Illustration

Hybrid inverterFortress Power

Fortress Power FP-Envy Duo 21

Name: Fortress Power FP-Envy Duo 21
Brand: Fortress Power

Hybrid inverter, dc-coupled hybrid (pv + battery). 2 models, 13.8 kW–16 kW AC at 208 V / 240 V.

UL 1741 SBCEC listed · Nov 21, 2025

Model

Rated AC power16 kW
CEC weighted efficiency97.0%

Models & power ratings

CEC Grid Support Inverter List (Oct 7, 2026) · NLR SAM inverter library · 2 models

Model	Nominal AC	Grid voltage	CEC continuous	Rated AC (SAM)	CEC weighted eff.	DC test window	CEC listed	UL 1741 SB
FP-Envy Duo 21	13.8 kW	208 V	13.9 kW	13.9 kW	96.5%	250–440 V	Nov 21, 2025	SB
FP-Envy Duo 21	16 kW	240 V	16.2 kW	16.2 kW	97.0%	250–440 V	Nov 21, 2025	SB

Some models are also on the CEC Battery Inverter list — one product, two listings.

DC input (PV side)

CEC Grid Support Inverter List (Oct 7, 2026) · NLR SAM inverter library

CEC test DC voltages (min / nom / max)250 / 360 / 440 V
DC input at rated output (CEC test)16.7 kW

Efficiency

CEC Grid Support Inverter List (Oct 7, 2026) · NLR SAM inverter library

CEC weighted efficiency97.0%
Night-time standby (tare)29.36 W
Power to start converting41.5 W

CEC weighted efficiency is measured by an accredited lab at six power levels and three DC voltages — the number to compare between inverters.

Grid & smart-inverter certification

CEC Grid Support Inverter List (Oct 7, 2026)

UL 1741 SB (3rd ed.)Yes — Intertek, certificate Sep 1, 2025
UL 1741 SA (SA8–SA13)Yes — Intertek
Firmware tested (SA)fA1.0
Volt-VAr with reactive power priority (SA13)Yes
Freq-Watt / Volt-Watt (SA14–15)Yes
Disable permit service / limit active power (SA17–18)Yes
CSIP (IEEE 2030.5) conformanceYes — Intertek, Oct 28, 2025
Power control system (PCS)Stated in CEC listing (power control system)
CEC listedNov 21, 2025
Last CEC updateJan 12, 2026

UL 1741 SB is required for new interconnections in California (Rule 21) since 2026.

Panel compatibility & string sizing

NLR SAM inverter library · NLR PVWatts v8 · CEC PV Module List · Cali-Graf calculation

CityColdest air, °CHottest cell, °C

FP-Envy Duo 21: max DC 440 V · MPPT 250–440 V (CEC test window)

Most-permitted panels in Southern California

Panel	Power	Voc cold	Vmp hot	Panels per string	Installed together
Qcells Q.PEAK DUO BLK ML-G10.C+ 410	410 W	48.1 V	30.6 V	9–9	—
Qcells Q.PEAK DUO BLK ML-G10+ 410	410 W	48.1 V	30.6 V	9–9	—
LONGi LR5-54HABB-400M	400 W	39.3 V	25.3 V	10–11	—
JA Solar JAM54S31-405/MR	405 W	39.4 V	25.5 V	10–11	—
Hyundai Solutions HiN-T440NF(BK)	440 W	40.9 V	27 V	10–10	—
Silfab Solar SIL-440QD	440 W	41.1 V	28 V	9–10	—
Qcells Q.TRON BLK M-G2+ 430	430 W	41.3 V	28 V	9–10	—
Qcells Q.TRON BLK M-G2.H+ 430	430 W	41.3 V	28 V	9–10	—
REC Group REC460AA Pure-RX	460 W	68.8 V	47.1 V	6–6	—
Elin (Sirius PV) ELNSM54M-HC-410	410 W	39.3 V	25.3 V	10–11	—
Qcells Q.TRON BLK M-G2.C+ 430	430 W	41.3 V	28 V	9–10	—
Tesla TSP-420	420 W	43.4 V	27.7 V	10–10	—

Voltage check only, from CEC panel data and NLR weather for the city. Final design must follow the inverter manual and NEC 690.7.

Compare with similar 16 kW inverters

CEC Grid Support Inverter List (Oct 7, 2026) · building permits

Inverter	Power	CEC weighted eff.	DC test window	UL 1741 SB	Latest CEC	SoCal permits
Fortress Power FP-Envy Duo 21	13.8 kW–16 kW	97.0%	250–440 V	Yes	2025	0
Shenzhen Lux Power Technology LXP-LB-US xK	8 kW–16 kW	97.0%	210–480 V	Yes	2025	1
Suzhou Ample ESS AP-LxK-SPUS	7.98 kW–15 kW	96.5%	108–480 V	Yes	2026	—
SRNE Solar HEBP48150U320-H	15 kW–15 kW	96.5%	135–500 V	Yes	2026	—
SRNE Solar HEBP48160U340-H	16 kW–16 kW	96.5%	150–500 V	Yes	2026	—

Same type and grid voltage, power range covering this model; same fields from the same sources.

About Fortress Power

CEC Grid Support Inverter List (Oct 7, 2026)

ManufacturerFortress Power
Listed in CEC asFortress Power LLC
Websitefortresspower.com
Models on CEC lists554

Other series

EdgeOn Duo 12EdgeOn Duo 12 LiteEdgeOn Duo 15EdgeOn Duo 15 LiteEdgeOn Duo 15 ProEdgeOn Duo 7.5EdgeOn Duo 9FP-Nano-30k-LFP-Nano-xxk-NFP-ENVY-xxK

Questions & answers

How efficient is the Fortress Power FP-Envy Duo 21?

The California Energy Commission lists a weighted efficiency of 96.5–97.0% for Fortress Power FP-Envy Duo 21 models, measured at six power levels and three DC voltages.

What sizes does the Fortress Power FP-Envy Duo 21 come in?

The CEC list includes 2 models from 13.8 kW to 16 kW AC: FP-Envy Duo 21, FP-Envy Duo 21.

Is the Fortress Power FP-Envy Duo 21 certified to UL 1741 SB?

Yes — the CEC Grid Support Inverter List shows UL 1741 SB for all models.

Can the Fortress Power FP-Envy Duo 21 be used with a battery?

The CEC lists it as a dc-coupled hybrid (pv + battery).

What is the FP-Envy Duo 21’s DC input voltage range?

CEC tested it at 250–440 V DC.

Sources

California Energy Commission — Grid Support Inverter List (solar and battery inverters), data as of Oct 7, 2026. Manufacturer-reported, confirmed by CEC against certificates and test reports.
NLR (formerly NREL) — System Advisor Model CEC inverter library (version 2026.7.3).
NLR (formerly NREL) — PVWatts v8, NSRDB PSM v3 typical-year weather for Los Angeles, Palmdale, Riverside, Santa Clarita, Chula Vista, Huntington Beach.
California Energy Commission — PV Module List (module electrical data for the compatibility check).
Building permits — Southern California permit portals. Equipment matched from permit descriptions.
Cali-Graf calculations — formulas and inputs are shown next to each calculated value (efficiency from area, temperature-corrected voltages, string sizing, energy estimates).