Solar Panels Last 25 Years – But Will They Stay Safely
Attached to Your Roof?
The Importance of Reliable Solar Mounting Systems
White Paper
March 2014
By:
Cinnamon Solar
HatiCon Solar
Orion Solar Racking
Quick Mount PV
Solar Marketing Group
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1.
Introduction............................................................................................................. 5
2.
Anatomy of Solar Panel Mounting Systems ........................................................ 6
3.
Potential Problems With Rooftop Solar Systems................................................ 8
3.1 Installation Practices ............................................................................................ 8
3.1.1 Leaks Around Mounts that Attach the Racking to the Roof ........................... 8
3.1.2 Missed Rafters When Attaching Mounts ...................................................... 10
3.1.3 Improper Grounding of Panels or Racking ................................................... 11
3.1.4 Improper Wiring ........................................................................................... 12
3.1.5 Improper Attachment of Panels to Racks, or Racks to Mounts ................... 14
3.1.6 Snow and Ice Damage ................................................................................. 15
3.2 Component Selection ......................................................................................... 15
3.2.1 Corrosion of Rooftop Mounting Components ............................................... 15
3.2.2 Corrosion of Grounding Components .......................................................... 16
3.2.3 Improperly Sized or Poorly Designed Roof Flashings ................................. 18
4.
Costs of Potential Rooftop Mounting System Failures .................................... 19
4.1 Roof Leaks ......................................................................................................... 19
4.2 System Outage................................................................................................... 20
4.3 Fire Hazard......................................................................................................... 21
5.
Industry Reliability and Safety Measures........................................................... 21
5.1 Standards for Solar Panels and Solar Panel Mounting Systems ....................... 21
5.2 Codes for Wiring and Grounding ........................................................................ 22
5.3 Codes for Flashings and Waterproofing ............................................................. 22
5.4 Authorities Having Jurisdiction (AHJ) and Local Building Inspections ............... 22
6.
Conclusion ............................................................................................................ 23
7.
Appendix A – Applicable UL Standards ............................................................. 24
7.1 UL 1703 – Solar Panels ..................................................................................... 24
7.2 UL 2703 – Solar Panel Mounting Systems......................................................... 24
7.3 UL 1741 – Inverters ............................................................................................ 24
8.
Appendix B – Flashing and Waterproofing Codes and Standards .................. 25
WHITE PAPER | The Importance of Reliable Solar Mounting Systems
Acknowledgments
This White Paper was written by Cinnamon Solar and Solar Marketing Group with the
support of HatiCon Solar, Orion Solar Racking and Quick Mount PV. We would like to
thank the following contributors to this paper: Barry Cinnamon, Eduardo Lainez, Carter
Lavin, Liz Oh, Bob Sinai, and Jeff Spies.
Notice
All information provided in this White Paper, including commentary, opinion,
conclusions, references, and other documents (together and separately, “materials”) are
being provided “as is”. The authors make no warranties, expressed, implied, statutory,
or otherwise with respect to materials, and expressly disclaim all implied warranties of
noninfringement, merchantability, and fitness for a particular purpose.
Trademarks
Company names and product names may be trademarks or registered trademarks of
the respective companies with which they are associated. Any trademarks that appear
in this White Paper are the property of their respective owners.
Copyright
© 2014 Cinnamon Solar and Solar Marketing Group LLC. All rights reserved.
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Executive Summary
There are currently approximately 400,000 homes in the U.S. with rooftop solar arrays.
By 2016 the number of solar homes will exceed one million, or roughly 5 gigawatts
(GW) of solar capacity. And by 2024 – just ten years from now – rooftop solar panels
are likely to be more common than satellite dishes.
It would be concerning for both consumers and contractors if these systems (consisting
of solar panels, inverters, racking, roof penetrations, and rooftop wiring connections)
started experiencing problems in significant numbers – such as roof leaks, loose panels
or defective wiring. The solar industry, standards organizations, and code officials have
been working diligently to improve the safety and reliability of equipment, as well as the
quality of the installations themselves.
To gain additional insight into the reliability of solar mounting systems, primary data was
gathered on 20 rooftop systems (averaging 10 years old) in the San Francisco Bay
area. Research findings were very encouraging: the systems that were installed using
proper mounting systems, flashed mounting points, wet-rated wiring and grounding
components, and all stainless steel fasteners were still in very good shape. In general,
the reliable systems that were surveyed exhibited three common characteristics: they
followed best installation practices at the time, used solar-specific components, and
were installed by conscientious contractors.
Looking ahead, we see two trends that are likely to enhance residential rooftop system
reliability and cost effectiveness. The first is the adoption of safer power electronics,
particularly inverters and related circuitry that prevent arc faults, shock hazards and
potential fires. The second trend is the use of more factory-assembled or integrated
systems (such as panels with built-in optimizers or microinverters and panels with
integrated racking).
By following best installation practices and using approved solar rooftop components,
research indicates that the millions of new solar customers over the next ten years will
be able to enjoy the benefits of clean, renewable and inexpensive electricity without any
significant upkeep or maintenance costs.
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1.
Introduction
There are currently approximately 400,000 homes in the U.S. with rooftop solar arrays.
By 2016 the number of solar homes will exceed one million, or roughly 5 gigawatts
(GW) of solar capacity.1 Customer economics are driving the growth of the rooftop solar
industry, and the combination of lower installed system prices and higher electric rates
make these economics even more favorable. But this rapid pace of growth could be
threatened if ongoing maintenance costs significantly reduce customers’ expected cash
flows.
