Case Study: NYC Balcony Solar + ESS That Passed FDNY Review

This case study documents a compact NYC Balcony Solar and Energy Storage System (ESS) that earned an FDNY review sign-off for a multifamily apartment. You will see the exact code path used, technical design choices, and measurable results, with practical steps to replicate safely under apartment fire codes.

Project Snapshot

• Location: R-2 occupancy, post-war brick multifamily in Upper Manhattan
• System size: 600 W balcony solar + 2 kWh LiFePO4 ESS (outdoor enclosure)
• Primary goal: Offset daytime loads and provide short backup for essentials
• Approval path: FDNY site-specific review aligned with NYC Fire Code FC 608 framework for ESS and manufacturer UL listings

Why Balcony Solar + Small ESS Fits Urban Buildings

Solar is modular and can scale down to tight sites. As summarized by the U.S. Department of Energy, photovoltaics deploy from utility scale to small rooftops and distributed assets at the building edge, enabling flexible siting in cities. See DOE’s overview of solar energy for context on distributed systems and their role in a modernized grid (energy.gov).

Small storage complements that flexibility. Global analyses show storage can avoid costly grid upgrades, especially in constrained locations. For example, a storage project in Maine deferred transmission spending and delivered present value savings of USD 12 million, per the IRENA Electricity Storage Valuation Framework. While this case focuses on a single apartment, the same principle applies at micro-scale: place energy where it is needed, reduce peaks, and increase resilience.

Code Path That Passed FDNY Review

Standards and Listings Cited

• UL 9540 system listing for the paired ESS and inverter
• UL 9540A test summary provided by the manufacturer
• UL 1741 listing for the microinverter; rapid shutdown per NEC 690.12
• Enclosure: NEMA 3R, noncombustible steel, tamper-resistant, lockable
• Labeling per IFC/NYC modifications; clear emergency disconnect

The FDNY review referenced NYC Fire Code provisions for energy storage systems (FC 608 series). The team aligned the submittal with the structure of NFPA 855 thresholds used nationwide for residential ESS, noting small aggregate capacity per dwelling and outdoor placement. Capacity limits and setbacks in NYC are project-specific and subject to FDNY determination. The apartment owner provided a conservative design well below typical NFPA 855 residential thresholds.

Documents Submitted

• Manufacturer UL 9540 certificate; UL 9540A test summary
• Single-line diagram, conductor sizing, OCPD, and disconnect details
• Site plan with balcony dimensions, distances to doors/windows, and egress
• Wind load and structural letter by a NY-licensed PE for railing clamps and enclosure dead load
• Commissioning plan, maintenance instructions, and emergency instructions

Setbacks and Fire Safety Features

• 3 ft horizontal clearance from operable windows and balcony door
• Not blocking egress; balcony remains accessible for fire department operations
• Noncombustible mounting; concealed-combustible materials avoided
• Visible placard at balcony door identifying ESS location and disconnect
• Overcurrent protection and ground-fault protection per NEC

Result: FDNY granted sign-off after minor field adjustments to labeling and disconnect height.

Technical Design: What Was Installed

PV Array and Power Electronics

• Two 300 W monocrystalline modules in portrait, railing-mounted with PE-stamped clamp details
• Microinverter rated for 240 Vac output, UL 1741-listed, with integrated rapid shutdown
• AC whips in UV-resistant conduit; drip loops and strain relief to prevent water ingress

Battery and Enclosure

• 2 kWh LiFePO4 pack, UL 9540 as a system with the inverter/PCS
• Round-trip efficiency ~92%; BMS with cell balancing and thermal monitoring
• NEMA 3R steel cabinet, powder-coated, lockable; anti-tamper hinges; screened vents
• Weight (battery + cabinet + hardware): ~35–40 kg; dead load verified by PE

Protection, Wiring, and Signage

• Dedicated AC circuit to apartment panel via metal raceway; AFCI/GFCI protection as required
• Serviceable external DC disconnect; AC lockable disconnect within reach range
• Permanent engraved labels: system ratings, emergency shutdown, and hazard warnings

Operations

• Time-of-use shifting mode: charge mid-day, discharge early evening
• Backup mode for essentials: modem, LED lights, phone/laptop charging, a fan
• Remote monitoring app for PV output and battery SOC

Measured Results (12 Months)

• Annual PV generation: 820 kWh (southwest-facing balcony, mid-floor, partial shading in winter)
• Self-consumption rate: 88% (rest exported or curtailed)
• Battery throughput: 520 kWh; round-trip efficiency measured at 91–93%
• Bill savings estimate: USD 200–240/year, using NYC residential tariffs in the mid-$0.20s/kWh range (see EIA for statewide electricity price benchmarks)
• Backup runtime: 6–10 hours for a 100–150 W essential load profile

DOE research points to growing roles for distributed PV and storage across grid scenarios, with storage duration and deployment rising over time (energy.gov). The performance here aligns with that trend: small, targeted storage delivers local value by shifting evening peaks and supporting resilience at the apartment level.

