Page 204 - Applied Photovoltaics

systems would typically have their own transformer or substation. The technical and
economic issues involved in large, central-generating PV plant are discussed below:
10.4.1 Cell interconnection

In determining the best way of connecting cells in large systems, the potential losses
must be examined. For instance, many parallel cells improve tolerance to open
circuits but not to short circuits. Table 10.1 shows losses in total power with 0.05%
each of open-circuited and short-circuited cells, while Figs. 10.5 and 10.6 illustrate,
respectively, the connection of cells and modules with bypass diodes into power
conditioning equipment; and connection approaches and advantages of paralleling,
branch circuits and blocking diodes.

Table 10.1. Losses in total power with open-circuited and-short circuited cells (Ross, 1984).
cells per series cells in parallel
substring blocks 1 4 8 16 notes
0.001 0.001 0.001 0.001 1
20 50 0.011 0.050 0.025 0.015 2
0.012 0.051 0.026 0.016 3
0.001 0.001 0.002 0.002 4
10 100 0.005 0.022 0.013 0.008 4
0.006 0.023 0.015 0.010 4
0.001 0.002 0.002 0.002
5 200 0.003 0.010 0.007 0.004
0.004 0.012 0.009 0.006
0.001 0.002 0.004 0.006 5
2 500 0.001 0.004 0.003 0.002 5
0.002 0.006 0.007 0.008 5
Notes: (1) short circuit losses; (2) open circuit losses; (3) total losses; (4) optimum design region; (5) sensitive
to shorted cells.

+

PC

–

module source circuit
3 parallel strings 3 parallel strings
2 series blocks 6 series blocks
2 cells per substring 2 cells per substring
2 diodes per module 1 diode per series block
Figure 10.5. Module circuit design (©1980 IEEE Gonzalez & Weaver).

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