The Solis S1-W4G-ST (USB, No SIM) (model SOL-S1-W4G-ST-S6-USB) is a Wi-Fi + 4G cellular data logging stick for Solis S6 series inverters. It uses a USB-type connector and connects to SolisCloud via 2.4 GHz Wi-Fi as primary and automatically switches to 4G cellular as fallback if Wi-Fi goes down — ensuring uninterrupted monitoring without any manual intervention. This No SIM version ships without a SIM card: you supply your own standard Nano SIM on any UK data-enabled plan. Data uploads every 5 minutes to the SolisCloud app (iOS and Android). Up to 10 inverters can be chained via RS485. Bluetooth for local configuration and one-key RS485 address assignment. Three LEDs: NET, COM, PWR. IP65. Dimensions: 128 × 50 × 34 mm, 79 g. 2-year warranty.
Wi-Fi+4G
Dual Path
Auto
4G Failover
No SIM
Bring Your Own
10 inv.
Per Logger
IP65
Protection
2-Year
Warranty
ℹ USB connector — Solis S6 series only: The SOL-S1-W4G-ST-S6-USB uses a USB-type COM port connector. It is compatible with Solis S6 series inverters. For earlier Solis models with a 4-pin COM port (4G, 5G, S5 series), the S1-W4G-ST (4-Pin) version is required. Check the Solis Datalogger Compatibility Guide at solis-service.solisinverters.com.
ℹ No SIM included — bring your own Nano SIM: This version ships without a SIM card. Insert any Nano SIM card on a UK 4G data-enabled plan (pay-as-you-go or contract). Data usage is very low — only used when Wi-Fi is unavailable or fails. Any UK network SIM works. If you want a pre-installed SIM with a multi-year data plan, the S1-W4G-ST (USB, With SIM) is available separately.
Which Solis Data Logger? S1 vs S2-WL-ST vs S5 (USB versions)
Scenario
S1-W4G-ST (this product)
S2-WL-ST USB
S5-WiFi-ST
Wi-Fi unavailable on site (remote / no broadband)
✅ Uses 4G cellular
❌ Wi-Fi required
❌ Wi-Fi required
Wi-Fi unreliable — need automatic failover
✅ Auto-switches to 4G
⚠ LAN alternative
❌ No fallback
Need wired Ethernet (LAN) monitoring
❌ No LAN port
✅ Built-in RJ45
❌ No LAN port
Need Modbus TCP for Home Assistant
❌ Not supported
✅ Via LAN port
❌ Not supported
Router uses 5 GHz / band-steering issues
⚠ 2.4 GHz only
⚠ 2.4 GHz only
✅ Dual-band
Up to 10 inverters via RS485
✅ Yes
✅ Yes
✅ Yes
Solis S6 inverter (USB port)
✅ USB version
✅ USB version
✅ USB version
Key Features
Wi-Fi + 4G Cellular with Automatic Failover — Uninterrupted Monitoring
The S1-W4G-ST operates primarily on 2.4 GHz Wi-Fi. If the Wi-Fi connection fails — router outage, ISP issue, signal drop — the logger automatically switches to 4G cellular without any manual action. When Wi-Fi is restored, it switches back. This dual-path failover means monitoring data continues uploading to SolisCloud regardless of local network conditions. Critically useful for properties with unreliable broadband, commercial sites, remote installations or anywhere that long Wi-Fi outages occur.
Wi-Fi primary4G auto-failoverZero manual action
No SIM Included — Use Any UK Nano SIM on Any Network
This variant ships without a SIM, giving flexibility over network and plan choice. Insert a standard Nano SIM from any UK 4G network. Data usage is minimal — the cellular connection is only active when Wi-Fi is unavailable, uploading small data packets at 5-minute intervals. A basic pay-as-you-go SIM with a data add-on, or a low-cost IoT SIM plan, is sufficient for most installations. Multi-network SIM versions (pre-installed, 5-year or 10-year plans) are available separately if preferred.
Nano SIM slotAny UK networkLow data usage
USB Connector — Plug Directly into Solis S6 COM Port
Uses the same USB-type COM port as Solis S6 series inverters. The connector is touch-safe and locks in place. No adapters or tools required. Power is drawn directly from the inverter.
The one-key address assignment function, triggered via the SolisCloud app over Bluetooth, automatically scans the RS485 bus and assigns sequential addresses to all connected inverters. Up to 10 inverters can be monitored through one logger. Eliminates manual address entry on each inverter display during commissioning.
One-key assignmentUp to 10 invertersBluetooth trigger
Bluetooth — Local Wi-Fi Config, No AP Mode Required
Configure the Wi-Fi network (SSID and password), check device status, and update firmware via Bluetooth connection in the SolisCloud app. No AP mode setup sequence needed — no phone disconnection from home Wi-Fi.
