Technical Standards for Solar Home Systems (SHS)

To assure the quality of a photovoltaic power system and its correct functioning and guarantee costumers' satisfaction it is important that the components of the system and the system as a whole meet certain requirements.

The GTZ prepared a publication which gives an overview of different standardisation activities and existing standards that are relevant for Solar Home Systems (SHS) and  Rural Health Power Supply Systems (RHS):

GTZ, Division 44, Environmental Management, Water, Energy, Transport: Quality Standards for Solar Home Systems and Rural Health Power Supply. Photovoltaic Systems in Developing Countries, February 2000.

The following Wiki-Page is an extract of the publication regarding SHS.

Introduction

PV systems for applications in developing countries have been tested, optimised and disseminated throughout the world over the last 20 years. A wide variety of demands have been made of the components and systems, partly for reasons due to countryspecific characteristics or regional availability, but also because there were no binding standards, or if there were, they were often not known.

The project activities in technical and financial co-operation at bilateral and multilateral level have moved away from the pilot phase and towards the dissemination of PV systems. Yet, secure technical standards are required for dissemination in order to minimise the need for adjustments after the fact and the related costs in the case of large unit numbers.

An international survey carried out in preparation for this publication showed that several different standardisation activities are in progress. Probably the most interesting international project is the so-called "Global Approval Program for Photovoltaics (PV GAP)", but also technical specifications such as those that have been proposed by the World Bank or the University of Madrid have already been elaborated in great detail.

The publication provides an overview of standards that are relevant for Solar Home Systems (SHS) and in Rural Health Power Supply Systems (RHS). It is intended to facilitate the selection of PV systems and components, especially in tenders, and to provide the impetus for a standardisation of PV systems on a scale that is as broad as possible. Moreover, it also identifies those components for which there is still a need for technical specifications.

This should lead, in the long term or better yet in the medium term, to binding, internationally recognised technical standards, especially for the use of photovoltaic systems in developing countries.

In preparing this publication, all of the well-known national and international institutions concerned with standardisation activities in the field of photovoltaics were contacted in writing. The existing photovoltaics projects of GTZ were also included in the survey.

In the course of the survey, information and documentation obtained from the World Bank, the World Health Organization (WHO), the international standardisation institution IEC, the European standardisation institution CENELEC, the U.S. standardisation office IEEE, as well as a series of projects, firms and experts, were compiled and evaluated.

The available PV-relevant standards were evaluated and summarised in the form of a table with a breakdown by components.

The list of standard specifications for tenders for SHS and RHS forms the largest part of the publication. Eleven different documents with specifications for PV systems and their components were evaluated for this purpose and summarised in a table. These documents varied widely in terms of quality and scope; some of them were intended for the specification of individual components, others as tender documents for whole systems.

Based on these documents, standard specifications were prepared that can be used directly as text modules for international tenders. The minimum requirements were chosen in such a way that a reliably functioning Solar Home System can be set up according to the current state-of-the-art.

Systems and components that are used for power supply to rural health stations (RHS) have to meet higher standards as a matter of principle. The available experience with PV systems in this area of application to date as well as a series of documents, especially from WHO, were evaluated and condensed. A separate list of specifications was compiled for the RHS sector.

A separate set of standard texts for tenders for Photovoltaic Pumping Systems (PVP) entitled "Proposal for Tender Documents for the Procurement of Photovoltaic Pumping Systems (PVP)" is also available from GTZ, Div. 44, Sustainable Energy Systems.

IEC Draft Standard for Small-Scale PV Systems

In June 1997, the Technical Committee TC 82 WG 3 of IEC drafted its first standard with the title "PV Stand-Alone Systems - Design Qualification and Type Approval". This draft refers to individual home application with a solar generator with a maximum of 1000 Wpeak and electrical loads like lamps, radio, TV, refrigerator and telecommunication facilities. In this draft test procedures are described that can be used to determine the electrical and technical operating characteristics of PV systems and their components.

The current draft, however, is more or less a loose collection of individual documents, and is by far not yet complete for an international standard. Important information such as minimum requirements, system layout, installation, etc., are still missing or are extremely incomplete. In the meantime, there are indications that this draft will be replaced by a new proposal of a European group of experts with representatives of the French GENEC, the Spanish CIAMAT, the German TÜV-Rheinland and the European joint research institute ISPRA.

The Global Approval Program for Photovoltaics (PV GAP)

In the interest of world-wide quality assurance and as a reaction to the lack of standards up to now, various PV producers, lending institutions (e.g. the World Bank) and governmental as well as private organisations came out in favour of a world-wide programme for quality assurance of small-scale PV systems. At the 14th PV Conference in Barcelona, Spain in July 1997, the “Global Approval Program for PV (PV GAP)” was launched. The founding members established the following mission as the goal of PV GAP:

PV GAP is a global, PV industry-driven organisation that strives to promote and maintain a set of quality standards and certification procedures for the performance of PV products and systems, to ensure high quality, reliability and durability.

