EoW November 2011

technical article

Cables for Photovoltaic Applications By Jorg Bor of Freidrich Lütze GmbH & Co KG, Stefan Grunwald of Lutze Inc, and Ilona Hirtz of Kabelwerke Villingen GmbH

Abstract The recent growth of the renewable energy market applies to both wind energy as well as to solar energy. In many countries this growth is supported by governmental subsidies. renewable energy plants demand high thermal and mechanical requirements from cables and other components. Therefore, some national standardisation bodies defined general requirements for cables used in solar plants. In 2005 UL 4703 was published in the USA. In Germany a joint working group “Cables for Photovoltaic Application” was established in the same year, which resulted in a specification published in February 2008. The performance requirements in high temperatures have been set very high for cables. Various German institutes accepted this specification and now offer certifications for it. There has been a huge demand in the European as well as Asian markets for such certified cable. Due to the differences the UL 4703 requirements cannot be combined together with the German specification. The different solar-cable requirements have advantages as well as disadvantages in respect to the specific regional conditions. 1 Introduction The renewable energy market is growing rapidly. A tenfold increase for the next five years is anticipated by Merill Lynch [1] . This growth applies to wind energy as well as to solar energy. Due to public interest, a number of governments have decided to support the renewable energy economics Outdoor applications in

with large amounts of subsidies. Thus, even a further increase in this market can be expected.

established a working group called “Cables for Photovoltaic Application” which resulted in a public specification. This document was published in February 2008 [2] . Due to the close cooperation between different institutes, this specification is identical to the TÜV-Specification 2 PfG 1169/08.2007 and the VDE-Specification E PV 01:2008-02. DKE-Subcommittee UK 411.2 released the document for publication and application, but due to CENELEC rules it was not adopted as a national standard in Germany.

2 External Conditions The photovoltaic market is a very specific market. Various national regulations are to be taken into account. The system size can vary from a small home power supply with a nominal power of few kilowatts up to large centralised solar plants in the Gigawatt range. The components used in these systems must be suitable for these specific applications. One common determining factor for all photovoltaic power systems is the out- door use, which brings along high temperatures and, of course, high UV radiation. Weathering and humidity need to be taken into account, as well. Furthermore, safety and reliability aspects are very important. The improvements of the solar panel technology define the electrical perfor- mance of components. Usually solar systems are working with low voltage direct current, and the panels are switched in parallel. Thus, the current is the determining electrical parameter. In terms of cables, this results in different conductor cross sections.

4 Technical Details of the German Specification

In this German specification [2] the requirements have been raised to a very high level regarding the high temperature performance of cables. Additionally, high mechanical stability is required; the cable has to be flame retardant and free of halogens. To meet this specification the manu- facturers generally use halogen free flame retardant cross linked polyolefin copolymers as material for insulation and jacketing. The solar cable according to DKE is a two- layer insulated single core cable with a minimum wall thickness of 0.5mm in each layer. The most important tests required in this specification [2] are discussed in the following clauses: 4.1 Temperature range Solar cables according to the German specification [2] are defined for an environ- mental temperature range from -40°C up to +90°C. The maximum conductor temperature is specified at +120°C.

3 Common

Specification of German Technical Institutes

In 2005 the German national electro- technical standardisation body, DKE,

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EuroWire – November 2011