National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

Accelerating PV Cost 

Effectiveness Through Systems 

Design, Engineering, and Quality 

Assurance 

Phase I Annual Technical Report 

4 November 2004 — 3 November 2005 

J. Botkin 

PowerLight Corporation 

Berkeley, California

Subcontract Report 

NREL/SR-520-40335 

July 2006 
Accelerating PV Cost 

Effectiveness Through Systems 

Design, Engineering, and Quality 

Assurance 

Phase I Annual Technical Report 

4 November 2004 — 3 November 2005 

J. Botkin 

PowerLight Corporation 

Berkeley, California

NREL Technical Monitor: R.L. Mitchell 

Prepared under Subcontract No. ZAX-5-33628-03 

Subcontract Report 

NREL/SR-520-40335 

July 2006 

National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
This publication was reproduced from the best available copy 

submitted by the subcontractor and received no editorial review at NREL.

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Table of Contents 

Abstract ............................................................................................................. vi

Executive Summary............................................................................................ vii

1 Introduction...........................................................................................1

1.1 Objective........................................................................................................1

1.2 Background....................................................................................................1

2 Results & Recommendations................................................................3

2.1 Task 1: Design & Performance Reliability Improvements..............................3

2.1.1 Site Audit Tool.............................................................................................3

2.1.2 Monitoring & Diagnostics ............................................................................6

2.2 Task 2: High Reliability Cost Reductions........................................................9

2.2.1 PowerLight Fixed Tilt Roof System – RFT10...............................................9

2.2.2 Tall Buildings and Mechanically Attached Roof Membranes .....................20

2.2.3 Alternative PV Backing Material ................................................................23

2.2.4 PowerGuard Cost Reduction.....................................................................23

2.3 Task 3: Reliability Evaluation .......................................................................24

2.3.1 PowerGuard System Testing ....................................................................24

2.3.2 PowerLight Metal Roof System .................................................................37

2.3.3 PowerLight Fixed Tilt Roof System ...........................................................40

2.3.4 ICC Certification........................................................................................46

2.4 Task 4: Quality System Improvements.........................................................47

2.4.1 Supply Chain Management Procedures....................................................48

2.4.2 Supply Chain Quality Standard .................................................................49

2.5 Task 5: Manufacturing Improvements ..........................................................50

2.5.1 Manufacturing Yield Improvement.............................................................50

2.5.2 Optimization of Inventory Levels ...............................................................55

2.5.3 Labor Reduction........................................................................................55

2.6 Task 6: Environment, Safety & Health..........................................................61

2.6.1 Kaizen Events...........................................................................................61

2.6.2 Waste Stream Reduction ..........................................................................64

2.7 Task 7: Commercial Demonstration .............................................................68

2.7.1 System Performance.................................................................................69

2.7.2 Cost Reduction .........................................................................................73

3 Acknowledgements.............................................................................77

 iii
List of Figures 

Figure 1: PowerGuard tiles showing interlocking tongue and groove profile..................1

Figure 2: Building cross-section showing PowerGuard System Components................2

Figure 3: RMR System..................................................................................................2

Figure 4: RFT10 Array ..................................................................................................2

Figure 5: Example of rooftop dimensioning process using laser tool.............................4

Figure 6: Basic flow-chart for processing audit data in CAD tool ...................................5

Figure 7: Xantrex S-Series inverter installation with PowerLight DAS ...........................7

Figure 8: Campbell CR1000 Data Logger .....................................................................8

Figure 9: Comparison of site performance index using a reference cell and 

pyranometer...................................................................................................9

Figure 10: Deflector designed to hold pavers................................................................11

Figure 11: Rendering of array of foamless tiles.............................................................12

Figure 12: Detail of array showing northeast corner......................................................12

Figure 13: Foamless Product........................................................................................13

Figure 14: Foamless Product - with west wind deflector installed..................................13

Figure 15: Foamless Product – showing north and west wind deflectors.......................14

Figure 16: Wire rope connecting supports.....................................................................15

Figure 17: Ball on wire rope engaging keyhole slot in south end of support ..................16

Figure 18: Wire rope and keyhole slot in north end of support ......................................16

Figure 19: Attachment points for spreader bar on southern support..............................17

Figure 20: Attachment of spreader bar to northern support...........................................18

Figure 21: Spreader bar spanning four supports...........................................................18

Figure 22: Prototype parts with securement features ....................................................19

Figure 23: Southern support with keyhole slot and spreader bar attachment points......19

Figure 24: Two methods of measuring the tensile bond strength of the mortar to the 

XPS. ............................................................................................................30

Figure 25: Shear test on XPS spacer bonded to mortar................................................30

Figure 26: Impact test on mortar. ..................................................................................31

Figure 27: Strength of groove test.................................................................................32

Figure 28: Compressive strength test. ..........................................................................32

Figure 29: Tile uplift test................................................................................................33

Figure 30: Tensile test of PowerGuard tile made with continuous process....................36

Figure 31: Examples of external flange frames .............................................................37

Figure 32: Examples of internal flange frames ..............................................................37

Figure 33: S5 clamp and PV mounting clip to secure two PV modules. ........................38

Figure 34 Ground testing of mounting clip and frames.................................................38

Figure 35: Mounting clip uplift test.................................................................................39

Figure 36: Lateral load test on RMR mounting clip........................................................39 

Figure 37: Wind tunnel model for an RFT10 array installed on the edge of a building...41

Figure 38: Lateral load test on RFT10 assembly. A compressive load is applied to 

the north side of the tile................................................................................42

Figure 39: Lateral load test on an RFT10 assembly. A tensile load is applied to the 

east side of the assembly.............................................................................42

Figure 40: Uplift test on an array of RFT10 tiles. A vertical force is applied to the 

center tile. ....................................................................................................43

Figure 41: Loading test on a PV module supported with RFT10 mounting clips............43

Figure 42: Grounding test on an RFT10 assembly........................................................44

Figure 43: Friction test on an RFT10 assembly.............................................................44

Figure 44: Wind design chart for RFT10 arrays in the middle of the roof in 

Exposure C..................................................................................................45

 iv
Figure 45: Typical plot from coating monitoring station .................................................52

Figure 46: New pumping station for mixed liquids.........................................................53

Figure 47: Control panel for pumping station ................................................................53

Figure 48: PV prep line .................................................................................................54

Figure 49: PV prep line .................................................................................................54

Figure 50: Existing Process ..........................................................................................60

Figure 51: New Equipment Layout................................................................................60

Figure 52. Layout of the Surface Treatment Section of the Equipment .........................61

Figure 53: Tile Assembly Layout after Kaizen Event .....................................................64

Figure 54: Test of corner supports in double stacked pallets.........................................67

Figure 55: Demonstration array with reduced coating thickness during installation.......74

Figure 56: PowerGuard tile with reduced coating thickness (on right)...........................74

Figure 57: Wiring gutter during installation (designed changed after this installation)....75

Figure 58: RFT10 system during installation .................................................................76

Figure 59: Completed array from Southeast .................................................................76

Figure 60: Completed array from East ..........................................................................77

List of Tables 

Table 1. PowerGuard Product Improvements ...............................................................24

Table 2: Mortar testing results ......................................................................................33

Table 3: Summary of New Design ................................................................................59

Table 4: Cost analysis of different packaging strategies for 750-kW installations..........65

Table 5: Cost analysis of different packaging strategies for 250-kW installations..........66

Table 6: Existing Systems for Comparing System Performance ...................................70

Table 7: Test Systems for Comparing System Performance.........................................71

Table 8: Results of system performance monitoring .....................................................71

Table 9: Sites for Cost Reduction Assessment .............................................................73

 v
Abstract 

During Phase I of this PV Manufacturing R&D subcontract, PowerLight®1 Corporation 

has made significant progress toward the reduction of installed costs for commercialscale, rooftop PV systems. PowerLight has worked to reduce operating costs by 

improving long-term reliability and performance through the development of more 

sophisticated tools used in system design and monitoring. Additionally, PowerLight has 

implemented design improvements with the goal of reducing cost while maintaining 

and/or improving product quality. As part of this effort, PowerLight also modified 

manufacturing and shipping processes to accommodate these design changes, 

streamline material flow, reduce cost, and decrease waste streams. During Phase II of 

this project, PowerLight plans to continue this work with the goal of reducing system cost 

and improving system performance. 

 

1

 “PowerLight” and “PowerGuard” are registered trademarks of the PowerLight Corporation. 

Reference in Subcontract Deliverables to any specific commercial product, process, or service by 

trade name, trademark, logo, manufacturer, or otherwise, does not constitute or imply its 

endorsement, recommendation, or favoring by the United States Government, the National 

Renewable Energy Laboratory, or the Midwest Research Institute. The views and opinions of any 

author or authors expressed in any Deliverable report or referenced in any Deliverable do not 

necessarily state or reflect those of the United States Government, the National Renewable 

Energy Laboratory, or the Midwest Research Institute. 

 vi
Executive Summary 

PowerLight ® Corporation provides the products and services required to install largescale solar electric generation at any suitable site. PowerLight designs and installs 

complete systems, ensuring reliability, efficiency, and cost-effectiveness. 

In 2004, PowerLight initiated the PV Manufacturing R&D subcontract, “Accelerating PV 

Cost Effectiveness though Systems Design, Engineering, and Quality Assurance.” This 

work effort focuses on cost reductions for PowerLight’s commercial rooftop product 

offerings: PowerGuard® Roof System; PowerLight Fixed Tilt Roof System (RFT10), and 

PowerLight Metal Roof System (RMR). 

As part of this effort, PowerLight focused on developing improved tools for system 

design and monitoring in order to optimize system performance and minimize downtime 

under Task 1. PowerLight selected a laser-based site audit tool to facilitate the design 

process. In addition, PowerLight tested alternative hardware for data acquisition and 

reference sensors. Coupled with the more sophisticated alert algorithms under 

development, these devices provide PowerLight with better monitoring and diagnostic 

tools that will improve system performance and availability. Overall, these 

improvements will lead to better layout design, fewer design-related delays during 

installation, and maximized system output. 

Prior to the start of this subcontract, PowerLight had completed design work on the first 

version of a mounting system with sloped PV, RFT10. Like PowerGuard tiles, this 

system was design for installation on flat roofs without penetrations, but it does not have 

the foam insulation of the PowerGuard tiles. Under Task 2, PowerLight prototyped a 

modified design based on updated wind load requirements, resulting in a more versatile 

product for a wider range of applications. PowerLight advanced this new design to full 

commercial deployment. Additionally, PowerLight developed design guidelines for 

installations on tall buildings and initiated efforts to develop guidelines for 

accommodating mechanically attached membranes. PowerLight also realized significant 

cost reductions by reducing raw material use in the production of PowerGuard tiles. 

Other work on PowerGuard enabled PowerLight to adjust to changes in PV backing 

materials. 

PowerLight evaluated product improvements through comprehensive testing in order to 

verify that product quality is maintained throughout the design process. This reliability 

evaluation included wind studies; structural evaluation; seismic modeling; thermal 

monitoring; and electrical testing. Additional testing will be carried out in Phase II of this 

project. In addition to testing, PowerLight initiated pursuit of ICC certification; this effort 

has been suspended due to the limited potential benefits to the inspection process. 

Under Task 4, PowerLight worked with suppliers to establish supplier quality standards 

with the goal of achieving a 99% first time acceptance of select products. By ensuring 

that suppliers have adequate quality systems in place, PowerLight avoids costly field 

repairs and delays. This also ensures that PowerLight’s systems perform at their 

maximum output, satisfying customers’ expectations 

By continuing to implement lean-manufacturing techniques, PowerLight achieved a 

99.96% yield for PowerGuard tile production, outstripping the Phase I goal of 99.7%. 

This yield is the result of improvements in manufacturing equipment and inputs from 

factory workers. 

 vii
To address ES&H concerns, PowerLight evaluated means of decreasing site waste by 

20%. Initially, PowerLight planned to develop reusable containers for shipment. 

However, due to prohibitive cost and space requirements of this option, PowerLight 

instead modified shipping practices and succeeded in increasing packing density, 

thereby reducing shipping costs by 20%. 

The design improvements implemented during Phase I were evaluated through 

commercial demonstration projects. PowerLight reduced backerboard cost for a 

PowerGuard tile by 17.8% through a reduction in raw materials and labor, as well as 

optimized shipping density. Following implementation of improved monitoring 

capabilities, PowerLight found test systems performing at higher operating levels with 

increased availability, as compared to control sites in similar locations. 

 viii
1 Introduction 

1.1 Objective 

The overall objective of this subcontract is the reduction of installed system costs for PV 

systems utilizing PowerLight Corporation’s rooftop products. 

1.2 Background 

PowerLight manufactures its flagship product, the PowerGuard tile, in a facility in 

Berkeley, California. PowerGuard building-integrated photovoltaic roofing tiles generate 

electricity from solar energy. A PowerGuard tile consists of a flat plate photovoltaic (PV) 

laminate mounted onto a flat, rigid, extruded polystyrene (XPS) board. The XPS board 

is covered with a cementitious coating. Two edges of the XPS board are routed into a 

tongue profile, while the other two edges are given a groove profile. This design allows 

PowerGuard tiles to be assembled adjacent to each other in an interlocking fashion, as 

shown in Figure 1 below. 

Figure 1: PowerGuard tiles showing interlocking tongue and groove profile. 

PowerGuard tiles provide benefits in addition to the electricity produced in the form of 

added insulation and protection of the roof membrane from ultraviolet light. PowerGuard 

systems can reduce the heat transfer into a building and reduce operating costs. 

 1
Figure 2: Building cross-section showing PowerGuard System Components 

Adjacent tiles are tied together electrically through connectors supplied on each PV 

module, thus creating an electrical string of PV modules. One or more strings are then 

electrically connected in parallel at a remote location creating a solar electric array. The 

resulting DC current from the array is passed through a DC/AC inverter and isolation 

transformer before being tied into the building’s electric distribution panel. Figure 2 

depicts the system components for a PowerGuard array. 

PowerLight also manufactures a PV mounting system for metal roofs called PowerLight 

Metal Roof System (RMR), using custom clips, shown in Figure 3, and a 10-degree 

sloped PV mounting system for flat roofs, RFT10, shown in Figure 4. 

PowerLight is in the process of implementing design improvements to all three products 

to expand market applications, reduce cost, and improve quality and reliability. This 

report outlines the activities completed in Phase I of this subcontract. 

Figure 3: RMR System Figure 4: RFT10 Array 

 2
2 Results & Recommendations 

2.1 Task 1: Design & Performance Reliability Improvements 

The objective of this task is to improve the tools used to design and monitor PV arrays in 

order to optimize performance and minimize downtime. As part of this effort, PowerLight 

initiated development of an array-design tool with improved quality of data transfer from 

the roof to the system designer. In addition, PowerLight began development of an 

improved monitoring and diagnostic system to optimize system performance. 

2.1.1 Site Audit Tool 

Background 

An accurate site audit is an important step in the design of a PV system. If the site audit 

does not capture all potential obstacles or shading issues, installation costs can 

increase, and system performance can suffer. The current methods used to measure 

rooftops involve the use of distance measuring wheels and tape measures, generally 

measuring from the closest edge of the roof to the point or object being measured. This 

method results in points being defined from numerous reference points, and, 

occasionally, disorganized information and missing critical dimensions. 

PowerLight is developing an improved procedure and improved tools for measuring the 

available space on flat rooftops for installation of solar panel arrays. These will provide 

increased accuracy of distances measured, as well as a reduction in errors caused by 

omission of critical dimensions. 

Approach 

PowerLight reviewed available tools that would help an auditor create an accurate and 

complete site plan without undue expense. Two tools were evaluated. A laser-based 

tool allows one person to complete a site audit using a stationary target. The other tool 

is a global positioning satellite (GPS) auditing system made by Tectonics Corporation. 

PowerLight performed a cost-benefit analysis of the two tools and conducted a field trial 

with the laser tool. The field trial consisted of verifying distance measurements and 

developing a procedure to yield the most accurate site audit from a minimum number of 

measurements. PowerLight also designed a prototype stationary target that enables the 

audit to be performed by a single operator. 

Results 

PowerLight has concluded that the laser approach is preferable to the GPS system 

primarily because it guarantees a consistent level of accuracy from site to site. The 

concern with GPS-based systems is that the accuracy and availability of data will differ 

from site to site. The laser tool approach lends itself to a more organized and more 

easily tracked set of dimensions. Missing dimensions will be caught quickly as the 

operator moves through the process of identifying all the features of the rooftop. It also 

reduces the overall number of measurements necessary, as each point is defined by 

only two dimensions. 

Figure 5 illustrates how the laser-tool is used on a simple rooftop example. The 

stationary target is placed at a convenient central location on the roof. Six 

 3
measurements are made from key locations determined by the roof’s shape and 

perimeter lines. These locations are identified by the numbered circles in the figure. 

2

5

6

5

5

3

STATIONARY TARGET

LASER TOOL

LASER BEAM

ROOF EDGE

LASER BEAM

3

5

6

6

2

1

4

4

2

4

3

5

1

1

4

6

SAMPLE ROOFTOP

SIX MEASUREMENTS PROVIDE ALL X AND Y COORDINATES NECESSARY TO 

DEFINE THE ENTIRE OUTLINE OF THIS ROOF.