PV GAP is domiciled at the Central Office of the IEC in Geneva, Switzerland, and works closely together with the IEC and its suborganisation, IEC’s Quality Assessment System for Electronic Components (IECQ). Existing IEC standards for quality approval and certification of components and systems are the basis of its work, and progress is being made on the development of new standards that are still lacking. As long as there are no binding standards for certain components, recommendations are made (Recommended Standards) for the interim, which are generally based on national or regional standards.

Furthermore, test laboratories are identified world-wide, also in the developing countries, which can carry out the type tests on the components described in the standards, reliably and reproducibly.

A Reference Manual was put together, which came out in the first edition in January 1998, and can be purchased from PV GAP for 175 US$. The manual first describes in detail the ideas, the organisation and the planned procedures for a quality assurance of PV components in the framework of PV GAP. The technical part essentially consists of a list of standards that may be relevant for PV components. A comprehensive training manual entitled "Quality Management in Photovoltaics" was published in August 1999 which contains specific quality assurance standards for PV components as well as an updated list of relevant IEC standards. It also comprises proposed standards that are currently in progress (IEC TC 82 Work in Progress) ³.

Moreover, a quality seal of approval is given for PV components that were tested under PV GAP conditions. This quality seal of approval is to become established if at all possible in international tenders as the prerequisite for the approval of components and systems. Qualified and recognised producers, sales and installation companies or system integrators have the right to display the quality seal of approval for PV components and systems.

The organisational structure of PV GAP provides for the following working groups:

Organization Working Group: To develop a permanent legal entity for PV GAP and a "Seal of Quality." This group will develop a PV GAP organizational structure. This group will work on an interface with the Switzerland-based International Electrotechnical Commission Quality Assurance Program (IECQ), along with the criteria for awarding the "GAP Seal."

Standardization Working Group: PV GAP will not write standards, but will accept and promote globally the IEC standards. If no IEC standard is available, then, based on peer review, PV GAP will accept existing or future standards of other bodies as "GAP Temporary Standards (GAP TS)," and promote their use globally. These GAP TS will then be submitted to IEC TC 82 to develop them into permanent IEC standards, which, when completed, will replace the GAP TS.

Handbook Working Group: A PV GAP Handbook will be established, combining inputs from the many other organizations that already have developed a handbook or parts thereof. This PV GAP Handbook then will be promoted globally. The Handbook will incorporate all of the PV GAP-approved standards.

Testing Laboratories Working Group: This group will establish criteria and compile a list of testing laboratories to be qualified to test PV components and systems according to IEC and PV GAP Temporary Standards. Reciprocity of test results from PV GAP-qualified Testing Laboratories will be established.

PV GAP Membership: PV-related industrial and commercial organisations, their representatives, producers, system suppliers, traders/retailers, installation companies as well as supporting organisations and individuals can become members of PV GAP. They must abide by the principles of PV GAP, especially in regard to the established quality standards. The advantages of membership are primarily the better marketing of products that have the PV GAP quality seal. As far as governmental and internationally financed projects are concerned, especially in development co-operation, preference will in all likelihood be given to the use of products that meet the PV GAP specifications. Moreover, members benefit from diverse information services and discounts on purchases of IEC and PV GAP publications and standards as well as the PV Reference Manual.

Sponsors and Partnerships of PV GAP (as at 10/98): Chairman: Dr. P. Varadi, P/V Enterprises, USA Secretary: Mr. R. Kay (acting) - IECQ - Switzerland Treasurer: Mr. M. Real - Alpha Real - Switzerland

Organisations represented on the PV GAP Executive Board:

Board Members: JEMA – Japan; EPIA – Belgium; NREL – USA; SEIA – USA; Newcastle Photovoltaic Applications Centre – UK; UNDP – USA; JRC, Ispra – Italy; JQAO – Japan.

Advisory Board Members: PowerMark – USA; WIP – Germany; Fraunhofer Institute – Germany; NOVEM - The Netherlands; EDF – France; ISPMA – India; National Technical University, Athens – Greece.

It remains to be seen how PV GAP develops in the future and whether offices issuing tenders and international donor organisations refer to the quality standards made by PV GAP. As the example of the Training Manual prepared for the World Bank in 1999 shows, however, the PV GAP’s quality assurance function has already met with international interest. If these standards become established in future tender procedures, tests according to PV GAP standards will be binding on the suppliers.

Reliability

SHS reliability, in the sense of lack of failures, depends not only on the reliability of the components, but also on some other features of the system which can directly affect the lifetime of batteries and lamps, such as size, the voltage thresholds of the charge regulator, the quality of installation, etc. Each component of the system must fulfil similar quality and reliability requirements because, if there is only one bad component in an otherwise perfect system, this will limit the quality of the whole.