Fortunately, when properly designed and installed, rooftop solar power systems are
extremely reliable. Typical lifetime failure rates of the panels themselves are
approximately one in 2,000.2 Once they are installed and operating, almost all panels
sold in the U.S. are guaranteed to provide 80% of their original rated output after 25
years (representing an annual degradation rate of less than 0.5%).
Although the panels themselves are reliable, based on field experience there are two
areas in which customers could conceivably experience maintenance costs: inverters3
and mounting systems. This White Paper will address the latter, and provide
recommendations on how to virtually eliminate expensive issues with rooftop mounting
systems.
Solar mounting systems consist of a number of field-assembled parts and have to be
integrated with existing roofing materials, as well as the underlying structural
components of a house. Unfortunately, problems on a rooftop can be expensive to
repair – hence the need to find practical ways to maximize a system’s safety and
reliability.
To gain additional insight into the reliability of solar mounting systems, primary data was
gathered on 20 rooftop systems in the San Francisco Bay area. The average age of
these systems was 10 years. These systems were installed on a variety of residential
roof types by experienced contractors, passed applicable inspections, and are still
operating properly. Although this sample is not a statistically significant survey size, nor
1
According to the Solar Energy Industries Association (SEIA), by 2016 the residential solar market will
be growing at a rate of 2GW each year, or over 330,000 homes per year. SEIA estimates about 4GW of
residential solar will be installed in 2014-16, which translates to 660,000 new solar homes. At about 5 kW
per system, that works out to a residential installed base of about 5 GW of solar on rooftops by the end of
2016. Citation: http://www.seia.org/research-resources/solar-market-insight-2013-q3
2
http://www.renewableenergyworld.com/rea/news/article/2011/03/the-bottom-line-impact-of-pv-modulereliability
3
Inverters convert the direct current (DC) power from solar panels into household alternating current
(AC) power. Virtually all of the inverters sold in the U.S. are guaranteed to last 10 to 25 years, so it is
reasonable for a homeowner to expect a replacement over the life of a solar system. Out-of-warranty
replacement costs, including labor, range from about $200 for a microinverter to about $2,500 for a string
inverter. In addition, inverter monitoring systems occasionally lose their internet signal and report a failure
even though the rooftop panels and inverters are still functioning properly; this problem is almost always
self-correcting once the internet connection is restored. While important, solar panel and inverter reliability
are not addressed in this White Paper.
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representative of all climate regions in the U.S., the results of these 20 “real world” field
inspections – combined with the experience of the White Paper contributors – provide
useful insight into mounting components and installation practices that can virtually
eliminate expensive problems with rooftop mounting systems.
2.
Anatomy of Solar Panel Mounting Systems
In order to generate a meaningful amount of energy from diffuse sunlight, rooftop solar
arrays are generally fairly large (e.g., several hundred square feet or more), and are
composed of multiple smaller panels (each typically 40”x65”) to accommodate various
roofing configurations and obstructions. Figure 1 below shows how solar panels and
associated components are attached to a typical residential rooftop.
Figure 1. Anatomy of Solar Panel Mounting Systems
A. Solar panels (also referred to as modules) convert sunlight to DC power. Solar
cells are laminated behind tempered glass for durability and encased in a sturdy
aluminum frame. These frames are designed so that panels, when properly
mounted, can withstand the expected wind and snow loads that occur in a
particular location.
B. Mounting clamps are generally aluminum brackets with stainless steel bolts that
hold the solar panels securely against the underlying racking. Some mounting
clamps also provide an electrical grounding path between the panel and
underlying racking.
C. Racking (often using a parallel metal rail structure) provides a level framework on
the roof to which the solar panels are mounted. For cost and durability reasons,
racking is typically fabricated from extruded aluminum.
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D. Mounts (also referred to as L-feet, standoffs or stanchions) attach the racking
securely to the roof surface. Mounts vary depending on roof type and material;
mounts are available for most common roof types including composition shingle,
shake, slate, metal shingle, clay or concrete tile, low-slope (flat), and corrugated
or standing seam metal. Mounts are generally available so that panels can be
installed at different heights off of the roof, generally from about 1.5” to 12”
(shorter mounts may provide better aesthetics but restrict air flow underneath the
panels). Depending on the layout of the array, type of roof, wind load and size of
racking, there may be one or two mounts for each panel. For example, a 20panel array (about 5 kW) will typically require 25 to 40 mounts. Mounts are
attached to the racking above with stainless steel bolts and the rafters below the
roof surface with lag bolts.
E. Flashings provide a water-resistant seal between the mounts and roof surface.
The basic function of a flashing is to redirect any water that leaks through or
around the mount or fastener to a sheet of durable metal, thereby preventing the
water from leaking through to the underlying roof decking.
F. Direct current (DC) wiring (for string inverters) uses positive and negative wires
from each panel connected to the wires on adjacent panels. A “home run” wire is
connected from the last panel in the string to complete the circuit. All wires must
be secured to the racking or panels so that they do not hang down or rest on the
roof surface.
G. Alternating current (AC) wiring (for microinverters and AC modules) uses AC
cables (trunk cables or daisy chain cables) connecting each microinverter to
adjacent microinverters. Cables must be secured to the racking or panels so that
they do not hang down or rest on the roof surface.