INDIVIDUAL MEASUREMENT I.D. NUMBER, STORED IN LASER TOOL 

MEMORY

TWO MEASUREMENT I.D. NUMBERS REQUIRED TO DEFINE EACH 

CORNER OF ROOF EDGE, (THESE NUMBERS BECOME “USER INPUT” 

FOR VBA SOFTWARE TO DEFINE X AND Y COORDINATES IN CAD)

Figure 5: Example of rooftop dimensioning process using laser tool 

 4
This “ordinate” style of dimensioning lends itself to transfer from the rooftop into a 

computer aided design (CAD) system. The laser tool can store the distances measured, 

which can then be downloaded to an ASCII text file on the CAD station. 

PowerLight is developing Visual Basic (VBA) software to read the distances from this 

text file and draw lines from point to point to create an accurate layout of the rooftop. 

The software flow chart is illustrated in Figure 6. The VBA software queries the CAD 

operator to input two ID numbers to define the first point of the drawing. These ID 

numbers are then found in the text file, and the corresponding distance is passed to the 

VBA software variables to be used as X and Y coordinates of the point in CAD. 

LASER TOOL

TEXT FILE USER INPUT

MATCH USER INPUT TO I.D.

GET NEXT USER INPUT

VARIABLES

I.D DISTANCE

1 15.0

2 50.0

3 25.0

4 25.0

5 20.0

6 40.0

I.D DISTANCE

1 15.0

2 50.0

3 25.0

4 25.0

5 20.0

6 40.0

3,2

3,4

6,4

6,1

5,1

5,2

Start X

Start Y

Next X

Next Y

Draw line from 

Start Point X,Y

Draw line to 

Next Point X,Y

Figure 6: Basic flow-chart for processing audit data in CAD tool 

The VBA software then queries the CAD Operator for the next two ID numbers, 

redefining the variables and drawing the line to the new X and Y coordinates in CAD. 

This process is repeated until the CAD Operator selects the “end” button on the query 

dialog box. 

Conclusion 

PowerLight has made significant progress in the implementation of new array design 

tools. These improvements will lead to greatly enhanced accuracy of site audits, 

resulting in improved system design and efficiency. Overall, the direct labor associated 

with system design will be reduced, and the risk of costly delays for installation projects 

will be greatly diminished. 

 5
2.1.2 Monitoring & Diagnostics 

Background 

PowerLight actively monitors over 40 MW of installed PV systems. Monitoring includes 

daily alerts on system availability and performance, as well as weekly trend analyses. 

With such a large number of systems, implementing a sophisticated diagnostic system 

results in streamlined customer support and optimized system performance. 

Approach 

PowerLight is pursuing a two-pronged approach to meet the objective of improved 

system availability and performance through more sophisticated diagnostic capabilities. 

As part of this effort, we procured, tested, and fielded advanced monitoring system 

hardware with the goal of improving access to system performance information – both in 

terms of the level of information available and the timeliness of its reporting to customer 

service staff. Concurrently, we worked to improve the analytical system used to 

evaluate system performance data and send alerts and alarms to customer service staff. 

This analytical approach will result in faster recognition of more subtle performance 

problems and reduce instances of nuisance alerts and alarms. The combination of 

advanced hardware and improved analytical tools will lead to an improvement in overall 

system reliability and performance. 

Advanced hardware monitoring systems reviewed for this project include stand-alone 

data acquisition systems (DAS) and data collection modules embedded in system 

inverter (power conditioning) units. PowerLight tested two types of hardware monitoring 

systems, installed in five test systems. The performance of these test systems was 

compared to that of a group of control systems. The various test and control sites are 

identified in Table 6in section 2.7.1. 

As a first step toward improved monitoring capabilities, PowerLight looked for alternative 

data loggers with better real-time data and alarm functionality than those used currently. 

PowerLight focused on data loggers that have embedded web servers and firewalls and 

that can post data to the web in XML format. These features are desirable for many 

corporate clients concerned with network security issues. 

PowerLight purchased and evaluated four new data loggers: Campbell CR 1000, Omni 

DataWeb 4008, Omega Omp-MODL, and Meteocontrol Weblog device. Each of the 

data loggers have real time alarm capabilities and advanced network security options. 

PowerLight also evaluated the use of the embedded data monitoring and alarming 

capabilities of the Xantrex S series inverters as one advanced hardware monitoring 

option. In October, PowerLight completed the commissioning of the communications 

module of the 100 kW S-Series inverter located at Site 24. We began monitoring the site 

with this communications module once the site host completed the installation of the 

necessary local network cables and security access. 

The real-time Xantrex Graphical User Interface (GUI) will improve our ability to monitor 

the site and increase system availability in two ways. Information will be available in real 

time, giving instant notification of inverter status, including specific fault information when 

the inverter is in a faulted condition. In addition, the GUI will enable some remote 

inverter control, allowing PowerLight staff to reset many faults and restart the inverter 

from our offices in Berkeley, eliminating the lag time between fault notification and onsite reset. Figure 7 shows the installed inverter at Site 24. The communications module 

of the inverter is mounted on the left hand side of the inverter (not visible in photo). 

 6
PowerLight’s standard data acquisition system is in the middle background of the photo 

(circled) behind the glass jar-style energy meter. 

Figure 7: Xantrex S-Series inverter installation with PowerLight DAS 

The second approach to improving system performance and reliability is through 

improved analysis of the performance data collected from each system. Currently, 

PowerLight receives performance index alerts for systems when the performance index 

(PI) drops below a user-defined threshold for the site. Performance index is determined 

by dividing the actual energy produced by a site during the day by the amount of 

expected energy for the day. Expected energy for the day is calculated using basic 

system parameters and meteorological data recorded at the site, including irradiance 

from a LICOR pyranometer, ambient temperature, and wind speed. While adequate, 

PowerLight worked to improve the following aspects of this monitoring approach: 

1) Current performance index alert thresholds are set to ensure that we are aware 

of performance problems while minimizing the number of nuisance alarms from 

expected influences like soiling. With a more sophisticated alert algorithm, 

PowerLight could be more sensitive to performance problems that occur between 

the threshold and the 100% performance index level. Currently, we do not 

receive alerts for potential performance problems that do not cause the PI to dip 

below the user-defined threshold. 

2) Calculating expected energy for the day using pyranometer data sometimes 

results in inaccurate PI values because the spectral response of the pyranometer 

is different from that of the PV array. This effect is particularly pronounced on 

cloudy days and in winter. 

To address these limitations, PowerLight conducted two studies. In the first study, 

PowerLight devised and tested several sophisticated alert algorithms for performance 

index. We have developed and tested six different algorithms using between five and 

seven months of recorded data for nine different systems. To date, PowerLight has 

developed algorithms to compare sites in similar regions and to evaluate trends in long-

 7
term system performance. These algorithms provide better reference points for 

expected system performance, resulting in fewer nuance alarms and more alarms for 

non-outage-related problems. Overall, these algorithms are expected yield improved 

performance alerting once implemented. PowerLight will continue to develop and 

validate these and other algorithms in the second phase of the project. 

The second study involved the difference between PIs as calculated using different 

irradiance sensors, namely pyranometers and reference cells. As mentioned above, the 

spectral response of the pyranometers is different from that of a reference cell, with the 

response of the reference cell being closer to that of the array. Because of this, PIs 

calculated with reference cell data should be steadier and produce fewer nuisance 

alarms and inaccurate PI values than PIs calculated using pyranometers. 

Results 

PowerLight has reached the following conclusions based on the testing of the various 

data loggers: 

 The CR1000 offered the most functionality and ease of use. 

 The Omni also offered the same functionality as Campbell's data logger and was 

relatively easy to use. 

 The Omega was the most difficult to set-up, and tech support has so far been 

poor. The system also did not integrate well with some of the weather sensors 

currently used by PowerLight. 

 The Weblog device, produced by a German company called Meteocontrol, has 

proven to be effective in European systems and is of interest for U.S. 

applications. However, there are some preliminary problems that prevent its 

commercial use at the moment. For example, the modem is not compatible with 

U.S. telecommunications, and error codes are in German. 

Based on these conclusions, PowerLight installed a Campbell CR1000 logger, shown in 

Figure 8, at a major customer site in Oakland for further evaluation. The installation 

occurred without any problems and to date the unit is performing very well. 

Figure 8: Campbell CR1000 Data Logger

To determine whether replacing pyranometers with reference cells will improve PI 

evaluation, we monitored five sites with both types of sensors at each location. The 

data from the reference cell produced a steadier calculation of PI for all sites. Figure 9 

shows the comparison between PI as calculated using pyranometer data and PI as 

calculated using reference cell data for a sample site. The circled regions highlight the 

steadier nature of the PI calculated with reference cell irradiance data. 

 8
Sample System PI as Calculated from Reference Cell and Pyranometer Data Charted Against 

Energy Produced and Insolation Measured by these Instruments

0

2

4

6

8

10

12

14

16

18

2/24/05 3/1/05 3/6/05 3/11/05 3/16/05 3/21/05 3/26/05 3/31/05 4/5/05 4/10/05 4/15/05 4/20/05 4/25/05 4/30/05 5/5/05 5/10/05

Daily Insolation (kWh/m2) and Energy (MWh)

0

20

40

60

80

100

120

140

160

Performance Index %

pyranometer_tracked referenceCell_tracked totalEnergy (MWh) currentPI newPI

Figure 9: Comparison of site performance index using a reference cell and pyranometer. 

In addition, PowerLight tested the six performance alert algorithms from the first study 

on the two sets of performance indices (pyranometer-based and reference cell-based) 

and concluded that PIs calculated with reference cells result in 37% fewer nuisance 

alarms. Further work on this study will include the investigation of PIs for a larger pool of 

systems. 

Conclusion 

To optimize system performance, PowerLight is improving the tools used to design and 

monitor PV arrays. As part of this effort, PowerLight is investigating the use of alternative 

hardware for data acquisition and reference sensors. In field tests to date, the CR1000 

data logger has performed reliably, following a straightforward installation. The use of a 

reference cell, in place of a pyranometer, provides in more consistent performance 

tracking and is estimated to result in 37% fewer nuisance alarms. PowerLight has also 

made significant progress in the development of sophisticated performance diagnostics. 

Continued validation work on these algorithms is required prior to implementation. 

2.2 Task 2: High Reliability Cost Reductions 

The objective of this task is to lower balance-of-system costs by making improvements 

to the design of PowerLight systems in an effort to broaden the market for its rooftop 

products. 

2.2.1 PowerLight Fixed Tilt Roof System – RFT10 

As part of this effort, PowerLight is developing a foamless tile design targeted for 

customers without added-insulation needs. The new product is called RFT10. It 

features a 10° sloped PV module and an aluminum and stainless steel support structure. 

 9
Prototype Design 

Background 

The thermal insulation benefit of PowerGuard tiles is valued by many customers, but not 

by all. Customers who want to install a PV system on the roof of a building in which 

temperature is not controlled may not place a high value on increasing the insulation 

value of the roof. For those customers, a lower cost option that does not include thermal 

insulation would be attractive. For this reason, PowerLight has developed an alternate 

tile design without the XPS insulation. 

Approach 

At the start of this subcontract, PowerLight had completed design work on the first 

version of the foamless tile. A small system was installed in December 2004 based on 

this initial design. Since the start of this subcontract, the foamless design has been 

modified to accommodate a larger PV module with higher output. Several features were 

redesigned based on lessons learned during this installation and also to improve 

function or reduce cost of the parts. 

Like the PowerGuard tile, the new foamless product is designed to install on a flat roof 

without penetrations through the roof membrane. The foamless product was designed 

with the PV module at a fixed slope of 10°. In order to ensure the safety of this design, it 

was necessary to understand the behavior of the tiles in the range of wind conditions to 

which installed arrays would be subjected. An extensive series of wind tests were 

initiated to quantify the wind performance of the product. These tests were a 

combination of computational fluid dynamics (CFD) modeling and wind tunnel testing. 

CFD modeling is a useful tool for comparing the performance of various designs without 

the cost of testing in a wind tunnel. Once a design has been optimized using CFD, it can 

be tested in the wind tunnel to verify the model predictions. 

The wind performance of the foamless product is related to the specific weight of the 

array (the weight per unit area). One of the results of the wind testing was the 

calculation of the specific weight required to withstand various wind conditions. For 

areas that do not experience high velocity winds, a low array weight can be used. In 

higher wind zones, the array weight must be increased to ensure that the array stays in 

place. Each module has a wind deflector on the north side. As part of this effort, the 

design of the wind deflector was modified so that it could hold concrete pavers. The 

number of pavers inserted into each deflector is determined by the specific weight 

required. 

The improvements described above are all incorporated into the new production version 

of the foamless product. The installation of a large-scale system was initiated in late 

July and is expected to be completed soon. This installation will help to verify the 

efficacy of the improvements and provide more information on the ease of installation of 

the design. 

Results 

The finished design of the foamless product is shown in Figure 10 through Figure 12. 

Figure 10 shows the wind deflector, which now can accommodate concrete pavers to 

adjust the specific weight of the array. 

 10
Figure 10: Deflector designed to hold pavers 

Figure 11 shows a rendering of an array of foamless tiles. Wind deflectors are installed 

on the east and west end of each row. The northwest corner of the array is shown in 

Figure 12 with the wind deflectors removed from one tile. 

 11
Figure 11: Rendering of array of foamless tiles 

Figure 12: Detail of array showing northeast corner 

 12
Figure 13 through Figure 15 show photographs of the current design of the foamless 

product. 

Figure 13: Foamless Product 

Figure 14: Foamless Product - with west wind deflector installed 

 13
Figure 15: Foamless Product – showing north and west wind deflectors 

Array Securement Design 

Background 

For most applications, RFT10 can be installed without being fastened to the building 

roof. In sites that have severe wind loads, however, positive securement of the array 

may be required. In most cases, the weight of the system is adjusted with concrete 

pavers to meet the wind loads of each building site. If the wind loads are high enough 

that the minimum array weight required by the wind loads exceeds the number of pavers 

that can be accommodated, then the array requires positive securement to the roof. 

When positive securement is required, the array must be able to transmit lateral load 

across the array to the anchor points. Additionally, some method of attaching the array 

to the anchor points must be provided. In order to incorporate these features into the 

design of the RFT10 product, PowerLight calculated the magnitude of the lateral loads 

under varying wind conditions. Using the results of wind tunnel tests and computational 

fluid dynamic modeling carried out under Task 3 of this project, PowerLight analyzed the 

loads to which the array is subjected and created a design for the securement. 

Approach 

Once the basic design was completed, as discussed in the previous section, PowerLight 

began working on additional features that would allow the system to be installed in sites 

at which the array needed to be positively secured. 

Wind tunnel testing was carried out under Task 3 of this project to determine the 

magnitude of the lateral loads that the wind applied to the array. With an array in the 

middle zone of a roof in the wind tunnel, the failure velocity was measured with gradually 

increasing array weights. The friction coefficient between the array and the roof was 

measured, and the results were used to determine how much force was applied laterally 

by the wind. This was extrapolated to the point at which the array was prevented from 

moving by securing it to the roof. This load was used in creating the design for the 

additional features that allow the array to be secured to the roof. 

 14
Once the loads were understood, the first step was to create a design that allowed 

lateral transfer of loads from one module to another. The basic design consists of a PV 

module, supports, and a wind deflector, as shown in Figure 13. These form the top two 

legs of a triangle. The roof forms the bottom leg of the triangle. However, when a large 

load is applied laterally, the supports slide on the roof, as the triangle becomes stretched 

across the roof. To prevent this, PowerLight added a wire rope that connects each 

support to the next one, preventing them from sliding apart and creating a strong 

triangular structure. 

Once the array was capable of transferring lateral loads, PowerLight developed a design 

for attachment points to connect the array to an anchor on the roof. The loads on this 

anchor depend on the number of rows within the array. PowerLight created design 

guidelines to calculate the load that must be supported by the anchors. 

Results 

The changes to the RFT10 design are shown below. A wire rope was incorporated into 

the design to allow the array to transfer lateral loads, as discussed above. The wire rope 

is shown in Figure 16. At each end of the wire rope, a swaged-on ball engages a 

keyhole slot that is stamped into each end of each support piece. Figure 17 and Figure 

18 show the engagement of the ball with the keyhole slot in the supports. 

Figure 16: Wire rope connecting supports 

 15
Figure 17: Ball on wire rope engaging keyhole slot in south end of support 

Figure 18: Wire rope and keyhole slot in north end of support 

PowerLight added features to the support pieces that provide attachment points to 

anchors on the roof. At the southern edge of the array, these features consist of 

 16
extended tabs and square holes that support an aluminum spreader bar. The square 

holes fit carriage bolts that connect the supports to the spreader bar. The spreader bar 

allows up to four supports to be connected to one anchor point. The attachment of the 

spreader bar to the southern supports is shown in Figure 19. At the northern edge of the 

array, similar square holes were added to the support, but in this case, the spreader bar 

could be installed beneath the wind deflectors, as shown in Figure 20. Figure 21 shows 

how the spreader bar can span up to four supports. 

Once the array is assembled on the roof and the anchor points are located, one or more 

holes are drilled in the spreader bar to attach it to the anchor(s). 

