It turns out that electrical fires involving photovoltaic systems can lead to some unexpected problems for fire departments. So says the Fire Protection Research Institute, guardians of the National Electrical Code.
Here's part of the rub: It is customary to shut down the electrical system in buildings where fire erupts. And that's easy enough to do when there are no PV panels on the roof. But PV systems generally only have a single disconnect point that isolates them from the main electrical system. Flipping this switch cuts the link between the power lines and the PV panels, but doesn't stop juice from flowing in the PV system itself, assuming the sun is shining.
The other problem is that fire departments often depend on the utility to cut the power to buildings where there is an emergency. But any PV panels on the building are typically beyond the jurisdiction of the utility. Often times, firefighters don't know who to call in order to de-energize the panels.
These issues have resulted in a set of recommendations from the FPRI which include a better standard way of handling emergency shut-downs, better labeling on PV-enhanced electrical systems for emergency responders, and a better means of generating emergency contact information.
In addition, the FPRI says that on-going operation and maintenance concerns for solar power systems need to be addressed. FPRI worries that these systems normally see outdoor weather conditions that speed the aging process. It says the infrastructure needs to be in place to make sure these systems get the kind of on-going maintenance that will assure their safe operation.
As is so often the case with enhancements to fire and safety codes, these recommendations come from real experiences. For example, says FPRI, a California fire last year involved a large PV solar array comprised of 166 strings of 11 modules each on the roof of a department store. Two separate electrical fires broke out remote from each other, caused by electrical arcing. Fortunately the resulting two-alarm fire was didn't get past the solar modules and didn't get through the store’s roofing materials. The responding fire department couldn't readily isolate the burning modules. This fire happened on a bright sunny day, and the modules continued to generate electricity throughout the event with no way to de-energize them.
Some of these issues are addressed in the 2011 release of the National Electrical Code, but of course, not all jurisdictions immediately adopt code changes.
You can read more about these issues at the FPRI's NEC site: http://www.necplus.org/Features/Pages/ThePoweroftheSunResearchinSupportofSafePhotovoltaicPower.aspx?sso=0