H. Microinverters (for AC systems only) on some rooftop systems mount to the back
of or underneath each panel to convert from DC current directly from the panel to
household AC current.
I. Grounding components minimize electrical shock hazards. Every conductive
metal component in an array that is likely to be energized in the event of an
accidental fault must be securely grounded. Generally, small accessories such
as mounts, flashings and clips do not need to be separately grounded.
Rooftop solar arrays endure substantial forces, which is why they require well-designed
solar panels, racking and mounts. Racking manufacturers provide engineering reports
so that installers can determine the appropriate number of supports required depending
on the wind and snow loads for a specific location. Although downward forces are
obvious (such as the weight of the panels themselves and additional snow loads), the
more challenging engineering requirement is to withstand upward forces generated by
high winds.
High winds can create an upward force (uplift) of 25 pounds per square foot (psf), and
more in high wind zones. A typical 40”x65” solar panel would therefore experience an
uplift force of 450 pounds; 8 panels in a row on a single set of rails would experience an
uplift force of 3,600 pounds. If there were 14 lag bolts (7 on each rail) supporting these
panels, each lag bolt would have to resist a force of 260 pounds – hence the importance
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of securing these lag bolts properly to the underlying rafters. Downward forces from
snow and wind can also be substantial. Since these forces are directed towards the
roof, they will not pull out the mounting systems; however, they could theoretically
cause a section of a roof to fail or cause a solar panel to break (especially if the solar
panel is attached to the racking at the farthest edges of the panel).
Fortunately, the vast majority of homes in the U.S. can support the extra weight of solar
panels (less than 3 psf) in conjunction with anticipated wind and snow loads. When
properly installed on a racking system, the solar panels themselves are designed to
support these forces, and are typically rated for 2,400 Pascals uplift (about 850 pounds
per panel) and 2,400 to 5,400 Pascals downforce (850 to 1,900 pounds per panel).
3.
Potential Problems With Rooftop Solar Systems
Attaching solar panels to a rooftop is similar to many other roof equipment installation
projects such as satellite dishes and rooftop HVAC equipment – but with far more parts
to install and more roof penetrations. Residential rooftop installations typically require
about 500 individual mounting, assembly, and fastening components to attach and
ground 20 solar panels. Each component is a potential point of failure if not sourced,
assembled, and installed properly.
The White Paper contributors have been directly involved in thousands of rooftop
installations for over 25 years. Based on our experiences, the two general areas in
which problems can occur relate to installation practices and component selection.
3.1
Installation Practices
3.1.1 Leaks Around Mounts that Attach the Racking to the Roof
Figures 2 and 3 below show water leakage around the edges of poorly installed solar
mounts. In these cases there was no flashing around the fastener (a lag bolt) that
attached the mounts to the roof, even though the installers used a generous amount of
caulking type sealant. As a result, water seeped into the gaps that inevitably form in
sealants, through the roofing material, and into the house. These leaks could eventually
rot the roof deck and rafters; damage interior walls, ceilings, and furnishings; and create
mold or mildew hazards.
Figure 2. Leaking L Foot
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Figure 3. Leaking Solar Mount
If the gap around the fastener is small, then potentially only a tiny trickle of water will
initially seep into the roof and cause wood rot that must be repaired. If the gap is large,
or a small gap expands from cycles of water freezing and thawing over the years, then a
substantial amount of water could leak into the house. Additionally, leaves, dirt, or other
debris that accumulate around the bracket can create a dam effect and channel more
water into the gap.
Although seemingly unimportant at first, a small gap around any of the roof penetrations
needed for a rooftop array can end up costing a homeowner a few thousand dollars for
small repairs to the roof and interior, and tens of thousand dollars if larger sections of
the roof and interior need repairing. Fortunately, it is fairly straightforward to minimize
the chances of leaks around roof attachments.
Best solar and roofing industry practices require the use of “flashed” mounts that create
a watertight seal around the perimeter of the fastener that attaches to the underlying
rafter. For optimal effectiveness, the most reliable waterproof mounts have an elevated
sealing area, durable seals around the fasteners; and metal flashing that extends
above, below, and to the sides of adjacent roof shingles so that water does not seep
under the flashings. The component in Figure 4 below is a flashed mount designed for
composition (asphalt) shingle rooftops. The components in Figure 5 are a tile hook
mount with a flashing designed to go over the mounting points.
Figure 4. Composition Shingle Flashing & Mount
(courtesy Orion Solar Racking)
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Figure 5. Flat Tile Flashing & Mount
(courtesy Quick Mount PV)
3.1.2 Missed Rafters When Attaching Mounts
Rooftop solar arrays are anchored by connecting
the mounts (which support the racking) to the
structural rafters that support the roof surface. If
an installer fails to center one or more lag bolts in
the rafters, a loosened lag bolt can become a
source of water intrusion into the roof and home.
Figure 6 to the left shows a lag bolt that missed a
rafter by about 2” to the left. Signs of water
damage are evident around the lag bolt.
Over a period of a few years, wind gusts and daily
thermal cycling push and pull the lag bolt, freezethaw cycles may expand any tiny gaps around the
base of the lag bolt, and debris may accumulate around the base of the mount. This
combination of forces on a lag bolt that missed a rafter will eventually expand the hole in
the roof around the bolt, thereby causing a noticeable leak and possibly affecting the
structural integrity of the rooftop system.