The design improvements shown in these pictures have been incorporated into the 

production parts. Figure 22 and Figure 23 show the first prototype parts made with 

these improvements. 

Conclusion 

These improvements to RFT10 expand the range of sites where this product can be 

installed. The improved design can now be installed on most flat-roof buildings in wind 

zones up to 120 mph.2

 This is an important step in the development of this product, as 

this low-cost mounting system can now be installed at almost any potential site. 

Figure 19: Attachment points for spreader bar on southern support 

 

2

 As defined by ASCE Standard 7-05 

 17
Figure 20: Attachment of spreader bar to northern support 

Figure 21: Spreader bar spanning four supports 

 18
Figure 22: Prototype parts with securement features 

Figure 23: Southern support with keyhole slot and spreader bar attachment points 

 19
2.2.2 Tall Buildings and Mechanically Attached Roof Membranes 

Objective 

The objective of this subtask was to develop design guidelines for PowerGuard systems 

installed on tall buildings and buildings with mechanically attached roof membranes. 

Background 

PowerGuard is a ballasted, lightweight PV roofing system. Depending on the array 

geometry, a PowerGuard system may weigh 4-9 lb/ft2

. The array weight is far less than 

typical wind uplift pressures on most buildings, which can range from 20 lb/ft2

 to over 

100 lb/ft2

. PowerGuard remains stable when subjected to high wind uplift pressures due 

to the permeability of the system, which equalizes pressures on the top and bottom 

surface of the tiles. While this phenomenon is well documented in the wind and roofing 

industries, wind tunnel testing in accordance with the American Society of Civil 

Engineers (ASCE) Practice No. 67 is the only recommended approach for quantifying 

the wind performance of a permeable roofing system. 

PowerLight has conducted extensive wind tunnel testing in compliance with the ASCE 

standard. Prior testing was conducted on buildings with heights up to 50 ft. Due to 

limitations on the size of the wind tunnel selected and the ability to fabricate accurate 

scale models of PowerGuard systems, it is not possible to model wind loads on a 

PowerGuard system installed on a building taller than 55 ft. When PowerGuard systems 

were installed buildings taller than 50 ft, wind tunnel data had to be extrapolated to the 

taller building heights. While preferable to interpolate between test data points, this 

method was considered acceptable for buildings up to 80 ft in height, but undesirable 

when extrapolating to buildings that were several hundred feet in height. 

PowerGuard can be accurately modeled at a scale as low as 1:32. At this scale, a 55’ 

tall building creates the maximum allowable blockage in the wind tunnel. When the 

maximum allowable blockage is exceeded, the atmospheric boundary layer will not be 

simulated properly, which would result in an inaccurate modeling of the flow over the 

wind tunnel models. Wind tunnel experts suggested that pressure measurements be 

taken for a model of a tall building at a smaller scale. The results could then be 

compared to those for low-rise buildings for which PowerGuard failure data had been 

collected during prior tests. One could then identify the pressure conditions on rooftops 

that are likely to induce a failure in PowerGuard systems on a building of any height. 

This approach eliminated the need to include a model of a PowerGuard system on top of 

a tall building. 

Mechanically attached roof membranes also present a design challenge for ballasted PV 

roofing systems. In certain wind conditions, these membranes may billow because the 

membranes are secured only along the edges. Prior testing showed that if billowing 

occurs, the membrane may lift over 12” in height, which is substantial enough to 

dislodge a lightweight, ballasted roofing system. However, there is disagreement among 

industry experts regarding the conditions that would cause membrane billowing and the 

appropriate method for assessing the billowing potential of a given site. There is clear 

agreement that billowing potential is dependent on the following parameters: wind 

speed; wind gust duration; width of the membrane between fasteners; quality of the roof 

seal around the perimeter of the building; permeability of the building walls; geometry of 

openings in the building walls, such as windows and doors; permeability and geometry 

of the building’s HVAC system; geometry of partitions within the building; and 

permeability of the roof deck. 

 20
If all of the above parameters could be easily quantified, a test program could be carried 

out over a range of parameters and applied to specific buildings. At the beginning of this 

project, PowerLight expected to define a test program with a consultant and launch into 

the testing of the various parameters, leading to the creation of design guidelines for PV 

systems on mechanically attached membranes. The creation of the test program has 

been a much greater challenge than anticipated. Many of the parameters are 

impractical, if not impossible, to quantify on specific buildings. It is especially 

challenging to determine the permeability of the HVAC system, building walls and roof 

decks without incurring a significant expense, as well as inconveniencing the building 

occupants. It is possible that these parameters could be studied for a broad range of 

building types and then applied to specific buildings. 

Despite the above challenges, PowerLight has made some important progress on this 

task as discussed in the following sections. 

Wind Tunnel Pressure Measurements on Tall Buildings 

Pressure measurements were measured on buildings with heights of 30’, 60’, 120’, and 

240’. Parapet heights varied from 0’ to 4’. 

Mean uplift pressures on the rooftop were calculated and compared to code predictions. 

We found that the code under-predicts uplift pressures on the rooftops of buildings over 

60’. It is believed that the test results are accurate and that the code is in error. The 

testing used in the code data was done with older technology and was extrapolated from 

data measured on shorter buildings. The error in the code has apparently not resulted in 

failures in the field. Roof deck failures may have not occurred because the roof decks of 

tall buildings are designed to not only withstand wind uplift but also provide 

reinforcement to the building against wind drag and wind-induced oscillation. However, 

the error in the code could have negative consequences for roof cladding systems, such 

as PowerGuard. 

The data collected in this study was used to calculate a correction factor so that 

PowerGuard failure data collected on low-rise buildings could be extrapolated to taller 

buildings and account for the high uplift pressures on tall buildings. This correction 

factor was then used to finalize wind design guidelines for PowerGuard systems on 

buildings up to 240’ in height. 

Mechanically Attached Roof Membrane Wind Securement 

At the beginning of this task, PowerLight had the following questions with respect to 

mechanically attached roof membranes: 

1. Is it possible to inspect a building and engineering drawings of a building to 

determine if membrane billowing is a potential risk? 

2. If testing is needed to assess the potential for membrane billowing, how would the 

testing be done? 

a) What is the range of typical permeabilities of commercial walls and roof 

decks? 

b) What is the range of typical permeabilities of typical HVAC systems? 

c) Once test data is collected, how can it be applied to existing buildings? 

 21
To determine the answer to the first question, PowerLight consulted with wind and 

roofing experts. All wind and roofing experts consulted agree that with the data currently 

available, it is not possible to determine whether or not membrane billowing can occur 

through inspections. Manufacturers of mechanically attached roof membrane systems 

design the securement of these systems under the assumption that some billowing could 

occur. 

Based on this assessment, PowerLight contacted several wind testing experts, including 

three at wind tunnel facilities, to determine the best method of evaluating the billowing 

potential of commercial buildings with mechanically attached roof membranes. Most 

experts could not think of a straightforward way to investigate this problem because of 

the difficulty in modeling the movement of the roof membranes and the porosity of 

building materials. However, one test facility with strong expertise in building and roof 

aerodynamics conceived of a unique wind tunnel testing program. However, the test 

program had some gaps, as it did not clearly address items 2(a) through 2(c) above. 

It was clear that this needed to be determined before investing in the test program. 

An extensive search was conducted to quantify these parameters. Initially, we believed 

that the energy efficiency industry would be a good source of data. However, it turned 

out that most of the available data is for residential buildings only, while the commercial 

sector is the focus of this study. Finally, we identified an infiltration expert, who is 

knowledgeable in both commercial and residential buildings. This expert believes he 

could fill in the gaps in the proposed wind-testing program by accessing existing, 

unpublished infiltration data for commercial buildings, as well as conducting 

measurements on actual buildings. 

The result of this research is that a clear test program has been developed to investigate 

the billowing potential of mechanically attached roofs. The first step in this program is to 

quantify the permeabilities of walls, roofs, and HVAC systems of typical commercial 

buildings. Once significant progress has been made in this subtask, PowerLight will 

investigate the feasibility of quantifying these parameters in existing buildings. If it is 

believed that this method is feasible, the program will move into the second stage of this 

effort. 

This stage consists of wind tunnel testing on buildings with the range of permeabilities 

identified. The wind testing will identify which building features would likely induce 

membrane billowing, when subjected to various wind flows, and what sections of the roof 

would be affected. 

Conclusions 

Wind tunnel testing on tall buildings has been completed and results have been 

incorporated into PowerGuard design guidelines. 

The development of design guidelines for wind securement on mechanically attached 

roof membranes requires further research and testing. A path for a test program has 

been set and will be carried out during Phase II of this subcontract. The result of the test 

program will be design guidelines for securing ballasted PV systems when installed on 

mechanically attached roof membranes. 

 22
2.2.3 Alternative PV Backing Material 

Background 

Historically, PV vendors have used Tedlar®1, a fluoropolymer manufactured by Dupont, 

as a backing material. Recently, some vendors have been switching their backing 

material from Tedlar to PET (polyethylene terephthalate, a plastic resin and form of 

polyester). The structural integrity of the PowerGuard tile depends in part on the 

adhesive bond between the XPS standoffs and the PV backing material. Extensive 

testing was conducted on the bond between XPS and Tedlar to ensure a reliable bond 

would be maintained over the design life of the product. This testing had to be repeated 

in order to ensure an adequate bond to the PET backing material. 

Approach 

In order to accommodate this change, PowerLight had to look for different adhesives to 

use in the assembly process of PowerGuard tiles. An adhesive had been identified, and 

in November, the first full scale production occurred using this new adhesive. Despite 

good results in test conditions, initial results in the factory did not yield the required bond 

strength. A variety of tests showed that the surface energy of the PET needed to be 

increased through the application of a corona discharge treatment. Once a procedure 

was implemented to apply this treatment, the bond reached the required strength and 

production resumed. 

Results 

The initial approach to find a new adhesive did not yield acceptable results. The second 

approach, using a modified process, yielded excellent results and also provided a lowercost solution than the first approach would have. Once the details were worked out, a 

new PV preparation line was designed and implemented as part of Task 5. 

2.2.4 PowerGuard Cost Reduction 

Background 

Excluding the PV module, the mortar coating is the most expensive component of the 

PowerGuard tile. In an effort to reduce product cost, PowerLight focused on reducing 

direct material cost for the backerboard. 

Approach 

PowerLight identified the following three options to reduce the cost of the mortar coating: 

1. Reduce the amount of latex in the mortar - The latex in the PowerGuard coating 

increases flexibility, compressive strength, freeze-thaw resistance, workability of 

the wet mix in the production line, and the bond strength of the mortar to the 

extruded polystyrene (XPS) foam. PowerLight’s initial estimate was that a 

reduction in the latex content of the mortar could save $40,000 per year at 

current production levels. 

2. Reduce the thickness of the mortar - The standard thickness of the PowerGuard 

mortar is 0.24”. However, the UL listing and fire rating for PowerGuard is 

applicable to a mortar thickness as low as 0.125”. A reduction in the thickness of 

the mortar would also result in a substantial savings, as stated above. Possible 

negative affects of a reduction in thickness include reduced resistance to impact; 

 23
difficulties in maintaining a thinner coating in the production line; and reduced 

bond strength to the XPS spacers if insufficient mortar is between the spacer and 

XPS backer board. 

3. Evaluate alternate latex and potential latex suppliers - At the beginning of this 

project, PowerLight had received quotes from a latex supplier that could replace 

the current supplier at significant cost savings. 

In order to evaluate the feasibility of these approaches, PowerLight carried out a 

comprehensive testing program, as discussed in Section 2.3.1. 

Results 

Based on the results of the reliability evaluation, PowerLight implemented process 

changes to adopt the reduced mortar thickness. Efforts to change the mortar 

composition did not yield satisfactory results. However, PowerLight was able to 

negotiate a lower price on the latex with the current supplier. These changes have 

resulted in significant cost savings. 

2.3 Task 3: Reliability Evaluation 

2.3.1 PowerGuard System Testing 

Objective 

PowerLight identified ten possible product improvements that would result in increased 

markets for PowerGuard, reduced cost, and/or improved reliability and quality. To take 

advantage of these benefits, the proposed product improvements need to be 

researched, validated, and implemented when results are favorable. 

The ten product improvements are summarized in Table 1. The product improvements 

and thermal monitoring project are then described in more detail in the following 

sections. 

Table 1. PowerGuard Product Improvements 

Item Product Improvement Benefit 

1 Create design 

guidelines for 

mechanically attached, 

single-ply membrane 

roofs 

Increase the range of approved roofing types for 

PowerGuard systems. 

2 Update product design 

guidelines to address 

wind performance of 

PowerGuard when air 

gaps are present under 

the perimeter curb. 

Large air gaps under the PowerGuard perimeter curb 

may affect wind performance. The result of this 

research will improve the reliability of PowerGuard 

systems while also ensuring that the systems are not 

over-designed. 

 24
Item Product Improvement Benefit 

3 Update product design 

guidelines to address 

wind performance of 

PowerGuard when 

installed on top of 

gravel-ballasted roofs. 

Significant cost savings could be achieved if gravel 

can be left in place underneath PowerGuard systems. 

4 Finalize design 

guidelines for a lightweight curb. 

A lighter-weight curb would expand the market for 

PowerGuard to include roofs with a low dead-loading 

capacity. In addition, a lighter weight curb would save 

money by reducing the amount of roofing pavers used 

to ballast the system. 

5 Reduce latex-content 

of the PowerGuard 

mortar coating 

The latex is the most expensive component in the 

PowerGuard mortar coating. Reducing the amount of 

latex in the mortar would result in a significant savings. 

6 Reduce mortar 

thickness 

Reducing direct material consumption results in 

reduced cost of for the PowerGuard tile assembly. 

7 Alternative latex Identifying alternative latex would allow PowerLight to 

negotiate lower pricing with vendors. 

8 Shipping Cost 

Reduction 

Reducing system cost and site waste 

9 Alternative PV Backing 

Material Validation 

Allowing the use of PET-backed modules reduces the 

environmental impact of producing PowerGuard tiles. 

10 Validation of in-line PV 

attachment 

manufacturing process 

Converting the production of PowerGuard tiles into a 

single continuous process will reduce cost by 

eliminating labor between steps. 

Wind Research on Mechanically Attached Membrane Roofs 

Background 

Mechanically attached membrane roofs are a common roofing system on flat, 

commercial buildings. Because these systems offer an inexpensive way of installing 

white, reflective roofs without the use of adhesives that contain volatile organic 

compounds, mechanically attached membrane roofs are becoming increasingly more 

common. 

Under some wind conditions and on certain types of buildings, the mechanically 

attached roof membrane can billow, which could compromise the structural integrity of a 

ballasted PV system. Design guidelines for ensuring the structural integrity of a 

PowerGuard system on this type of roofing system have not yet been available due to 

the following challenges: 

1. It has been difficult to identify situations where membrane billowing could occur, 

since it depends greatly on a building’s wall and roof deck permeability, the 

quality of the roofing system design and installation, the permeability of the 

HVAC system, and the wind conditions at the site. With the exception of wind 

 25
conditions at the site, most of these parameters are unknown for a particular site 

without a costly and time-consuming research program. 

2. PowerLight has not yet found a cost-effective mitigation strategy to ensure that 

the structural integrity of a ballasted PowerGuard system is maintained on sites 

that have a risk of membrane billowing. 

A significant increase in approved roofing types for PowerGuard systems could be 

obtained by resolving these technical challenges. Over the past five years, PowerLight 

has researched this problem extensively with world-renowned experts in mechanically 

attached membrane roofs and wind testing. Roof membrane manufacturers, scientists, 

and engineers specialized in the testing of these roofing systems, aerodynamics experts, 

and roofing consultants were consulted to develop a strategy that would bring clarity to 

the problem. This past research resulted in the following conclusions: 

1. Roof membrane billowing can occur on these types of roofs to the extent that 

light-weight ballasted PV systems could dislodge. However, it is also believed 

that some buildings, especially those in low wind zones and with small wall 

openings, never have a billowing problem. 

2. In most cases, billowing occurs along the outer edges of the roof (with 25’ of the 

edge on most buildings); however, in some cases, it could also occur in the 

middle of the roof. 

3. Within some limits, roof membrane manufacturers, roofing consultants, and 

building owners are not concerned if the roof membrane billows. If the 

membrane is not structurally damaged, remains water tight, and does not make 

noise within the building, the roofing industry accepts that light to moderate 

billowing may occur, and the mechanical fastening of the roofing system is 

designed accordingly. 

4. No one in the roofing, HVAC, or energy efficiency industry has identified a simple 

and inexpensive way of quantifying building-wall and roof deck permeabilities. 

Further, although abundant data for these parameters is available for residential 

buildings, very little published data beyond expected ranges of permeabilities is 

available for commercial buildings. 

5. No one in the roofing industry has developed a method for determining the 

likelihood that membrane billowing could occur beyond “engineering estimates.” 

6. Buildings with large openings, such as roll-up doors, or buildings that could 

develop large openings during a wind storm, such as broken windows during a 

hurricane, are highly susceptible to membrane billowing. In some cases, 

membranes can be completely torn off the roof. 

7. Wind tunnel experts did not believe that this problem could be simulated in a 

wind tunnel in a way that would yield useful data. 