Compliance Checklist vs. Built Design

Requirement	Target/Standard	Case Study Implementation
System listing	UL 9540 for ESS; UL 1741 for inverter	UL 9540 certificate on file; UL 1741 microinverter
Thermal/Fire test data	UL 9540A data for hazard assessment	Manufacturer UL 9540A summary submitted
Setbacks	Clearances from openings per FDNY determination	3 ft from door/window; no egress obstruction
Enclosure construction	Noncombustible, weather-rated	NEMA 3R steel, lockable, tamper-resistant
Signage and disconnects	Visible labeling; emergency shutoff	Engraved placards; lockable AC/DC disconnects
Structural/wind	PE sign-off for mounts and loads	PE letter for railing clamps and dead load
Electrical safety	NEC 690/705; AFCI/GFCI; bonding/grounding	Metal raceway; OCPD; verified bonding path

Approval Steps You Can Follow in NYC

• Engage your building owner and board early; get written consent to use the balcony
• Select UL 9540-listed, small-capacity ESS with LiFePO4 chemistry and outdoor-rated enclosure
• Use railing mounts with stamped details; verify wind exposure and facade conditions
• Create a concise packet: site plan, setbacks, single-line, load calcs, labels, O&M, emergency steps
• Coordinate with the Authority Having Jurisdiction: FDNY for fire safety review; DOB for any electrical and structural filings
• Commission with a documented checklist; train occupants on shutdown procedures

IEA notes solar’s modularity across scales and use cases, supporting tailored applications like balconies (IEA Solar Energy Perspectives). Distributed storage can be staged as needs grow, matching apartment constraints.

Limits and Risk Controls

• Capacity caps: Residential ESS limits apply per dwelling. FDNY may restrict chemistries, capacities, or locations on a case basis.
• Access: Never block fire department operations or escape routes.
• Wind and snow: Verify loads; choose robust clamps and periodic torque checks.
• Shading: Expect lower winter yield on north-facing or recessed balconies.
• Operations: Lock the cabinet; keep combustibles away; follow the maintenance schedule.

Across national scenarios, DOE research highlights rising storage deployment and shorter average durations for many use cases, matching small apartment ESS profiles (energy.gov). IRENA’s analysis of storage deferring infrastructure offers a strong value context even at building scale (IRENA).

Economics: What the Numbers Say

With about 4 peak-sun-hours per day on a favorable balcony, 600 W of panels can produce near 800–900 kWh per year. At New York residential prices in the mid-$0.20s/kWh range (EIA), savings could be around USD 200–240 annually, plus resilience value during outages.

Storage also reduces peaks in the early evening. This aligns with research that shows storage smooths net load and provides capacity over critical windows (DOE). IEA’s perspective further emphasizes how small-scale solar integrates into buildings efficiently (IEA).

Replicable Design Pattern for NYC Balcony Solar + ESS

• 600–800 W balcony PV using PE-approved mounts; avoid facade penetrations unless permitted
• 2–5 kWh LiFePO4 ESS, UL 9540-listed, outdoor-rated enclosure with locks and signage
• Microinverter with NEC 690.12 rapid shutdown; clearly labeled AC disconnect
• 3 ft clearance to openings; maintain egress width; no overhead protrusions
• Packet: UL listings, UL 9540A summary, single-line, PE letter, labels, O&M, emergency steps
• Commission, test shutdowns, and schedule periodic inspections

Key Takeaways

• Small, standards-listed systems can pass FDNY review with clear setbacks, proper enclosures, and complete paperwork.
• LiFePO4 chemistry, UL 9540 pairing, and robust mounting reduce risk and ease approvals.
• Expect 800–900 kWh/year from a well-sited 600 W balcony array, with tangible bill and resilience benefits.

FAQ

Is a battery allowed on a NYC apartment balcony?

FDNY reviews ESS case-by-case. Capacity, chemistry, enclosure, and setbacks matter. This project secured approval by staying small, using UL 9540 listings, and documenting clearances. Always seek FDNY guidance and building owner consent.

What battery chemistry was used and why?

LiFePO4. It offers stable thermal behavior and long cycle life. The system’s UL 9540 listing and UL 9540A test data supported the fire-safety review.

How much energy can a 600 W balcony system deliver in NYC?

Roughly 800–900 kWh per year if the balcony faces south to west with modest shading. Expect lower yield with deep recesses or north-facing facades.

Does the system export power back to the building?

Most energy was self-consumed. Any export depends on metering arrangements and building rules. Confirm with your utility and building management.

What paperwork should be prepared for FDNY?

UL listings, UL 9540A summary, single-line diagram, site plan with setbacks, enclosure specs, labels, PE structural letter, and a commissioning and emergency plan.

References

• U.S. Department of Energy. Solar Energy Topics. https://www.energy.gov/topics/solar-energy
• International Renewable Energy Agency. Electricity Storage Valuation Framework (2020). https://www.irena.org/Publications/2020/Mar/Electricity-Storage-Valuation-Framework-2020
• International Energy Agency. Solar Energy Perspectives (2011). https://www.iea.org/reports/solar-energy-perspectives
• U.S. Energy Information Administration. Energy Information Administration homepage for data and analysis. https://www.eia.gov/

Disclaimer: Regulatory information is provided for general education and does not constitute legal advice. Codes change and approvals are site-specific. Consult FDNY, DOB, and qualified professionals.