The following is a synopsis of the new FM Global Property Loss Prevention Data Sheet 1-15 “Roof Mounted Solar Photovoltaic Panels.” This is a new data sheet, issued in July 2014 with October 2014 revisions. This review is a follow-up adjunct to Risk Logic’s article of January 2014.
The publication of FM Global’s Data Sheet provides some new insight and tools which can be utilized to design and assess risk factors associated with rooftop installations of solar PV panels.
Herewith are various bullet points and commentary which are of interest within DS 1-15:
- Wind resistance, understandably, is a major consideration. Although there are many references to design factors, we are asked to utilize one of two methods to evaluate wind pressure resistance for ballasted or anchored PV panels:
- Prescriptive calculation methods provided in SEAOC PV2; or
- Conduct boundary layer wind tunnel (BLWT) testing
- The SEAOC (Structural Engineers Association of California) PV2 is a particularly interesting document, as it provides a look at the complex factors and calculations for a relatively simple installation. The use of the SAEOC PV2 document is also likely to be a far more practical alternative to wind tunnel testing, which is likely to be costly and time consuming. It should also be noted that a separate SEAOC PV1 similarly addresses seismic issues for PV panels.
- PV installations that are clamped on standing seam roofs require clamping at every seam. It is not permissible to clamp every other seam, as this can result in an unbalanced wind load to the roofing system.
- The use of wind deflectors on the high side of the panels is indicated as a means to create a “closed array” (where wind is limited on the underside of the panel). Unfortunately, there is no methodology provided to assess the efficacy of this type installation, and it is likely to require boundary layer wind tunnel testing.
- FM disallows the use of any PV panel systems using foam plastics, unless specifically FM approved as part of the assembly. FM Approval Standards 4476 and 4478 for Flexible and Rigid PV Modules address fire, simulated wind uplift, hail damage, and heat aging of the panels a part of the finished roof assembly.
- Another interesting and very practical recommendation is for aisles or spacing to allow access to the PV array. Also recommended is that the public fire service perform a plan review of proposed roof and panel layouts with respect to access.
- Continuing with the theme of Nat Cat Hazards, all of the following are included as appropriate design considerations: analyze for snow loading using DS 1-54, and use appropriately hail rated panels for hail areas indicated as “Moderate,” or greater severity, per DS 1-34; consider rainfall intensity (DS 1-54) and water flows to roof drainage with respect to obstructions that may be caused by panel installations, or curbing; and attach panels to the building frame in areas where seismic activity is likely per DS 1-2.
- A section entitled “Operation and Maintenance” provides valuable information on routine inspection and testing of PV systems. As with most any type of system, routine visual inspections and proper preventive maintenance go a long way toward preventing loss.
- The Data Sheet considers ground faults to be a very significant fire hazard, and indicates that adherence to current electrical codes and practices may not provide adequate protection against a fire initiating from a ground fault condition. There are specific recommendations for current monitoring/sensing equipment to address DC ground fault situations, as well as several other items for electrical safeguards.
Unfortunately with this Data Sheet, FM Global fails to provide us with any illustrative loss history. However, they do furnish an excellent reference section which incidentally cites articles on two separate fires involving solar rooftop installations. Both of the cited articles can be found online as of this writing.
Risk Logic, Inc. can answer your questions regarding this Data Sheet and advise you as to how it can apply to your facility.
BP – Bürstadt, Germany June 21, 2009
Target – Bakersfield, CA April 5, 2009