8. PowerLight tested numerous methods of mitigating a billowing roof membrane; 

however, the only successful strategy was to add securement to the membrane 

between the secured seams, which are typically 6’ on center. This concept costs 

between $10,000 - $40,000 to install on a 100 kW system. In addition, this 

method requires many roof penetrations, almost defeating the purpose of a 

lightweight, ballasted PV system. This approach does not address whether or 

not extra securement is required for a specific application. As such, the added 

cost may be incurred unnecessarily. 

 26
After five years of research, this research program had appeared to reach a dead end. 

However, work during this phase has resulted in a new approach that was developed 

with the help of an aerodynamics expert and an expert in building infiltration, which 

PowerLight is considering. 

Approach 

A new approach has been developed that would identify the wind conditions and building 

types that could cause a membrane to billow. To the extent possible without revealing 

confidential information, this plan is summarized as follows: 

1. A wind tunnel model would be fabricated with various wall porosities that span 

expected extremes. 

2. Pressures on the building walls, ceiling and roof would be measured at a 

reference wind speed. 

3. The pressures measured could be used analytically to determine whether the 

pressures across a roof membrane are substantial enough to lift the membrane 

in various regions of the roof. 

4. It is hoped that in many cases, a building’s HVAC system may provide sufficient 

pressure relief to prevent the membrane from lifting. If this is the case over a 

wide range of building surface porosities, then it would not be necessary to 

quantify the actual porosity of surfaces in specific buildings. 

5. If we find that the typical HVAC system is not permeable enough to prevent 

billowing, and that billowing is highly dependent on wall and roof deck porosity, 

an expert in the area of building infiltration will be consulted to develop a field test 

protocol or analytical approach to estimating a specific building’s porosity. This 

will allow the wind tunnel results to be applied to specific buildings. 

6. If cases are identified where billowing is expected, some new mitigation 

strategies will be modeled analytically or in the wind tunnel. 

Results 

The creation of the test program has been a much greater challenge than anticipated. 

Many of the parameters are impractical, if not impossible, to quantify on specific 

buildings. It is especially challenging to determine the permeability of the HVAC system, 

building walls and roof decks without incurring a significant expense, as well as 

inconveniencing the building occupants. It is possible that these parameters could be 

studied on a broad range of building types and then applied to specific buildings. 

However, there is a concern that it would be expensive and/or inaccurate to quantify the 

necessary parameters on specific buildings. The result of the test program would be 

guidelines for determining if billowing could occur on specific buildings, and, if it is 

expected, suggested for reducing the risk of membrane billowing. 

 27
Wind Research – Gaps Under the PowerGuard Perimeter Curb, Gravel Under 

PowerGuard Systems, and Light-weight Perimeter Curb 

Background 

Several questions have arisen regarding the wind performance of PowerGuard: 

1. Current wind design guidelines are based on wind tunnel testing where the scalemodel perimeter curb was placed on a model roof with a very flat surface so that 

little to no air could penetrate beneath the curb. On some buildings, the roof is 

not perfectly flat due to the presence of overlapping roof seams and the normal 

development of low and high areas on the roof surface over time. When the curb 

is placed on a non-flat surface, allowing air to penetrate beneath the curb, is wind 

performance affected? 

2. Prior research in the wind testing industry has shown that air gaps under an array 

of roofing pavers reduce wind performance. On gravel-ballasted membrane 

roofs, a significant amount of air is trapped within the voids in the gravel. 

Although the effect of trapped air under the system has not been quantified for 

PowerGuard, gravel is typically removed from gravel-ballasted roofing systems 

before installing PowerGuard to ensure structural integrity in high winds. Despite 

a possible reduction in wind performance, can gravel be left in place on some 

buildings in low wind zones and still exceed design wind conditions? 

3. The weighted PowerGuard curb sometimes exceeds the roof loading capacity of 

some buildings, while also necessitating the shipping and handling of large 

quantities of heavy roofing pavers on each project. Is it possible to reduce the 

weight of the curb for some projects? 

PowerLight developed one test program to address these questions, as described 

below. 

Approach 

Wind tunnel testing was conducted on scale models of PowerGuard arrays in various 

configurations. First, tests were conducted on some control configurations to compare 

to prior results. A good match was obtained, and new configurations were tested. 

These configurations included: (i) the presence of gaps underneath the curb to simulate 

a non-flat roofing surface; (ii) the introduction of gaps underneath the entire array to 

simulate the presence of gravel; and (iii) a lightweight curb. 

Results 

Results for the curb with gaps, simulating a non-flat roofing surface, showed that the 

wind performance is highly sensitive to the presence of gaps. Test results showed that 

when gaps are present under the curb, performance may be reduced or increased 

depending on whether a proprietary edge treatment is installed around the curb. This 

edge treatment was developed during these tests and increased the performance of the 

array beyond that of a PowerGuard system installed on a perfectly flat roof. These 

results show that gaps under the curb can help or hinder wind performance depending 

on the curb design. PowerLight is pursuing the development of a full-scale curb that 

incorporates the edge treatment. The cost of the curb is not expected to increase due to 

this design modification. 

 28
Results of the testing on an array installed over gravel showed that in many cases, 

gravel will need to be removed from underneath the array, but on buildings under 30’ in 

a wind zone of 85 mph, gravel may be left in place.

The lightweight curb results showed that a reduced-weight curb can be used on many 

projects in low wind zones, provided that a perimeter treatment is used when curb gaps 

are present. 

The wind tunnel results described above are currently being incorporated into 

PowerGuard design guidelines. 

Mortar Research – Reduced Latex Content, Reduced Mortar Thickness, and 

Alternative Latex 

Background 

As part of the cost reduction effort described in Section 2.2.4, PowerLight produced 

prototype backerboards with reduced latex in the mortar and reduced mortar thickness. 

In addition, efforts were underway to evaluate the possibility of using an alternate latex 

to reduce cost. PowerLight implemented a research and testing program to evaluate the 

feasibility of these potential changes to the PowerGuard production process. 

Approach 

To evaluate the reduction in latex content and the reduction in coating thickness, 

PowerLight performed the following tests on three types of samples: control samples 

with a standard thickness and latex content; samples with reduced latex; and samples 

with reduced mortar thickness: 

1. Resistance to freeze-thaw cycling (based on ASTM C666) 

2. Tensile bond strength of mortar to foam before and after freeze-thaw cycling 

3. Shear bond strength before and after freeze-thaw cycling 

4. Resistance to impact 

5. Reinforcement strength of groove (control and reduced thickness only) 

6. Compressive strength before and after freeze-thaw cycling (control and reduced 

latex only) 

7. Full-scale uplift test (reduced thickness only) 

Freeze-thaw resistance is a critical parameter for any concrete product installed in a 

freezing climate. The water-to-cement ratio and latex content are the key parameters 

affecting freeze-thaw resistance of the mortar. 

ASTM C666 is the standard test to evaluate the freeze-thaw resistance of concrete. 

Samples are placed in a container with water, and the containers are placed in a 

temperature-cycling chamber where temperatures oscillate between -18o

C and 5oC for 

300 cycles. 

Tensile bond strength of the mortar to the XPS spacers and backerboard is important 

because this bond is what holds the PV module in place when handled or when under a 

tensile load, such as during a windstorm. Two types of tests are used to evaluate the 

strength of this bond., To test the bond of the mortar to the XPS backerboard, wooden 

blocks are adhered to the mortar surface and pulled off the backerboard using an 

actuator connected to a load cell. To test the bond of the XPS spacers to the mortar, a 

 29
wooden block is adhered to the top of each spacer, and this block is in turn connected to 

the actuator and load cell. Figure 24 shows this test set-up. 

Support stand for 

securing the actuator 

and load cell 

Load cell 

Tongue of XPS 

backerboard 

Mortar surface 

Spacer imbedded in 

mortar

Wooden block 

adhered directly to 

mortar surface 

Figure 24: Two methods of measuring the tensile bond strength of the mortar to the XPS. 

Although it is not expected that PowerGuard tiles will experience large shear loads, 

experience on our production line has shown that a poor bond between the XPS spacer 

and mortar may be more easily identified by a shear test than by a tensile test. 

PowerLight performed shear tests on three types of sample tiles: standard mortar 

formula and thickness; reduced latex formula; and reduced mortar thickness. The first 

type of samples served as the control group against which the results of the other two 

were compared. A photo of the test set up is shown in Figure 25. 

Figure 25: Shear test on XPS spacer bonded to mortar. 

Impact resistance is another important property of the mortar. During shipping and 

installation, PowerGuard tiles may experience impact loads against the sides of the tiles. 

The mortar reinforces the fragile edges of the XPS foam to protect it from chipping and 

deformation. Damage on the order of a few inches along the perimeter of the tile is 

considered to be acceptable; however, more substantial damage could compromise the 

structural integrity of the tongue-and-groove interconnection between tiles. To ensure 

 30
that a reduction in latex content or mortar thickness would not result in unsatisfactory 

impact resistance, PowerLight devised an impact test. The test consisted of a pendulum 

with a mass attached to the end. The pendulum was elevated at various heights to 

determine the energy required to cause impact damage to the edge of the tiles. A photo 

of the test is shown in Figure 26. 

Figure 26: Impact test on mortar. 

As discussed above, the mortar reinforces the XPS foam edges against horizontal 

impact loads. Similarly, the mortar also reinforces the top of the foam along the routed 

groove edges to resist uplift loads more effectively. PowerGuard wind design guidelines 

are based on wind tunnel tests in which the wind velocity that initiates tile uplift is used 

as the failure velocity. In a worst-case wind event, PowerGuard tiles may experience 

small vertical oscillations. The mortar along the groove edges adds considerable 

strength to the foam, so that foam breakage above the groove will not be a mode of 

failure. Reduced latex content or reduced mortar thickness may reduce the strength of 

this reinforcement. Therefore, PowerLight devised a test to measure the strength of the 

groove reinforcement. Small sections of the tile perimeter were cut and mounted in a 

tensile tester. A wooden fixture with the form of the XPS tongue was inserted into the 

groove edge of the test sample. The wooden fixture was lifted while the test sample was 

held in place. The load that caused failure was recorded for control samples and 

samples with reduced latex and reduced mortar thickness. A photo of the test set up is 

shown in Figure 27.

 31
Figure 27: Strength of groove test.

PowerGuard tiles are not subjected to large compressive loads, so in a sense the 

compressive strength of the mortar is not part of the design criteria. However, it is well 

known in the concrete industry that the compressive strength of concrete is an indicator 

of concrete quality and freeze-thaw resistance. In addition, the test is very easy to 

perform and requires minimal material for the test. The compressive strength test on the 

mortar is based on the ASTM test C597. In this test, 1” diameter x 1” height samples of 

mortar are fabricated and allowed to cure. The samples are then compressed until 

failure occurs, and the load causing failure is recorded. This test was conducted on 

samples with the standard amount of latex and with a reduced amount of latex. 

Freeze/thaw testing was planned to be done following a series of tests on unconditioned 

samples. A photo of the test set up is shown in Figure 28. The minimum compressive 

strength is 3500 psi. 

Figure 28: Compressive strength test. 

Full-scale testing was also conducted on samples with reduced latex and reduced 

mortar thickness. In this test, a 3x3 array of tiles was assembled on the shop floor. A 

perimeter curb was installed around the array of tiles. The center tile was connected to 

a load cell and cable and winch assembly. The center tile was lifted until failure 

occurred. A photo of this test set up is shown in Figure 29. 

 32
Figure 29: Tile uplift test. 

PowerLight contacted a manufacturer of alternative latex to obtain pricing for their 

product. The pricing was significantly less than that of the current vendor. Initially, this 

made the new latex an attractive replacement, but the supplier of the standard latex 

reduced their price to match the new one. This change in pricing eliminated the 

incentive to devote testing time to the new latex, and this effort was abandoned. 

Results 

Error! Reference source not found. shows the results of the mortar testing. The 

impact and compressive strength of the samples with reduced latex content were 

determined to be unsatisfactory. However, the performance of the reduced mortar 

thickness samples in all tests was found to be adequate. The cost savings afforded by 

this design change are substantial, so this improvement was immediately incorporated 

into the production line. 

Table 2: Mortar testing results 

Item Test Reduced Latex Reduced Mortar 

Thickness 

1 Freeze-thaw resistance N/A* Pass 

2 Tensile strength Pass Pass 

3 Shear strength Pass Pass 

4 Impact resistance Fail Pass 

5 Reinforcement strength of XPS groove Pass Pass 

6 Compressive strength Fail N/A 

7 Full scale tile uplift N/A* Pass 

*These test were not completed due to failure of impact resistance and tile uplift tests. 

 33
Shipping Cost Reduction 

Background 

As part of Task 6 of this contract, PowerLight had the goal of reducing shipping costs 

and site waste by at least 20%. In order to accomplish this, PowerLight changed the 

height of the stacks of PowerGuard tiles from 12 tiles to 15. The details of this effort are 

discussed under Section 2.6.2 “Waste Stream Reduction.” 

This change in stack height increases the loads applied to the tiles at the bottom of the 

stack during shipping. Prior to implementing this change in production, we wanted to 

make sure that it would neither decrease product reliability nor increase shipping 

damage. To evaluate this, we implemented a shipping test with the increased stack 

height. 

Approach 

In the shipping tests, control pallets with a standard number of tiles were shipped 

alongside pallets with an increased number of tiles. Standard shipping practices were 

followed. A datalogger capable of measuring shock was placed in a pallet to record 

accelerations in three directions. Tiles were inspected before and after shipping. The 

acceleration data was analyzed to determine the loads to which the tiles were subjected. 

Once the change was implemented in production, PowerLight planned to inspect the 

pallets of tiles as they were unloaded at job sites during the first months after the 

process change. This approach would provide feedback from a much larger sample 

size. 

Results 

No damage was found during the first round of shipping tests, so the change was put 

into production. There were six reported instances of damage reported during the first 

few shipments. PowerLight engineers conducted a second round of testing with 

accelerometers and found that the loads applied to the tile could be greater during 

handling with a forklift than those measured during shipment by truck. Field crews were 

instructed to avoid sudden bumps with the taller stacks. At the same time, PowerLight 

had been working on reducing the thickness of the mortar coating on the PowerGuard 

backerboards. This change was implemented while these initial shipments were taking 

place. The change in mortar thickness results in a lighter tile. When the lighter weight 

tiles were put into production, no more shipping damage was observed. PowerLight 

continues to inspect shipments periodically to ensure that no damage is occurring, but 

many thousands of tiles have been shipped with the increased stack height without any 

problems. 

Alternative PV Backing Material Validation 

Background 

As discussed in Section 2.2.3, PowerLight modified the manufacturing process for 

PowerGuard tiles to accommodate new backing material being used on PV modules by 

some suppliers. An extensive validation program was implemented to verify structural 

integrity of the PowerGuard tiles made with this new process. 

 34
Approach 

Much of this testing was done in conjunction with a search for new adhesives and 

process changes that would provide an adequate bond to the PET. Initial tests were 

carried out on a variety of samples, and when a promising material was found, it was 

subjected to a full range of tests. 

In this test, samples consisting of PET-backed modules adhered to XPS standoffs were 

fabricated. Unconditioned samples were used as controls, and some samples will be 

conditioned in a temperature cycling test, humidity-freeze test, and water-immersion test. 

All conditioning tests are based on UL 1703 and IEC 61215 tests. 

Results 

PowerLight completed testing on small-scale samples with chosen adhesive. Once the 

testing was completed on small-scale samples, full-scale tiles were made with the new 

adhesive. In this case, the small scale testing had to be done twice. Initial tests showed 

good results using a reactive hot-melt adhesive, but when it was implemented on fullscale tiles, the results were not acceptable. Modifications were then made to the 

adhesive process wherein the PET material was treated with a corona-discharge probe 

prior to being adhered to the spacers of the PowerGuard backerboard. The addition of 

this process allowed the use of a lower-cost adhesive. Once this change was made, we 

had good results both in the lab and in the factory. 

Because of this change to the adhesion process, the testing plan had to be expanded to 

include some testing of the PV modules to ensure that the corona-treatment process did 

not damage the backskin in any way. PowerLight conducted testing of the electrical 

resistance of the backskin of several modules before and after corona treatment. The 

resistance was within specifications before and after treatment. 

Validation of In-Line PV Attachment Manufacturing Process 

Background 

As part of the ongoing effort to remove any non-value added activity from the 

manufacturing process for PowerGuard, PowerLight is investigating combining the two 

parts of PowerGuard production into one continuous operation. Currently, the 

backerboards are made and then stacked for curing of the cementitious coating. Once 

the coating is cured, the PowerGuard tiles are assembled with the PV laminates and 

packaged for shipment. The next goal in improving the manufacturing process is to add 

the PV laminates during the coating process so that once the coating is cured; the tiles 

are ready to be packaged for shipment. This will eliminate the labor involved with 

stacking and unstacking the tiles between operations. It will also reduce the floor space 

required for the manufacturing process and reduce opportunities for damaging work-inprocess. 

To ensure that this change does not negatively affect the bond between the XPS spacer 

and mortar, testing was conducted on tiles made in a batch process and compared to 

tiles made during pilot runs of the inline PV attachment process. 

Approach 

Testing consisted of a destructive tensile test on the tiles to ensure the tiles can meet an 

uplift requirement of 50 lbs. per square foot (psf). The test setup is shown in Figure 30. 

