Sun & Shade With a Double-Duty PV Pergola

Advanced

Inside this Article

Although “rooftop solar” has become synonymous with residential-scale solar-electric systems, your home’s roof isn’t necessarily the only—or best—location for a PV array. It certainly wasn’t for our situation.
This glass-on-glass Lumos Solar GSX PV module and rack system provides a weathertight roof surface, yet allows light to pass between the cells, creating a lively shaded space beneath the pergola.
Mike Singer and the author assemble bents of 8-by-8s on the ground.
Monica Martin and Mike bolt the first bent to its foundation brackets.
Joining bents together with the first south crossbeam.
Cranking in big lag screws is hard work in the hot sun. Matthew Reynolds takes a breather.
The finished pergola with six 13-foot-long 6-by-6 rafters spaced for the PV module span.
Six GSX mullions were bolted in place to the rafters with 16 3/8-inch lag screws per mullion.
Top- and bottom-edge GSX transoms were installed with internally routed PV interconnect jumpers. Jumper locations and connector polarity were meticulously marked in advance to avoid irreversible errors—once the PV modules were in place, accessing the wiring would be nearly impossible.
Top- and bottom-edge GSX transoms were installed with internally routed PV interconnect jumpers. Jumper locations and connector polarity were meticulously marked in advance to avoid irreversible errors—once the PV modules were in place, accessing the wiring would be nearly impossible.
GSX documentation showed PV wiring within the racking structure, but routing jumpers from one column of PV modules to the next required cutting slots at the ends of the mullion sidewalls. This allowed interconnect jumpers to be fed through the transom. Then, the transom was slid into place as the wires were slid into the slots. Rubber grommets on the wires help protect the insulation.
GSX documentation showed PV wiring within the racking structure, but routing jumpers from one column of PV modules to the next required cutting slots at the ends of the mullion sidewalls. This allowed interconnect jumpers to be fed through the transom. Then, the transom was slid into place as the wires were slid into the slots. Rubber grommets on the wires help protect the insulation.
The first module in place! The spans of the structure made positioning the heavy glass modules tricky.
The hardware assembly in place—the top plate, modules, transoms, and mullion, including rubber gaskets. The double-sided tape on the transom still has its red backing. A strip of blue tape was applied to mask a line of caulk.
Progress was incremental, module by module. Top plates couldn’t be secured until adjacent modules were placed, and adjacent rows needed to be in place before the seam could be caulked.
PV wires exit the GSX assembly through the bottom of a transom and pass through a four-pole disconnect before travelling underground to the inverter 175 feet away.
Excessive labeling satisfies NEC requirements, nerd inquiries, and “don’t touch” scare tactics.
The 5 kW SMA Sunny Boy 5.0 US grid-tied inverter with Secure Power Supply connects to a subpanel in the shed.
Twenty 265 W Lumos Solar GSX PV modules, rated at 5.3 kW, are expected to produce 7.6 MWh per year, about 87% of the home’s yearly load. GSX modules have 60 bifacial monocrystalline cells in a 39.5-by-67-inch footprint. Without any perimeter frame, the double layer of glass is just under one-third of an inch thick; each module weighs 67 pounds.
About 380 square feet of covered patio space provide shade and rain protection. The space is ready for a barbecue, cafe table, and—once the jasmine grows up the trellis—maybe a daybed.

Several obstacles—shade, orientation, size, complicated roof angles, dormers, and vents—can preclude a rooftop PV installation, but that doesn’t mean you have to give up your PV dreams. This was the case for our home in southern Oregon.

In a climate that can reach triple-digit temperatures in the summer, my fiancée Sarah and I value the canopy of oak trees that shade the roof of our rural 1960s ranch-style home. Their shade significantly reduces our reliance on mechanical air conditioning. And, while a PV system ranked high on our list of home improvements, it seemed absurd to cut down shade trees so we could install a rooftop PV system to make electricity, which would then be needed to provide cooling that the trees had provided originally. Besides, Sarah is a botanist specializing in native plant habitat restoration—there would be no tree-cutting on our little plot of nature.

A solution wasn’t that difficult: Our south lawn was big, with room for gardening and entertaining, and a near-unobstructed solar window. Adding a ground-mounted PV array would have been relatively straightforward but without ancillary benefits. Instead, we decided to build a pergola shade structure and mount the PV array on top of it. We’d gain a cool hangout zone in the yard, and the PV modules could do double-duty: making electricity and acting as a roof over the new patio.

Choosing PV

I’d long been attracted to bifacial and other glass-on-glass PV modules. With no back sheet, bifacial PV modules can achieve higher power production due to additional reflected and ambient sunlight reaching the back surface of the cells. In locations with the right reflective surface below the array (such as light-colored concrete, white gravel, snow, water, etc.), production can be boosted by as much as 25%.

For our application, additional appeal was the slick look of glass-on-glass modules. From underneath, you can see the silicon cells—unlike other PV modules, which have opaque backings. Between the individual cells, a small amount of sunlight can stream through. The effect beneath the array is like dappled sunlight coming through trees.

Pages

Comments (3)

RMichael Curran's picture

Those huge beams look nice but weren't they overkill for the loads they had to support? Plus I bet they were expensive. Didn't their weight make construction more difficult?

Gotta admit it's a very nice looking finished product. Nice job!

Edit: Just saw your cost summary at the end. The beams weren't cheap but having lots of friendly labor is a great offset!

Chris Clark_3's picture

Nice project with helpful discussion and photos of details. I built a similar awning PV system using Lumos 180w panels a few years ago and have been very happy with the performance and aesthetic. Located on west side of house, its shade in summer has made a previously intolerably hot side of the house a pleasant place to spend summer afternoons and evenings while providing 100% of my electric needs. Shade structures like this pergola also make it easier to deal with winter snow shedding by avoiding the problem of ice damming underneath the array if rack-mounted on rooftop. Also, no issues with future re-roofing.
I wonder if you were able to determine how much drop in performance to expect with such a long dc run (175') ahead of the inverter. Also, with barbecue plans, I'd suggest keeping the grill outside the perimeter of overhead panels as smoke will otherwise collect and spread beneath all panels, over time creating a greasy film that may reduce the benefit of a bifacial surface you paid a premium for.
I like your idea to use wire for a trellis on south side to provide shade in summer but some solar gain in winter. (If growing annuals like beans or morning glory, or perennials like grapes).

Ben Root's picture
Hi Chris, Thanks for writing. Your project sounds great. We'd love to see Pics. I sized the DC wire run for short circuit current and the 156% rule. This gave me #6 for the 175 ft. run. Actually though, the MPPT circuit in the inverter should typically hold the voltage and current from the array near max power levels. That means 310 V (10 modules in series) and 8.56 amps. Using those values, the typical voltage drop should be about 1.2 volts (0.38%). Pretty reasonable. (Now, making those eight #6 connections inside that little DC disconnect was truly a hassle...no room to bend and work. And that much wire was expensive, a cost that your attached awning could avoid.) I'm glad that PV has become plug and play for so many people these days, making the technology easy, cheap(er) and more prevalent. But I'm also glad that we can still design custom systems to meet our individual needs, and preferences.
Show or Hide All Comments

Advertisement

X