative energy demands, consistent with
the needs and financial situation of the customers.
Then, in relation with each model of the proposed range of systems, electrical architectures
are proposed to technical project managers to assist in designing the systems.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60617 DB , Graphical symbols for diagrams
IEC 62257-9 (all parts), Recommendations for renewable energy and hybrid systems for rural
electrification
IEC 62257-12 (all parts), Recommendations for renewable energy and hybrid systems for

rural electrification
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
___________
“DB” refers to the IEC on-line database, available at

3.1
Renewable Energy
REN
energy from a source that is not depleted when used
3.2
hybrid system
multi-sources system with at least two kinds of technologies
3.3
dispatchable power system
power system is considered dispatchable if delivered power is readily available at any
specified time. (e.g. a diesel generator)
3.4
non-dispatchable power system
power system that is resource dependent and whose power might not be available at a
specified time (e.g. solar grid connected system)
3.5
storage
storage of energy produced by one of the generators of the system and which can be
reconverted through the system to electricity
3.6
micropower plant
power plant that produces less than 50 kVA through the use of a single resource or hybrid
system
3.7
microgrid
grid that transfers a capacity level less than 50 kVA and powered by a micropower plant
3.8
Individual Electrification System
IES
micropower plant system that supplies electricity to one consumption point usually with a
single energy resource point
3.9
Collective Electrification System
CES
micropower plant and microgrid that supplies electricity to multiple consumption points using a
single or multiple energy resource points
3.10
isolated site
electric characteristic to define a specific location not currently connected to a
national/regional grid
3.11
remote site/area
geographic characteristic to define a specific location far from developed infrastructures,
specifically energy distribution

– 10 – IEC TS 62257-2:2015 © IEC 2015
4 Methodology for non-technical preliminary studies
4.1 Place and role of preliminary studies in a decentralized rural electrification
project
It is strongly recommended that it is unwise to launch an electrification project against the
wishes of the local institutions and populations. A good understanding of the needs and
wishes of the local populations is recommended, to know what is their demand, their capacity
and willingness to pay for a modern energy service.
If all the socio-economic data are available, they have to be properly collected and processed
for this purpose.
If not, a preliminary study is recommended that will be the first stage in the establishment of a
feasibility study for a decentralized rural electrification project. Its role is to allow a better
understanding of the areas concerned by the various project experts and such a study would
make available some of the data needed for technical evaluations, economic, financial and
legal analyses, and for the carrying out of the project in general.
In this Clause, a method is suggested to obtain the various information needed.
Some of the information described in the following subclauses might be obtained from govern-
mental organizations prior to specific sites visits.
4.2 Specifications of the preliminary study
4.2.1 General
A socio-economic study shall provide a certain amount of data to the experts in charge of the
financial, techno-economic and organizational studies. It also allows a better understanding of
the global environment of the project and can provide information to the community about the
scope of the project.
The following subclauses suggest some considerations concerning data to be collected and
analysed in consideration with the following criteria:
• general information on the environment of the project;
• techno-economic study;
• organizational study;
• financial analysis.
Figure 1 is an illustration of the main topics that should be investigated in the socio-economic
study.
Preliminary study
General information
Organisational
on the environment
study
of the project
- sociological data - possible sources of financing
- community's priorities for development - existing local infrastructures
- economic activity - private sector dynamics
- development projects under way in the region - community-level dynamics
- externalities (environmental impact) - public-sector dynamics
- level of education
Techno-economical Financial
study analysis
- demographic and geographic data
- number of customers and
- the load distribution curve of the village or
variations in time
the distribution of customers per service
- average selling price
- fuel price
- access fee for electricity
IEC
Figure 1 – Example of the content of a non-technical preliminary study
4.2.2 Data for a better understanding of the project environment
4.2.2.1 General
The following topics should be considered by project contractors. It is their role to determine
the relevant importance of each of these categories in regard to a specific project or
programme.
4.2.2.2 Sociological data
This data is important for an understanding of the local population. It is essential to look at the
organizational, cultural and ethnological structures of the society. In particular, one should
investigate the way of life, the sanitary conditions, the national and local languages, the level
of education and literacy, the technical sophistication level and the presence of organizations
and associations. In addition, the role of male and female in the social organization of the
village shall be taken into account.
4.2.2.3 The communities’ priorities for development
It is important to understand the population’s opinions of their village. What are their priorities
for improvement in their daily life? (Such as water pumping, construction of a hospital, of a
school, communications infrastructure, electricity, etc.).
In the case of a rural electrification project, what are the priorities for the village as expressed
by the population and the local authorities?