 35
Figure 30: Tensile test of PowerGuard tile made with continuous process 

Results 

PowerLight conducted a series of pilot runs to determine the feasibility of the continuous 

manufacturing process. Samples were taken from these pilot runs and tested in 

PowerLight’s testing facility. The initial results showed a slight decrease in bond 

strength. However, the results also indicated that the load may have been applied 

unevenly during the testing. The test apparatus will be improved for the next round of 

developmental tests. Based on the results, the manufacturing engineers began looking 

into alternate methods of handling the tiles during the continuous process so that there 

would be no disturbance of the bond. Another pilot run is planned for early 2006. 

Thermal Monitoring 

Background 

PowerGuard tiles are the most lightweight and wind resistant ballasted PV product on 

the market. PowerGuard tiles are installed directly on the roof surface and have 

horizontal PV orientation, both design features that improve wind performance. 

However, these aspects can result in higher PV temperatures when compared to sloped 

PV modules that are elevated off the roof surface. The purpose of this effort was to 

document that PowerGuard systems in hot climates operate within an acceptable 

temperature range. PowerLight continues to work with industry experts to ensure that 

established PV test standards, such as UL1703 and IEC 61215, are predictive of 

PowerGuard’s long-term reliability. 

Approach 

Four PowerGuard systems in hot climates were instrumented with thermocouples and 

monitored remotely via a data acquisition system (DAS). Three thermocouples were 

placed on two PV modules in each system. 

 36
Results 

Peak PV temperatures were within the expected range. PowerLight is in the process of 

reviewing the data with Sandia National Labs, to ensure that established industry 

standards for PV testing would predict PowerGuard’s long-term durability. 

2.3.2 PowerLight Metal Roof System 

Objective 

The PowerLight Metal Roof System (RMR) is a PV mounting system for metal roofs that 

does not require penetrations through the roofing. Two engineering requirements must 

be met with this design: (1) the structural components must withstand all environmental 

forces such as wind, seismic, and gravity; and (2) all accessible conductive parts of the 

array must be grounded according to the National Electric Code (NEC) requirements. 

The objective of this task was to ensure that RMR designs, which vary to accommodate 

different PV frames, meet these engineering requirements. The approach used to 

investigate these issues and the results of work performed during this phase are 

summarized below. 

Background 

Each PV module manufacturer has a unique PV frame design. The frames can be 

categorized into two types: external flange frame (EFF) and internal flange frame (IFF). 

Photos of these two frame types are shown in Figure 31 and Figure 32. 

Figure 31: Examples of external flange 

frames 

Figure 32: Examples of internal flange 

frames 

Standing seam and corrugated metal roofs can be used as a mounting structure for PV 

modules. PowerLight has developed standardized mounting clips to mount EFF and IFF 

PV frames to structural components, such as S5 clamps or Unistrut. These structural 

components are then attached to the metal roofing using standard industry practices. A 

photo of an S5 clamp is shown in Figure 33. 

 37
S5 clamp PowerLight mounting clip 

Figure 33: S5 clamp and PV mounting clip to secure two PV modules. 

The complete assembly – the PV mounting clip, PV frame, and structural components – 

must meet certain design requirements. The design must meet UL and IEC standards, 

which dictate wind loading and grounding requirements. To ensure that the clip designs 

meet these criteria, the assemblies were tested to these standards, as described below. 

Approach 

Grounding Tests 

UL 1703 specifies that the resistance between accessible conductive components in a 

PV system cannot exceed 0.1 Ohms. PowerLight evaluated the IFF and EFF clip 

assemblies to ensure that the resistance was below this value. In this test, leads of a 

highly sensitive mili-ohmmeter are connected to two adjacent PV frames in order to 

measure the resistance across the clip assembly, as shown in Figure 34. 

Leads of mili-ohm 

meter connected to 

PV frames 

Mounting clip 

Figure 34: Ground testing of mounting clip and frames. 

Uplift Resistance Tests 

UL requires that PV modules pass a loading test where 45 psf is applied to the module 

surface. Permeable PV roofing systems typically have excellent pressure equalization, 

resulting in lower wind loads on the module. PowerLight tested the IFF and EFF clips in 

a tensile test, as shown in Figure 35. A vertical load was slowly applied until failure 

occurred, and the load causing failure was recorded and compared to the UL 

requirement. 

 38
Tensile test fixture Mounting clip 

Figure 35: Mounting clip uplift test. 

Lateral Load Testing 

For most PV systems on a metal roof, wind and gravity loads create a negligible lateral 

load on the mounting system. However, the design must be able to withstand seismic 

loads. 

PowerLight used International Building Code (IBC) guidelines to calculate expected 

lateral loads on the PV array in a severe seismic event. Then a lateral loading test was 

conducted to determine if the assembly could withstand the predicted load. A photo of 

the test setup is shown in Figure 36. 

Clip attachment 

points 

Clip attachment 

points 

Uni-strut to 

distribute 

applied lateral 

load 

Load cell and 

linear actuator, 

held in place by 

forklift 

Figure 36: Lateral load test on RMR mounting clip. 

Results 

The IFF and EFF clip assemblies passed the grounding, uplift, and lateral load tests. 

PowerLight obtained UL listing for these assemblies following evaluation. 

 39
2.3.3 PowerLight Fixed Tilt Roof System 

Objective 

The purpose of this task was to: 

• Conduct wind tunnel testing to evaluate the sensitivity of the RFT10 product to 

building height, parapet height, and array orientation, 

• Create wind design tools to be used to determine the securement requirements 

for various wind conditions, 

• Conduct full-scale load testing on the RFT10 product to ensure that expected 

wind loads will not cause structural damage to components, 

• Conduct ground testing to ensure that all accessible conductive parts are 

adequately bonded to a common earth ground, and 

• Conduct seismic testing and analyses to verify that the RFT10 assembly can 

withstand typical seismic events. 

Background 

Prior to the start of this contract, preliminary wind tunnel testing on RFT10 had been 

completed for a limited set of conditions. The test results showed the behavior of RFT10 

in these conditions, but further testing was required to quantify the wind performance in 

the whole range of site conditions in which RFT10 is likely to be installed. In particular, 

the effect of tall buildings, varying parapet height, and high wind zones needed to be 

determined. 

Wind tunnel testing was conducted on 1:32 scale models of RFT10 tiles. At this scale, 

the rigidity of the interconnect joints may deviate from the full-scale product. The RFT10 

interconnects have some flexibility in the vertical and horizontal directions. Preliminary 

wind testing showed that the mode of failure for RFT10 arrays is usually by array sliding 

and, in some cases, by lifting in the edge and corner regions of the roof. To address 

these issues, testing on full-scale tiles in the laboratory was conducted to evaluate the 

structural integrity of the array during simulated sliding and uplift wind failure conditions. 

RFT10 systems have accessible conductive components throughout the field of the 

array. Each conductive component must be bonded to a common earth ground 

according to NEC. During this phase, grounding tests were conducted internally to 

ensure an adequate ground was achieved. Additionally, PowerLight obtained UL listing 

for the grounding clips for two types of PV modules (EFF and IFF), following evaluation. 

Experience with PowerGuard projects has shown that for sites in moderate to severe 

seismic zones, sufficient documentation is needed to convince building officials that 

ballasted PV roofing systems with no mechanical fastening to the building structure will 

remain safe during and after a seismic event. PowerLight hired a seismic modeling 

consultant to predict the behavior of an array of RFT10 during a severe seismic event. 

The goal of the testing and analysis was first to document the ability for the RFT10 

interconnects to withstand seismic forces, and second to analytically study the array’s 

response to various seismic events and building types. 

The approach used for the testing on RFT10 is described below, followed by a 

discussion of the results. 

 40
Approach 

Wind Testing and Wind Design Tools 

A scale model of the RFT10 array was fabricated. For these tests the following 

parameters were varied: building height, parapet heights, array position, and array 

weight. The friction coefficient between the model array and model building was 

adjusted to represent worst-case field conditions such as a slippery single-ply roof 

membrane. 

For each test configuration, the array was set up on the model building, and the wind 

speed in the tunnel was slowly increased until failure occurred. In some cases, failure 

occurred due to tile lifting around the edges of the array, and, in others, the entire model 

array slid on the roof surface. Figure 37 shows a typical test configuration. 

Figure 37: Wind tunnel model for an RFT10 array installed on the edge of a building. 

Wind tunnel data was used to create design charts for RFT10 systems. The charts 

show the type of securement needed for various building heights, local design wind 

speeds, and type of surrounding terrain. 

Structural Testing 

Four types of structural loading tests were done RFT10 assemblies. First, a lateral 

compressive load in the north-south direction was applied to a RFT10, as shown in 

Figure 38. The force was applied at the north end of the tile, while the south end was 

restrained. The purpose of the test was to simulate a strong wind hitting the north end of 

the array, causing the first row of tiles to be pushed into the interior sections of array. 

The force was increased until some part of the structure yielded. The force and 

displacement were then measured. 

 41
Figure 38: Lateral load test on RFT10 assembly. A compressive load is applied to the 

north side of the tile. 

In a second test, a lateral compressive load was applied to the east side of a tile with the 

west side restrained. This configuration simulated a wind load hitting the outer eastern 

edge of the array. As before, the force was increased until some part of the structure 

yielded. The force and displacement were measured. A photo of the test set up is 

shown in Figure 39. 

Figure 39: Lateral load test on an RFT10 assembly. A tensile load is applied to the east 

side of the assembly. 

The third test simulated wind uplift failure. The purpose of this test was to ensure that 

the retaining clips were sufficiently strong to keep the PV module from being pulled loose 

under the most sever uplift loads that might be encountered. A photo of the test set up 

is shown in Figure 40. 

 42
Figure 40: Uplift test on an array of RFT10 tiles. A vertical force is applied to the center 

tile. 

The strength of the PV mounting clips in the RFT10 assembly was evaluated in a 

loading test based on UL1703 and IEC 61215. In this test, 50 psf was applied to the 

module and clips. A photo of this test is shown in Figure 41. 

Figure 41: Loading test on a PV module supported with RFT10 mounting clips. 

Grounding Test 

The RFT10 assembly has many accessible conductive components that must all be 

electrically connected together to create a reliable bond to earth ground. A test was 

conducted to verify that the resistance across the assembly was below an industryestablished maximum of 0.1 Ohms. A photo of the test set up is shown in Figure 42. 

 43
Figure 42: Grounding test on an RFT10 assembly. 

Seismic Testing 

The goal of the testing and analysis was first to document the ability for the RFT10 

interconnects to withstand seismic forces, and second to analytically study the array’s 

response to various seismic events and building types. 

First, friction coefficients between the assembly and various roofing surfaces were 

measured. A horizontal load was applied evenly to the sides of three tiles until motion 

occurred. The load causing motion was automatically captured by the data collection 

system and used to calculate the friction coefficient on a membrane roof. A photo of the 

test set up is shown in Figure 43. A typical low value was chosen for further evaluation 

of system performance in a seismic event. 

Figure 43: Friction test on an RFT10 assembly. 

Once the friction coefficient had been measured, the seismic modeling consultant began 

the analysis to determine the loads that would be applied to the RFT10 product during a 

 44
seismic event. This analysis takes into account: (i) the friction coefficient between the 

PV system and the roof; (ii) variations in building flexibility and local soil conditions; and 

(iii) several types of earthquakes. 

In Phase 2 of this contract, structural tests will be conducted to ensure that the RFT10 

assembly will remain in a safe condition after a seismic event. The tests will be similar 

to the structural tests that were performed to simulate wind loads, as shown in Figure 38 

and Figure 39. The seismic tests differ in that the loads are applied to the assembly by 

the roof surface. A modified test set up will be created to simulate this type of loading. 

Results 

Wind Testing and Wind Design Tools 

The wind tunnel test results provided a failure velocity and failure mode for each 

configuration that was tested. A safety factor was applied to all failure velocities. 

PowerLight reviewed the results extensively to identify worst-case conditions and to 

identify the dominant trends in the data. The results were then incorporated into a series 

of charts to be used as guidelines for array design. 

Figure 44: Wind design chart for RFT10 arrays in the middle of the roof in Exposure C. 

A sample chart for the middle roof position, Exposure C terrain is shown in Figure 44. 

To use this chart, the designer first determines the building height, the location of the 

array on the roof (edge, corner or middle), type of surrounding terrain (Exposure A, B, C, 

or D), and the 3-second gust design wind speed for the location as defined by ASCE. 

The designer can then determine which type of securement is needed for the particular 

system. The securement types are defined as follows: 

1. No ballast: the system may be installed with any additional ballast or securement. 

2. With ballast: additional weight needs to be installed. 

3. No ballast, with securement: perimeter penetrations need to be installed. 

 45
4. With ballast and securement: additional weight and perimeter penetrations need 

to be installed. 

Structural Testing 

The wind tunnel test results discussed above show that for sites in high wind zones, the 

array must be secured to the building. In these cases, anchor points will be placed 

around the perimeter of the array. The lateral load testing showed that under these 

conditions, the structure of the array must be augmented so that lateral loads can be 

transmitted through the array without deforming the individual structural elements. This 

additional structure is needed only for the north-south direction. In the east-west 

direction, the standard structure is sufficiently strong to transmit the loads. PowerLight 

designed a connector that will tie each support piece to the adjacent north and south 

support. This will be used only in sites where positive securement of the array is 

required. 

Ground Testing 

Results of the grounding tests indicated that the RFT10 assembly meets all safety 

requirements. A UL listing for the RFT10 clips was obtained, as stated above. 

Seismic Testing 

The friction test results were provided to the seismic modeling consultants, who used the 

data to complete their model of RFT10 behavior. The model predicts the maximum 

displacement of the array in a severe seismic event. The model showed that the 

maximum displacement of the array in a severe event was less than the standard offset 

from the array to the edge of the roof. Thus, with the standard offset, we know that no 

section of the array will become dislodged during seismic activity. This ensures that the 

array does not pose any threat to public safety. 

2.3.4 ICC Certification 

Background 

At the inception of this project, PowerLight planned to obtain an Evaluation Report (ER) 

from the International Code Council (ICC), with the goal of streamlining the permitting 

process. 

An ICC-ER for PowerLight’s ballasted PV roofing products would demonstrate that the 

products comply with the International Building Code (IBC), including sections pertaining 

to fire safety, structural integrity, long-term durability, and wind safety. These concerns 

are among the most commonly raised questions from building inspectors. 

Approach 

PowerLight completed an extensive test program for all roof products, as discussed 

above, and initiated communications with ICC. An application package was submitted 

with engineering drawings, installation guidelines, and a sample Evaluation Report as 

requested by ICC. 

PowerLight’s expectation was that ICC would respond with a list of documentation and 

testing requirements, and that the test requirements could be easily met. 

 46
Results 

On further evaluation, PowerLight determined that pursuing ICC certification would 

provide little additional value to the end customer. The expected benefit of having an 

ICC-ER is to facilitate permitting and PowerLight has found that this is no longer needed. 

Recently, questions from building officials during the permitting stage have decreased 

drastically. There are two reasons for this change: (1) the quality and 

comprehensiveness of PowerLight’s submittals to building departments have improved 

significantly through continuous improvements based on feedback received from 

building inspectors; and (2) PowerLight’s portfolio of successfully completed projects has 

increased to a point that brings a new level of assurance to building officials. In many 

cases, the building departments have worked on prior PowerLight projects, and 

therefore they are more familiar with the technology. 

In addition, ICC responded with a list of testing and documentation requirements, 

including documentation of wind resistance. Initially, this did not appear to present a 

challenge. However, more in-depth discussions with ICC revealed that because the 

wind testing of PowerLight’s products were not performed in an ICC accredited 

laboratory, the wind testing would need to be repeated under the supervision of ICC 

staff. PowerLight estimated that this would cost about $100,000 for the ICC wind 

requirement alone. This additional cost combined with the lack of need to facilitate 

permitting has led PowerLight to decide not to pursue an ICC certification. 

Conclusion 

PowerLight chose to suspend its pursuit of an ICC-ER, as the UL listings, IEC 

certifications, and ASCE-compliant wind tunnel testing satisfy the requirements and 

expectations of building inspectors and end users. Should an ICC-ER be required due 

to changing market conditions, PowerLight will resume ICC evaluation efforts. 

2.4 Task 4: Quality System Improvements 

The objective of this task is to implement a supplier quality assurance program with the 

goal of achieving a 99% first-time acceptance of select supplied products and/or 

services. 

Background 

For PowerGuard, all tile components pass through PowerLight’s factory. PowerLight 

has the opportunity to inspect all incoming material. However, such inspections are 

clearly non-value added activities. It is far more efficient to establish quality systems at 

PowerLight’s suppliers to make sure that non-conforming material never leaves the 

supplier. 

For products other than PowerGuard, all materials are shipped directly to the job site. 

For these products, it is vital that PowerLight’s suppliers maintain adequate quality 

assurance systems to ensure that non-conforming material is not sent to the job site. 

Defects in the field result in much higher costs than those found in the PowerLight 

factory or during fabrication. As such, PowerLight’s supply chain department creates 

partnerships with suppliers to establish quality systems that will be effective in 

minimizing and detecting non-conforming material before it is shipped. To accomplish 

this, a supplier quality standard is needed. 

