Design basis
Clear assumptions before drawings move forward.
The purpose of the design basis is to remove ambiguity early. It gives
the EPC team, client, and commissioning lead a shared technical basis.
Representative equipment and preliminary compatibility check
This example uses published manufacturer data to make the stringing
decision traceable. The products are representative only and are not a
procurement selection.
Check
Calculated result
Limit and disposition
Nominal DC array
136 x 550 W = 74.8 kWp
60 kW AC total; DC/AC ratio 1.247
String Vmp at STC
17 x 41.95 V = 713.2 V
Within the 200-1000 V MPPT range
String Vmp at NOCT
17 x 38.97 V = 662.5 V
Within range; project hot-cell Vmp remains pending
Cold string Voc at -10 deg C
952.9 V, including +3% Voc tolerance
Below the 1100 V maximum input voltage
Cold string Voc at -40 deg C
1022.2 V sensitivity check
Below 1100 V at the module's lower operating limit
One string per MPPT
Imp 13.12 A; adjusted Isc 14.72 A
Below the 26 A operating and 40 A short-circuit limits
Two strings on one MPPT
2 x 13.12 A = 26.24 A
Excluded: exceeds the published 26 A input-current limit
Manufacturer references:
LONGi LR5-72HPH data sheet
and
Huawei SUN2000 M3 technical specifications.
The -10 deg C and 70 deg C temperatures are illustrative. Current
regional product revisions, project design temperatures, hot-cell Vmp,
cable sizing, protection, yield, structure, fire access, and grid
requirements must be confirmed before design issue.
Controlled single-line diagram
The A3 drawing develops the concept into tagged equipment, explicit string-to-MPPT allocation, AC collection, grid connection, monitoring, protective earthing, and controlled design notes.
Representative concept only. Cable sizes, protective-device ratings, fault duty, RCD requirements, surge protection, export control, and local grid requirements remain project-specific.
