Solar PV and Standing Seam:
The Perfect Marriage for Commercial Rooftops
Rob Haddock,
Posted
01/09/2012
Looking at solar photovoltaic (PV) costs and roof costs together
as a single asset reveals the strengths of the standing seam metal
roof, making it the most highly favored PV mounting platform for
both practical and economic reasons. Roofing costs have always been
regarded as a significant line item in the overall construction
budget, but those costs pale in comparison to the installed cost of
a power generation system that can climb to more than $50 per
square foot.
Given these facts,
mounting a PV system onto a conventional roof type is a bit like
putting a Formula 1 racecar engine on a Ford Taurus chassis-it just
doesn't make sense! Not only is standing seam a much better
mounting platform than other roof types, but the cost advantages
also make the marriage of PV to metal a nobrainer. Metal roof
manufacturers and contractors should know the benefits of their
product range as it relates to solar technologies, which Solar
array direct attached to a SSMR. The standing seams create a
perfect platform to attach solar have become the buzz of the green
movement.
The metal roofing community has always been apologetic for
higher initial costs when compared to conventional roof types,
presenting life cycle cost arguments to justify their premium price
tag. Not anymore. When power generation is a building design
objective, metal is actually the low-cost alternative not only from
a life cycle basis, but also from the initial cost standpoint. This
makes the decision for metal roofing a slam-dunk under such
circumstances, and opens a whole new market for the retrofit of
existing flat roofs.
Comparing costs
When installed on built-up (BUR) and single-ply membrane roof
types, PV arrays are mounted on racks. A framework of aluminum must
be constructed and mechanically attached through the roof membrane
into the building structure to support PV modules. Aside from the
obvious disadvantage of punching a lot of holes through the roof,
such a scheme is also expensive. Installed mounting system costs
range from $0.60 to $1.00 per watt on commercial systems.
In limited instances, the framework is ballasted (to avoid roof
penetration and at a lower cost), but this method is constrained to
new construction because the building structure must be designed
for the added load of the ballast.
On the other hand, when the roof type is standing seam, such
framework (or ballast) is 
unnecessary, and direct mounting costs
range from $0.15 to $0.20. This means an initial cost savings of $
0.45 to $ 0.80 per watt. It may not sound like much, but to
translate into square-foot costs, multiply by 10 watts per square
foot (net output of crystalline PV systems). That results in $4.50
to $8 per square foot initial cost savings by mounting to standing
seam rather than traditional commercial roof types. Such savings
are often 15 percent or more of the completed system cost
(including both roof and PV).
The good news doesn't stop there. Usable life of crystalline PV
is 30 to 40 years. Usable life of most roof membranes (other than
standing seam metal roof) is 12 to 20 years. This means that the
roof will require replacement before the PV system and in some
cases, more than once. To do this, the PV modules, together with
their racking system must be removed and then reinstalled following
roof replacement, adding logistical difficulty and considerable
cost to an already expensive roof replacement.
The added cost of the removal and reassembly of the PV together
with roof replacement ranges to an additional $15 to $20 per square
foot or $1.50 to $2.00 per watt. Additionally, while this process
takes place, the system produces no power, which can mean tens of
thousands or more of lost dollars on a large system.
Details of mounting to SSMR
The benefits of structural standing seam metal roofing (SSMR)
and PV lie with the methods of mounting the array and the longevity
of the completed system. To begin with, the SSMR generally provides
a service life in excess of 40 years, outlasting the PV array. The
PV array is mounted on SSMR using aluminum seam clamps that pinch
the seam within the clamp via round-point stainless steel
setscrews. This obviates the need for both racking and roof
penetration. The holding strengths of these clamps are, in many
cases, published and can exceed the beam strength of the panel seam
as well as its attachment to the structure. Interface hold-down
hardware is bolted to the clamp body and anchors the PV modules to
the top of the seam clamps.
It is common that solar modules are installed in landscape
orientation (long dimension traversing seams) and ganged together
with adjacent modules upslope and downslope, sharing a mounting
point and attachment clamp. Given a module width of 3-plus feet,
and assuming industry standard structural purlin spacing of 5 feet,
the resulting attachment frequency of PV modules to the SSMR is
equal to or greater than the attachment frequency of the SSMR to
the building structure.
Depending upon wire-management techniques and other details, it
is not only a possible but common practice to mount massive power
generation arrays on metal rooftops with zero penetration of the
roof. The round-point setscrews ensure no breach of metallic
coatings or galling of the roof materials, leaving weather
integrity and roof warranties intact.
Because of the longevity of the SSMR, roof replacement prior to
expiration of PV service life is not an issue. And, if that isn't
enough, the recyclability, durability and maintenance freedom of
metal are also far superior to other roof types. On top of all the
foregoing benefits, the installation costs are also significantly
lower. The SSMR provides a convenient grid-work of beam-like
configurations so direct attachment is simple and the mounting is
much less labor intensive, translating into significant cost
savings over other roof types.
One thing is certain. Initial PV costs for SSMR are
significantly lower than for other roof types. Total life cycle
costs analysis that considers necessary roof-replacement costs
during the usable life of the PV will also demonstrate that using
metal roofing under the PV not only conserves the environment, but
conserves the cash as well.
Rob Haddock is the founder of S-5! and has 35
years in the industry. Starting out as a metal building erector,
today Haddock is a well-known metal roof consultant, author,
speaker and inventor. For 15 years, Haddock operated one of the
nation's largest metal roofing companies with approximately 10
million square feet of successful installations nationwide. He also
serves as director of the Metal Roof Advisory Group Ltd., a
consulting firm performing a variety of services for a worldwide
clientele.