PV Generator

• PV modules certified according to the international standard IEC-61215 or to the national standard of PV modules used by the relevant country. (R)

This requirement currently excludes thin-film PV modules, although certification procedures for such modules are also available (IEC-61646, SERI/TR-213-3624). Thin film modules are permitted in some projects supported by the World Bank and promising new modules are emerging onto international markets but until now the field experience with commercially available thin-film modules has been rather discouraging ^6,7. Their use in largescale programmes is therefore still considered to be extremely risky and it is recommended that they should only be accepted if supported by comprehensive long term guarantees.

[6] M.J.Manimala. "Solar Photovoltaic Lanterns in rural India: a socio-economic evaluation of the schema as implemented in the state of Maharashtra in India". 12th EC PV Solar Energy Conference. Amsterdam. 1994

[7] E. Dunlop et al. "Electrical Characterisation and Analysis of Operating Conditions of Amorphous Silicon Building Integrated Photovoltaic Modules". 14th EC PV Conference. Barcelona. 1997

Support Structure

• Support structures should be able to resist, at least, 10 years of outdoor exposure without appreciable corrosion or fatigue. (C)
• Support structures must withstand winds of 120 km/h. (R)

Several materials can be used for support structures, including stainless steel, aluminium, galvanised iron with a protective layer of about 30 μm, treated wood, etc.

• In the case of framed PV modules, only stainless steel fasteners (screws, nuts, rings, etc.) may be used for attaching them to support. (C)

It is worth mentioning that frameless PV modules bonded to a frame with suitable adhesive products, while today scarcely used onto SHS market, are performing well in general PV applications and can also be accepted.

• Tilt angle should be selected to optimise the energy collection during the worst month, i.e., the month with the lowest ratio of monthly mean daily irradiation to the monthly mean daily load. Generally, constant user load can be assumed. Then, the following formula can be used
  Tilt (°) = max {|Φ|} + 10°}
  where Φ is the latitude of the installation. (R)

This formula leads to a minimum tilt angle of 10°, which is sufficient to allow rainwater to drain off the surface. It may also be useful to note that slight azimuth deviations from south/north (+/- 30°) and in the tilt angle (+/- 10°) have a relatively small influence on the energy output of a PV array.

Most of the consulted experts are opposed to manual tracking because it implies a risk of damage to the modules, and a risk of energy lost through poor or no adjustment. However, it has been used in some places with positive results not only in terms of energy gain, but also in terms of user participation. Naturally, adequate training is needed and the tracking features, including any hinges and other coupling devices needed to allow the modules to be moved, must also meet the requirements specified above. Hence:

• Static support structures are generally preferable to tracking-ones (R)
• In the case where manual tracking (2 or 3 positions per day, moving from East to West) is used, all of its features must meet the support structure requirements specified above (C).

 

Battery

For the battery, the most important feature of its operation in SHSs is cycling. During the daily cycle, the battery is charged during the day and 11 discharged by the night-time load. Superimposed onto the daily cycle is the seasonal cycle, which is associated with periods of reduced radiation availability. This, together with other operating parameters (ambient temperature, current, voltages, etc.) affects the battery life and maintenance requirements. In order to maximise the lifetime of lead acid batteries, the following operating conditions must be avoided⁸:

• High voltages during charging (to prevent against corrosion and loss of water)
• Low voltages during discharge (corrosion)
• Deep discharge (sulphation, growth of dentrites)
• Extended periods without a fully charging (sulphation)
• High battery temperatures (all ageing processes are accelerated)
• Stratification of the electrolyte (sulphation)
• Very low charge currents (sulphation)

These rules lead to specifications for sizing (both battery and PV generator) and for battery protection procedures (charge regulator). However, it must be pointed out that some of the rules are generally in contradiction with each other (e.g. full charging needs high voltages but high voltages accelerate corrosion), so compromises must be found taking into account the particular local conditions: solar radiation, PV module and battery prices duties and taxes, local manufacturing, recycling infrastructure, etc. Perhaps this explains the lack of consensus on this issue among the different information sources (standards, experts, etc.) that have been consulted during the preparation of this standard, and the requirements given below should therefore be adapted to suit the local circumstances.

The need to prevent excessive discharge leads to the need to limit the maximum depth of discharge to a certain value, PD_MAX, which usually ranges from 0.3 to 0.6, but can approach 0.8 according to the type of battery. The supply to the load must be cut when this limit is reached. The available or useful capacity, C_U, is therefore less than the nominal capacity, C_B, (which refers to the whole charge that could be extracted from the battery if no particular limitations were imposed) and equal to the product C_B x PD_MAX, , such that:

[8] G. Bopp et al., "Energy Storage in Photovoltaic stand alone energy supply systems". Progress in Photovoltaics (to be published).

The wiring

Source: Universal technical standard for solar home systems, Version 2, Thermie B SUP 995-96, EC-DGXVII, 1998, updated in 2001.

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