This document discusses how temperature affects photovoltaic (PV) systems. It notes that PV power and open-circuit voltage decrease as temperature increases. The document describes an experiment that measured temperatures on a residential roof in Phoenix, Arizona, finding that temperatures under PV modules were not as high as expected. It concludes that temperature affects PV performance and must be considered in conductor sizing according to National Electrical Code tables which reference temperature data sources.

1. ©2008-2012 Enphase Energy
The Effects of Temperature on PV Systems
Mark Baldassari
Director, Codes and Standards

2. 2©2008-2012 Enphase Energy | Confidential
Quick Introduction to Enphase
The Enphase Microinverter System
Effects of Temperature on PV Systems
Enphase Test Results
Questions
Agenda

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Introducing Enphase

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Enphase Growth
> 43,000 Systems> 1,800,000 Units
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0%
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Effects of
Temperature on PV
Systems

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Why is Temperature Important?
What is the Temperature Outside?
How Hot is it Under the Module?

23. 23©2008-2012 Enphase Energy | Confidential
Power and Voc are inversely proportional to temperature
As temperature goes up, PV Power and Voc go down
Effect on PV Modules
0
5
10
15
20
25
30
35
40
45
50
0
50
100
150
200
250
300
350
-35 -25 -15 -5 5 15 25 35 45 55 65 75 85
Voc(V)
Power(W)
Temperature (oC)
PV Power and Voc vs. Temperature
Power
Voc
P = Pmpp(1 + TC Pmpp(T - 25)/100)
P = 235(1 - 0.45(T-25)/100)
Voc = Voc(1 + TC Voc(T - 25)/100)
Voc = 37(1 - 0.37(T-25)/100)

24. 24©2008-2012 Enphase Energy | Confidential
NFPA 70: NEC 2008 supplies ampacity tables and
describes calculation methods
See Section 310.15 and Table 310.16
Effect on Conductor Ampacity
0
20
40
60
80
100
120
140
160
20 30 40 50 60 70 80 90
ConductorAmpacity(A)
Temperature (oC)
Conductor Ampactiy vs. Temperature
10 AWG
6 AWG
2 AWG

25. 25©2008-2012 Enphase Energy | Confidential
NOAA, Weather Underground, iPhone apps,
etc.
American Society of Heating, Refrigeration and
Air-Conditioning Engineers, ASHRAE.org
– Solar America Board for Codes and Standards,
SolarABCs.org
Determining Outside Ambient Temperature

26. 26©2008-2012 Enphase Energy | Confidential
Measure temperature on typical residential Rooftop in
Phoenix Arizona
Experiment

27. 27©2008-2012 Enphase Energy | Confidential
Thermalcouples Mounted

28. 28©2008-2012 Enphase Energy | Confidential
Data Collected

29. 29©2008-2012 Enphase Energy | Confidential
Temperature Results

30. 30©2008-2012 Enphase Energy | Confidential
Temperature affects PV Power and Voc
ASHRAE data is referenced in the NEC as a
reliable source for historical temperature data
Temperature on the roof determines conductor
ampacity, use the Code
Temperature under the PV module is not as
hot as you might think
Conclusions

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Questions

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Experience Enphase