Case study · Essential facility

142 kW on a fire station that could not go offline.

Orlando Fire Station 6, 3900 E Concord Street. A rooftop grid-tie array designed to Risk Category IV over an active apparatus bay, sealed for the City of Orlando in August 2021.

Design model347 modules

main roof +
apparatus bay

Location3900 E Concord St, Orlando

System142.27 kW DC · 112.7 kW AC

Risk categoryIV · Essential facility

AHJCity of Orlando

The system

347 modules, four inverters, one 800 A service.

Four SolarEdge inverters feed an AC accumulation panel, with a data logger tied back to the station IT room.

System data Orlando Fire Station 6

DC system size	142.27 kW
AC system size	112.7 kW
DC/AC ratio	1.26
Modules	347 × 410 W, 72 half-cut cells
Inverters	2 × SolarEdge SE43.2K, 1 × SE17.3K, 1 × SE9K
Optimizers	164 × P860, 22 × P505
Racking	GridFlex, ballasted
Roof type	TPO membrane
Design wind speed	140 mph, Exposure C
Risk category	IV · Essential facility
Service	800 A, 120/208 V, 3-phase 4-wire
AHJ	City of Orlando
Sealed	August 2021
Role	Design engineer & engineer of record

Fire Sta. 6 · PV sizingE.R. 8/23/21

DC = 347 × 410 W = 142,270 W

= 142.27 kW

AC = 2(43.2) + 17.3 + 9.0 = 112.7 kW

DC/AC = 142.27 ÷ 112.7 = 1.26 ✓

Wind: 140 mph · Exp. C · Cat. IV

Service: 800 A · 120/208 V · 3Ø

Max V-drop (system) = 1.20% ✓

Sun path, Orlando 28.5° N · today

Constraints

Three things made this set harder than its size suggests.

Risk Category IV

Essential facility · ballasted racking

A fire station has to stay standing and operating through the design storm. That pushes the importance factor to the top of the table, so every attachment, ballast block and uplift check is run against a heavier load than the same array on a house next door.

140 mph over TPO

Exposure C · single-ply membrane

A single-ply membrane roof will not take arbitrary penetrations, and Exposure C at 140 mph is unforgiving at roof edges and corners. The layout keeps modules inside the field zones and off the high-uplift perimeter.

Fire-rated penetrations

Sheet E-03 · Details A + B

Conduit runs cross rated concrete walls into the apparatus bay. Each crossing is drawn as a detail with a rated fire-barrier foam step and a condensation break, so the inspector is not left interpreting a note.

Sheet E-03 showing equipment elevations and fire barrier penetration details — Sheet E-03Details A + B

details A + B:
the rated wall crossings

Sheets

What the reviewer received.

Photographs sell the finished job. These sheets decide whether the permit clears on the first pass.

Full electrical one-line diagram for Orlando Fire Station 6 with conduit schedule, voltage-drop tables and placard schedule — Electrical diagramConduit schedule + V-drop

Sheet index What each sheet carries

Electrical diagram One-line

Every string traced from module to the 800 A service entrance
Four inverter groups, an AC accumulation panel, fused and non-fused disconnects and the utility transformer
Conduit schedule
DC and three-phase AC voltage-drop tables: total system drop 1.20%
OCPD sizing checked against NEC 690.8(B)
A drawn placard schedule showing each label's type and location

Equipment elevations Sheet E-03

Inverters and the AC accumulation panel, dimensioned on the apparatus bay wall
The SolarEdge data logger in the IT room
The service entrance disconnect on the building exterior, within 10 ft of the point of interconnection
Details A and B, the rated wall crossings: detail 3 above

Outcome

Sealed, permitted, built.

The set was sealed in August 2021 and permitted by the City of Orlando.

A municipal reviewer should never have to phone the engineer to understand a drawing. If the detail is on the sheet, the review moves. Eduardo Rodriguez, P.E.

The same approach scales down. A residential retrofit gets the same discipline on a shorter sheet index: calculations shown, labels drawn, details resolved.

Back to all projects

Your project

Have a commercial or municipal roof in play?

Send the address, roof type and utility. I'll tell you what the set needs before you quote it.

Start a project (786) 556-5574

big roof or small,
same discipline