Figure 6. Lag Bolt Missed Rafter
It is surprisingly difficult to hit the center of each rafter.4 Even highly trained and
conscientious installers will miss a certain percentage of rafters in the installation
4
To properly bolt the racking system to the rafters, installers must first find the rafters underneath the
roof shingles and roof sheathing. Rafters are typically 1.75” wide and spaced every 16” or 24”; however,
in some cases rafters are not perfectly straight (they can warp slightly over the years). Once the center of
a rafter is located – using rough indications from a stud-finder device, pounding on the roof, or measuring
from a known rafter location – a small pilot hole is drilled through the roof surface. If the installer feels
resistance in her drill for several inches, then she has hit a rafter; if there is only initial resistance, she
may have missed a rafter and must try again – either to the left or the right. In order to meet the
International Residential Code (IRC) requirements for securing the fasteners into the rafter, the lag bolt
must be positioned in the center third of the rafter. In practice, this level of precision can be challenging.
Since there are no affordable instruments that can literally “see” through the roof surface and identify the
exact center of a rafter, it is not surprising that even experienced installers occasionally miss rafters.
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process. Moreover, since attic areas below rooftop arrays are not always easily
accessible, it is almost impossible to verify proper installation of every single mount.
Therefore, the most practical solution to this problem is to use appropriate roof flashings
to minimize the chances of leakage if a rafter is missed. In addition to being required by
many local building departments, this simple flashing solution adds only a few extra
steps and $200 to $500 per solar installation.
3.1.3 Improper Grounding of Panels or Racking
Like all electrical equipment, solar panels and the racks to which they are attached must
be grounded to minimize fire and shock hazards. For most home appliances, the slightly
longer middle prong of a standard three-prong outlet provides the grounding path to
prevent shock. “Grounding” a solar array refers to the installation of a dedicated heavyduty wire from the rooftop array all the way to the main service panel or to a grounding
rod installed, literally, in the ground.
If the grounding connection to the equipment is not properly made (or degrades over
time) and there is an electrical short in the array, it is possible that anyone touching a
metal part may get a shock. Although the possibility of such a shock event is very low,
the severity of the potential injury is significant because of the high voltage and risk of
falling off the roof. A recent report entitled “The Solar America Board for Codes and
Standards” (Solar ABCs) describes the real-world issues related to reliable grounding
methods in more detail.5
Figure 7 below shows a rooftop system that did not have a grounding conductor
attached to each individual panel. Although the racking components were grounded, to
save time and money the installer simply did not ground the 36 panels in this array. As
shown in Figure 8, the proper installation practice at that time was to install a grounding
lug and wire to each individual panel.
Once the pilot hole is drilled, sealant is applied around the hole and the lag bolt is tightened down into the
roof to attach the bracket. If the lag bolt spins easily when it is tightened, the installer missed the rafter or
just caught the edge of a rafter and has to start again with a pilot hole slightly to the left or right. This
process must be repeated about 40 times for a typical installation. If a rafter is missed, the mount may
look as if it is installed correctly, the lag seems to be in place, the racking will still rest on top of the mount,
and soon solar panels will completely cover the mount, but water will still be able to enter the gap.
5
From Solar ABCs Module Grounding Report “there is a lack of confidence in existing approved
grounding methods, due largely to failures in the field from loss of mechanical integrity, installation error,
and damage from corrosion.” Citation: http://www.solarabcs.org/about/publications/reports/modulegrounding/pdfs/IssuesRecomm_Grounding2_studyreport.pdf.
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Figure 7. Ungrounded Rooftop Solar Panels
Figure 8. Proper Solar Panel Grounding after
12 Years on the Roof
3.1.4 Improper Wiring
Once the racking is installed on the roof and the solar panels are attached to the
racking, installers make wiring connections underneath the solar panels. Proper wiring
is essential and can prevent a variety of potential problems. For example, the insulation
on wires that dangle down onto the roof’s rough surface will abrade over time and
eventually expose the copper wire underneath (as shown in Figure 9 below) presenting
a shock hazard to anyone on the roof.
Figure 9. Dangling Wires Under a Solar Array
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Exposed wires anywhere on the system (even if the wires are not dangling) present a
tempting chewing target for rodents or birds that sometimes nest underneath the
panels. Squirrels gnawing through high voltage DC wires caused the fire damage in
Figures 10 and 11 below, and their nest added fuel to the fire. Fortunately, the fire was
contained to an area directly around the nest and self-extinguished (the squirrel was not
as fortunate). Nevertheless, the panel glass shattered, the junction box melted, and a
section of the roof had to be repaired.
Figure 10. Fire-Damaged Solar Panel
Figure 11. Fire-Damaged Shingles and
Burnt Squirrel’s Nest
Additionally, a short circuit can result from wires being pinched between the panels and
racking. Over time, the insulation on a pinched wire can fail, and the resulting short will
force the inverter to shut down the entire system. The system will remain off until the
short circuit is repaired, a fuse or breaker is reset, and the system is restarted.
To prevent these problems, installers frequently use wire (zip) ties or wire clips to fasten
wiring to panels and racks – between 50 and 100 wire ties in a typical installation. While
plastic wire ties are inexpensive, they may not maintain their strength if exposed to
continuous sunlight and extreme rooftop heat. A more durable solution is the use of
metal wire clips to fasten wires. Although these metal fasteners are more expensive
than plastic wire ties (typically $10 for 100 wire ties compared to $100 for 100 metal
clips), the superior durability of metal clips reduces the possibility of fire or shock
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hazards. Figure 12 below shows trunk cable properly attached to racking using stainless
steel clips.
