This section discusses the integration of a classic solar generator (see Section 4.3.3) comprising nSP parallel strings composed of nMS modules wired in series. The parallel strings are interconnected using generator junction boxes. For many larger systems, the various arrays are first wired in array junction boxes, whereupon the wires from these boxes are then wired into generator junction boxes.
Special types of PV plants with string or module inverters which greatly reduce the wiring workload are discussed in Section 5.2.
During the realization of a series connection of PV modules it is essential that the whole string wiring is ungrounded and completely decoupled from any other system component. In the interest of system
Figure 4.73 Fully insulated, non-confusable special PV connectors and the attendant coupling accessory for PV system string wiring. These devices far exceed protection class II requirements (Photo: Multi-Contact AG)
realization and servicing safety, it is useful if each string can be subdivided into separate substrings, whose maximum open-circuit voltage is 120 V (extra low voltage; such DC voltages are non-hazardous in most cases) and which are only wired in series when the system is commissioned. Moreover, string wiring safety can be substantially enhanced through the use of specially insulated PV plug-in connectors for solar module wiring in lieu of conventional screw connections in module junction boxes (shown in the system in Figure 4.47; also see Figure 4.73; the lower device is latchable and the upper one is not). Many manufacturers sell modules that integrate clearly marked wire connectors that are compatible with system plug-in connectors (see Figure 4.74), in lieu of conventional screw connections. This greatly simplifies the mounting process and reduces its cost.
Although it takes considerable force to open such a plug-in connector, in recent years it has become a requirement to be able to latch these connectors in such a way that they are locked, so as better to avert arcing in the event of the connector opening adventitiously. Such latchable PV plug-in connectors are available from various vendors (see Figure 4.73 (bottom), Figure 4.74 and Figure 4.79).
Figure 4.74 Laminate with special jacks that enable non-electricians to perform wiring in a trouble-free manner. The jacks integrate two connection wires and a special plug-in connector, which is latchable (see Figure 4.73) (Photo: Multi-Contact AG)