Once the construction permit is approved, you or your solar installation company will have a few preliminary tasks to undertake before the big job begins. While the installation is a straightforward process, a lot of building and electric codes come into play, so the margin for error is small. For example, if you run out of the proprietary fasteners used on the array racks or rails, or find out that you've rented the wrong diameter of conduit bender, the job will grind to a screeching halt. So get organized, do your homework, ask a lot of questions, devise a game plan, create a To-Do list, and (at the very least) have an experienced installer oversee your work. (You can search for professionals in your area using the free NABCEP installer directory.)
A PV array is installed on a Milwaukee residence above asphault shingles.
This section describes the most common type of home PV installation and is divided into the following tasks:
Most solar suppliers have restrictions and deadlines when it comes to returns and exchanges, so as soon as the merchandise arrives:
After measuring voltage on the modules, be sure to re-cover the module glass with its packaging, then leave that in place until the installation.
The NEC and most AHJ's require that solar components be installed according to the instructions provided by the manufacturer. That's because the product engineering specs are based in part on the method of installation used. A building inspector on site may ask to see one or more of these guides, or other product literature, so be sure you insert all the documenation in your construction binder. The binder should contain:
Take plenty of time to read the literature before you start the installation. Use the instructions to write out a to-do list. This will allow you to lay out your equipment, hardware and tools in an organized manner as you move through each task For instance, installing a mount requires a certain size socket or drill bit, while attaching wire to terminals requires a specific amount of torque when tightening the screws. And don't forget to review all the applicable codes discussed back in Step 2 of this tutorial.
Whether you're working on your own home, or someone else is working on it, OSHA safety rules should always be observed. A lot can go wrong when installing a solar power system, like falling off a ladder or roof, or getting zapped with electricity or an arc blast. That's why the OSHA guidelines are no joke. Even if a contractor is liable for any mishaps to the crew, your home is no place for a debilitating injury occur. As a property owner, you have the right to insist on compliance and to report major violations to a higher authority if necessary.
Here are the most common rules that should be observed on site:
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For every 4 feet of height, the base of ladder should be 1 foot away from the side. The ladder should extend at least 3 feet above the roof, so you can grip the extra rails as you climb off or onto the surface.
For more info on working with electricity, check out the website Electricians' Toolbox.
A staging area is a central place where equipment and tools are kept while construction is in progress. While it's helpful to keep this location as close as possible to the roof access point (or other array site), it's more important that you keep your gear safe from the elements and theft. You should also keep sidewalks and the street clear.
You should never pile equipment or supplies on the roof, since that structure has a limited load capacity. Any material you do bring up there should be spread across many square feet, rather than concentrated in a single spot.
If applicable, post your building permit, construction bond and any other required documents before the installation begins. If you have new workers on the job, they should be briefed on the following:
Needless to say, you or your contractor should plan the installation to coincide with a week of mild temperatures and no precipitation. Most residential installations take one to three days with a crew of 2-6 installers. The time it take to finish the job depends not only on the size of the array and the components used, but also on the wire run between the array and the main service panel. You'll have to construct wall mounts for the inverter and other, smaller electrical components, and an awning if the inverter will be subject to direct sunlight.
If battery back-up is included in the design, add another day or two to the project.
Common tools used in home solar electric installations include:
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You'll also need a wire pulling tool (photo upper right) and, depending on the roofing surface, tools to cut the shingles. You won't need a generator for this project. Other supplies will be needed to seal roof penetrations (e.g. Geocell), fasten wires in place beneath the array, fasten and secure conduit, create metal-to-metal grounding connections (e.g. Wiley WEEB's), cap wire splices, provide a workspace on the ground (i.e. sawhorses and plywood top), and mount the inverter and electrical boxes at their designated locations.
Occasionally, a specialty or proprietary tool must be used, especially when installing rails or mounts, so be sure to check the manufacturer's instructions to see if that's the case. And don't hesitate to contact a supplier or manufacturer for technical assistance. Most companies have a hotline set up to help installers who run into trouble.
Most rooftop installations begin by measuring and marking the spots where holes need to be drilled for the racking mounts. The general area and rooftop chosen for the array is based on the shading assessment conducted during the site survey. Fire regulations also stipulate the amount of roof space that must be kept open on the upper ridge, sides of the roof, and valleys (if any). Aside from those constraints, think about how the array will look tfrom the street. Ideally, you'd want to place your modules in a balanced and symmetrical fashion, as shown in the photo below.