 47
2.4.1 Supply Chain Management Procedures 

Approach 

PowerLight’s goal has been to bring supplier’s quality systems up to a level at which no 

inspection of incoming material is required. Additionally, PowerLight was to address 

field-quality issues by expanding documentation procedures and the existing closed-loop 

corrective/preventative action process to include site quality. 

PowerLight expected to host a series of supplier quality seminars that would introduce 

PowerLight’s suppliers to our quality standards and requirements. As this effort has 

progressed, it has required a different approach than originally anticipated. PowerLight 

has created a quality standard that is primarily focused on PV suppliers as quality issues 

with PV have the greatest impact on installation costs and system performance. This 

standard is discussed below. 

For suppliers of other parts, primarily fabricated metal components, PowerLight’s 

supplier base has changed over the course of the last year. As PowerLight’s volume 

has increased, we have switched to some larger volume suppliers of metal parts. Most 

of these suppliers already have robust quality programs that conform to PowerLight’s 

requirements. PowerLight has undertaken to audit the quality programs of suppliers 

using an ISO 9000 standard based procedure. Suppliers were trained if there was not 

an adequate QA system. The training sessions are followed with another audit. These 

audits are performed by either PowerLight or a third party inspector. 

Results 

PV Specification Package – PowerLight has set up long-term supply agreements with 

key PV suppliers. These agreements detail product expectations beyond what is 

typically called out in manufacturing cut sheets and specifications. These agreements 

include specific detail on delivered power requirements. Powerlight insists that the 

average power output of the modules in a given shipment are at or above the nameplate 

rating of the modules. This avoids the uncertainty associated with the manufacturing 

tolerance on output power. Warranty, certification, packaging, and inspection 

requirements are also included in these supply agreements. Further quality assurance 

protocol has been established to ensure that modules are adequately characterized to 

ensure accurate performance modeling and maximized system performance. This is 

described in Deliverable 1.4.2. 

Manufacturing Facility Audits/Visits – PowerLight visits all the manufacturing facilities 

from which we order PV prior to placing our first order. During this initial visit we review 

the overall production process and quality protocols. Most facilities are ISO 9000 

registered which covers most concerns regarding material traceability. We also check 

for general conformance to industry standard practices. At this time, our audit form is 

based on ISO 9000 quality standards. This form is filled out, and any areas on noncompliance are reported back to the supplier. These items are usually negotiated with 

each manufacturer depending on their relative importance to the products we are 

ordering. As stated above, PowerLight has also trained suppliers whose quality systems 

have been found to be inadequate. 

Source Inspections – PowerLight contracts with local inspection companies to conduct 

periodic source inspection of outgoing material from the manufacturing facilities. This 

approach allows us to discontinue incoming material inspections. In so doing, we can 

ship PV directly to the installation site without warehousing the material. 

 48
Conclusion 

The accomplishments described above are vital to the continued reduction of installed 

system cost. By ensuring that suppliers have adequate quality systems in place, 

PowerLight avoids costly field repairs and delays. This also ensures that PowerLight’s 

systems perform at their maximum output, satisfying customers’ expectations. 

2.4.2 Supply Chain Quality Standard 

PowerLight was to develop a supplier quality standard, defining the required quality of 

the supplier’s products and services as well as performance metrics. 

Approach 

Historically, PowerLight’s most costly quality issues have been related to PV modules. 

Therefore, PowerLight concentrated quality efforts for the most part on the PV suppliers. 

PowerLight worked with PV suppliers and independent testing facilities to establish 

meaningful and quantifiable quality metrics for PV modules. This appeared to be a 

straightforward undertaking at the outset. However, it quickly became much more 

complex. For example, discrepancies exist in test results from one test lab to another, 

further complicating this effort. In conjunction with work being done under Task 1 to 

improve system performance, PowerLight embarked on a program to quantify the 

variations in testing results and to create a consistent method for quantifying PV output. 

PowerLight became aware of the magnitude of testing discrepancies when comparing 

the output of suppliers’ flash testers with that of independent third-party testing labs. A 

group of PV modules were tested by a supplier and then sent to an independent testing 

lab where they were fully characterized. The flash test results provided an indication of 

the variation in calibration between the different testers but did not establish a 

benchmark. 

Next PowerLight established a quality standard that defined an initial qualification 

technique to be used with each supplier. In conjunction with the independent testing lab, 

PowerLight created a testing protocol that benchmarks module performance in a way 

that provides an accurate prediction of system performance. Each manufacturer will 

send representative samples to this lab for this benchmark testing along with their flash 

test results. This method will provide a comparison between that manufacturer’s flash 

test data and predicted system performance. 

For ongoing quality control, each supplier is required to supply flash test data from each 

module. These data are adjusted based on the stored comparison between the 

manufacturer’s flash tester and the benchmark test. The results can then be used to 

ensure that the supplier’s modules meet PowerLight’s specification and that the installed 

systems will perform as expected. 

Results 

PowerLight has established a quality standard for PV modules as discussed above. 

During Phase II, we will work with each module manufacturer and the independent test 

lab to collect the benchmark test data. 

We now get all flash test data for every PV shipment sent to us in electronic format prior 

to release of shipment. Depending on specific shipping terms negotiated with the 

supplier, we sometimes receive this data while the modules are en route but reserve the 

right to refuse the shipment if we find the data to be out of agreed specification. 

 49
PowerLight catalogs these flash test data and is working on improved access for the 

catalogued data. In Phase II, we will be developing a system that will allow us to query 

this data by purchase order number or job number. This system will give us efficient 

access to information on exactly which modules are at which installations and what their 

measured outputs are. Additionally, we will be able to track PV serial numbers by 

project number so that we can track the PV output of a given system and compare this 

to its theoretical output at STC based on manufacturing flash test data. 

This system will allow us to track module performance over time and update our 

simulation assumptions accordingly. 

Conclusions 

PowerLight’s quality standard for PV modules is currently the most advanced in use by 

the PV industry. This will benefit PowerLight by ensuring that our installed systems 

perform at maximum output and satisfy our customers’ expectations. Additionally, this 

standard will provide an example for the industry to follow, benefiting all PV 

manufacturers, installers, and customers, and leading to improved system performance 

throughout the industry. 

2.5 Task 5: Manufacturing Improvements 

The objective of this task is to implement lean-manufacturing techniques in order to 

maximize yield, improve cost, reduce labor, and reduce inventory levels. The targeted 

goals of this task include the development of manufacturing tools capable of reducing 

the labor required to manufacture PowerGuard tiles by 30%, increasing manufacturing 

yield to 99.7%, and increasing inventory turns to at least eight per year. 

2.5.1 Manufacturing Yield Improvement 

Background 

Over the past several years, PowerLight has been implementing lean manufacturing 

concepts in the production of PowerGuard. This process is being continued under the 

current subcontract. 

One of the main goals of lean manufacturing is the elimination of waste. Processes for 

which the customer is not willing to pay are identified as non-value added (NVA) 

processes. Inspection of parts is an example of one NVA process. Pull manufacturing 

is another key concept in lean manufacturing. Upstream stations in a manufacturing 

process only make product when the next station downstream requires them. This 

method minimizes the amount of work-in-process, which helps to keep costs low and 

minimizes the risk of damaging parts between stations. Excess handling is eliminated in 

the ideal setup, and all inspection is replaced by error-proofing where parts are made so 

that they can only be assembled the correct way. Waste can also be eliminated through 

the application of the 5-S principles, as follows: 

• Seiri (Organization) or Sort- eliminate unnecessary items 

• Seiton (Order) or Set in order- storage system & layout, provide for easy access 

• Seiso (Cleanliness) or Shine 

• Seiketsu (Neatness) or Standardize- continue the first three S's all the time 

• Shitsuke (Discipline) or Sustain – develop these into a constant habit – this is the 

most important 

 50
Many of these lean concepts are implemented through kaizen events. During a kaizen

event, the workers are asked to create a solution to a particular manufacturing 

challenge. The challenge can be organization of tools, layout of the workspace, layout 

of the workflow, improvements in ergonomics, or anything else that affects worker 

productivity, product quality, product cost, or safety. By involving the workers in the 

process of continuous improvement, they can have a sense of ownership for the product 

and the process, and they can be a source of good ideas since they are involved in the 

manufacturing process every day. 

Approach 

Improvements in yield were pursued primarily in two areas. The final assembly process 

has been labor intensive and prone to variable results. By automating portions of this 

section of the manufacturing line, labor costs could be reduced, yield could be improved, 

and manufacturing capacity could be increased. The first areas to be automated were 

the cleaning of the PV modules and the application of a surface treatment process for 

PET-backed modules prior to assembly into PowerGuard tiles. While the previous 

process did not produce a large number of rejects, there was no mechanism in place to 

ensure that these two steps are being carried out properly or to detect rejects. 

Machinery was specified that would produce consistent, adequate results for these 

steps. 

The second area where yield improvement was pursued was in the mixing of the 

ingredients for the cementitious coating. Different liquids are mixed together, and then 

this mixture is combined with dry ingredients to create the coating. The process of 

mixing the liquids together is controlled by a programmable logic controller and is 

essentially error-proofed. The mixing of the liquids with the dry ingredients, however, 

was less precise and had no safeguard. The implementation of a new liquid pumping 

system was undertaken to deliver a preset flow rate to match the flow rate of the dry 

ingredients. This modification was expected to improve the quality of the coating, as 

well as reduce the labor requirement by decreasing the amount of monitoring required to 

operate the coating process. 

In addition to the improvements listed above, two kaizen events were planned during 

Phase I of this project as part of Task 6. These provided an opportunity for the workers 

to be involved in the improvement process. The kaizen events focused on improving 

quality control and process efficiency, as discussed below. 

Other improvements to the manufacturing process were planned. Product yield must be 

maintained or improved, as these improvements are implemented. Experiments were 

carried out to reduce the cost of the coating materials. Testing was done to ensure that 

product quality is not compromised by these changes. The stack height of PowerGuard 

pallets was increased to improve shipping density and lower cost. Testing ensured that 

the increased stack height would not cause tiles on the bottom of each stack to be 

damaged during shipping. 

Floor space restrictions and scheduling issues have resulted in a large number of 

PowerGuard tiles being sent to a temporary storage warehouse. This has added cost 

and created many opportunities for product to be damaged during shipping and 

handling. PowerLight continues to work on ways to minimize this transfer of materials by 

improving the scheduling process. This will result in lower cost and fewer rejects. 

 51
Results 

The greatest impact on the measured yield of PowerGuard tiles was achieved through 

the implementation of the error-proofed mixing system for the liquid and dry ingredients 

of the coating. This new pumping station was combined with an improved data 

monitoring system. Two parameters are monitored as primary indicators of coating 

quality: the polymer-to-cement ratio and the water-to-cement ratio. The new monitoring 

system collects data on material flow and calculates these parameters in real time. A 

plot of these parameters is then stored for each day of production, providing traceable 

information for each lot of PowerGuard backerboards made. Figure 45 shows a typical 

plot from one production run. A solid line is displayed above and below each parameter 

plot showing the acceptable range for that parameter. The system is programmed to 

start collecting data when the flow rate exceeds a threshold level. This produces the 

slight scatter of outlying points each time the system starts and stops. 

Water/Cement & Polymer/Cement: 02/09/06

0 500 1000 1500

Data Points

Ratios

Note: Each data point 

represents a 10 second 

average.

water/cement

polymer/cement

Figure 45: Typical plot from coating monitoring station 

The implementation of the new pumping station improved the control of the mixing 

process and reduced labor required at the same time. Prior to the implementation of this 

new station, the mixture was controlled by an operator based on an analog flow meter. 

The mixture could vary widely depending on the skill and attentiveness of the operator. 

Figure 45 shows that the two critical parameters are now being maintained very tightly. 

An operator checks the function of the mixing system at the start of the coating run; after 

this initial check, it requires no attention. Figure 46 and Figure 47 show the new 

pumping station. 

 52
Figure 46: New pumping station for mixed liquids 

Figure 47: Control panel for pumping station 

The implementation of the new PV preparation line has improved PowerLight’s quality 

control in this area, though it is difficult to quantify the improvement since there was no 

way to measure the quality previously. The new equipment provides consistent and 

effective cleaning and surface treatment for the PV modules prior to the final assembly 

process for PowerGuard tiles. The surface treatment function is used only for modules 

that have a polyethylene terephthalate (PET) backing material. While the PV modules 

are being processed, the system also scans and stores the serial numbers so that each 

 53
module can be tracked to its final installation site. These improvements help ensure that 

product performance and reliability will be maximized throughout the life of the product. 

Figure 48 and Figure 49 show the new PV preparation line. 

Figure 48: PV prep line 

Figure 49: PV prep line 

Conclusion 

The goal of this task was to improve yield to above 99.7% (reject rate of less than 0.3%). 

The yield statistics for PowerGuard production show an average yield of 99.96% (reject 

rate of 0.04%). This is compared to an average yield of 99.5% from the previous year. 

The improvements in the manufacturing equipment were vital to achieving this yield. 

The involvement of the workers in the improvement process through kaizen events was 

 54
also an important part of the process, as discussed in Task 6: Environment, Safety & 

Health. 

2.5.2 Optimization of Inventory Levels 

To facilitate reductions in inventory levels, PowerLight formed an interdepartmental team 

to coordinate manufacturing and installation processes in order to remove unforeseen 

delays, which result in the storage of finished goods. The continuing goal of this team is 

to find ways to increase inventory turns to at least eight per year. 

By forming an interdepartmental team to study these schedule issues and to look for 

ways to avoid them, much of the wasted activity involved with storage and extra handling 

of material could be eliminated. In addition, by increasing inventory turns, the cost of 

inventory on hand will be reduced. 

Approach 

PowerLight has created a team to coordinate manufacturing and installation processes 

in order to remove unforeseen delays. This team had its first meeting in June 2005. 

The team consists of representatives from the following departments: 

Projects – responsible for installing product at the job sites 

Production – responsible for manufacturing PowerGuard tiles 

Logistics – responsible for delivering goods to the job sites 

Purchasing – responsible for supplying materials to Production and Projects 

Production planning – responsible for scheduling material shipments and production. 

Findings 

The main issues discussed include: 

 

1. Eliminating transfer of work-in-process from the PowerLight factory to warehouse 

storage 

2. Planning production to accommodate smaller production runs to eliminate floor 

space constraints and to provide a consistent daily list of activities in the factory 

3. Working with PV suppliers to improve the delivery schedule 

4. Modify the PowerLight factory to accommodate more finished goods. 

2.5.3 Labor Reduction 

In order to decrease labor costs, PowerLight was to design new tools for material 

handling in the PowerGuard manufacturing process. The goal was to design equipment 

that would enable a worker to move components that are currently too awkward for 

single-person handling through the factory without assistance from other workers. The 

expected results of this task included the development of manufacturing tools capable of 

reducing the labor required to manufacture PowerGuard tiles by 30%. 

A portion of these efforts focused on reducing labor costs, improving the consistency of 

processes, and reducing the amount of material handling during the process of 

preparing PV modules for assembly into PowerGuard tiles. 

 55
Approach 

PowerLight has completed the design of a new portion of the assembly line that will 

change several parts of the PV module preparation process from a series of 

inconsistent, labor-intensive steps to a controlled, repeatable, and automated continuous 

process. 

PV modules must be cleaned and tested prior to being assembled into PowerGuard 

tiles. The serial numbers must also be scanned. A surface treatment process is 

required on modules with PET backskins, and a PowerGuard label must be printed and 

adhered. The cleaning and surface treatment processes are difficult to control and labor 

intensive. In order to ensure the quality of the process and to reduce labor costs, a new 

conveyor line was designed to perform all of these functions. 

The first step in designing the new line was to create a comprehensive specification that 

could then be given to potential contractors who would design and build the equipment. 

Once a contractor was selected to design and build the equipment, the details of the 

process were discussed in order to define how each part of the process would be carried 

out. Input was solicited from engineers and factory workers within PowerLight. A single 

contractor was hired to design and construct the line. Other contractors were hired to 

provide design of subcomponents and a control system. 

Results 

We developed the specification below to define the new system. 

SPECIFICATION

I. Overview 

A. This document describes the specification for the automated photovoltaic 

preparation line (PVPL). The current PVPL is a manual process. The module is 

first manually moved to the cleaning station where the module is manually 

cleaned using isopropyl alcohol. The module is then corona treated on sections 

where the spacers will be adhered. This is followed by scanning the serial 

number, and testing the PV module using the Dark I-V machine. Also, the Dark 

IV machine prints a label for all the tested modules. Currently the operations are 

performed in independent stations, hence the modules are manually moved from 

one station to another.

B. The proposed line will move PV modules automatically from one station to 

another. The automatic material transfer will be achieved using a PLC controlled 

conveyor system. The Dark IV machine will be used to test the modules, scan 

serial numbers, and print labels. The modules will be cleaned using a piece of 

equipment manufactured by Wandres Corp. The system will also incorporate 

corona treating equipment, which will corona treat the sections on the modules 

backing where spacers will be adhered. 

II. Safety 

A. The equipment must comply with all applicable OSHA safety requirements. 

Emergency stops shall be located on each side of the conveyor line and on the 

corona treatment machine. An additional emergency stop will be located on the 

cleaning machine and will be supplied by Wandres Corp. as part of that 

equipment. All of these emergency stops will be connected so that the entire 

system shuts down if any of them are triggered. 

