48.5″ · 1,232 mm wide · 1.93″ (49 mm) frame · 76.1 lb (34.5 kg)

Solar panelFirst Solar

First Solar FS-6 420

Name: First Solar FS-6 420
Brand: First Solar

264 cells, thin-film. Power classes 385–440 W in the CEC list; datasheet covers 420–450 W.

CEC listed · Dec 17, 2018UL 170312-yr product + 30-yr performance warrantythin-film

Power class

Power (STC)420 WCEC nameplate
Efficiency≥17.0%datasheet minimum
%/°C Pmax−0.245CEC listing test
Performance warranty30 yrdatasheet

Power classes

CEC PV Module List (Oct 7, 2026) · Cali-Graf calculation · First Solar datasheet · 12 models

Model	Pmax	Voc, V	Isc, A	Vmp, V	Imp, A	Efficiency	PTC	CEC listed
FS-6385	385 W	214.30	2.49	172.80	2.23	≈15.6%	358 W	Dec 17, 2018
FS-6390	390 W	214.80	2.49	173.90	2.24	≈15.8%	363 W	Dec 17, 2018
FS-6395	395 W	215.40	2.50	175.00	2.26	≈16.0%	368 W	Dec 17, 2018
FS-6400	400 W	216.10	2.51	176.10	2.27	≈16.2%	373 W	Dec 17, 2018
FS-6405	405 W	216.80	2.52	177.20	2.29	≈16.4%	378 W	Dec 17, 2018
FS-6410	410 W	217.40	2.52	178.30	2.30	≈16.6%	382 W	Dec 17, 2018
FS-6415	415 W	218.10	2.53	179.30	2.31	≈16.8%	387 W	Dec 17, 2018
FS-6420	420 W	218.50	2.54	180.40	2.33	≥17.0%	395 W	Dec 17, 2018
FS-6425	425 W	218.90	2.54	181.50	2.34	≥17.2%	396 W	Dec 17, 2018
FS-6430	430 W	219.20	2.54	182.60	2.36	≥17.4%	401 W	Dec 17, 2018
FS-6435	435 W	219.60	2.55	183.60	2.37	≥17.6%	409 W	Jan 21, 2020
FS-6440	440 W	220.00	2.55	184.70	2.38	≥17.8%	414 W	Jan 21, 2020

≈ efficiency = Pmax ÷ panel area 2.475 m² (datasheet size) for classes outside the datasheet.

Build & dimensions

First Solar datasheet · Cali-Graf calculation · CEC PV Module List (Oct 7, 2026)

Dimensions79.1 × 48.5 × 1.93 in2,009 × 1,232 × 49 mm
Module area2.48 m² (26.6 ft²)length × width
Weight76.1 lb (34.5 kg)
Cells264 cellsthin-film
FrameAnodized Aluminum
Cable / connectorMC4-EVO 2 or TE Connectivity PV4-S

Heat & cold behaviour

CEC PV Module List (Oct 7, 2026) · Cali-Graf calculation · First Solar datasheet

	CEC listing test
Pmax coefficient γ	−0.245 %/°C
Voc coefficient β	−0.274 %/°C
Isc coefficient α	+0.049 %/°C
Operating cell temperature	NOCT 48.8 °C

Vmp coefficient ≈ γ − α (CEC); used only for the hot-roof voltage estimate.

At normal operating conditions (NOCT, 800 W/m²) — datasheet

Class	Pmax, W	Voc, V	Isc, A	Vmp, V	Imp, A
420 W	317.2	206.30	2.04	168.70	1.88
425 W	320.9	206.60	2.05	169.80	1.89
430 W	324.7	207.00	2.05	170.90	1.90
435 W	328.5	207.30	2.06	172.00	1.91
440 W	332.4	207.70	2.06	173.10	1.92