– 12 – IEC TS 62257-2:2015 © IEC 2015
4.2.2.4 Economic activities and possible development
Knowledge of the economic activities in the community allows a better general understanding
of the environment of the project; it also helps in understanding the dynamics of local
development, in order to evaluate the evolution of demand in energy in the coming years.
One can compile the economic activities of the village (commerce, handicrafts, animal
husbandry, agriculture, etc.) and look at their relative importance. It would also be useful to
look at potential activities due to electricity.
4.2.2.5 The development projects under way in the region
One should look at the local development projects under way, who are the instigators and
who are the beneficiaries, what the impacts on the population are, and what would be the
impacts on a future electrification project.
4.2.2.6 Environmental considerations
One of the clear drivers in the use of renewable technology is the favourable impact of these
systems on the environment as compared to the conventional sources, primarily diesel and
grid extension. The impact of any technology choice on the environment, from a carbon, plant
footprint, noise and visual impact should be assessed. Understanding the desires of the local
participants will be important in this endeavour.
4.2.3 Necessary data for the techno-economic study
4.2.3.1 General
Although this information is not strictly in the domain of the socio-economic expert, it shall be
collected in the initial phases of any analysis as it is essential to the techno-economic study.
The socio-economic expert is therefore asked to collect this data, being usually the first
project person to visit a rural community.
4.2.3.2 Geographic and demographic data
In particular one shall obtain the geographical coordinates of the village, its topography, local
fauna, and the geographical distribution of the inhabitants. The geographic layout of the
community is important because it impacts the economics of meeting the power requirements
for the community. If the community is widely dispersed, the cost of a local distribution
network may be prohibitive, at which point individual home systems or small cluster systems
may be the most cost-effective solutions. The analysis will require specification of the
location, power, and energy requirements of each load. It is also important to obtain an
understanding of the acceptance of different qualities of service that these electrification
options offer. If possible, one should collect data on the climate, local natural resources, site
transportation issues and other important sighting issues such as land ownership and right of
way issues.
4.2.3.3 Human resources
The personnel resources available in the community, region and country shall be considered
when conducting an analysis for renewable based power systems. The infrastructure required
for the project installation, long-term operation, and system maintenance shall be in place to
insure its long-term sustainability. In most cases, a multi-layer infrastructure is required, a
local system operator who is able to address short-term incidents, a regional service centre
capable of conducting system repair and component assessment and a country or globally
regional centre that can provide timely replacement of major components and detailed
service. Without a specified institutional framework, it will be impossible to provide a quality
level of service at a cost that can be sustainable over the life of the project. The whole
infrastructure framework relies on people with the right level of training and equipment to
perform their specified tasks in the right geographic area with enough systems to guarantee a

successful business model. If the infrastructure is not currently in place, care shall be taken to
investigate whether the resources are available to create one.
4.2.3.4 Energy – resources assessments
Data on the local (renewable) energy sources such as wind, insulation, biomass and hydraulic
potential should be collected. If a sufficient amount of reliable data is not available, the project
should be postponed until the necessary data have been collected. For wind and solar
energy, a measurement program may be necessary. For wind measurements, a duration of at
least one full year or the ability to comfortably correlate the data to other long-term data
collection sites, is recommended.
Information on the daily or seasonal resource pattern is also important in the assessment of
the available resource. Modern site assessment techniques should be utilized to establish the
best possible prediction of the resource and the energy production potential, including the use
of resource assessment modelling techniques such as the Wind Atlas Analysis and
Application Program (WASP) Riso National Laboratories, Denmark; MesoMap, True Wind
Solutions, United States; and the Wind Resource Assessment and Mapping System
(WRAMS), National Renewable Energy Laboratory, United States .
This data can then be used in performance simulation models such as RAPSIM, Australia;
RETScreen, Canada; HOMER, Hybrid2, PVSYST, and Wattsun, United States . At locations
without electric service, it will also be important to obtain an assessment of all of the
electrification options for the community or dwelling in question. This would include
information like the distance to any existing distribution network and the cost of diesel fuel
transported to the site.
4.2.3.5 Environmental conditions – climate
Data on the local environment and climate should be collected. For warm climates with high
temperatures, humidity and possibly corrosive environments may influence design criteria,
choice of material and systems layout. For cold climates with low temperatures, icing, snow
load and again possible corrosive environment may, in different ways, influence design
criteria, choice of material, systems layout and performance. Altitude may also be an
important parameter. Local conditions may also influence transport, installation and access to
the site as well as operation and maintenance costs. Extreme conditions such as
earthquakes, floods and hurricanes/typhoons may influence design criteria and expected
systems lifetime. Data on all these matters should be collected and, if possible considered in
relation to any national and/or international standard.
4.2.3.6 Existing energy supply
The structure of the existing energy supply in terms of fuel, gas, wood, candles and other
sources should be mapped with respect to sources, amounts, availability and costs. Existing
infrastructure in terms of power plants, fuel storage and distribution lines should be listed and
specified in considerable detail. Costs and metering principles should be accounted for, and
subsidies, if any, on the existing energy supply should be accounted for. Special care should
be taken in the determination the real cost of diesel fuel delivered to an existing diesel power
station. The number of hours of service per day and the customer’s impression of the level of
service are important factors to consider for any existing power stations.
4.2.3.7 Present and future consumer demands
The expected loads in a community, as well as the projected growth, or reduction, of those
loads will impact the specification and configuration of the hybrid system. Determining the
initial loads and the growth projections can be very difficult, and is often based on historical
___________
This information is given for the convenience of users of this document and does not constitute an endorsement
by IEC.
– 14 – IEC TS 62257-2:2015 © IEC 2015
values for similar situations. It is very clear that the load and projected growth have a clear
relation to system design and the life-cycle cost of energy for systems providing various levels
of service. The quality of the electric service, the number of hours per day the system is
expected to operate, and whether there are large inductive loads, such as motors, need to be
considered. Investigation should also be made into areas of potential power use, for example
animal driven agricultural water pumps that could be electrified or grain drying operations that
could be converted to biogas.
4.2.4 Necessary data for the financial analysis
4.2.4.1 General
The financial expert needs a number of data to make his analysis, and the socio-economic
expert shall provide them. For the financial analysis, one shall know the following:
4.2.4.2 Number of customers and variation in time
This data is deduced from the data on the demand expressed by the population for a modern
energy service. In ord
...