Figure 12. Trunk Cable Properly Attached to Racking
(courtesy HatiCon Solar)
3.1.5 Improper Attachment of Panels to Racks, or Racks to Mounts
If panels, racking and mounts are not properly
attached, they could conceivably blow off the roof
during a storm. A windstorm may not only destroy
one or more solar panels in the array, but may also
present a legal liability to the homeowner or solar
installer. Windstorms of this magnitude are rare, and
the authors of this report are not aware of any
professionally installed residential rooftop systems
that literally “blew off of a roof.”
Manufacturers of panels and racking carefully
specify the type of hardware and exact methods of
installation that are necessary for their products.
Figures 13 and 14 show the use of “field-improvised”
fasteners (a hex bolt and washer) to attach a solar
Figure 13. Field-improvised Fastener
panel to a galvanized steel rail, instead of a
properly designed solar panel mounting system. Figure 15 shows what happened to an
adjacent fastener on this array after a few years of thermal cycling: the hex bolt and
washer slipped off the back of the solar panel. In a high wind situation it is possible that
this unattached solar panel will blow off the roof.6
6
Figures 13, 14 and 15 images courtesy of “Run on Sun” in Pasadena, CA.
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Figure 14. Field-Improvised Hex Bolt and
Washer and Fastener
3.1.6 Snow and Ice Damage
Figure 15. Hex Bolt and Washer Slipped Off
Panel Flange (Panel is Now Unattached)
F
In areas that experience snowfall, rooftop systems should be designed and installed to
withstand the expected weight of the accumulating snow. Generally, this means keeping
the panels away from valley areas on the roof where additional snow may accumulate.
However, the weight of the snow itself is not the only problem. As the snow melts and
then freezes at night, additional forces from ice buildup occur on the panels, racking and
mounts. These thaw-freeze cycles may dislodge the panels, bend the racking, and/or
loosen the mounts. Ice dams may develop under the panels and under the shingles as
puddles of water from snow and ice melt and refreeze, backing up other melt water. The
most common result is that water seeps through the fasteners from the loosened
mounting system, damaging the roof and rooms below.
The best way to avoid ice dams forming is to mount the panels on the roof properly.
Typically this means that the panels should not be too close to the roof surface (e.g.,
ideally 3” to 5” or more above the roof), and the panels should be mounted higher up
the roof closer to the roof’s ridge to minimize the amount of melted snow and slush that
can slide down the roof and lodge underneath the panels. Since most ice damming
occurs at the eaves, arrays in snowy climates should avoid mounting close to the eave
to minimize damage from ice dams. Finally, using properly flashed mounts will minimize
the chances of leaks through the fasteners.
3.2
Component Selection
3.2.1 Corrosion of Rooftop Mounting Components
Metal components on rooftops are exposed to rain as well as daily heating/cooling
cycles. Components made of improper materials will corrode over time and can
eventually fail, causing severe damage to the panels and rooftop.
For expediency and cost issues, non-outdoor rated materials are sometimes used in
rooftop installations. Ordinary steel, even when painted or galvanized, will rust and
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weaken over time in certain environments. Although commonly used, wood and plastic
components are generally not durable enough to provide structural strength after longterm exposure to bright sunlight and heat. Almost all plated or coated fasteners will
corrode and weaken on rooftops. Coastal environments make these problems even
more severe because of additional corrosion from salt-water droplets in the air. Figure
16 below shows aluminum racking and clips (both good) mounted with a corroded lag
bolt to a decaying wooden support (both bad).
Figure 16. Decaying Wood Support and Rusted Lag Bolt
For these reasons, best practices for solar installers include using aluminum-framed
panels and aluminum racking in combination with aluminum or stainless steel mounts.
Almost all fasteners (e.g., nuts, bolts, and washers) are stainless steel to prevent
corrosion and weakening over time.
3.2.2 Corrosion of Grounding Components
The electrical industry has a wide variety of grounding components that are used to
connect electrical equipment safely. Unfortunately, most of these components are
designed for indoor applications, not for rooftop applications.
On roofs, components are exposed to the elements, so the use of common indoor
grounding components frequently leads to rusting corrosion after only a few years. More
significantly, copper in contact with aluminum outdoors rapidly corrodes from a galvanic
reaction between the metals, leading to a degraded grounding connection.
The images below demonstrate how grounding components can corrode. Figure 17
below shows a braided copper grounding wire attached to the identified grounding lugs
on a module; galvanic corrosion between the aluminum and copper caused both metals
to degrade. Correct practice is to prevent copper and aluminum from coming into
contact, typically using an appropriate barrier material (like stainless steel) between the
adjacent aluminum and copper components.
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Figure 18 shows a grounding lug that is intended to provide the necessary isolation
between the copper wire and aluminum frame of the module. Although there was no
corrosion of the aluminum and copper, the carbon steel fasteners used to attach the lug
and wire rusted and lost some of their strength.