Bluetooth local configNo AP modeOTA firmware
Three LEDs — NET, COM, PWR
NET: server/network connection (Wi-Fi or cellular). COM: RS485 inverter communication. PWR: power status. Solid = ok; flashing = connecting; off = fault. Immediate on-site diagnosis without the app.
NETCOMPWR
IP65, −30°C to +65°C, 128 × 50 × 34 mm
Dust-tight and water-jet resistant. Operating range −30°C to +65°C, 5 – 95% RH, storage to −40/+70°C, max 4,000 m altitude. Compact at 128 × 50 × 34 mm, 79 g.
IP65−30°C to +65°C79g
Technical Specifications
Communication
Wi-Fi Standard
802.11b/g/n — 2.4 GHz only
Cellular
4G LTE / GSM/GPRS: 850/900/1800/1900 MHz
SIM Type
Nano SIM (not included — user-supplied)
Bluetooth
Yes — local configuration and debugging
Inverter Communication
RS485 (Modbus RTU)
Failover
Auto-switches from Wi-Fi to 4G if Wi-Fi unavailable
Data
Upload Interval
5 minutes
Platform
SolisCloud
App
SolisCloud (iOS and Android)
Multi-Inverter
Max Inverters per Logger
10 (RS485 daisy-chain)
One-Key Address Assignment
Yes
Configuration
Wi-Fi Setup
Bluetooth via SolisCloud app / AP mode (browser)
Power
Operating Voltage
DC 5V (±5%)
Power Consumption
≤5 W
Physical
Connector
USB — Insert+Lock
Dimensions (L×W×H)
128 × 50 × 34 mm
Weight
79 g
Indicators
3 × LED: NET, COM, PWR
Buttons
1 × RESET (short = data push; long = factory reset)
Environment
Protection
IP65
Operating Temperature
−30°C to +65°C
Operating Humidity
5 – 95% RH (non-condensing)
Storage Temperature
−40°C to +70°C
Storage Humidity
<40%
Max Altitude
4,000 m
Compatibility
Compatible Inverters
Solis S6 series (USB-type COM port)
Not Compatible
Solis 4G, 5G, S5 series — use S1-W4G-ST (4-Pin) instead
Warranty and Certification
Warranty
2 years
Certifications
CE, FCC
Manufacturer
Ginlong Technologies Co., Ltd (Solis)
Frequently Asked Questions
What SIM card do I need?
You need a standard Nano SIM on a UK 4G-enabled data plan. Any UK mobile network works (EE, Vodafone, O2, Three, giffgaff, etc.). Data usage is very low because the cellular connection is only used when Wi-Fi is unavailable — at 5-minute intervals, each data packet is a few kilobytes. A basic pay-as-you-go SIM with a small monthly data add-on (e.g. 100MB/month) is more than sufficient. Dedicated IoT SIM plans are also suitable. If you prefer a pre-installed multi-network SIM with a 5 or 10-year plan, the S1-W4G-ST (USB, With SIM) version is available separately.
What happens if both Wi-Fi and 4G fail at the same time?
If both connections are unavailable, data will not upload to SolisCloud. However, the inverter continues to operate and generate independently of the logger. SolisCloud will show a gap in the monitoring data for the offline period. Once either connection is restored, the logger resumes uploading. Note: the S1-W4G-ST does not have built-in local storage for retransmitting missed data — unlike the S2-WL-ST. If data continuity during outages is critical, consider the S2-WL-ST instead.
Which Solis inverters are compatible with the USB version?
The USB-connector S1-W4G-ST is compatible with Solis S6 series inverters. Solis S6 models have a USB-type COM port. Earlier series (4G, 5G, S5) use a 4-pin COM port and require the S1-W4G-ST (4-Pin) version. Check the Solis Datalogger Compatibility Guide at solis-service.solisinverters.com.
How is the cellular failover triggered?
The logger monitors the Wi-Fi connection continuously. If it loses connectivity to SolisCloud via Wi-Fi, it automatically activates the 4G cellular connection without any user action or manual reconfiguration. When Wi-Fi connectivity is restored, the logger returns to Wi-Fi as the primary path. The failover and switchback are seamless and transparent to SolisCloud.
Does the S1-W4G-ST support Modbus TCP like the S2-WL-ST?
No. The S1-W4G-ST does not have a wired LAN (Ethernet) port and does not support Modbus TCP. If you need Modbus TCP for Home Assistant or a local BMS integration, the S2-WL-ST (USB) is the correct product for S6 inverters.
Related Products
Solis S2-WL-ST (USB)
Wi-Fi + LAN for S6 inverters — with Modbus TCP
Solis S2-WL-ST (4-Pin)
Wi-Fi + LAN for Solis 4G/5G/S5 inverters
Solis S5 Wi-Fi Data Logger (4-Pin)
Dual-band 2.4/5 GHz Wi-Fi — 4-pin for S5 series
Solis S1-W4G-ST (USB, With SIM)
Same logger with pre-installed multi-network SIM
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
Average
Good (New Build)
Required Heating
0
Watts
0
BTUs
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