Shoot for symmetry and balance a when locating a solar array. You should also keep the wires out of view.
First, take your the site drawing (Step 5 -System/Array Sizing) and do some quick math to make sure the array will fit the space as envisioned in this design. (For this taks, you'll need to know the dimensions of the modules, plus the required space between modules (where the midclamps are inserted) and 2-3 inches extra at the ends of each rail. This math will give you exact rail lengths for each row. After checking to make sure the drawing is accurate, you can mark out the corners of the modules.
Another potential obstacl that may come up (usually during the site visit, but sometimes during the installation) is the location of a roof vent. If it's right in the way of where a module will sit, you'll have to adjust your layout. If caught during a site visit, you can also ask the homeowner if you can reroute the vent to another spot on the roof. This is usually done when there's limited available space for the array, or if you need to place a module there in order to have two strings of the same size (a requirement for most string inverters).
Next, you'll measure and mark the placement of the mounts according to this product's installation instructions. Of course, each mount must be attached to a rafter or beam that holds up the roof. So before you start marking out your locations, you must locate the rafters first. These are typically placed 24 inches apart, usually designated on drawings as simply "24"O.C.
Before installinga solararray, be sure you understand how the roof is constructed. It's essential to secure your mounts to the beams, trusses or rafters, which all refer to the 2 X 6 or 2 X 4 inch studs holding up the plywood decking and other roofing material. These studs are normally spaced 24 inches apart, and have a relatively narrow 1 1/2 inch thickness in which to drill into.
Although it's not a best practice, many installers hammer nails in the roof to locate rafters. A better method is to mark the sides of roof where the eaves reveal the wooden beams. Then you can run a chalk line upward from those points. Sometimes the beams are a little bowed and don't run up in straight line. For this reason, you'll have to tap the roof with a hammer to exactly locate the beam or rafter along each module row. A stud finder also works for this task. Since the width of the lumber is only 1 1/2", the task of drilling into the middle of one can be a challenge.
After the rafters are more or less located, the next task is to determine where the rails will go (since they sit atop the mounts). Typically, a module is supported by rails set 6 to 8 inches inward from either end of the module as it protrudes past the rails. (It should be the same distance on either side.) You'll have to consult the rail product instructions for the exact measurements.
When securing each mount to a rafter, its lag screw must clear the decking below the roofing surface and securely fasten into wood. The instructions for the mounting product will give you the correct length and diameter of the lag screw (commonly 5/16"). The length of the bolts, of course, must take into account how much roofing surface you have to drill through before the screw reaches the stud. And once the screw passes into the wood, there needs to be enough thread to drive it in a good ways. Wind load calculations for the rails will factor in the maximum allowable withdrawal. This refers to the wind's ability to create sufficient torque to unwind screws from their positions. (In the movie Twister, you can see the withdrawal scenario graphically illustrated.)
Hoosic Valley School
Geocell or some other type of polyurethane caulk is used whenever hole penetrations are made into a roof. In the photo above, the caulk is applied to the back of a mounting bracket. It should also be applied to drill holes, the back of flashing and on the back of shingles loosened in order to insert flashing.
Before you install any lag bolts, you'll have to make room for the flashing that will sit under the amount. Flashing directs water away from the lag screw hole, thus helping in the cause of protecting the roof and attic from sustaining any water damage in the years to come. While there are many types mounts on the market, your best bet is the one that comes with flashing, and even a black rubber boot, as shown in the photo below. In a typical scenario, an installer loosens (and sometimes cuts) the shingles around the location of the mount, then slips the flashing into place. Afterward, whatever shingles still fit in the space can be reinserted. Hard and thick masonry tiles require a bit more labor and additional tools.
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At left, a typical mount installed in an asphault shingled roof (photo: A&R Solar). At right, a standoff mount product graphic from Quickmount PV.
Be sure to caulk the back of the flashing and any drill hole penetrations with Geocell or some other polyurethane caulk before you insert the lag screw with an impact driver. And don't forget to fill in any other holes you might have made trying to locate a stud. (If you hammered in nails to find the studs, DO NOT remove them.) You'll also need to caulk the back of the flashing before sliding it into place among the shingles or tiles. Aterwards, replace any removed tiles that will still fit around the mount.
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Continued on Page 12-B (More Installation Tasks.)
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