Figure 17. Corroded Braided Copper Grounding Wire
18. Corroded
Screws
Securing
a Grounding
Lug of specialized
To facilitate properFigure
grounding,
the solar
industry
has developed
a number
washers and lugs that simplify this grounding with standard solar panels, racking, and
inverters. Figure 19 below shows a grounding lug designed for easy fastening to solar
racks. Figure 20 shows a specialized grounding washer that is sandwiched between a
panel and the rack below to provide an easy to install grounding connection.
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Figure 19. Rack Grounding Lug
(courtesy Orion Solar Racking)
Figure 20. Weeb Panel Grounding Lug
(courtesy HatiCon Solar)
There are certain new solar panel models that include integrated racking and grounding.
These panels are designed so that when the panels are mechanically connected
together, a reliable grounding path is established among all the panels in the array.
Once installed, the only remaining task is to run a grounding conductor to a single point
on each array. When these systems are properly installed, the possibility of a missed or
inappropriate grounding connection is greatly reduced.
3.2.3 Improperly Sized or Poorly Designed Roof Flashings
Most installers now recognize that using flashings to waterproof the penetrations for
solar mounting attachments is critically important for long-term reliability. Unfortunately,
most locally available roof flashings are designed for pipe penetrations, which do not
experience the daily forces caused by expansion and contraction on a metal racking
system bolted to a wood roof, and do not meet the needs of sealing solar mounts for
25+ years.
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Many standard flashings lack a durable seal around the penetration or use metal that
could corrode after 10-15 years. Figure 21 below shows a flashing with a durable rubber
seal around the top that is designed specifically to meet the needs of solar installations.
Figure 21. Flashing with Rubber Seal
(courtesy Quick Mount PV)
4.
Costs of Potential Rooftop Mounting System Failures
Rooftop mounting system failures are still relatively infrequent. However, the problems
these failures can cause are not trivial. Repair costs (when not covered by warranties)
for these problems can range from a few hundred dollars for a half-day job, to over ten
thousand dollars and several weeks of active (on the job) and inactive (waiting for
various contractor trades to coordinate) repair work.
4.1
Roof Leaks
If mounting systems are improperly installed
as in Figure 22 to the right, roof leaks can
start within a year or two after heavy rains.
Repair costs vary depending on the scope
and duration of the leak and can be
minimized if the leak is noticed and fixed
expediently. To repair damage from a leaking
roof under a solar array, the following steps
are generally necessary:
1. Remove the array (either sections or the
entire unit). It is virtually impossible to
repair leaks that are underneath an
Figure 22. Water Damage around Lag Bolt
existing solar array; simply patching the
from Missed Rafter
leak is usually not effective since the
original source of the leak (usually an improperly installed mount) must be
remediated. In order to get access to leaking shingles and repair the roof
subsurface, one or more solar panels must be removed. Often it is not obvious
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exactly where the leak is located, so large segments of the array must be
dismantled.
2. Repair roof, underlying sheathing, and rafters (assuming a partial re-roof job for
the area under the array). Estimated typical costs for removing and reinstalling a
5kW array range from $2,500 to $7,500 (not including replacement of the roof) and
vary based upon array configuration, age of the array, ease of access, and condition
of wiring and racking.
3. Reinstall the array. Once the new roof is finished, it is necessary to reinstall roof
mounts (usually with new flashings), racking, panels, wiring, and grounding, and
then the system must be re-commissioned. The older the system, the more likely
wiring, grounding and racking hardware will need replacement. Note that the
contractor who does the removal and replacement work must re-commission the
system and will typically take ownership of some future warranty obligations.
After the leak is fixed, homeowners will still need to repair the damage to the home
caused by the leak. These repair costs can vary significantly depending on the extent of
the leak and the severity of the damage. Generally the major repair costs will be to the
damaged interior walls and ceiling. This often comes in the form of replacing the drywall
and trims with repair costs typically exceeding $2,000. After the damaged interior
surfaces are replaced, they must be repainted, which can add another $500 or more to
the total repair cost.
Homeowners’ insurance usually covers costs to repair water and roof damage, although
coverage varies by carrier and insured limits. To date, there have been very few
insurance claims related to rooftop solar power systems. With such a limited claims
history, the insurance industry has not adopted generalized policy requirements for
rooftop solar.
Generally, rooftop systems would be covered by a homeowner's policy as long as the
homeowner's total amount of insurance reflects the correct value of the home. If a claim
resulted from a product or installation issue, generally the homeowner would be
compensated for his or her losses (typically for removal of the array, repair/replacement
of the roof, repair of inside damage, and re-installation), and then the insurance
company would seek reimbursement from the manufacturer’s or installer's insurance
company.
4.2
System Outage
System failure can result from a short circuit caused by one of the rooftop wires being
pinched between panels and mounting components, or wires in conduit that may be
shorted. The solar array will stop producing power until the system is repaired. While
the system is inoperative, the homeowner or third-party system owner will lose any
potential power production during that period.
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The diagnosis and repair process for wiring problems usually takes an installer two to
eight man-hours once on site. Generally a two-person crew performs this repair work,
since panels may need to be removed and wires replaced in conduit. The installer
would normally cover this repair work within the five- to ten-year installer warranty
period. The cost of the repairs to the installer can range from $300 to $1,000 to cover
the installer’s time, labor, and materials.
4.3
Fire Hazard
According to the U.S. Fire Administration, cooking, defective heating systems, and
electrical malfunctions cause most residential fires. To date, of the over 400,000 solar
homes, there have been only a handful of residential fires caused by rooftop solar
power systems – statistically insignificant, but important nonetheless. The solar industry
continues to develop equipment and installation procedures that will hopefully avert the
possibility of rooftop solar power entering into these fire statistics.
