Victron Energy
Cerbo GX Modbus TCP for KNX solar, battery SOC and self-consumption automation
Victron Energy (Almere, Netherlands) makes off-grid and hybrid solar power systems — MultiPlus inverter/chargers, MPPT solar controllers, and the Cerbo GX energy computer. Native Modbus TCP server makes Victron the easiest solar/battery system to integrate with KNX.
Role in our panels
How we use Victron Energy
The Victron Cerbo GX (successor to the CCGX) is the central hub of any Victron installation — it aggregates data from all connected Victron devices (MultiPlus inverter/charger via VE.Bus, MPPT solar controllers via VE.Direct or VE.Can, BMV battery monitors via VE.Direct) and presents a unified data model. The Cerbo GX runs a built-in Modbus TCP server on port 502 that is enabled by default from firmware v2.30 onwards — no additional hardware or configuration is required to access the full register map. Key Cerbo GX Modbus TCP registers for KNX integration: AC Load Power (Reg 817, W, read-only), AC Grid Power (Reg 820, W, positive=import/negative=export), Battery SOC (Reg 843, % × 10 — divide by 10 for DPT 5.001), PV Power MPPT1 (Reg 850, W), MultiPlus State (Reg 844: 0=Off/1=Low Power/9=Inverting/10=Absorption/11=Float). The Intesis IN701KNX gateway reads all required registers and maps them to KNX group addresses — typical mapping: GA 9/2/0 (PV power DPT 13.010), GA 9/2/1 (grid export/import DPT 13.010), GA 9/2/2 (battery SOC DPT 5.001), GA 9/2/3 (AC load DPT 13.010). Self-consumption KNX logic is built in the KNX logic controller (MDT SCN-IP000.02, LOYTEC LVIS-ME3, or Gira HomeServer script): IF GA 9/2/1 (grid export) > 2000W THEN write SG Ready State 3 to heat pump KNX relay GA (surplus PV heats DHW); IF GA 9/2/1 > 4000W THEN activate EV charger KNX control GA. The logic must include hysteresis timers (minimum 10 minutes) to prevent oscillation during cloud transients. For EV charger control: Easee Home charger via KNX binary output from Cerbo GX logic controls charge start/stop based on surplus PV availability. Battery SOC low load shedding scene: IF GA 9/2/2 (battery SOC) < 20% AND GA (grid status) = fault (island mode) THEN activate KNX scene 'Emergency' — setback HVAC setpoints by 3°C, pause EV charger, reduce lighting levels to 30%. This scene protects battery reserve for critical loads (refrigeration, medical equipment) during extended grid outage. Recovery scene: IF battery SOC > 50% THEN restore normal scenes. The MultiPlus mode register (Reg 33 — 0=charger off, 1=inverter off, 3=on) is also writable via Modbus, enabling KNX to switch MultiPlus between charging-only and inverting modes for grid import tariff optimisation.
Victron Cerbo GX (CCGX successor) has a built-in Modbus TCP server on port 502 — no additional hardware needed. Key registers: AC Load Power (Reg 817, W), AC Grid Power (Reg 820, positive=import/negative=export), Battery SOC (Reg 843, %), PV Power MPPT1 (Reg 850, W), MultiPlus State (Reg 844, 0=Off/1=Low Power/9=Inverting/10=Absorption/11=Float). Intesis IN701KNX: map each register → KNX GA. GA 9/2/0 (PV power DPT 13.010 W), GA 9/2/1 (grid export DPT 13.010 W), GA 9/2/2 (battery SOC DPT 5.001 %). KNX logic: export > 2000W → SG Ready State 3 on heat pump.
Used in these project types
Victron Energy products
Key components we install
Cerbo GX
Central Modbus TCP hub for all Victron devices. Runs Linux OS with VRM portal cloud connectivity and built-in Modbus TCP server on port 502. Connects to MultiPlus via VE.Bus (RJ45), MPPT controllers via VE.Direct or VE.Can (up to 5 VE.Direct ports), BMV battery monitor via VE.Direct, and SmartShunt via Bluetooth or VE.Direct. Optional GX Touch 50/70 display (HDMI, touchscreen) for local visualisation. DIN-rail mountable with optional DIN-rail adapter accessory. Central panel component in all Victron KNX integration projects — PanelCraft mounts Cerbo GX alongside Intesis IN701KNX on DIN rail with shared 24V DC supply.
