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NFPA is planning on publishing a new and much-needed document, NFPA 855 Standard for the Installation of Stationary Energy Storage Systems (ESS). The document is in the Custom 2020 code development revision cycle and, assuming the document successfully gets through the process, is scheduled to be issued by the Standards Council in August 2020. The focus of this column will be on those ES systems using batteries for storage.
One of the many great things about living in the Aloha State is our weather and the many days of sunshine we have. Those of you who have been lucky enough to visit us may have noticed that the sun even shines brightly when it rains. We call it liquid sunshine.
The sun makes Hawaii an excellent place to generate energy from the sun. Scientific American recently noted that rooftop solar systems generate 33 percent of Hawaii’s electricity.
In our home, rooftop solar water heating and photovoltaic systems provide about 70 percent of our power needs. This includes running the air conditioner during weekdays when no humans are present, so our dogs can lounge the day away in cool comfort.
The first cost-effective residential consumer photovoltaic (PV) systems installed in Honolulu simply generated electricity that was fed back into the grid. Lucky early customers had net metering agreements with the utility where excess power generated fed back into the system, running the electrical meter backward. Those homes got one-for-one reimbursement (in a sense) for each kilowatt-hour used.
This program of net metering became so popular that our electric utility was overwhelmed to the point where it was destabilizing the grid. Keep in mind, Honolulu does not have the advantages of mainland states by sharing power with neighboring utilities.
This problem eventually led to a revamping of the net metering program and now new residential consumers whose systems feed back power to the grid are only reimbursed for a fraction of the power they generate for the utility.
When the utility changed the net metering agreement, the sale of PV systems dropped tremendously and most system providers went out of business. Solar PV was no longer a good deal for homeowners.
More recent improvements in the development of photovoltaic storage system batteries have made these systems affordable and cost-effective to residential consumers and the industry is beginning to recover slowly.
I may be clueless, but I cannot understand why our local power utility is so committed to making Hawaii use 100-percent renewable energy. Most of our energy comes from the burning of fossil fuels. I often joke that its current business model is to sell less-and-less electricity for higher-and-higher prices. Taken to its absurd extreme, the model results in the sale of no electricity for an infinite price.
I am interested in storage systems to generate the additional 30 percent and ultimately getting off the grid.
As noted, I have the luxury of being grandfathered under the old net metering arrangement. But there is the small issue of the monthly connection charge. Regardless of how much or how little electricity one uses, the utility charges a connection fee. Currently, it is a very reasonable $18 month. There is concern that one way for the utility to prolong the current business model will be to dramatically increase the connection charge (pure speculation from this conspiracy theorist, for sure).
Fire Safety Concerns
We all know the reasons why certain batteries cannot be stowed in checked bags on air carriers. Also, many of us in the business are aware of the research being done to address the special protection needs for lithium-ion battery storage in warehouses.
The rise in popularity of battery storage systems for solar PV systems has led to a rise in the concern for the fire safety of these systems. It looks as if NFPA 855 will address these concerns.
Please note the following information is based on the proposed draft of the standard and it is certain there will be changes by the time the NFPA releases the final document.
The proposed scope of NFPA 855 is the “design, construction, installation, commissioning, operation, maintenance, and decommissioning of stationary energy storage systems (ESS), including mobile and portable ESS installed in a stationary configuration.”
An ESS is defined as “one or more devices, assembled together, capable of storing energy in order to supply electrical energy at a future time to the local power loads, to the utility grid, or for grid support.”
Before we get into the body of the proposed standard, it would be good to look at excellent information provided in the several annex sections, in particular:
Annex B provides examples of the specific fire hazards involved with a wide variety of battery types including lithium-ion batteries. Annex F contains information currently appearing in other codes and standards.
Chapter 4 provides general requirements for ESS systems and comes right out of the gate by letting us know what the major issue is.
“4.1.1 General ESS Gas Release. ESS shall not release toxic or highly toxic gas creating conditions in excess of the permissible exposure limit (PEL) in the room or space in which they are located during normal charging, discharging, and use.”