Away from lab conditions — CEC listing test points

Class	Pmax at NOCT	Vmp × Imp at NOCT	Pmax at 200 W/m²	Low-light efficiency vs STC
385 W	300.5 W	164.5 V × 1.83 A	81.3 W	106%
390 W	303.8 W	165.55 V × 1.83 A	82.2 W	105%
395 W	308.4 W	166.6 V × 1.85 A	83.5 W	106%
400 W	311.7 W	167.65 V × 1.86 A	84.4 W	105%
405 W	316.4 W	168.69 V × 1.88 A	85.6 W	106%
410 W	319.8 W	169.74 V × 1.88 A	86.5 W	106%
415 W	323 W	170.69 V × 1.89 A	87.4 W	105%
420 W	321.5 W	171.03 V × 1.88 A	83.7 W	100%
425 W	331.2 W	172.79 V × 1.92 A	89.6 W	105%
430 W	336 W	173.83 V × 1.93 A	90.9 W	106%
435 W	332.9 W	174.06 V × 1.91 A	86.6 W	100%
440 W	336.3 W	175.11 V × 1.92 A	87.5 W	99%

Pmax = Vmp × Imp from the CEC listing; low-light efficiency = Pmax at 200 W/m² ÷ (20% of STC Pmax).

Electrical & strength ratings

Max system voltage1500 V
Max series fuse5 A
Max reverse current5 A
Design load push / pull50 psf2,400 Pa
Module temperature−40 °F to +185 °F−40 °C to +85 °C

Certifications

CEC PV Module List (Oct 7, 2026) · First Solar datasheet

UL 1703UL 61730IEC 61730ISO 14001ISO 45001ISO 9001

UL 1703CEC listing
UL 61730datasheet
IEC 61730datasheet
ISO 14001factory, datasheet
ISO 45001factory, datasheet
ISO 9001factory, datasheet

Warranty & degradation

First Solar datasheet

Product warranty12 years
Performance warranty30 years, linear

Independent reliability testing

Kiwa PVEL Scorecard

PVEL Scorecards

First Solar named Top Performer, 2018–2023

This exact series is not listed in published PVEL Top Performer tables. Results below are for the manufacturer.

Inverter compatibility & string sizing

CEC PV Module List (Oct 7, 2026) · Cali-Graf calculation · NLR PVWatts v8 · inverter datasheets · NLR SAM inverter library · CEC Grid Support Inverter List (Oct 7, 2026)

CityColdest air, °CHottest cell, °CString inverter

232.2 V

Voc when cold

per panel

154.3 V

Vmp when hot

per panel

Max panels / string

max DC 600 V

Min panels / string

MPPT from 60 V

Defaults come from NLR TMY weather (coldest hour, hottest modeled cell). Code calculations (NEC 690.7) use the ASHRAE extreme annual minimum, which is usually colder — enter it above. β is the CEC-measured coefficient; NEC 690.7 calculations use the datasheet value.

String inverters most named in SoCal permits

Inverter	Max DC input	MPPT	Window source	Panels per string
Tesla 1538000-xx-y	600 V	60–480 V	datasheet	1–2
Solis (Ginlong) S6-EH1P10K-H-US	600 V	80–520 V	datasheet	1–2
Solis (Ginlong) Solis-1P7.6K-4G-US	600 V	100–500 V	datasheet	1–2
Qcells Q.VOLT H7.6SX	498 V	234–498 V	CEC test window	2–2

Microinverters (one per panel)

Microinverter	Recommended module power	Max DC input	MPPT	Voc cold / Vmp hot	Check	DC/AC
Enphase IQ8PLUS-72-2-US	235–440 W	60 V	29–45 V	232.2 / 154.3 V	✗ Not allowed: cold Voc above max input	1.45
Enphase IQ8X-80-M-US	320–540 W	79.5 V	43–60 V	232.2 / 154.3 V	✗ Not allowed: cold Voc above max input	1.11
APsystems (Alt Power System) DS3-L	265–570 W	60 V	28–45 V	232.2 / 154.3 V	✗ Not allowed: cold Voc above max input	0.54
Enphase IQ8M-72-2-US	260–460 W	60 V	30–45 V	232.2 / 154.3 V	✗ Not allowed: cold Voc above max input	1.29
Enphase IQ8A-72-2-US	295–500 W	60 V	32–45 V	232.2 / 154.3 V	✗ Not allowed: cold Voc above max input	1.2

Voltage check against the microinverter datasheets — confirm the pairing on the manufacturer’s module compatibility list. Rows appear only when the panel’s power is inside the microinverter’s recommended module power range.

