Utility Solar Battery Fire in Arizona

The Fire Department was called about 6 p.m. Friday (4/19/19) about smoke rising from the APS McMicken Energy Storage site. The responding firefighters were evaluating the lithium battery when there was an explosion that left the firefighters with serious chemical and chemical-inhalation burns. One of the firefighters was in critical condition at the Maricopa Medical Center's burn unit in Phoenix and in surgery until 1 a.m. before becoming stable.

This incident illustrates that utility scale battery systems can be very dangerous. Further information is not available as of the posting of this article. As more information becomes available, the Solar Center will provide updated coverage.

 The battery system is one of two identical battery systems installed in late 2016 and became operational in early 2017.

There is a good article on these battery systems on the  APS website at On Edge of Phoenix, APS Tests the Relationship of Solar and Batteries

The McMicken unit is contained at the head of the feeder in an existing substation.

Note, these are smaller, earlier batteries that those described in our earlier APS battery article: APS announces 'Solar after Sunset" battery storage inititative

Recent APS presentation slide on these systems, still no further incident details.

Still no report as of 7/5/20


Many others have taken note of this fire such as Littleton (NH) fire chief raises concerns about battery energy-storage facility

SRP is proposing three new Price Plans for Rooftop Solar

SRP is proposing three new price plans for residential customers who produce their own energy with rooftop solar and other technologies. Two of these options have no demand charge associated with them. See the SRP Proposal. Be sure to open the 'View graphics'. Specific rates are not shown. There were rate setting board hearings for residential and business electric and solar customers in front of the SRP Board at the Arizona Heritage Center in Tempe on March 4th, 11th, and 25th at 9:30 a.m. Follow this link to learn more. The complete Proposed adjustments are available on-line. The new solar price plans are E-13, E-14 and E-15. The base E-27 'Customer Generation' Price Plan is not much changed.

UPDATE: SRP is considering another solar rate alternative.  The Arizona Republic has a good article on this in the 3-14-2019 issue:


Rapid Shutdown of Photovoltaic Module Series Strings

Rapid Shutdown of Photovoltaic Module Series Strings

With the increasing number of Photovoltaic (PV) power systems being installed on buildings and the concern of emergency first responders (firemen) that these high voltages on buildings represent a hazard to first responders, the National Electrical Code (NEC) has added requirements intended to address this hazard. Many PV power systems use a design with many series connected PV modules (termed ‘strings’) to simplify wiring and increase efficiency. Presently these systems can use strings with cold open circuit voltages of up to 600 volts DC on residences, up to 1000 volts on non-residential buildings, and up to 1500 volts in utility scale installations. The problem is that even if the wires from the PV array are disconnected, high voltages remain and emergency responders could be exposed to high voltages even if all electrical power is shut off for the building.

To address this hazard, the NEC added Section 690.12 Rapid Shutdown of PV Systems on Buildings in the 2014 edition. The requirements were refined in the 2017 edition. Methods and designs for achieving the proper rapid shutdown are not addressed by the NEC but instead are addressed in the product standards (such as UL Standards) for this type of equipment. The figure below from the September/October issue of Solar Pro magazine (see solarprofessional.com) illustrates the requirements.

RapidShutdown2014 vs 2017

There are many ways that the PV industry is addressing these requirements:

Module Level Electronics (MLE), the inclusion of electronic devices within the PV modules:

  • Micro Inverters, one per PV module (or sometimes for 2 modules), to produce AC power from the PV array area. Due to inverter requirements, these inverters must shut down any time the AC power is disconnected or fails (utility outage).
  • Power conditioners for each PV module that are controlled by the central inverter and are designed to shut down whenever the inverter is shutdown.
  • Other shutdown devices such as small remote switching devices, controlled by the inverter or a separate rapid shutdown switch..

Array rapid shutdown devices that are placed within the array boundary and disconnect the PV array whenever the inverter is shutdown.

Inverter location – simply placing the string inverter close to the PV array, within the array boundary. Inverters are being designed to allow such low profile mounting.

In Arizona there is no state wide building code, cities and counties determine the applicable codes and versions of codes.  For instance, Phoenix is now on the 2017 version of the NEC and the 1' boundary applies, while Scottsdale is on the 2014 version of the NEC and the 10' boundry applies. The installer will have to obtain building permits and follow the applicable code version.


Activating rapid shutdown:  PV systems installed following either the 2014 or 2017 versions of the NEC will have a reflective label (left image) near the electrical service showing the switch that will put the PV system in shutdown mode.  This label may be either on the AC disconnect (center image- for systems that shutdown upon loss of the utility connection) or on a separate switch (right image).  PV systems using micro-inverter and installed following earlier NEC versions may not be labeled.


Note: Several Arizona cities have adopted the 2017 NEC and now require Rapid Shutdown-  Phoenix, Glendale, Peoria (10-1-19)