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Optimised distribution panels for the PV market

27 June 2011

Photovoltaic power generation is booming, we are told, but the challenge is to make its installation as efficient and as economical as possible. Here we see how a purpose-built, modular distribution system is helping to speed panel building for this important area of renewables market

Installation of photovoltaic (PV) systems has already become a part of the standard repertoire of many electricians, but PV installation requires some rethinking when it comes to planning, dimensioning and component selection. The German company, Hensel has a bit of a head start in this area, developing special installations for PV systems at an early stage in their development. A good example is the company’s ‘ENYSUN’ distribution programme, of which more later.

A PV system comprises two major components, the PV panels themselves and the inverters that convert the dc from the panels into usable ac. A number of PV panels are interconnected to form PV strings and several such strings form the dc power supply unit, or ‘PV generator’. Each PV generator supplies up to 1,000V and they are connected via special junction boxes to the inverters. Several inverters are then interconnected via inverter collectors and from there linked to the grid or private mains supply of the PV system owner.

Clearly, there are a number of interconnection interfaces in this arrangement, each with its own special requirements.

PV generator junction boxes are, almost by definition, outdoor installations, and they must be able to handle quite severe climatic conditions. At the same time they must be mechanically robust, all of which places high demands on the design and the materials of construction.

PV components on the dc side need to be seen as placed under voltage, even if the system is separated from the ac side. Protection to Class II or equivalent specification is usually considered the best option, particularly when the dc networks are not grounded. In such cases, empty boxes, tested in accordance with IEC 60 439 and fulfilling the requirements of protection class II, must be used. Cable junction boxes in accordance with IEC 60 670-22 may not be used, since this standard does not meet class II requirements.

The ENYSUN programme
Hensel offers special PV generator junction boxes within its ENYSUN range that conform to the relevant standards. The housings, made from impact and UV resistant thermoplastic, are ready for connection and already pre-wired and equipped with surge protection and are thus ready to use. Plug-in connections for the PV strings and the inverter also save installation time.

On the ac side, inverter collectors provide the connection between inverters and the power distribution. For this area, high installation flexibility is required, as arrangements will inevitably differ from site to site. In order to cope with this, ENYSUN inverter collectors are supplied as modular housing sets, which can be individually customised.

Unlike the distributors in buildings, for which the simultaneity factor ranges from 0.3 to 0.6, it is 1 for PV systems. This must be taken into consideration when dimensioning the distributors, otherwise the equipment may exceed its maximum temperature, and circuit protectors will trip at levels below the rated current. Heat dissipation from ENYSUN PV inverter collectors is aided by additional ventilation slots and larger housings.

An interface is required to feed and measure the solar generated power to the user network, its dimensioning depending upon the capacity of the PV array and the size of the load. These systems also provide space for measuring instruments, the inverter collector connections and, when required, an isolator.

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