 56
III. Requirements Summary: 

A. Throughput: minimum: 2 Modules per minute. 

B. The equipment shall be configurable for different module sizes. 

1) PV module size: Length: 45” to 65”; Width: 20” to 40” 

2) Module Weight: 15lbs – 50lbs 

C. PV module backing material: Poly-Ethylene Therephthalate (PET) or Tedlar 

D. Available utility hookup: 

1) Electric power: 120-208 VAC or 460 VAC 3-phase 

2) Air: 100 psi 

E. The PVPL manufacturer shall integrate the Dark IV testing equipment, PV 

cleaning equipment, and the Corona treatment equipment. 

 57
IV. Process Flow: 

LOAD 

PV 

SCAN PV S/N REMOVE 

FAILED 

MODULE 

COUNT PV #

NO

NO 

TEST PV PASS

CLEAN PV

CORONA 

TREAT LONG 

SPACER 1

CORONA 

TREAT SHORT 

SPACERS

CORONA 

TREAT LONG 

SPACER 2

SCAN PV S/N

PRINT LABEL 

ADHERE 

LABEL BY 

HAND 

PV COUNT = 

SAMPLESIZE 

YES

A PROXIMITY 

SENSOR 

STOPS THE 

CONVEYOR 

UNTIL PV IS 

UNLOADED 

UNLOAD 

PV 

 58
V. Other Requirements: 

A. The quote for the PVPL shall include integration and implementation costs. 

B. The quote shall be itemized 

C. The subcontractor shall provide detailed documentation on the construction, 

operation and maintenance of the equipment 

D. The subcontractor shall provide an extensive list of spare parts that will be 

needed for this system 

E. The quote shall include critical spare parts to be delivered with the system 

F. The subcontractor shall provide a document describing the warranty on the 

system 

DESIGN

The equipment was designed concurrently with the control system. A series of meetings 

took place at PowerLight with all of the contractors working on the various components 

to ensure that everyone was aware of any changes in the plan and to discuss any 

technical issues that were encountered. As much as possible, standard components 

were used. A panel-cleaning machine was specified to automate the cleaning of the PV 

modules. The scanning of the serial numbers has been accomplished by PowerLight for 

some time with a custom-designed machine that also tests the modules and prints 

labels. The components of this machine were modified and rearranged to incorporate 

them into the new line. 

Table 3: Summary of New Design 

Current Process Proposed Process 

1. Labor Intensive – Seven 

Employees used currently 

1. Semi-automated – Will require only 

two employees for loading and testing 

PV 

2. Process – Poor repeatability, 

unreliable, no process controls 

2. Process – PLC Controlled 

3. Corona Treatment – Equipment not

dependable, requiring regular 

maintenance, tool life 2 – 3 months, 

labor intensive 

 3. Corona Treatment – Dependable, 

industrial grade, minimal 

maintenance, automated 

4. Cleaning – Labor intensive, 

inconsistent process 

4. Cleaning – Automated, consistent 

and repeatable 

Figure 50 shows the layout of the existing process. The layout and some components of 

the new design are shown in Figure 51. 

 59
Figure 50: Existing Process 

Panel Cleaning Machine 

Surface Treatment Machine

Figure 51: New Equipment Layout 

 60
Figure 52. Layout of the Surface Treatment Section of the Equipment 

2.6 Task 6: Environment, Safety & Health 

The objective of this task is to reduce waste streams from both manufacturing and 

installation processes while working to improve the efficiency, ergonomics, and general 

safety of the workspace. 

2.6.1 Kaizen Events 

One of the goals of this task is the implementation of employee-suggested changes that 

result in improved efficiency, ergonomics, or general safety of the work environment. 

The tool used to implement these changes is called a kaizen event. Kaizen events will 

be discussed further in the Background section below. 

Background 

Currently, the PowerGuard manufacturing process is not continuous, as batch 

processing is employed. Once the backerboards are made, the coating must cure 

before the PV laminate can be adhered. A second curing step is required for the 

adhesive that is used to attach the PV laminate to the backerboard. When PowerLight 

first opened the Berkeley factory, the PV laminates were attached to the backerboards 

during the coating process. At that time, however, the coating process was not 

sufficiently well controlled to provide a consistent quality in the finished PowerGuard 

tiles; as such, the processes were separated. The coating process and final assembly 

process were improved significantly over the course of the next few years. The coating 

process is now tightly controlled, and the quality of the finished product is consistently 

very good. In light of this, it seems appropriate to combine the steps again to create one 

continuous process. This will have the benefit of reduced labor in material handling and 

improved use of factory floor space, allowing higher weekly production volume. 

 61
In order to set up a continuous, combined process, various changes needed to be made 

to the equipment layout and to details of the process. Hereafter, this process will be 

called the inline PV attach process. 

In order to define and test these changes, PowerLight held a kaizen event with the 

factory workers to evaluate the feasibility of attaching PV modules to the wet 

backerboards. 

Kaizen is a Japanese term that means continuous improvement. During a kaizen event, 

the workers are asked to create a solution to a particular manufacturing challenge. The 

challenge can be organization of tools, layout of the workspace, layout of the workflow, 

improvements in ergonomics, or anything else that affects worker productivity, product 

quality, product cost, or safety. The factory workers are a source of good ideas since 

they are involved in the manufacturing process every day. By involving the workers in 

the process of continuous improvement, they can have a sense of ownership for the 

product and the process. 

Approach 

The focus of the first kaizen event was to address issues concerning the shift to a 

continuous manufacturing process. The event started with a meeting to discuss the 

issues and come up with suggestions for improvements. The permanent manufacturing 

employees, the production supervisors, and engineers participated in the event. The 

following issues were identified at the meeting: 

1. Layout of the process: The various pieces of equipment had to be rearranged so 

that the material could flow continuously. The normal setup had the coating 

process and the final tile assembly process separated by a large amount of 

space where the coated backerboards were stacked while the initial curing took 

place. The workers came up with their preferred layout of the equipment. 

2. Spillage of the wet mortar on the conveyor: When the viscosity of the mortar 

varies, it can fall off the edges of the backerboards and get on the conveyor 

rollers. During the current process, the mortar is cured by the time that the PV 

laminates are attached. Any mortar on the bottom of the backerboards can be 

cleaned off. Even if it is missed, it will not stick to the top of the PV laminates 

when the tiles are stacked. With a combined, continuous process, the wet 

coating can get on the bottom of the backerboards and be transferred almost 

immediately to the top of the PV laminates. Better control of the viscosity will 

reduce this risk. 

3. Contamination of the PV alignment fixture: The current alignment fixture 

registers the backerboard by contacting the edges of the coating. With the 

coating uncured, the alignment fences would quickly become contaminated with 

coating. 

4. Spacers can lose contact with the backerboard when the tiles are lifted for 

stacking: When long spacers are adhered to the PV laminate, the spacers tend 

to pull away from the backerboard when the tile is lifted, disrupting the bond 

between the spacer and the coating. 

The following were observed during the run: 

1. The new layout proved to be effective for the pilot run. The coating edges must 

be trimmed after the coating process because they slump a bit during the 

insertion of the spacers and handling of the backerboards. If the coating edges 

 62
are trimmed too early, the coating will slump again, requiring the trimming to be 

repeated. If the trimming happens too late, the coating is too stiff and can break 

off at corners. The decision was made to trim the coating before the final 

assembly process. This worked well, though the PV alignment fixture was 

contaminated with coating as discussed below. 

2. One difficulty that was encountered during the pilot run was the fluctuation of the 

liquid flow during the mixing of the coating. This had to be monitored very 

precisely in order to ensure that the viscosity of the coating was just right. More 

care than usual was taken to ensure that there was no spillage of the coating for 

the reasons discussed above. PowerLight subsequently installed a precise 

metering pump that controls the viscosity much more consistently, as discussed 

in Section 2.5.1. 

3. As expected, the PV alignment fixture was contaminated with coating during the 

run. To compensate for this, the PV attach fixture was cleaned regularly during 

the pilot run. Based on the observations from this run, changes were discussed 

that would prevent this contamination. If the fences that are used to align the 

backerboard are moved so that they register against a lower portion of the 

tongue and groove profile, then the wet coating will not contaminate them. 

4. As expected, once the PV laminate was adhered to the spacers, the backerboard 

was prone to sagging away from the spacers. When this happens, the spacers 

lose contact with the coating, disrupting the bond. If the coating is very fresh, 

then the spacer will adhere again when it is pushed back into the coating. 

However, it would be best to avoid this disruption altogether. Based on these 

observations, the spacer layouts of PowerGuard tiles are being evaluated to see 

if they can all be changed to use more short spacers rather than fewer long 

spacers. This will eliminate the disruption of the bond with the coating. 

The focus of the second kaizen event was to design a new layout for the final assembly 

stations for PowerGuard tiles. The event started with a meeting to discuss the issues 

and come up with suggestions for the layout. The permanent manufacturing employees, 

the production supervisors, and engineers once again participated in the event. Several 

possible layouts were examined, and it was decided to experiments with a few. The 

assembly stations and associated equipment are easily moved around, so it was not 

difficult to rearrange them and try more than one layout. 

Results 

The first kaizen event was very successful. The ideas contributed by the employees 

were implemented for the layout of the pilot run, and their observations are being used to 

modify the equipment and some aspects of the tile design to improve the manufacturing 

process. These improvements will yield lower labor costs, lower space requirements, 

and lower cost for the PowerGuard manufacturing process. A continuous process will 

drastically reduce excess material handling, while reducing opportunities for damage to 

the product. The floor space required will be reduced as well. Once the tiles are 

completed during a continuous process, they can be packed in tightly for curing and then 

moved only when they are ready to be packaged and shipped. 

The second kaizen event was also successful. After trying out several layouts, the 

workers agreed that one of them worked better than the other option. Once the 

equipment layout was decided on, the associated electric and pneumatic connections 

were moved to provide power for the new setup. The final layout is shown in Figure 53. 

 63
Figure 53: Tile Assembly Layout after Kaizen Event 

The kaizen event was also important in giving the workers an opportunity to take part in 

improving their work environment. This gives them a sense of ownership that can help 

improve product quality and generate many good ideas. 

2.6.2 Waste Stream Reduction 

One of the expected results of this task is the development of an improved shipping 

method for PowerGuard tiles that would reduce shipping costs and site waste by at least 

20%. At the start of this project, PowerLight expected to achieve this goal through the 

implementation of reusable shipping containers that maximize shipping density to the 

installation site and collapse for return shipment. In addition, PowerLight planned to 

investigate means of incorporating recycled materials into the design, when developing 

these reusable containers. 

Background 

Throughout its history, PowerLight has demonstrated a dedication to environmental 

protection and the health and safety of its workers. In 2003, PowerLight was awarded 

Green Business status by the county of Alameda, California demonstrating the 

commitment of the company to these concerns. PowerLight continues to look for new 

ways to mitigate environmental impact. 

Site waste continues to be an opportunity for decreased waste streams and reduced 

cost. Removing packaging waste from the job site adds cost in the form of labor and 

disposal charges. It is also very important to PowerLight’s corporate goals to create 

minimal environmental impact in the installation of PV arrays. For all of these reasons, it 

is important to reduce site waste. 

Approach

PowerLight has looked for ways to reuse shipping containers in the past, but the cost 

has always been prohibitive due to the transportation cost associated with returning the 

containers to the factory. Prior to the start of this project, new analysis had shown that 

the cost of the return shipment could be offset by maximizing shipping density to the 

installation site. For example, by building containers that double shipping density and 

 64
then collapse for return shipment, the total number of trips to or from the site would be 

reduced. 

The first step in this process was to evaluate the cost of different types of shipping 

containers. The preferred solution would be containers that are completely reusable. 

However, if that was not feasible, PowerLight wanted to investigate alternatives that 

would reduce site waste and environmental impact by increased shipping density and 

the use of recycled material. 

PowerLight looked into a variety of materials for both reusable and single-use 

packaging, including recycled plastic and recycled cardboard. The cost analysis for 

reusable containers is shown in Table 4 below. 

Table 4: Cost analysis of different packaging strategies for 750-kW installations 

Base 

case

Reusable 

containers

Increased 

stack 

height 

Double 

stack 

Job size (kW) 750 750 750 750

Module (W) 200 200 200 200

No. of modules required 3750 3750 3750 3750

Tiles per pallet 12 20 15 10

Pallets per truck 22 22 22 44

Cost per truck $3,000 $3,000 $3,000 $3,000 

No. of trucks required 15 9 12 9

Shipping cost to site $45,000 $27,000 $36,000 $27,000 

Cost per pallet $6 $20 $6 $7 

No. of pallets 313 188 250 375

Cost of pallets $1,878 $3,760 $1,500 $2,625 

Total cost to site $46,878 

$ 

30,760 $37,500 $29,625 

Return 

Capacity of truck for empty pallets 1056 1056 1056 1056

No. of trucks required 1 1 1 1

Return cost $ - $3,000 $ - $ - 

Total cost including return $46,878 $33,760 $37,500 $29,625 

Packaging/Transportation Savings 28% 20% 12%

 65
Table 5: Cost analysis of different packaging strategies for 250-kW installations 

Base 

case

Reusable 

containers

Increased 

stack 

height 

Double 

stack 

Job size (kW) 250 250 250 250

Module (W) 200 200 200 200

No. of modules required 1250 1250 1250 1250

Tiles per pallet 12 20 15 10

Pallets per truck 22 22 22 44

Cost per truck $3,000 $3,000 $ 3,000 $3,000 

No. of trucks required 5 3 4 3

Shipping cost to site $15,000 $9,000 $ 12,000 $ 9,000 

Cost per pallet $6 $ 20 $ 6 $7 

No. of pallets 105 63 84 125

Cost of pallets $630 $1,260 $ 504 $875 

Total cost to site $15,630 $10,260 $12,504 $9,875 

Return 

Capacity of truck for empty pallets 1056 1056 1056 1056

No. of trucks required 1 1 1 1

Return cost $ - $3,000 $ - $ - 

Total cost including return $15,630 $13,260 $ 12,504 $9,875 

Packaging/Transportation Savings 15% 20% 26%

As demonstrated in Table 4, if a reusable container has a life of five trips and costs 

$100, it will provide a 28% savings in packaging/transportation costs for large 

installations. As system size goes down, the benefit is reduced, as shown in Table 5 for 

a 250 kW system. For a 200-kW system, no cost savings is realized. A primary 

obstacle to implementation of reusable containers was the variety of sizes of 

PowerGuard tiles. PowerGuard tiles are sized to conform to the size of the PV module 

being used, and it is an advantage to be able to use the standard sizes offered by a 

variety of manufacturers. Even with a small number of sizes (three or four), the number 

of reusable containers that would need to be on hand at any one time would be 

prohibitively large, especially in the context of additional storage costs. 

Another issue that has hampered this effort is the recent volatility in the PV supply. 

Delays in PV supply have forced PowerLight to store material for a portion of a job while 

waiting for PV to be delivered to finish production. This also increases the number of 

shipping containers that would need to be on hand. The cost of these shipping 

containers and the cost of storing them have proven to be prohibitive, though at some 

point in the future, changing conditions may make this viable. 

Since reusable containers proved infeasible at this time, PowerLight looked for ways to 

increase shipping density and, thereby, achieve the site-waste and cost reduction goals. 

PowerGuard tiles were generally stacked 12 high on each pallet. This was primarily 

 66
done to allow workers to stack the tiles easily in the factory and to unstack them easily at 

the job site. A stack of twelve PowerGuard tiles is approximately 60 inches high. Most 

trucks have an interior height between 98” and 110”. If we could change the stack to 

close to 100”, then we would use much more of the available volume of the truck bed, 

reducing the number of trips required to bring material to a job site, thereby, reducing 

transportation costs. Unstacking a pallet that is eight feet tall, however, becomes 

nontrivial. This was seen as a potential liability. We then investigated the possibility of 

taking two pallets with stacks of PowerGuard tiles and placing one on top of the other for 

shipping. When the stacks were unloaded from the truck, the two pallets could be 

separated either prior to lifting to the roof or after they had been lifted to the roof. This 

would maintain an ergonomic unstacking height for the workers. PowerLight 

investigated the use of corner supports that were strong enough to support the second 

stack on top of the first one. Corner supports were found that were made from recycled 

plastic bags and were easily strong enough to provide the needed support. Figure 54 

shows an initial test of these supports. 

Figure 54: Test of corner supports in double stacked pallets 

Unfortunately, this approach also ran into problems. To offset the cost of the second 

pallet and the stronger corner supports, each stack would need to be at least 20 tiles, or 

10 tiles per pallet, to achieve significant savings, as shown in Table 4 and Table 5. 

While truck beds are available that can accommodate a 102” stack, these are not as 

common as trucks with lower ceilings, making the taller trucks more costly. This 

 67
required the stack height to be reduced to 18, and at this level, the benefit was reduced 

to almost nothing for the majority of system sizes. 

The final approach was to increase the stack height as much as possible without adding 

a second pallet. With some experimentation, we found that the workers were able to 

stack and unstack up to 15 tiles. Table 4 and Table 5 show that this reduces shipping 

costs, as well as the associated site waste by up to 20%. The main issue with this 

approach was the compressive strength of the spacers of the bottom tiles. Shipping 

tests were carried out with accelerometers mounted on the top and bottom of stacks of 

various heights; the results of these tests are discussed below in the next section. 

