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Our Barn Roof Gets an 18-kW Solar Array

We’re installing 72 photovoltaic modules on the standing-seam roof of our Vermont barn

Posted on Jun 13 2013 by Alex Wilson

When we started planning the rebuild of our house and the rest of the farm in West Dummerston, Vermont, my wife and I knew that we wanted to produce all of our energy on-site. That meant a solar-electric or photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) system that would generate as much electricity as the house and barn are consuming — net-zero energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines..

We also wanted to protect as much of the 10 acres of agricultural land as possible. That meant we wanted to avoid a ground-mounted PV system. Wherever land can be used for farming — now or in the future — I prefer to install PV arrays on buildings, keeping the land open for agricultural uses.

Fortunately, the 1812 barn has a long roof facing almost due south. That would be the perfect location for the solar array. Our builder, Eli Gould, spent several months restoring the barn, which involved replacing damaged posts, adding sturdy granite supports under those posts, rebuilding several dry-stone walls to support the barn sills, lowering and leveling the floor, replacing some timber framing elements (including about a dozen round-log joists that we cut on the land), and reinforcing the roof to hold the solar modules.

To maximize durability, we wanted the roof to be sturdy and not flex with wind or snow loads, so after stripping the layers of metal and asphalt roofing, we added a layer of 2x6 and 2x4 framing to the roof structure, flattening the roof plane at the same time. Zip sheathing went on over that, and then the roofing.

Standing-seam metal roofing

One of our goals for the whole project has been to maximize durability, so we spent quite a while debating different roofing materials. We wanted the solar panels to be able to attach to the roof without any penetrations, so that meant standing-seam roofing. S-5 brackets for the solar array tracks clamp on to the raised seams of the roofing with absolutely no penetrations of the roof. If panels have to be removed down-the-road for some reason, that’s relatively easy to do.

For the roofing itself, we chose 24-gauge Englert galvalume 1301 roofing with the company’s low-gloss Ultra Cool coating. According to James Hazen of the company, Englert’s paint line is one of the cleanest operations of its kind in the world, with 100 percent of solvent fumes from painting, drying, and curing operations captured. The captured paint fumes are burned with all the recovered heat used in manufacturing. The company expects a 150-year life for the roofing. Roofing contractor Travis Slade, of River Valley Roofing in Putney, Vermont, has done an incredible job installing the standing seam roofing.

Group net-metered system

We have a great location that can hold an 18-kilowatt (kW) PV array, but we don’t need a system that large. So last fall we began investigating community solar options, and we found a neighbor who wanted to buy 6 kW out of the 18 kW system. In other words, this neighbor will actually own a third of the PV system that’s on our barn roof.

This option for someone else to own part of a PV system in a different place is referred to as group net meteringArrangement through which a homeowner who produces electricity using photovoltaics or wind power can sell excess electricity back to the utility company, running the electric meter backwards., and Vermont is one of the few places where this can be done. Green Mountain Power bends over backwards to facilitate such systems, which is wonderful. Through this option, someone without a south-facing roof where PV modules can be installed can look elsewhere for a good south exposure.

Because the 12-kW system that we will own is still larger than we will need for our house and barn (at least until our farm needs expand), we will plan to sell our excess capacity to another Green Mountain Power customer.

Selection of the PV modules

At the recommendation of our solar installer, Integrated Solar Applications, in Brattleboro, we are installing highly rated REC 250PE modules. The modules are rated at 250 watts, have 15.1% module efficiency, and come with a 10-year product warranty and 25-year “linear power output warranty” (guaranteeing that the degradation of power output will not exceed a 0.7% per year). REC is a Norwegian company with the silicon raw materials produced in the U.S. and silicon wafer, PV cell, and PV module manufacturing being done in Singapore.

Poor reliability and early failure of PV modules has been in the news lately, so I’m relieved that ours aren’t simply commodity Chinese-made modules (though some Chinese products are no doubt fine).

In future columns I will address other features of our PV system, including “islanding” capability that will provide us with some electricity even when the electric grid is down.

Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. In 2012 he founded the Resilient Design Institute. To keep up with Alex’s latest articles and musings, you can sign up for his Twitter feed.


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Image Credits:

  1. All photos by Alex Wilson

1.
Jun 13, 2013 5:14 PM ET

Impressive array of solar panels
by Lucy Foxworth

I really like the S-5 clamps as well.


2.
Jun 13, 2013 10:20 PM ET

focusing on the roof
by Hobbit _

Having gotten a standing-seam metal roof recently myself, that's
the part that's grabbing most of my attention. Tri-flex *under*
the new framing? That's an interesting configuration; what was
the thought process behind that? I don't think it's supposed to
seal around fasteners like I & W shield does. Are the Zip
panels and tape the primary WRB?

You had a chicken-ladder all pre-padded up to protect the panels;
my contractor had to build one on site. No fall-arrest gear in
sight over here either.