Under certain conditions, Chapter 4 requires a hazard mitigation analysis which must address the following failure modes:
The following guidance is provided for the AHJ reviewing the analysis.
“22.214.171.124. The AHJ shall be permitted to approve the hazardous mitigation analysis as documentation of the safety of the ESS installation provided the consequences of the analysis demonstrate the following: (1) Fires will be contained within unoccupied ESS rooms for the minimum duration of the fire resistance rating specified in 4.3.6. (2) Suitable deflagration protection is provided where required. (3) ESS cabinets in occupied work centers allow occupants to safely evacuate in fire conditions. (4) Toxic and highly toxic gases released during normal charging, discharging and operation will not exceed the PEL in the area where the ESS is contained. (5) Toxic and highly toxic gases released during fires and other fault conditions will not reach concentrations in excess of immediately dangerous to life or health (IDLH) level in the building or adjacent means of egress routes during the time deemed necessary to evacuate from that area. (6) Flammable gases released during charging, discharging and normal operation will not exceed 25 percent of the LFL.
Table 4.4.2 contains a list of fire safety features required for indoor ESS installations. The table makes a distinction between dedicated-use ESS buildings and nondedicated-use buildings. Separation, smoke and fire detection, and fire suppression will be required for indoor installations in either case.
Regarding separation: “4.3.6 Separation. Rooms or spaces containing ESS shall be separated from other areas of the building by fire barriers with a minimum fire resistance rating of two hours and horizontal assemblies with a minimum fire resistance rating of two hours, constructed in accordance with the local building code.”
The requirements for fire suppression system reflects the lack of good information on how to properly protect these systems with sprinklers or alternate suppression systems.
The following is from Annex Section A.4.11.1: “Thermal Runaway. While nonwatery-based fire suppression has been shown to be effective at suppressing Class B and Class C fires in ESS enclosures, current suppression agents, both water-based and nonwater-based, are probably not going to be able to stop thermal runaway. No published case studies, test reports or data generated to date indicate otherwise.
“The current protection concepts in NFPA 855, including size and separation, maximum-rated energy and elevation are designed to try and keep a thermal runaway event from propagating from one ESS unit to another, contain a fire within a room or outdoor walk-in unit and not allow it to compromise exposures.”
Currently, the standard contains design discharge criteria of 0.30 gal./min./ft.2 over 2,500 ft.2 for sprinkler systems. There is an option to use a different density based on the results of large-scale fire testing.
Alternatives to sprinklers also may be used if their effectiveness is supported by large-scale testing.
Battery Storage System Requirements
Chapter 9 deals specifically with battery storage systems. Table 9.2. Electrochemical ESS Technology-Specific Requirements indicates which general requirements must be met based on the type of battery technology used. Compliance features included in the table are exhaust ventilation, spill control, neutralization, safety caps, thermal runaway, explosion control and size/separation.
The proposed standard also contains specific requirements in Chapter 17 which address one- and two-family dwellings and townhouse units. The key provision of the chapter is the location requirements.
17.5.1. ESS shall only be installed in the following locations: (1) In attached garages separated from the dwelling unit living area and sleeping units in accordance with the local building code (2) In detached garages and detached accessory structures (3) Outdoors on exterior walls or on the ground located a minimum of 3 ft (914 mm) from doors and windows (4) In enclosed utility closets and storage or utility spaces.
“126.96.36.199. If the room or space where the ESS is to be installed is not finished, the walls and ceiling of the room or space shall be protected with not less than 5/8-in. Type X gypsum board.”
No suppression is required for one- and two-family dwellings but there is a requirement for detection.
“17.8.1. Interconnected smoke alarms shall be installed throughout the dwelling, including in rooms, attached garages and areas in which ESS are installed in compliance with local building code.”
The members of the technical committee for energy storage systems should be congratulated for their effort. It is an excellent standard, well-written, very comprehendible and ahead of the curve — the avalanche of battery storage systems that are coming.
And it bears repeating: This column is based on the standard as currently proposed and that changes are likely before we see the final document from NFPA.