The larger the openings (space between wires), the bigger the critters which will have access to the solar array. The industry has coalesced around a maximum opening size of 1/2″, which blocks most critters without restricting airflow. 1/2″ wire mesh is sometimes called 2×2 mesh or #2 mesh.

A wire gauge of AWG 19 (about .04″ in diameter) is recommended for long-term durability. Note this is significantly thicker than chicken wire and will hold its shape once bent.

Note that galvanization (see “corrosion resistance,” below) also affects wire stiffness and strength. Wire mesh sold without galvanization will be much softer and less springy than galvanized mesh. We do NOT recommend non-galvanized mesh.

We recommend only galvanized, plastic-coated wire mesh. These two treatments should allow the mesh to last the lifetime of the PV system (despite some light cosmetic rust). Go with a well established manufacturer, since there is no easy way to judge the quality of these treatments on sight. The image at right shows a poor-quality wire mesh which rusted prematurely.

Wire meshes can be galvanized with two different techniques – Hot-Dip and Electroplating. Hot-dip galvanization forms a much thicker and more resilient barrier to moisture.

A typical residential PV array requires between 100 and 300 feet of wire mesh to enclose. Wire mesh is typically sold in 100-foot rolls, but some distributors cut it into shorter lengths (usually at a significant per-foot markup). The wire mesh width needed for a particular PV array depends on the racking system and installation method – but the most common are 4″, 6″ and 8″.

OSA is the percentage of a screen’s total area which allows air to pass through. A high OSA (say 90%) allows good ventilation; picture a screen with very thin wires and big openings. A low OSA (say 70%) allows air to pass through only 70% of its area, leading to high array temperatures and poor PV performance.

Screen Type	Specification	Open Screening Area
Typical AG wire mesh	No. 2 mesh, 19 gauge, galvanized & coated	81%
Window Screen	No. 16 mesh, 29 gauge	68%
Solatrim	Perforated sheet metal	45%

Please see our separate article on this important distinction!

In all but the driest, most inland locations, 304 stainless steel and/or aluminum should be used for any fasteners penetrating aluminum racking. This is supported by installer experience, construction industry best practice and PV racking manufacturer recommendations. Note that some grades of stainless steel (e.g. 400 series) corrode when in contact with aluminum module frames and racking. A quick way to tell the difference is to hold a magnet next to the fastener (304 stainless is NOT magnetic). While plain steel electroplated “Tek” screws are easy to find, solar technicians in coastal climates have found their thin zinc coatings aren’t up to the task.

Plastic – even the type rated for UV exposure – is not suitable for continuous outdoor exposure.

All of the specialty clips listed below are meant to grab onto the solar panel’s aluminum frame. Every model of solar panel uses unique dimensions for the frame, and some clips are incompatible with some frames. Many installers have found this to be a weak point of the SnapNrack clips, which require a deep lip on the PV frame to work. CritterBlok seems to have come up with a clever solution to this with their 2-part clamp design.

Specialty clips generally fall into two categories – Full-support clips and J-hooks.

Full-support clips, like SnapNrack’s old hangers and CritterBlok, suspend the wire mesh above the roof surface and prevent the mesh from being pushed in or pulled out. This makes them a top choice for metal roofs, where the homeowner does not want the mesh touching (and scratching) the roof surface. The risk with these clips is that they can come unclipped from the solar panels due to snow loads or curious animals. We’ve found CritterBlok does a great job of holding on to the module frame, while SnapNrack’s old hangers were not trustworthy.

J-hooks pin the wire mesh to the PV module frame, but require the mesh to rest on and be supported by the roof. They are therefore NOT suitable for metal roofs where roof-to-mesh contact can be noisy and unsightly. The main weakness of most J-hooks is that they rely on a pushnut to grip a “J” shaped wire. Pushnuts tend to be flimsy and susceptible to slippage, so we don’t feel they are appropriate for an installation that must stand up to 25+ years of weather and curious animals. SnapNrack appears to have gotten around the pushnut issue with their new clips, which use a threaded interface instead of a pushnut.

While plastic zipties continue to be used throughout the solar industry, they are simply not appropriate for continuous outdoor use on the time scale of a PV system. Do not be fooled by “UV-rated” zipties; while they do last longer than non-UV rated ones, they will break down and crack in the sun after 3 or 4 years.

Stainless steel zipties are a fantastic replacement for plastic zipties. At around 13 cents each, they are affordable enough to easily justify making the switch.

Hogrings are available in a wide range of materials. We recommend stainless steel or coated galvanized steel (which is less rust-resistant, but will last at least as long as the underlying wire mesh due to the hogring’s thicker wire gauge).

Shiny fasteners will stand out like a sore thumb on an otherwise discreet animal guard installation. Hog rings and cable ties can both be purchased pre-painted black, saving the installer the trouble of spray painting them at the end of a job.

There are a number of hogring tools on the market, and each is compatible with only certain size hogrings. Ensure the gauge (e.g. #14 or #15) and size (e.g. 9/16″) match the tool you plan to use.