1. Grid Tied PV Systems – Part 5
Session 16
Grid Tied PV Systems – Part 5
Balance of Systems
Three-Phase Systems
October 22, 2015

2. Session 16 content Grid-Connected PV Systems
Wrap-up of Residential PV System Example
Design Considerations for Large Scale Systems

3. Learning Outcomes
An examination of the impact of size (scale) on photovoltaic system design

4. Learning Outcomes
An examination of the importance of the Balance of System components

5. Grid-Tied PV Systems – The Design Process
Design Steps in any Residential Scale System
Examination of site and estimation of performance
Securing financing
Carrying out PV system engineering and design
Securing relevant permits
Construction
Inspection
Connection to the grid
Performance monitoring

6. Grid-Tied PV Systems – The Design Process
Steps in annual system performance design
Evaluation of solar availability and electrical consumption
PV array sizing
Inverter selection
Module selection
Balance of system

7. Grid-Tied PV Systems – PV system engineering and design
Step 5: Balance of System (BOS) component selection
Module extension wires
Junction box and/or Combiner box
Wire and Conduit to connect JB or CB to inverter
DC and AC disconnects at inverter
Wire and Conduit from inverter to Point of Utility Connection (PUC)

8. Grid-Tied PV Systems – PV system engineering and design
Block diagram of two source circuit PV system

9. Grid-Tied PV Systems – PV system engineering and design
AC disconnect between PV modules and service panel

10. Grid-Tied PV Systems – PV system engineering and design
AC disconnect between PV modules and service panel

11. Grid-Tied PV Systems – PV system engineering and design
Second AC disconnect between PV modules and service panel

12. Grid-Tied PV Systems – PV system engineering and design
Wiring of service panel

13. Grid-Tied PV Systems – PV system engineering and design
Service panel, PUC

14. Grid-Tied PV Systems – PV system engineering and design
Service panel, PUC

15. Grid-Tied PV Systems – PV system engineering and design
Service panel, PUC

16. Grid-Tied PV Systems – PV system engineering and design

17. Grid-Tied PV Systems – PV system engineering and design

18. Grid-Tied PV Systems – PV system engineering and design
PV wiring
THHN – Thermoplastic, High Heat, Nylon Coated – 90C
THWN – Thermoplastic, High Heat, Water resistant,
Nylon Coated – 75C
USE-2 – Underground Service Entrance
PV –

19. Grid-Tied PV Systems – PV system engineering and design
Voltage drop and wire sizing
NEC requirement:
Total voltage drop in feeder and branch circuits less than 5% (combined) or 3% (either)
Size
18 (s)
10 (s)
4 (str)
0 (str)
Rdc (W/kft)
7.77
1.21
0.31
0.12
Imax (A) 14 40 95
170

20. Grid-Tied PV Systems – PV system engineering and design
Branch circuits are source circuits that connect PV arrays to power conditioning
Feeder circuits are PV inverter output circuits that connect to the utility (service panel)
Rule of thumb: Don’t allow voltage drops to exceed 2% in any circuit

21. Grid-Tied PV Systems – PV system engineering and design
Ampacity and wire sizing
NEC requirement (690.8):
Ampacity > (1.25) * (1.25) * ISC = ISC
Temperature derating from Tambient > 300C (NEC )
3 hrs of max current flow
Focusing effects of clouds
T (0C)
26-30
31-35
41-45
Correction
1.00
0.96
0.82

22. Grid-Tied PV Systems – PV system engineering and design
M&V Example (modified)
ISC = 8.05A -> ISC = 12.6A
Case 1: Wire size 10 AWG
300C ampacity -> 40A
Suppose the ambient temperature will rise to 380C
Derating factor is 0.91
Derated ampacity -> 36A >> 12.6A
Case 2: Wire size 14 AWG
300C ampacity -> 25A
Suppose the ambient temperature will rise to 600C
Derating factor is 0.71
Derated ampacity -> 17.5A > 12.6A

23. Grid-Tied PV Systems – PV system engineering and design
1. Solar PV Inspection Walkthrough - Introduction 2. Solar PV Inspection Walkthrough - Inspector Safety 3. Solar PV Inspection Walkthrough - The Array 4. Solar PV Inspection Walkthrough - Combiner Boxes 5. Solar PV Inspection Walkthrough - Wiring Methods 6. Solar PV Inspection Walkthrough - Inverters 7. Solar PV Inspection Walkthrough - Interconnection 8. Solar PV Inspection Walkthrough - Following Up
Penn State
Solar Center