PERFORMANCE COMPARISON OF A BIPV ROOFING TILE 

SYSTEM IN TWO MOUNTING CONFIGURATIONS

Matthew Muller, Jose Rodriguez, Bill Marion

National Renewable Energy Laboratory • Golden, CO 80401

OBJECTIVES

Acquire data for typical hot months

SYSTEM DESIGN

 17 Polycrystalline Silicon PV roofing tiles (34 W each ) wired in series per installation method.

 Direct-mount and Counter-batten strings are wired for individual voltage measurements.

DAS

5 second sampling

Counter-Batten Mounted Tiles

Provide Air Flow

Warm Air Exits Ridge Vent Tape

Acquire data for typical hot months

in Golden, Colorado

Examine the thermal and power 

characteristics of a BIPV roofing 

system using two installation 

 The complete system is grid-tied and peak power tracked as a single string of 34 modules held at the same current.

South facing roof with tiles tilted at 15 degrees.

 Both systems are mounted over an existing asphalt shingle roof

5 second sampling

15 minute averaging

DC current entire system string

DC voltage per installation method

AC current

AC voltage

Provide Air Flow

Direct-mount 

til PROHIBIT

techniques, counter-batten and 

direct-mount.

Compare thermal characteristics of 

the BIPV installation against a 

similar free-standing, rack-mounted 

2 module temperatures per 

installation method

Attic temperature

Ambient temperature

Wind speed

Plane of Array Irradiance (POA)

PERFORMANCE COMPARISON

Side by Side Test-Bed Cool Air enters at eave

tiles PROHIBIT

eave to ridge 

air flow

module

CONCLUSIONS

Table 1

July-August data averaged for given irradiance ranges 

> 100 W/m2 > 900 W/m2

T_ambient ( ̊C) 27.5 28.6

POA (W/m2) 577.7 996.8

Wind (m/s) 2.07 2.49

T_pv_battens ( ̊C) 44.0 59.0

T pv direct ( ̊C) 48.9 67.4

Table 2 Irradiance-weighted temperatures

August July12-Aug31

Tweighted (counter-batten) 48.16  ̊C 49.34  ̊C

Tweighted (direct-mount) 53.9 ̊C 55.37  ̊C

Trise_coeff (PERT rack) 21.3 ̊C/kW/m2

Trise_coeff (counter-batten) 28.7 ̊C/kW/m2 27.7 ̊C/kW/m2

Trise_coeff (direct-mount) 37.1 ̊C/kW/m2 36.3 ̊C/kW/m2

In early morning and late evening the two systems operated at 

near equal temperatures.

 At peak irradiances and elevated attic temperatures the counterbatten system operated ~10  ̊C cooler.

The counter-batten system had a temperature rise coefficient that 

was 7.4  ̊C/kW/m2 higher than a similar free-standing, rack-mounted 

module. _p _ ( )

V_mp_battens (V) 72.4 66.6

V_mp_direct (V) 70.7 63.5

DC_Watts_batten (W) 288.9 468.5

DC_Watts_direct (W) 279.5 446.7

 



   E

TT

coeffrise

ambpv T _

T where E POA  pv ET 10

20

30

40

50

60

70

80

90

100

Aug 28th data POA/10 

(W/m2)

Tpv(C) directmount

Tpv (C) 

counter-batten

T attic (C)

Tambient (C)

The direct-mount system had a temperature rise coefficient that 

was 15.8  ̊C/kW/m2 higher than a similar free-standing, rackmounted module..

Temperature rise coefficients were 5-6  ̊C/kW/m2 lower than 

expected from the PVFORM model. (Further research is needed to 

explain this difference)

For the entire data set the counter-batten system produced 3.4% 

more DC power than the direct-mount system.

NREL is a national laboratory of the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC 

The information contained in this poster is subject to a government license.

2009 34th IEEE Photovoltaic Specialists Conference • Philadelphia, PA • June 7-12, 2009 • NREL/PO-520-46073

Acknowledgements Appreciation is extended to Open Energy Corporation (renamed Applied Solar) and Eagle Roofing for supplying materials and expertise for completing this project. 

This work was supported by the U.S. Department of Energy under Contract No. DOE-AC36-08GO28308 with the National Renewable Energy Laboratory.

T where E POA

E weighted p   

 0

10

300 400 500 600 700 800 900 1000 1100 Minutes from midnight

For irradiances above 900 W/m2 the counter-batten system 

produced 4.9% more DC power than the direct-mount system