Results 

The improvement that has proven to be successful is the increase in stack height from 

12 to 15 tiles. This solution reduces the amount of packaging by 20% as well as 

reducing the number of truck trips required by 20%. The shipping tests showed that the 

accelerations experienced by the stacks during shipping do not cause compressive 

failures of the spacers. There was some indication, however, that rough handling of the 

stacks during loading and unloading of a truck could cause stresses that were potentially 

harmful. It was unclear, however, how big a risk this was. PowerLight engineers 

decided to implement the change in stack height and then monitor the installations that 

followed to determine the frequency and cost of any damage incurred. It is reasonable 

to accept a certain amount of damage if the cost of dealing with this damage is far less 

than the amount of money saved by the increase in shipping density. It was decided 

that any damaged tiles would be replaced so that there would be no risk to the structural 

integrity of any part of the system. 

At the time of this report, PowerLight has shipped over 10,000 tiles with the new stack 

height, and there have been only 12 tiles damaged. The majority of this damage 

occurred during the first few shipments. Once the project managers became 

accustomed to dealing with the higher stacks, they were able to avoid damage to the 

tiles. 

Conclusion 

While the initial approach to decreasing site waste and packaging costs has not proven 

feasible, PowerLight has succeeded in accomplishing the goals of this portion of the task 

by reducing shipping costs by 20%. As conditions change, PowerLight will continue to 

look for ways to reduce costs and environmental impact. 

2.7 Task 7: Commercial Demonstration 

The objective of this task is to use commercial demonstration projects to assess the 

efficacy of the implemented modifications from the preceding Phase I task activities. A 

total of 2000 to 4000 PowerGuard tiles, totaling at least 500 kWp, was to be used at 

commercial demonstration sites for this assessment. The performance of these 

commercial demonstration projects was to be monitored to quantify improvements in 

system performance, and the costs were to be collected to evaluate the results of cost 

reduction efforts in Phase I. 

As discussed in Section 2.2.1, PowerLight has been developing a foamless tile design, 

called RFT10, targeted for customers without added-insulation needs. Like the standard 

PowerGuard tiles, RFT10 is designed to mount on flat roofs without the need for 

penetrations in most sites. 

 68
PowerLight has been working to reduce the cost of energy from rooftop PV systems by 

improving system performance and reducing installed system cost. The best way to 

gauge the effectiveness of these efforts is to monitor the performance and cost of actual 

installed systems. 

2.7.1 System Performance 

Approach 

Improvements in system performance and reliability are being measured by comparing 

new systems, which have improved monitoring and diagnostic equipment with historical 

data from a range of existing systems. The “control” sites, listed in Table 6, were 

existing sites that we are using for comparison with the new sites. 

 69
Table 7 lists the “test” sites that were installed during the course of this project with new 

monitoring and diagnostic equipment. 

Table 6: Existing Systems for Comparing System Performance 

System ID Site 

Type 

Location Inception 

Date 

Rated 

Power 

(kWp) 

Performance 

Index 

System 

Availability

System 1 Control Los Angeles, CA 4/30/2003 115.1 98% 100%

System 2 Control Hayward, CA 1/8/2004 261.0 95% 100%

System 3 Control Hayward, CA 2/14/2004 101.8 95% 100%

System 4 Control Hayward, CA 3/24/2004 114.0 101% 98%

System 5 Control Hayward, CA 1/5/2004 243.3 106% 100%

System 6 Control Hayward, CA 1/5/2004 279.7 105% 95%

System 7 Control San Francisco, CA 10/18/2003 234.5 97% 99%

System 8 Control San Francisco, CA 10/18/2003 234.5 99% 100%

System 9 Control San Francisco, CA 2/27/2004 207.0 102% 99%

System 10 Control Walnut Creek, CA 1/30/2003 93.6 108% 100%

System 11 Control Healdsburg, CA 6/18/2004 258.3 96% 99%

System 12 Control Healdsburg, CA 6/18/2004 199.1 106% 100%

System 13 Control San Mateo, CA 1/27/2003 233.7 94% 96%

System 14 Control Sacramento, CA 2/3/2004 201.4 96% 94%

System 15 Control Sacramento, CA 2/3/2004 201.4 95% 93%

System 16 Control Rohnert Park, CA 1/29/2003 96.0 95% 100%

System 17 Control Torrance, CA 2/6/2003 37.1 98% 96%

System 18 Control Torrance, CA 2/5/2003 124.7 105% 100%

System 19 Control Torrance, CA 2/5/2003 124.7 100% 100%

System 20 Control Torrance, CA 2/5/2003 124.7 101% 100%

System 21 Control Torrance, CA 2/5/2003 124.7 97% 100%

System 22 Control Vallejo, CA 3/14/2003 107.8 89% 100%

System 23 Control Vallejo, CA 3/14/2003 224.0 95% 98%

 Average 98.8% 98.6%

 70
Table 7: Test Systems for Comparing System Performance 

System ID 

Site 

Type Location 

Inception 

Date 

Rated 

Power 

(kWp) 

Performance 

Index 

System 

Availability 

System 24 Test Oakland, CA 6/9/2005 100 N/A N/A 

System 25 Test Oakland, CA 7/28/2005 265 N/A N/A 

System 26 Test Oakland, CA 7/28/2005 265 N/A N/A 

System 27 Test Oakland, CA 7/28/2005 252 N/A N/A 

System 28 Test Oakland, CA 7/28/2005 121.8 N/A N/A 

Results 

Performance Index and Availability figures are shown in Table 8 for the control group of 

sites for two periods: September 1, 2004 - August 31, 2005 and February 1, 2005 - 

January 31, 2006. This data is shown for the test group for the periods from February 1, 

2005 - January 31, 2006 only; data for Test System 24 are available from June 2005 and 

figures for Test Sites 25 through 28 include data from September 2005. Data for 

Systems 25 through 28 prior to September 2005 were excluded because of manual 

shutdowns associated with the project installation. Energy from these systems was 

tracked via the data acquisition system, but measures of availability and performance 

index for the site are slightly skewed by the frequency and duration of shut-downs 

related to breaker installations and other site work. During the period February 1, 2005 - 

January 31, 2006, twenty of the twenty-four control sites were off at some point during 

the year for planned maintenance or because of an unplanned outage (utility outage or 

inverter failure). None of the test sites suffered inverter outages during this period, and 

none were shut down for planned maintenance. 

Table 8: Results of system performance monitoring 

 Performance Metrics for 

09/01/04 – 08/31/05 

Performance Metrics for 

02/01/05 – 01/31/06 

System ID 

Site 

Type Location Inception 

Date 

Rated 

Power 

(kWp) 

Performance 

Index 

System 

Availability 

Performance 

Index 

System 

Availability

System 1 Control Los Angeles, CA 4/30/2003 115.1 98% 100% 95% 98% 

System 2 Control Hayward, CA 1/8/2004 261 95% 100% 91% 100% 

System 3 Control Hayward, CA 2/14/2004 101.8 95% 100% 95% 100% 

System 4 Control Hayward, CA 3/24/2004 114 101% 98% 98% 99% 

System 5 Control Hayward, CA 1/5/2004 243.3 106% 100% 101% 98% 

System 6 Control Hayward, CA 1/5/2004 279.7 105% 95% 102% 94% 

System 7 Control San Francisco, CA 10/18/2003234.5 97% 99% 95% 100% 

System 8 Control San Francisco, CA 10/18/2003234.5 99% 100% 95% 100% 

System 9 Control San Francisco, CA 2/27/2004 207 102% 99% 100% 100% 

System 10 Control Walnut Creek, CA 1/30/2003 93.6 108% 100% 106% 100% 

System 11 Control Healdsburg, CA 6/18/2004 258.3 96% 99% 102% 99% 

System 12 Control Healdsburg, CA 6/18/2004 199.1 106% 100% 108% 99% 

System 13 Control San Mateo, CA 1/27/2003 233.7 94% 96% 92% 94% 

System 14 Control Sacramento, CA 2/3/2004 201.4 96% 94% 93% 94% 

 71
 Performance Metrics for 

09/01/04 – 08/31/05 

Performance Metrics for 

02/01/05 – 01/31/06 

System ID 

Site 

Type Location Inception 

Date 

Rated 

Power 

(kWp) 

Performance 

Index 

System 

Availability 

Performance 

Index 

System 

Availability

System 15 Control Sacramento, CA 2/3/2004 201.4 95% 93% 93% 95% 

System 16 Control Rohnert Park, CA 1/29/2003 96 95% 100% 92% 100% 

System 17 Control Torrance, CA 2/6/2003 37.1 98% 96% 96% 96% 

System 18 Control Torrance, CA 2/5/2003 124.7 105% 100% 104% 100% 

System 19 Control Torrance, CA 2/5/2003 124.7 100% 100% 98% 100% 

System 20 Control Torrance, CA 2/5/2003 124.7 101% 100% 99% 100% 

System 21 Control Torrance, CA 2/5/2003 124.7 97% 100% 102% 100% 

System 22 Control Vallejo, CA 3/14/2003 107.8 89% 100% 87% 100% 

System 23 Control Vallejo, CA 3/14/2003 224 95% 98% 92% 97% 

 Average 98.8% 98.6% 97.2% 98.4% 

System ID Site 

Type Location Inception 

Date 

Rated 

Power 

(kWp) 

Performance 

Index 

System 

Availability 

Performance 

Index 

System 

Availability

System 24 Test Oakland, CA 6/9/2005 100 N/A N/A 106% 100% 

System 25 Test Oakland, CA 7/28/2005 265 N/A N/A 106% 100% 

System 26 Test Oakland, CA 7/28/2005 265 N/A N/A 111% 100% 

System 27 Test Oakland, CA 7/28/2005 252 N/A N/A 97% 100% 

System 28 Test Oakland, CA 7/28/2005 121.8 N/A N/A 103% 100% 

 Average N/A N/A 104.5% 100.0% 

 

Both the performance index and availability for the test sites are higher than for the 

control sites. This is due in part to the implementation of more advanced monitoring 

systems at these sites. However, these data are not sufficient to fully validate the more 

advanced monitoring. Availability and performance index are impacted by many factors, 

only one of which is the rapidity of PowerLight's response to a problem. For instance, the 

availability of System 6 is quite low because of an extended inverter outage at this 

system. Although PowerLight responded to the outage within 24 hours using our 

existing monitoring system, the inverter manufacturer was unable to diagnose the 

problem and fully repair the unit in a timely fashion; the inverter was down and/or 

running at half power for over two weeks. If such an outage had struck one of the test 

sites, availability would have been impacted similarly; although more advanced 

monitoring will help PowerLight respond to problems more quickly, it cannot change the 

amount of time that a system is off once a problem is discovered. 

We can conclude from this data that the test sites are operating at higher levels of 

performance index and availability than the control sites, but a longer measurement 

period will be necessary to give us confidence in the role that our advance monitoring 

systems have played in this improvement. We will continue to monitor these sites during 

the second phase of this contract. 

 72
2.7.2 Cost Reduction 

Approach 

The cost reduction activities have involved modifications to standard PowerGuard tiles 

as well as improvements to PowerLight’s newly introduced sloped product, RFT10. The 

sites that were used for these assessments are shown in Table 9. 

Table 9: Sites for Cost Reduction Assessment 

Site ID Location Product Inception 

Date 

Current 

Rated 

Power 

(kWp) 

Site 1 Oakland, CA PowerGuard August 2005 262 

Site 2 St. Helena, CA PowerGuard 

RFT10 

August 2005 229 

Site 3 Napa, CA PowerGuard 

RFT10 

September 

2005 

195 

Results 

In August 2005, PowerGuard tiles with reduced coating thickness were installed at a 

demonstration site in Oakland, California. This was PowerLight’s first opportunity to 

observe the quality of a large number of production tiles made with the new coating 

thickness, a cost-saving improvement implemented under Task 2: High Reliability Cost 

Reductions. It was also the first opportunity to install these tiles and confirm that the 

durability was not compromised. The array was constructed with 500 tiles that had the 

reduced coating thickness and approximately 1,300 tiles that had been made with the 

standard coating thickness. This allowed for a side-by-side comparison. 

The workers appreciated the lower weight of the new tiles, which made them easier to 

handle. PowerLight engineers were on hand during the installation to look for any 

damage and to discuss the new tiles with the installers. Out of 500 tiles, 12 were found 

with various amounts of damage. In some cases, this was due to handling in the factory 

or shipping. Approximately eight of these tiles had been damaged on-site. Most of the 

damage was aesthetic only and did not compromise the structural integrity, so the tiles 

were still usable. PowerLight engineers discussed the damage with workers at the site 

and in the factory to find ways to eliminate damage. Future installations will be 

monitored to ensure that damage is minimized. Figure 55 shows the array with the 

reduced coating thickness during installation. Figure 56 shows a close-up of the 

difference in coating thickness between a standard PowerGuard backerboard and the 

new backerboard. 

 73
Figure 55: Demonstration array with reduced coating thickness during installation 

Figure 56: PowerGuard tile with reduced coating thickness (on right) 

The reduction in coating thickness, increased stacking height, and reductions in labor 

resulted in a reduction in backerboard cost of 17.8%. 

In September 2005, PowerLight completed the installation of the first large-scale arrays 

of RFT10. The installation went smoothly with only a few exceptions. The most 

common problem encountered was galling and stripping of the threads of the studs that 

were pressed into the aluminum PV supports. PowerLight worked with the suppliers of 

the sheet metal parts and the studs to determine the cause of the stripping. Eventually, 

 74
the problem was linked to the temperature of the studs. The problem was duplicated 

reliably in the shop by using an oven to heat a plate with many studs pressed into it. 

The demonstration arrays were installed in August and September in the vicinity of 

Napa, California, where temperatures were routinely between 95°F and 100°F. A later 

installation done in New Jersey in the winter experienced no problems with stripping 

threads. PowerLight is looking into an appropriate lubricant that can be used to prevent 

the threads from being damaged during hot weather. 

Another problem encountered was the amount of labor required to install the NorthSouth wiring. These systems used an off-the-shelf wire gutter running between 

modules, shown in Figure 57. This system was difficult to keep aligned, and it did not 

accommodate variations in the roof contour easily. Based on this feedback, PowerLight 

subsequently redesigned the North-South wiring method so that it is much easier to 

implement, more flexible, and less expensive. 

Figure 57: Wiring gutter during installation (designed changed after this installation) 

The installation of these systems took less labor than was anticipated, with the exception 

of the North-South wiring. After the crews had one or two days’ of experience, they were 

able to assemble the array pieces very quickly. It took some experimentation to learn 

that the array alignment was easier to maintain if the modules were installed in NorthSouth columns rather than working from East to West in rows. Figure 58 shows an array 

during installation. Figure 59 and Figure 60 show a completed array. 

As part of the ongoing monitoring of this system, PowerLight personnel inspected the 

array after a storm in December 2005 to make sure that the system was unaffected by 

the high winds. The system was found to be in perfect order. No changes were 

observed after a careful inspection. 

 75
Figure 58: RFT10 system during installation 

Figure 59: Completed array from Southeast 

 76
Figure 60: Completed array from East 

3 Acknowledgements 

PowerLight would like to thank the Department of Energy – Energy Efficiency and 

Renewable Energy program, the National Renewable Energy Laboratory, and the PV 

Manufacturing R&D Project for co-funding this work effort under Subcontract No. ZAX-5-

33628-03. 

 77
F1146-E(12/2004) 

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

July 2006 

2. REPORT TYPE

Subcontractor Report 

3. DATES COVERED (From - To)

4 November 2004–3 November 2005 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Accelerating PV Cost Effectiveness Through Systems Design, 

Engineering, and Quality Assurance: Phase I Annual Technical 

Report, 4 November 2004 – 3 November 2005 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/SR-520-40335 

5e. TASK NUMBER

PVB66101 

6. AUTHOR(S)

J. Botkin 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

PowerLight Corporation 

2954 San Pablo Avenue 

Berkeley, California 94702 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

ZAX-5-33628-03 

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NREL 

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National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 11. SPONSORING/MONITORING 

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NREL/SR-520-40335 

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13. SUPPLEMENTARY NOTES

NREL Technical Monitor: Richard L. Mitchell 

14. ABSTRACT (Maximum 200 Words)

During Phase I of this PV Manufacturing R&D subcontract, PowerLight Corporation has made significant progress 

toward the reduction of installed costs for commercial-scale, rooftop PV systems. PowerLight has worked to reduce 

operating costs by improving long-term reliability and performance through the development of more sophisticated 

tools used in system design and monitoring. Additionally, PowerLight has implemented design improvements with 

the goal of reducing cost while maintaining and/or improving product quality. As part of this effort, PowerLight also 

modified manufacturing and shipping processes to accommodate these design changes, streamline material flow, 

reduce cost, and decrease waste streams. During Phase II of this project, PowerLight plans to continue this work 

with the goal of reducing system cost and improving system performance. 

15. SUBJECT TERMS

PV; manufacturer; cost; commercial-scale; rooftop; long-term reliability; system performance; system design; 

engineering; quality assurance; installed costs; 

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