Strong winds and home solar panels: installation best practices

Solar panels are designed to withstand severe wind, including hurricanes. Here's some guidelines to help ensure that your installation stays safe and secure.

Wind damaged solar array (Credit: FEMA)
Wind damaged solar array in Puerto Rico. (Credit: FEMA)

Solar panels intended for use on homes and businesses are remarkably strong and designed to withstand many different kinds of abuse from the weather, including rain, hail, and severe wind.

In North America, test standards require that solar panels must be able to support 5,400 Pascals (Pa) of force on the front of the panel. That works out to 0.783 pounds per square inch. An average sized solar panel is about 2,500 square inches, which means that one panel can support about 2,000 pounds!

That’s a remarkable amount of pressure. Because of these high design standards, you can be confident that your solar panels will do well in severe weather including wind.

However, as you can see in the photo above, failures can happen, especially when you’re dealing with hurricane-force winds. It is possible for panels to survive even in these conditions, and this article will give some best practices.

How much force can severe winds impart?

According to the National Hurricane Center, a Category 5 hurricane is the most severe type, with wind speeds starting at 157 mph. By their definition, you can expect catastrophic damage to occur:

A high percentage of framed homes will be destroyed, with total roof failure and wall collapse.

This means that the question of whether your solar panels can survive the most intense hurricanes is a little moot, because there’s a good chance that your roof won’t. However, most hurricanes are less severe: a Category 1 hurricane is one with sustained winds between 74 and 95 mph.

How much force does a Category 5 hurricane impart, exactly? 157 mph winds is equal to 2,940 Pa. That’s a lot of force that’s within the strength rating of a solar panel - but only if the wind is striking from the front.

How strong are solar panels?

As mentioned above, solar panels are required to meet certain test standards. When it comes to mechanical strength (ie. resistance to bending under stress), IEC 61215 is the relevant standard. It contains 19 module quality tests, including hail resistance and static mechanical loading, which is relevant when it comes to winds.

The minimum standard for the front of a solar panel is 5,400 Pa of loading. A panel must be able to hold this force for 1 hour to pass the test. The rear of a panel only needs to meet a lower standard of 2,400 Pa.

The front side test is often called the snow load, and the back side is also known as the wind load. This is because solar panels need to be able to hold the weight of snow on top, or withstand high winds that hit the rear of the panel, particularly in ground mounted applications.

You might think that rear loading isn’t an issue for roof mounted solar panels, but there is always a gap of several inches between the roof surface and the panels. That’s enough space for high winds to get under the panels and generate significant uplift force.

How do solar arrays fail in high winds?

Numerous components are involved in the installation of a rooftop solar array, and component failures or poor installation practices can lead to system damage in high wind situations. Here are some possible ways that a rooftop mounted solar array can fail in a hurricane:

  • Panel frames can bend, causing them to detach
  • The clips that secure panels to racking system can bend or break
  • The fasteners (bolts) that secure the clips to the rack can fail due to corrosion, self-loosening over time, or under-tightening by the installer
  • The footings that secure the rails to the building can detach due a failure of the footing or the roof structure
  • Impact damage to the panels
  • Poorly secured wiring can detach
  • Electronic components (such as microinverters and power optimizers) can suffer wind or impact damage
  • Wind-driven rain can penetrate into panels or electronics

Not all of these hazards (such as flying debris) can be avoided, but some installation practices and product choices can increase the robustness of a system.

Some solar panels are stronger than others

One of the easiest ways to have a more robust system is to choose solar panels with higher than minimum strength ratings described in IEC 61215.

Look up the manufacturer’s specification sheet to find a solar panel’s strength rating. These will be listed as front side or snow load and back side or wind load.

The minimum you’ll find for any panel should be 5,400 Pa snow and 2,400 Pa wind load. However, some manufacturers will exceed this standard. This is accomplished with stronger frames that have better resistance to bending. Here’s a few popular brands with better-than-minimum strength ratings:

  • SunPower X-Series and M-Series: 8,000 snow/4,000 Pa wind load
  • Panasonic EverVolt: 7,000 Pa/4,000 Pa
  • QCells Q.Peak Duo G10+: 8,100 Pa/4,000 Pa

By selecting a panel with a high strength rating, they’ll have less chance of bending in the wind and detaching from the racking system. It’s an easy way to have a stronger system.

Make sure that your racking system is rated for high winds

The panels themselves are only one factor when it comes to designing an array to survive high winds. Another important consideration is the racking system, which is the component that attaches solar panels to a rooftop.

In the photo at the top of this article, you can see that several panels are missing. This racking system is attached to a standing seam metal roof. While the anchors are still attached to the roof, the panels have been ripped away. Most likely, the anchors bent and failed, allowing the panels to detach.

