Tuesday, October 20, 2015

Is Rooftop Solar Catching Fire – Literally?

In May of 2015, a rooftop solar fire was ignited by the solar panels on the roof of an Apple-owned facility in Mesa, Arizona. That begs to question, with growing demand for green energy, what are the real risks of solar installation catching fire on a rooftop?
Utility scale and commercial rooftop solar power is becoming more prevalent as the United States and individual corporations look to reduce their dependence on fossil fuels. Rooftop solar photovoltaic (PV) farms consisting of solar panels are an excellent way to introduce clean, renewable energy and utilize unused rooftop space; however, these renewable power plants introduce new challenges to solar manufacturers, system engineers, O&M companies, and fire fighters.
Research conducted two years ago indicated that rooftop solar-caused fires are very rare. A German study found approximately 75 instances out of some 1.3 million installations, while a study in the United States found only 7 instances in the entire country. While rare, the potential for a rooftop solar fire still exists and with the number of renewable energy systems growing daily, the risk grows exponentially.
What Can Cause Rooftop Solar Fires
It all starts with the components of both the solar array and the roof. Mounting solar panels and system components on the roof of a building can affect the combustibility of the overall roof system. Here’s what can happen:
In a combiner box, numerous wires from PV panels are connected. It is here that there is considerable voltage before the current is converted from DC to AC at the inverter. Electrical arcs near the combiner box can cause the PV panels to ignite as the backings of some panels are constructed of highly combustible plastic. Once the electrical arcs ignite the roof assembly, the fire can quickly spread under the solar panels and potentially across the entire rooftop.
How System Engineers Avoid Rooftop Solar Fires
When designing a solar array, there are several factors that can help prevent fires and/or can limit fire spread if ignition occurs:
  • Using a complete system that has been tested to simulate actual field conditions.
  • Avoiding installation of PV system on an older rooftop and choosing roof assemblies that limit potential fuel contribution in the event of a fire.
  • Investigating the need to coat the roof in expanded or extruded polystyrene insulation or multi-ply roof covers.
  • Securing mineral wool or other fire-resistant compressible insulation between wood nailers, covered by steel flashing.
  • Evaluating the underside of the PV panel for the least combustible material usage.
  • Utilizing PV panels that have passed fire tests that include testing with the proposed roof assembly.
How O&M Providers Avoid Rooftop Solar Fires
Once a solar array is installed, it’s up to a Solar Operations and Maintenance (O&M) service company to keep the system safely performing at optimal levels. To do this, the O&M Company will need to perform regular, scheduledpreventative maintenance, provide emergency services, monitor the system and audit its solar energy production.
Visual Inspection
Attention to every detail is critical in the operation and maintenance of a solar power plant. Something as simple as a regular visual inspection can prevent the system from being damaged by rodents and other pests, which could compromise wiring or insulation.
Repairs & Replacement
As manufacturers are taking steps to reduce the potential for fire by improving upon the electrical components, it is also important for O&M companies to keep up with these developments, as well as new code requirements. Repairs or replacements as recommended by the original equipment manufacturers (OEM) and governing bodies should be conducted in a timely manner. While some of these issues may be warranty related and some may simply be upgrades or more advanced technology – others can be critical at preventing system failure, fire or other safety hazard. Some examples are:
Some solar panels now have micro-inverters on each PV panel, which convert voltage from DC to AC. While this can be expensive to implement in a solar power plant, it will reduce the change of a fire igniting on a rooftop PV solar array.
Arc Fault Detectors
Arc faults are caused by air gaps between electrical conductors. The most common causes are faulty manufacturing, installer error, or aging, degraded connectors. Electrical current flowing across this type of loose connection produces sparks which could cause a fire.
An arc fault current interrupter (AFCI) senses the DC current coming into inverters in smaller arrays or into combiner boxes in commercial and utility-scale systems. The increased electrical noise of an arc fault will trigger a system shutdown before it causes a fire.
These devices can be added to a solar installation by an O&M service company for a cost of anywhere from $25 and $100 to each inverter string. While the 2011 National Electrical Code (NEC) requires AFCIs in rooftop solar arrays, states are allowed to implement NEC requirements at their own pace.
Monitoring Systems
To further protect against the potential for arc faults, the O&M Company managing the installation should be monitoring for signs of future arc-fault failures and preventative maintenance should be conducted to prevent fires.
Preparedness In Case of Rooftop Solar Fire
Regardless of the materials used in the construction of a PV panel, system, or the roof, its mere presence changes the dynamic of a fire involving a roof assembly. Fire fighters and other emergency first responder personnel need to understand and be prepared with adequate training with these unfamiliar hazards. Instruction is needed on structural fire fighting in buildings and structures involving solar power systems that utilize solar panels to generate thermal and/or electrical energy. Some of the training needed involves:
  • Ventilation – Firefighters need to be aware that they may be limited in where they can cut and it can take longer to cut ventilation holes in roofs with solar panels covering the surface.
  • Electrocution – When high-pressure water is trained on the roof, there is the potential for electrocution. Additionally, opening holes in the ceiling or attic space from the inside of a building may put firefighters in contact with metal conduit that is no longer grounded due to partial roof collapse or heat damage and therefore dangerous to touch.
  • Roof Collapse – Due to the additional weight on a roof, solar panels may increase the risk of roof collapse.
  • Exiting Roof – With the presence of rooftop-mounted PV arrays, it may limit the areas in which firefighters can exit the roof.
In conclusion, as rooftop solar arrays continue to proliferate, the solar industry and those involved in emergency response need to be keenly aware of the risks, the challenges and the new technology developments as they continue to collaborate to keep safety at the forefront of renewable energy generation.
Miller Bros. Solar (MBS) is a chosen leader in operations and maintenance (O&M) solutions due to the company’s project expertise, full construction capabilities, and 160+ pieces of heavy equipment. MBS is one of the few electrical contractors that can simultaneously self-perform multiple utility scale solar projects while exceeding client expectations, controlling costs and adhering to timelines and customer schedules.
Miller Bros. Solar provides O&M services for solar projects in the following states: Connecticut, Delaware, Ohio, Georgia, Indiana, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, South Carolina, Vermont, Virginia, and West Virginia.
For more information, visit http://millerbrossolar.com or call 610-832-1000.

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