5.
Industry Reliability and Safety Measures
Solar equipment manufacturers are conscientious in ensuring that their equipment
meets or exceeds applicable standards (such as the Underwriter’s Laboratory or UL
standards that apply to solar panels and inverters), and responsible installers strive to
ensure that their work meets applicable codes (such as the National Electrical Code or
NEC). Nevertheless, problems can sometimes occur, as outlined in this White Paper.
To minimize these potential reliability and safety problems, there are standards that
apply to the equipment being installed, and there are codes that apply to the way in
which equipment is installed on rooftops. As a final check, most jurisdictions have a
program of local building inspections to ensure that installations use equipment that
meets these standards and are installed in a manner that meets local building codes.
5.1
Standards for Solar Panels and Solar Panel Mounting Systems
Underwriter’s Laboratory (UL) develops and manages the various standards that apply
to solar equipment. UL also provides testing services to manufacturers to certify that
products meet these standards. Several other testing laboratories, including ETL, CSA
and TUV, provide these testing services and can certify that products meet relevant UL
standards. More detail about the relevant UL standards is included in Appendix A.
UL 1703 is the standard that applies to flat-plate photovoltaic modules and panels; this
standard has historically focused on safety issues related to the solar panel itself and
the way in which it is wired (not including the way in which it is mounted). A new version
of UL 1703 includes additional fire testing requirements.
UL 2703 for solar panel mounting systems is a newer standard that addresses
combinations of solar panels and mounting systems, including grounding. Revisions
and improvements to this standard have been in progress since 2013. These revisions
are nearing completion and UL 2703 is anticipated to become an American National
Standards Institute (ANSI) accredited standard sometime in 2014.
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5.2
Codes for Wiring and Grounding
The National Electrical Code (NEC) is adopted by the vast majority of jurisdictions in all
50 states and is the benchmark for safe electrical design, installation, and inspection to
protect people and property from electrical hazards. The NEC is published and
managed by the National Fire Protection Association (NFPA). The NEC addresses the
installation of electrical conductors, equipment, and raceways; signaling and
communications conductors, equipment, and raceways; and optical fiber cables and
raceways in commercial, residential, and industrial occupancies. The NEC is typically
updated every three years, most recently in 2014.
5.3
Codes for Flashings and Waterproofing
All 50 states and the District of Columbia have adopted the International Building Code
(IBC) and International Residential Code (IRC) as models for their own State Building
Codes (SBC). These "model" codes form the framework for local fire, building, housing,
property maintenance, plumbing, electrical, energy, and mechanical codes. The
Authority Having Jurisdiction or AHJ (see below for explanation) will generally base its
local requirements for flashings and waterproofing on some version of the IBC or IRC,
as described in more detail in Appendix B.
5.4
Authorities Having Jurisdiction (AHJ) and Local Building Inspections
In construction, the AHJ is the governmental agency or sub-agency that regulates the
construction process. In most cases, this is the city or county in which the building is
located. The AHJ generally provides final approval for a rooftop solar installation. AHJs
look for conformance with applicable codes and standards and often interpret these
rules to meet their own local requirements.
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6.
Conclusion
As with any home renovation project, there are certain product features and installation
procedures that maximize the long-term performance and safety of a system. Solar
equipment manufacturers, standards organizations, code officials, and responsible
installers all strive to install reliable and safe systems.
Nevertheless, it is useful to reemphasize some of the key elements that are most likely
to ensure high-quality installations. The following recommendations are based on the
experiences of the White Paper contributors, thousands of installation anecdotes, and a
detailed survey of 20 existing rooftop systems:
Mounting systems must be designed for rooftop solar installations and not for general
equipment installations. Components must be listed to the appropriate standards, and
compatible with the equipment being installed. All structural components (including
fasteners) must be stainless steel or aluminum. Research findings did not uncover any
corrosion or structural failures on old systems that used components designed for solar
installations.
All roof attachments must include flashings designed for the solar mounts being used.
Roof attachments must be designed to work with the selected mounting system. Welldesigned flashings greatly minimize the chances of leaks around installed standoffs.
Notably, among the 20 homes surveyed, we did not identify any roof leaks from
mounting points that were properly flashed – even if some rafters were possibly missed.
Use wiring and grounding components designed and UL-listed for hot and wet rooftop
conditions. Components designed for ordinary indoor wiring are not suitable for solar
arrays. There have been significant improvements in the quality of grounding
components; use of these new components will maximize the long-term integrity of
grounding connections.
Use components that prevent arc faults where possible. Current codes require the use
of power electronics components that improve safety by reducing the possibility of fire
hazards or shocks from arc faults, although these components are only now becoming
UL-listed and widely available. These components are designed to instantly shut down
high voltage arcing (DC-DC converters and string inverters with arc-fault prevention
circuitry), or avoid high DC voltages in systems altogether (microinverters).
Choose equipment (panels, inverters, racking, grounding, and wiring) with built-in or
factory-assembled safety features. AC panels are available with integrated
microinverters and grounding. DC panels are available with integrated DC-DC
converters that have arc-fault prevention circuitry. Panels are available with integrated
racking and grounding. This integrated equipment is not only faster to install, but also
minimizes the potential use of inappropriate or incompatible components.