(You can also see that several panels are bent and cracked. According to the FEMA report, the damage was caused by an antenna that crashed onto to the roof.)

As a homeowner living in a hurricane zone, what can you do? An important thing is to look for a racking system rated for use in High Velocity Hurricane Zones (HVHZ). In Florida, HVHZ zones include Miami-Dade and Broward counties.

The Florida Building Code (FBC) certifies products for HVHZ, and Miami-Dade does as well. This means that you can look for solar racking products with a Florida certification for HVHZ, or a Miami-Dade Notice of Assessment (NOA). A Miami-Dade NOA or a Florida Product Approval for HVHZ meet the same standard.

Some racking products that meet hurricane zone standards

Here’s a list of some solar panel racking/attachment systems that meet FBC or Miami-Dade hurricane standards:

  • AceClamp Solar Snap
  • EcoFasten ClickFit, RockIt, and QB-1
  • IronRidge Flush Mount System (including FlashVue, FlashFoot2, L-Mount, QBase, and XR Rails)
  • Unirac Solar Mount PV
  • SnapNrack SpeedSeal
  • Sunmodo NanoMount, SoloFlash, and EZ Metal Roof Mount

Installers need to follow manufacturers specifications to ensure windproofness

Even if equipment is rated for hurricane zones, it must be installed correctly to meet its expected performance. For solar racking systems, a key detail is making sure that any bolts are tightened according to the manufacturer’s specifications. This means using a calibrated torque wrench.

FEMA, which investigated solar array failures after Hurricanes Irma and Maria in the US Virgin Islands, found that bolt failures were a common reason for solar array damage. In addition to making sure that bolts are tightened correctly, FEMA adds a further recommendation:

Specify double-nutting the panel clamp bolts. For the first nut, specify nuts that are furnished with T-bolts. For the second nut, specify a stainless-steel lock nut with a nylon insert.

Microinverters make for a more robust system

While they won’t do anything to prevent damage, using microinverters will help your system continue to work even if some panels are knocked offline.

Home solar arrays that use string inverters typically have their panels wired into 1 to 3 strings. Similar to Christmas lights, an entire string can be knocked offline if one part of the string is damaged.

That’s not the case with microinverters, where every panel works independently of each other. If some panels in a microinverter-based system are damaged, the others will continue to work.

There’s not much you can do about flying debris

IEC 61215 also includes testing for impact resistance. This involves firing 1-inch ice pellets at 51 miles per hour at the panel. A solar panel must be able to withstand 11 impacts without damage to pass the test.

While that’s a robust test in normal circumstances, a Category 1 hurricane has sustained winds of at least 74 mph. This means that debris could be flying around at a much higher speed than the panels are tested against.

Unfortunately, while the front glass of solar panels is very strong, there’s not much you can do about large objects (like the antenna that stuck the array pictured at the top of this article) or those flying at a high speed.

Inspect your system after a hurricane

After any high wind event, check your system for any damage. Look on your monitoring system to see if any individual panels have failed, then visually inspect the system, looking for cracked or bent panels, loose wiring, or other issues.

Unfortunately, not all damage is visible. Solar cells can experience what are known as microcracks, which is damage that isn’t visible to the naked eye but which can reduce the lifespan or power output of your panels. Microcracks are caused by bending (which is a reason why you should never walk on solar panels) and the damage might not be obvious right away. One way to avoid this is to choose a panel with a stronger frame, such as one of the SunPower, Panasonic, or QCells products listed above.

Summary: what solar homeowners can do to protect their system in a hurricane

While it’s impossible to completely protect your property in a hurricane, there are some steps that a solar homeowner can do to help lessen the chances of having damage to their system:

Use hurricane-rated equipment. Hurricane-rated equipment is designed to survive extremely high wind gusts. This means looking for equipment that is certified by the Florida Building Code or Miami-Dade for use in High Velocity Hurricane Zones (HVHZ).

Hire an installer who is knowledgeble about local codes. Building codes in hurricane-prone areas will specify guidelines for roofing structures and how solar panels are attached, which often means bolting into structural rafters. An engineering review and permit may be required by your local authorities. Make sure that your installer is up-to-date on your local building codes and your project is permitted.

Double check bolted connections before a hurricane event. Even if bolts were torqued according to the manufacturer’s specifications when the system was new, they can loosen over time. Before hurricane season, you may want to have an installer double check the connections to ensure that they are correctly tightened.

Choose solar panels with high wind and snow ratings. While all solar panels must meet robust standards for mechnical loading, some manufacturers exceed the minimum standards. Look on a manufacturer’s datasheet to find out if a panel exceeds the typical 5,400 Pa front side (snow) load and 2,400 Pa back side (wind) load ratings.

#Weather #Racking Systems

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