I have the parts for an S-5! snow-guard system ready to install
here, using the S-5-U type clips on 1.5" snap-together panels.
The seams will have to be squoze in just a little bit to allow
the clips to fit over the slightly fatter snap-down seams, but
I agree that it seems like a really nice system. [Ignoring the
potential long-term issues of dissimilar metals in the clamping
screws...]

On the topic of cheap panels ... after the drywall fiasco you'd
think that buyers would be a little more discerning about offshore
quality control. But I keep hearing these horror stories all the
time; it's pretty depressing how the dollar keeps trumping common
sense. Me, I won't be buying solar panels at walmart any time soon.

_H*


3.
Jun 13, 2013 11:02 PM ET

Tri-flex under the roof framing
by Alex Wilson

The Tri-flex was mostly aesthetic, but also provided some handy protection during a very wet spring. The barn is uninsulated, so no air barrier to speak of. The original roof sheathing boards have lots of gaps, so we wanted a black backer when you're in the barn looking up at the underside of the roof. I was surprised the builders didn't use a cheaper asphalt-impregnated felt paper, but left that up to them.


4.
Jun 15, 2013 12:42 PM ET

Kudos to group net metering ; maintaining ag under ground-mount
by Jonathan Teller-Elsberg

Congratulations on a beautiful array, and also for empowering (argh) your neighbors to join the party through group net metering.

I agree that it is more sensible to put PV up on roofs when possible, rather than over potential ag land. However, it is worth keeping in mind that field-based arrays of solar do not have to exclude agricultural use. I'm not sure how common it is to do so, but more than one European field array doubles as sheep grazing land. For that you'd probably space the solar panels further apart to ensure sufficient light reaching the ground for good grass production. It seems entirely plausible that, for the farmer's economics, the double harvest of lamb/wool and solar generation is a winner. There is also a case in North Carolina -- where things are a lot hotter than in Vermont -- where a ground-mounted solar array was built on extra-high posts above a small, commercial garden. In their case, they report improved tomato crop set as compared to exposed fields, because the weather has been so hot in recent years the tomato pollen has been sterilized. The partial shade cast by their PV array keeps temps to within fertile range.

So yes, when possible, put your solar on a roof. But where not possible, take time to consider and design continued ag use into a field-based array. (Including atypical ag such as shade plant nursery operations or mushroom cultivation.)


5.
Jun 17, 2013 6:42 PM ET

Grounding and panel support
by Richard Kinkel

Thanks for the story and I have to say I’m envious of your 18k system.

Pic 11 “Detail of grounding for the panels”

This pic shows the use of zip ties and IMHO have no business being used on a roof top system. Sure UV resistant zip ties cost 2 cents but will they last the 30+ years that we’re expecting the system to last? Stainless steel Acme cable clips ACC or equivalent are well worth the 40 cent premium at keeping he wires off the roof. Many residential systems are installed over asphalt shingles and keeping the wires off the roof is imperative for the long haul. Unfortunately I’ve seen too many installs where many of the wires are laying on the roof w/o even zip ties or any attempt at wire management.

The pic also shows the copper rail grounding wire is bent over onto the aluminum racking rail. Dissimilar metals not are good for system longevity.

“Ground for the panels” is a little misleading. Part of the equipment ground or the rail ground would be more appropriate. I looked through the pics but didn’t see any module grounding or WEEB clips. Was each module grounded with a tin coated copper lug in one of the UL approved 4 corner locations?

I’m guessing you live in snow country. Page 8 of the installation manual “In areas of snow build-up, panels can be subjected to forces in excess of the stated limit even when snow depth does not appear extreme, causing damage to the framework. If the installation is likely to be affected, further suitable panel support is recommended on the lower row of panels.” page also shows proper UL approved grounding. REC PE Installation Manual http://www.recgroup.com/Documents/Downloadcenter/Solar%20product%20downl...

Ground mount system also have the benefit of being easily serviced in addition to atypical ag as Jonathan eluded too.


6.
Jun 17, 2013 8:18 PM ET

Grounding and panel connections
by Alex Wilson

Richard,
I don't know any of these details, but will pass on these comments to Integrated Solar Applications (ISA), the installer. I had wondered about dissimilar metals (as noted in an earlier comment relative to securing the S-5 clamps). ISA, based in Brattleboro, Vermont, has a good reputation, and I'm confident that they're adequately addressing snow loads, grounding, and such.


7.
Jun 18, 2013 10:04 AM ET

thought on ag under ground-mounted systems
by Skip Harris

In many regions moisture is the limiting factor, so shading 50% or more of the ground area might be a positive for productivity...

In this area, the limitation appears to be sunlight rather than moisture.


8.
Jun 18, 2013 3:57 PM ET

dissimilar metals
by Rob Fisher

Alex,
The dissimilar metal issue is called galvanic corrosion. Aluminum and stainless steel are far enough apart in their galvanic compatibility that there could be and issue. Aluminum and copper are even father apart in compatibility. The good new is that the aluminum is the metal that will be corroding in both of those situations and there is much more aluminum than either of the other metals.