MultiPlus-II 5000
5 kVA (4000W continuous) hybrid inverter/charger for grid-tied and off-grid solar. Three modes: charger only (grid charges battery), inverter only (battery powers loads), PowerAssist (grid + battery power loads simultaneously). VE.Bus to Cerbo GX. Battery type: Lithium (Pylontech, BYD, Victron Lithium Smart) or lead-acid. KNX integration via Cerbo GX Modbus: MultiPlus state (Reg 844) maps to KNX for energy management visualisation. AC input current limit register (Reg 22) writable from KNX — enables grid tariff-based import limit control.
SmartSolar 100/50
100V 50A solar charge controller (5000W at 48V battery). VE.Direct connection to Cerbo GX (and simultaneously Bluetooth to VictronConnect app). Modbus TCP via Cerbo GX: PV power (Reg 850, W), PV yield today (Reg 784, kWh × 0.01), PV voltage (Reg 852, V × 0.01). Multiple SmartSolar units appear as separate registers in Cerbo GX register map. Used with 4–8 panel strings (400–1600W per string) in residential solar installations. KNX integration shows real-time PV generation from each MPPT on KNX visualisation GA.
BMV-712
High-accuracy battery SOC monitor using coulomb counting (current integration) for precise SOC calculation in lead-acid or lithium battery banks not using a Victron BMS. VE.Direct to Cerbo GX. Modbus registers: SOC (Reg 843 via Cerbo GX), voltage (Reg 840), current (Reg 841), power (Reg 842). For Pylontech and BYD batteries with own BMS communicating to Cerbo GX via CAN, the battery BMS SOC replaces BMV-712 SOC in Cerbo GX — BMV-712 not required. Used for lead-acid backup power banks and non-BMS lithium installations.
EasySolar-II 24
All-in-one unit combining MultiPlus-II 24V 3000VA inverter/charger + 70A MPPT solar controller + GX controller in a single wall-mount enclosure. Equivalent to Cerbo GX + MultiPlus-II + SmartSolar in one unit. Modbus TCP server built-in (same register map as Cerbo GX). Ideal for compact off-grid and hybrid installations (holiday cabins, garden offices) where DIN-rail panel space is limited. KNX integration via Intesis IN701KNX to built-in Modbus TCP server — no Cerbo GX required.
Victron Energy FAQ
What Modbus TCP registers does Victron Cerbo GX expose for KNX integration?
The Cerbo GX Modbus TCP server (port 502) exposes the full Victron register list available as a free download from the Victron Professional portal. Key registers for KNX: AC Grid Power (Reg 820, W signed — positive=import, negative=export), Battery SOC (Reg 843, % × 10), Battery Voltage (Reg 840, V × 10), PV Power MPPT1 (Reg 850, W), AC Load Power (Reg 817, W), MultiPlus State (Reg 844, enum). The complete register list PDF covers all Victron device types connected to Cerbo GX. Each device type (MultiPlus, MPPT, BMS) has its own register offset in the Cerbo GX address space.
Does Victron integration require an additional hardware gateway?
Victron Cerbo GX has a native Modbus TCP server built-in — no additional hardware is required on the Victron side. The only additional hardware needed is a KNX/Modbus TCP bridge: Intesis IN701KNX (DIN-rail, ETS6 application, reads Modbus registers and maps to KNX GAs) or Weinzierl KNX IP Interface 731 with Modbus TCP capability. PanelCraft mounts the Intesis IN701KNX alongside the Cerbo GX on the DIN rail in the same enclosure, powered from the shared 24V DC panel supply.
Can I control Victron battery charging mode from KNX?
Yes — the Victron MultiPlus mode register (Reg 33 via Cerbo GX Modbus TCP) is writable: 0=charger off (prevents grid charging battery), 1=inverter off (grid only, no battery discharge), 3=on (normal hybrid operation). This enables KNX-based grid tariff control: during off-peak tariff hours (e.g. 23:00–06:00), KNX time controller writes mode=3 (charge battery from grid); during peak tariff (07:00–22:00), KNX writes mode=1 (discharge battery to offset grid import). SG Ready relay control of connected heat pump remains independent from battery mode register.
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