Finally, select an installation company with a reputation for quality work, that uses its
own trained installation crews, and that is likely to be in business to honor applicable
warranties.
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7.
Appendix A – Applicable UL Standards
7.1
UL 1703 – Solar Panels
These requirements cover flat-plate photovoltaic modules and panels intended for
installation on or integral with buildings, or to be freestanding (that is, not attached to
buildings), in accordance with the National Electrical Code, NFPA 70, and Model
Building Codes. These requirements cover modules and panels intended for use in
systems with a maximum system voltage of 1000 V or less (residential systems are not
allowed to exceed 600 V per NEC requirements). These requirements also cover
components intended to provide electrical connection to mounting facilities for flat-plate
photovoltaic modules and panels.
7.2
UL 2703 – Solar Panel Mounting Systems
These requirements cover rack mounting systems, mounting grounding/bonding
components, and clamping/retention devices for specific (manufacturer/model
designation) flat-plate photovoltaic modules and panels that comply with the Standard
for Flat-Plate Photovoltaic Modules and Panels intended for installation on or integral
with buildings, or to be freestanding (i.e., not attached to buildings), in accordance with
the National Electrical Code, ANSI/NFPA 70 and Model Building Codes. These
requirements cover rack mounting systems and clamping devices intended for use with
photovoltaic module systems with a maximum system voltage of 600 V. These
requirements cover rack mounting systems and clamping, retention devices pertaining
to ground/bonding paths, mechanical strength, and suitability of materials only.
Revisions and improvements to this standard have been in progress since 2013. These
revisions are nearing completion and UL 2703 is anticipated to become an American
National Standards Institute (ANSI) accredited standard sometime in 2014.
7.3
UL 1741 – Inverters
These requirements cover inverters, converters, charge controllers, and interconnection
system equipment (ISE) intended for use in stand-alone (not grid-connected) or utilityinteractive (grid-connected) power systems. Utility-interactive inverters, converters, and
ISE are intended to be operated in parallel with an electric power system (EPS) to
supply power to common loads. For utility-interactive equipment, these requirements
are intended to supplement and be used in conjunction with the Standard for
Interconnecting Distributed Resources With Electric Power Systems, IEEE 1547, and
the Standard for Conformance Test Procedures for Equipment Interconnecting
Distributed Resources with Electric Power Systems, IEEE 1547. These requirements
cover AC modules that combine flat-plate photovoltaic modules and inverters to provide
AC output power for stand-alone use or utility-interaction, and power systems that
combine other alternative energy sources with inverters, converters, charge controllers,
and ISEs, in system specific combinations. These requirements also cover power
systems that combine independent power sources with inverters, converters, charge
controllers, and ISEs in system specific combinations. The products covered by these
requirements are intended to be installed in accordance with the National Electrical
Code, NFPA 70.
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8.
Appendix B – Flashing and Waterproofing Codes and Standards
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IBC 1503.2. Flashing shall be installed in such a manner so as to prevent
moisture entering the wall and roof through joints in copings, through
moisture-permeable materials and at intersections with parapet walls and other
penetrations through the roof plane.
IBC 1503.2.1 Flashing shall be installed at wall and roof intersections, at gutters,
wherever there is a change in roof slope or direction; and around roof openings.
Where flashing is of metal, the metal shall be corrosion-resistant with a thickness
of not less than 0.019 inch.
IBC 1506.1 The requirements set forth in this section apply to the application of
roof-covering materials specified herein. Roof coverings shall be applied in
accordance with this chapter and the manufacturer's installation instructions.
Installation of roof coverings shall apply to the applicable provisions of Section
1507.
IBC 1506.2 Compatibility of Materials. Roofs and roof coverings shall be of
materials that are compatible with each other and with the building or structure to
which the materials are applied.
IBC 1506.4 Product Identification. Roof covering materials shall be delivered in
packages bearing the manufacturers' identifying marks and approved testing
agency labels required in accordance with Section 1505 Bulk shipments of
materials shall be accompanied with the same information issued in the form of a
certificate or on a bill of lading by the manufacturer.
IBC 1507.2.9 Flashings. Flashings for asphalt shingles shall comply with this
section. Flashing shall be applied in accordance with this section and the asphalt
shingle manufacturer's printed instructions.
IBC 1507.8.7 At the juncture of the roof and vertical surfaces, flashing and
counter flashing shall be provided in accordance with the manufacturer's written
installation instructions, and where of metal, shall not be less than 0.019 inch
(0.48mm) (No, 26 galvanized sheet gage) corrosion-resistant metal.
IRC: International Residential Code 2012
o M2301.2.7 Roof and wall penetrations: Roof and wall penetrations shall
be flashed and sealed in accordance with Chapter 9 of this code to
prevent entry of water, rodents and insects.
o R903.2 Flashing: Flashings shall be installed in a manner that
prevents moisture from entering the wall and roof through joints in
copings, through moisture-permeable materials and at intersections with
parapet walls and other penetrations through the roof plane.
IBC: International Building Code 2012
o 1510.6 Flashings. Flashings shall be re-constructed in accordance
with approved manufacturer’s installation instructions. Metal flashing
to which bituminous materials are to be adhered shall be primed prior to
installation.
o 1507.2.9 Flashings. Flashing for asphalt shingles shall comply with this
section. Flashing shall be applied in accordance with this section and
the asphalt shingle manufacturer’s printed instructions.
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