Given that this system is designed to be installed on roofs, which get wet, I would guess that this system is designed with the larger amount of aluminum to act as the anode, spreading the corrosion over the greatest area. I would confirm this with the installer/manufacturer though.


9.
Jun 18, 2013 5:41 PM ET

Edited Jun 18, 2013 5:43 PM ET.

dissimilar metals
by Richard Kinkel

Rob,

“spreading the corrosion over the greatest area”

From my experience it tends to be localized. Here are some examples from an old Home Power Code Corner Article by John Wiles. http://www.nmsu.edu/~tdi/pdf-resources/cc137.pdf

Folks looking to design and install NEC compliant PV grounding should do a search for John Wiles and Ryan Mayfield + PV grounding.


10.
Jun 19, 2013 3:44 PM ET

dissimilar metals redux
by Rob Fisher

Richard,
Clearly your hands on experience is better than my obviously incomplete understanding.

Regarding Alex's copper/aluminum issues; it seems that if the lug is tin coated copper then it is installed according to Wiles article? And should be acceptable?


11.
Jun 19, 2013 7:53 PM ET

dissimilar metals
by Richard Kinkel

Rob,
Yes if a tin coated copper lug was used it would be correct for the rail bonding but hard to tell from the photo if that’s what was used. My issue was with the copper wire being bent over onto the aluminum rail. There also needs to be a way to bond the modules to the rail either as outlined in the article using one of the UL tested module locations or using a WEEB or equivalent system approved by your JHA.


12.
Jul 1, 2013 1:47 PM ET

Grounding and connection details
by Alex Wilson

I asked Mike Whigham of Integrated Solar Applications, the Brattleboro company installing our system, to comment on the questions raised about grounding, clips, and snow loads. Here's Mike's response:

Equipment Grounding: this is the appropriate term when referring to grounding equipment in the PV system such as rails and modules. In this case the bare copper ground is connected to the rail with a tin coated copper lug. The wire appears to be touching the aluminum rail but it is not. We typically bend the end of the wire down as it is a sharp end that can cut an installer, but is done so as not to touch the rail.

Zip Ties: We use a combination of UV-resistant zip ties, Acme cable clips and rubber gasketed Adele clamps depending on the application. We have seen issues with the Acme cable clips in locations where the wire comes into the rail at an angel (say from the rail above). Such tight bends can cause cutting of the PV wire at these junctions so we prefer to use zip ties in those locations. It’s not a cost questions as much as an appropriate application decision. Wire management is one element of racking and module design that needs some more R&D.

Snow Loading: Snow build up on the lower edge of modules is a very important part of proper design here in VT. There is a trend in our industry to minimize the number of roof attachments to save on parts and labor. We do not take that position, and in fact always adhere to the attachment requirements set forth by the racking and module manufacturers, as well as local building code. In this case we confirmed the maximum rail span and due to the seam spacing placed S-5! Clamps more frequently than required. The roof is very well attached to the sub-structure and we exceeded the number of required seam attachments to ensure a safe and stable array.

Michael Whigham
System Design and Sales
Integrated Solar Applications
121 Spring Tree Road
Brattleboro, VT 05301
http://www.isasolar.com/


13.
Oct 31, 2014 9:59 AM ET

Satisfaction with metal roof ?
by Michael Kinzlmaier

The roof looks great. In fact I am thinking of doing the same on my home ( i.e installing metal roof on the back of my home and then installing solar panels ). I am just wondering how satisfied you are with the roof after a year in service ? Is the roof noisy when the wind blows or when it expands/contracts ? I am looking at the Englert 1300 1.5" SS panel which is similar to the one you installed although .5" taller, it look to be an excellent product. Any advice you could give me would be greatly appreciated.


14.
Oct 31, 2014 11:17 AM ET

Re: Satisfaction with metal roof
by Alex Wilson

Michael,

We are very happy with the roof. I wanted to go with standing-seam metal so that we could avoid all roof penetrations for the solar module racking system attachments and wiring, but also for durability reasons. The particular Englert metal roofing we used is supposed to be particularly durable. Englert sent me accelerated aging test information that has led them to believe that this roofing will last 150 years!

As for noise, I rather like the sound of rain on a metal roof (call me weird), but it turns out that in our house, where we used the same roofing as on the barn, we can barely hear when it's raining--even if it's pouring. We installed 15" of Johns Manville spray-applied fiberglass insulation in our 16"-deep (scissor-truss) rafters, leaving an inch air space at the top. Spider goes in kind-of like damp-spray cellulose, and it provides tremendous sound deadening — probably not quite as good as cellulose, but very good. Anyway, the insulated roof very effectively blocks most of the noise from rain, and I've never heard any noise from thermal expansion and contraction.

I think the protrusion of the seams is more about the roofer than the metal roofing. Our seams protrude about 1". Our roofing contractor does a final turn-down fold in his standing seams, which some roofers do not do; I don't know what difference that makes, if any. He has the best reputation in the area for quality.


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