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Fox ESS 3.7kW AC-Coupled Battery Inverter G2 | AC1-3.7-E-G2
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£770.00
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£641.67
Exc. VAT
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The Fox ESS AC1-3.7-E-G2 (Gen 2) is a single-phase, high-voltage AC-coupled battery inverter with a 3.68 kW (3,680 W) rated output. It connects on the AC side of the installation and charges and discharges Fox ESS high-voltage LiFePO4 batteries, so you can add battery storage to an existing solar PV system without touching the PV strings or the existing PV inverter.
Four work modes (Self-use, Feed-in priority, Force time use and Back-up) cover solar self-consumption, off-peak tariff shifting and emergency power. A built-in EPS output keeps essential circuits running in a grid outage (3,680 VA continuous, 4,400 VA peak for 60 seconds, battery required), and export limitation through a CT or meter helps keep the site within its agreed export limit.
Engineered for real-world sites, the inverter is IP65 rated, naturally cooled at 35 dB, rated for -25 to 60 °C and mounts on a wall bracket at 22 kg. FoxCloud 2.0 gives remote monitoring by smartphone app or web portal over Wi-Fi, with LAN and 4G options.
3.68 kW
Rated AC output
4.4 kVA
EPS peak (60 s)
80–480 V
Battery voltage range
40 A
Max. charge / discharge
97.08%
Max. efficiency
IP65
Indoor or outdoor
Electrical safety and installation
Installation must be carried out by a competent, qualified electrician in line with BS 7671 and the Fox ESS installation manual, with Part P notification where applicable. Isolate the AC supply and the battery before opening the inverter and wait 5 minutes for it to fully de-energise. Fit an overcurrent protection device (MCB) between the inverter and the grid and never connect a load directly to the inverter output.
G98 / G99 - notify or apply to your DNO
At the 3,680 VA / 16.0 A G98 setting, the AC1-3.7-E-G2 sits at the 16 A per phase limit for the G98 route, which requires the DNO to be notified within 28 days of commissioning. At its full 4,048 VA / 16.7 A rating, or where the existing PV plus the new battery exceed 16 A per phase in total, a G99 application must be approved before installation. Always confirm the combined site capacity with your DNO.
Batteries and accessories are sold separately
The inverter is supplied without batteries. It works with Fox ESS high-voltage LFP batteries (80–480 V DC window) and cannot be paired with low-voltage 48 V batteries. Minimum and maximum module counts depend on the battery series, so check the Fox ESS inverter and battery configuration guide. A CT or smart meter is required for export limitation.
What does AC-coupled mean?
An AC-coupled battery inverter connects to the AC circuit rather than to the PV DC strings. Solar from the existing PV inverter feeds the home first, surplus AC power can charge the battery, and the battery discharges back through the AC1 when needed. The AC1 has no PV inputs; for a hybrid with MPPT inputs choose the H1 instead.
Key features
AC-coupled retrofit
Adds storage to an existing PV system without changing the PV strings or inverter. With no PV inputs, the AC1 suits retrofit jobs and sites where the PV inverter must stay. A second CT (CT2) can record the existing PV generation for monitoring.
High-voltage LFP architecture
Works with Fox ESS high-voltage LiFePO4 batteries across an 80–480 V window, with CAN communication to the battery and up to 40 A charge / discharge current. Fox ESS highlights the high-voltage design for high round-trip efficiency.
Built-in EPS backup output
Power essential circuits during a grid outage: 3,680 VA continuous, 4,400 VA peak (60 s), 220/230/240 V, 50/60 Hz. Wire loads to the inverter EPS port (internal bypass) or use an external contactor (bought separately). A battery is required.
Four work modes
Self-use (load, then battery, then grid), Feed-in priority (load, then grid, then battery), Force time use with flexible charge and discharge schedules and optional grid charging for cheap off-peak tariffs, and Back-up mode.
Monitoring and control
FoxCloud 2.0 by app or web portal, Wi-Fi with optional LAN or 4G, plus RS485, DRM, ripple control, USB, CAN and SG Ready interfaces. A local LCD with four touch keys and LED status indicators sit on the unit.
Robust, quiet build
IP65 enclosure for indoor or outdoor mounting (keep out of direct sunlight), natural cooling at 35 dB, -25 to 60 °C operation, plug-and-play wiring and built-in fuse protection in a 22 kg wall-mounted unit.
Built for installers
✓
Wall-mounted on a bracket: 434 × 418 × 185 mm, 22 kg
✓
Export limitation via CT or meter, DRM0 and ESTOP inputs
✓
Power factor regulation: unity, adjustable 0.8 leading to 0.8 lagging
✓
On-screen CT / meter self-test to catch a wrongly orientated CT, which would defeat anti-backflow
✓
Firmware upgrade by USB stick (USB 2.0, FAT16 or FAT32, under 32 GB)
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Site rules: not in direct sunlight, away from flammable materials, below 2,000 m altitude
Ideal for
Typical applications
✓
Retrofit battery storage on an existing solar PV installation
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Time-of-use tariff shifting: charge off-peak, discharge at peak rates
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Essential-circuit backup through the EPS output
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New builds where the PV inverter and battery storage are specified separately
System compatibility
Technical specifications
Compare the AC1 Gen 2 ratings
Both ratings share the same 80–480 V battery window, 40 A charge / discharge current, IP65 enclosure, 22 kg weight and 434 × 418 × 185 mm footprint.
Frequently asked questions
BTU & WATT Calculator
Room Dimensions
Room Type
Living Room
Bedroom
Kitchen
Bathroom
Conservatory
Hallway
Glazing Type
Single Glazed
Double Glazed
Triple Glazed
External Walls
0 Wall
1 Wall
2 Walls
3 Walls
4 Walls
Insulation Level
Poor
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Good (New Build)
Required Heating
0
Watts
0
BTUs
Documentation
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