DC Cables – An important factor in performance of Solar PV Installations

Energy delivered from a Solar PV system is not only dependent on the efficiency of the module but also on other system components like DC Cables, Connectors & Junction Boxes.

Electricity, Transformers, Motors, Switchgear, Cables, electrical wires, Meter & Measuring Instruments | DC Cables – An important factor in performance of Solar PV Installations - Electrical India Magazine on Power & Electrical products, Renewable Energy, Transformers, Switchgear & Cables
DC Cables - An important factor in performance of Solar PV Installations

Energy delivered from a Solar PV system is not only dependent on the efficiency of the module but also on other system components like DC Cables, Connectors & Junction Boxes. While designing the solar farm, engineers have to factor the losses from modules to the inverters to calculate the over-all performance ratio of the farm. Low quality solar cables and connectors will lead to small increases in resistance and result in higher losses of energy (I2Rt). The loss of energy already harvested, when calculated over a twenty five year life represents a substantial loss & would affect the profitability of the project.

A high quality Solar DC Cable is expected to perform for the complete lifetime of the installation which is about twenty five years. The cost of replacing a defective installed cable is very high. The replacement costs increase when factoring in manpower used for removal, reinstallation and testing of the system. In addition, there are losses in power output and revenue generation. The cost of these cables and connectors is very small in the total cost. Since the differential cost of the high quality cables is insignificant, it makes sense to invest with higher initial cost and reduce the “total cost of ownership” of a PV plant.

Solar cables have to withstand a wide range of environmental conditions – and continue to do so over a long period. High temperatures, UV radiation, rain, humidity, dirt and attack by moss and microbes are all a serious challenge to solar cables. Cables tested in accordance with EN, TÜV and UL requirements (120OC; 20,000 hours) can be used at environmental temperatures of – 40OC to +90OC. They should therefore achieve the target service life of 25 years. Apart from temperature, UV radiation is the other significant factor. Trials have shown that untreated material (free of any colour additive) will lose more than 50% of its performance capacity within less than six months. In order to avoid this deterioration, fine soot particles are added to the plastics (leading to a black colouring in the sheath). These particles absorb the UV radiation and convert it into heat. Optimum UV resistance can therefore only be achieved by using black solar cables with enough black carbon content.

There is a new European Standard EN 50618 published for Solar DC Cable, this standard specifies cables for use in Photovoltaic (PV) Systems, in particular for installation at Direct Current (DC) side, with a nominal DC voltage up to 1.5kV between conductors as well as between conductor and earth. These cables are suitable for permanent outdoor use for many years under variable demanding conditions. Relatively stringent requirements are set for these products in line with the expected harsh usage conditions. EN 50618 requires cables to be low smoke halogen free, flexible tin coated copper conductors, single core power cable with crosslinked insulation and sheath. The testing requirements in EN 50618 are more stringent, the most important change is that all the test are done on material taken from finished cable ensuring that the product to be installed is passing all the testing requirements. Cables are required to be tested at Voltage of 11KV AC 50Hz. An IEC standard for Solar DC Cables based on EN50618 is also in preparation.
To meet the stringent requirements insulation and sheath in modern solar cables consist of cross-linked polymers. Two different processes can be used for cross-linking – a choice between electron beam cross-linking and chemical cross-linking. Chemical cross-linking is a process that cannot be stopped once it has started. As a result, chemically cross-linked cables suffer from the same phenomenon as old car tyres. They can harden and become porous. By contrast, electron beam cross-linked cables are irradiated with beta rays. This improves the synthetic material. Once the cables have passed the electron beam, the cross-linking process is complete. These cables remain soft and elastic throughout their whole service life.

A chain is only as strong as its weakest link – which is why LEONI offers high quality electron beam cross-linked BETAflam® solar cables. These quality cables are produced in Switzerland and fulfil all the requirements: long service life, excellent weather resistance and security of investment for the operator of the facility. LEONI started electron beam crosslinking in 1984 and supplied beta beam irradiated cables for solar application in the 90’s. These are still performing in installations in Europe. LEONI produces and develops compounds for insulation and jacket materials in-house. With capacity improvements over a period of time, it today has the world’s largest beta beam cross linking facility contributing to the highest production of solar DC cables. LEONI first launched UL/TUV dual approved cables in 2005 & invented 1,000 VAC UL and 1,500VDC TUV cables which will be used for solar installations. LEONI can supply the complete system from junction boxes for module manufacturing to cable systems and connectors for Solar PV installations from its production facilities all over the world. To support our customers for fast installations of PV power plants LEONI has stocks available in India, Europe and USA.

LEONI BETAflam Solar products meet the highest requirements for solar PV system providing the same high expectations that are demanded from the solar modules – which are longevity and high weather resistance. We offer BETAflam Solar DC cables, TRAFOflex UV cable, SOLARpowerAlu-ATA cables, BETAsolar Junction Box and BETAsolar PV connectors.

Courtesy: LEONI Cable Solution (India) Pvt Ltd.

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