SolarEdge and other optimizer-based systems size strings by the optimizer rules — use the manufacturer’s designer. Reference inverters: most named in SoCal permits since Oct 2024.

Expected production in Southern California

NLR PVWatts v8 · Cali-Graf calculation

PanelsCity for chartSystem size

City	kWh / kW / yr	kWh / panel / yr	kWh / system / yr	Sun, kWh/m²/day
Los Angeles	1,676	704	11,967	6.08
Palmdale	1,835	771	13,102	6.69
Chula Vista	1,696	712	12,109	6.11
Huntington Beach	1,643	690	11,731	5.89
Riverside	1,696	712	12,109	6.21
Santa Clarita	1,724	724	12,309	6.28

Estimate for comparison, not a quote: shading, roof orientation and local losses change real output. Roof mount, 20° tilt, south, 14% system losses.

About First Solar

CEC PV Module List (Oct 7, 2026) · Kiwa PVEL Scorecard

ManufacturerFirst Solar
Listed in CEC asFirst Solar, Inc.
Websitefirstsolar.com
PVEL Top Performer (manufacturer)5 Scorecards (2018–2023)
Current panel series in CEC list14

Other series by SoCal permits

FS-6xxx-P-BFS-6xxx-P-B-2FS-6xxxA-P-BFS-6xxxA-P-B-2FS-7xxxA-FT1FS-7xxxA-TR1

Questions & answers

How efficient is the First Solar FS-6 420?

The First Solar datasheet guarantees at least 17% module efficiency for the 420 W class (up to 17.8% for 440 W). 420 W over 2.48 m² equals about 170 W per square meter.

How much energy does one panel produce in Los Angeles or Palmdale?

PVWatts v8 with typical-year weather gives about 704 kWh per year per 420 W panel in Los Angeles and about 771 kWh in Palmdale (20° roof, facing south, 14% system losses).

How much power does it lose on a hot roof?

With γ = −0.245 %/°C, at a 77 °C cell temperature (hottest modeled hour in Palmdale) output is about 12.7% below the STC rating.

How many panels fit on one string?

With the Tesla 1538000-xx-y (max DC 600 V, MPPT from 60 V, datasheet) in Los Angeles the calculator gives 1–2 panels per string (Voc at 2 °C = 232.2 V, Vmp at 74 °C cell = 154.3 V). Final design must follow the inverter manual and NEC 690.7.

What does the warranty cover?

12 years on the product and 30 years linear on performance (manufacturer datasheet).

How big and heavy is it?

79.1 × 48.5 × 1.93 in (2,009 × 1,232 × 49 mm), 76.1 lb (34.5 kg).

Has this panel been reliability-tested?

This exact series is not in published PVEL Top Performer tables; First Solar was named a Top Performer in 5 Scorecards (2018–2023).

Sources

California Energy Commission — Solar Equipment Lists, PV Module List, Inverter List (snapshot Oct 7, 2026).
First Solar — manufacturer datasheet “First Solar Series 6™ ADVANCED THIN FILM SOLAR TECHNOLOGY”.
Kiwa PVEL — PV Module Reliability Scorecard, Top Performer lists 2018–2023.
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, Chula Vista, Huntington Beach, Riverside, Santa Clarita.
Inverter datasheets — APsystems (Alt Power System), Enphase, Solis (Ginlong), Tesla (manufacturer documents).
Cali-Graf calculations — formulas and inputs are shown next to each calculated value (efficiency from area, temperature-corrected voltages, string sizing, energy estimates).