BMW i3 + Fronius Symo / Primo Gen24 Plus

Reusing a BMW i3 HV battery pack with a Fronius Gen24 Plus hybrid inverter. Fronius accepts BYD Battery-Box HV on the battery port — the BMS-EV controller emulates a BYD HV stack.

Short answer. A BMW i3 HV pack operates at 260–395 V DC and sits inside the Fronius Gen24 Plus battery port window of 150–530 V (three-phase Symo) or its single-phase Primo equivalent. Fronius Gen24 Plus supports the BYD Battery-Box Premium HV protocol natively. The BMS-EV controller emulates a BYD HV stack (BOX-8.0 / 10.2 / 12.8 profile) reporting BMW i3 pack telemetry.

What works

BMW i3 22 kWh, 33 kWh and 42 kWh packs.
Fronius Symo Gen24 Plus 3.0, 4.0, 5.0, 6.0, 8.0, 10.0 kW three-phase.
Fronius Primo Gen24 Plus 3.0, 3.6, 4.0, 4.6, 5.0, 6.0 kW single-phase.
Fronius Solar.web telemetry: SoC, pack power, charge/discharge energy.
Full backup / PV Point functionality with battery support (requires Fronius Backup option).

Supported inverter models

Inverter	Battery DC range	Power	Phase	Notes
Fronius Symo Gen24 Plus 3.0	150–530 V	3.0 kW	Three-phase	i3 fits
Fronius Symo Gen24 Plus 5.0	150–530 V	5.0 kW	Three-phase	i3 fits
Fronius Symo Gen24 Plus 8.0	150–530 V	8.0 kW	Three-phase	i3 fits
Fronius Symo Gen24 Plus 10.0	150–530 V	10.0 kW	Three-phase	i3 fits
Fronius Primo Gen24 Plus 3.0	150–530 V	3.0 kW	Single-phase	i3 fits
Fronius Primo Gen24 Plus 4.0	150–530 V	4.0 kW	Single-phase	i3 fits
Fronius Primo Gen24 Plus 5.0	150–530 V	5.0 kW	Single-phase	i3 fits
Fronius Primo Gen24 Plus 6.0	150–530 V	6.0 kW	Single-phase	i3 fits

Battery voltage range match

SoC	BMW i3 voltage	Fronius Gen24 Plus headroom
0% (cutoff)	~260 V	110 V above minimum (150 V)
50%	~355 V	Centre of window
100%	~395 V	135 V below ceiling (530 V)

Full BMW i3 pack voltage range fits inside the Fronius Gen24 Plus battery port window with margin at both ends.

CAN protocol mapping

Fronius Gen24 Plus supports several battery vendors — BYD Battery-Box Premium HV, LG RESU FLEX, and a limited set of others. BMS-EV emulates the BYD Battery-Box Premium HV profile because it is the most stable across Fronius firmware:

Battery identifies as BYD HVS/HVM stack on Fronius Modbus/CAN gateway.
SoC (0–100%) from BMW i3 BMS mapped to BYD SoC register.
Pack voltage, current, temperature min/max reported.
Charge/discharge limits from BMW BMS translated to BYD current limit fields.
Warning/alarm flags mapped to BYD alarm bit fields.

In Fronius Solar.web / installer menu, select battery vendor: BYD Battery-Box Premium HV.

Wiring architecture

┌─────────────────┐ ┌──────────────┐ ┌──────────────────┐ │ BMW i3 │ │ BMS-EV │ │ Fronius │ │ HV pack │ │ Controller │ │ Symo / Primo │ │ (260-395 V) │ │ │ │ Gen24 Plus │ │ │ CAN │ Protocol │ CAN │ │ │ BMW BMS kept │─────►│ translator │─────►│ Battery port │ │ │ 500k │ BYD HV emu │ 500k │ │ └────┬────────┬───┘ └──────────────┘ └────┬─────────┬───┘ │ HV+ │ HV- │ BAT+ │ BAT- └────────┴─────────────────────────────────────┘─────────┘

Installation requirements

Engineering values below are examples. Final conductor cross-section and protective-device sizing must be calculated for the actual pack, maximum current, cable length, installation method, ambient temperature and applicable local standards (IEC 60364-7-712, VDE-AR-N 4105, NEC 690).

HV cabling: 25 mm² copper for 3–10 kW Fronius Gen24 Plus.
Contactors: Reuse BMW i3 factory contactors, sequenced by BMS-EV via BMW SME.
DC fuse: 40–63 A gPV between pack and inverter DC input.
Communication: Shielded CAT-6 between BMS-EV controller and Fronius Data Manager CAN port (via BYD dongle interface).
Fronius firmware: Requires Gen24 Plus firmware ≥ 1.29 with BYD battery support enabled.
Fronius Solar.web license: Standard license is sufficient for battery monitoring; no premium subscription required for BMS-EV operation.

Known limitations

Fronius Symo Hybrid (the older non-Gen24 model) is not supported — the current BYD protocol is only implemented on Gen24 Plus.
Fronius Solar.web shows aggregated SoC and battery power; per-cell diagnostics require BMS-EV web UI.
Fronius Full Backup option (whole-house UPS) requires additional Fronius hardware (Wattpilot integration or transfer switch); the battery-side integration is unaffected.
Firmware updates to Fronius Gen24 Plus have historically changed BYD protocol subtleties; the BMS-EV controller is updated in response.
BYD emulation limits total pack size to whatever the Fronius firmware allows for a single BYD stack (~12.8 kWh in strict mode, ~40 kWh with multiple stacks emulated). For >40 kWh installations, consider two Fronius inverters.

FAQ

Why emulate BYD and not Pylontech or LG?

Fronius supports BYD Battery-Box Premium HV, LG RESU FLEX and a small allow-list. BYD HV is the most stable across Fronius firmware and the closest voltage-window match to BMW i3.

Do I need a Fronius Smart Meter?

Yes for grid-aware self-consumption logic (which is the whole point of hybrid inverters). Fronius Smart Meter 63A-3 for three-phase or 63A-1 for single-phase.

Which BYD Battery-Box model do I select?

The BMS-EV controller can emulate BYD HVS 5.1 / 7.7 / 10.2 / 12.8 depending on your i3 capacity. This is set once at factory and matches your invoice.

Does Fronius PV Point (backup on Gen24) work with i3 pack?

Yes. PV Point is single-phase backup during grid outage. With battery, it draws directly from the i3 pack via BMS-EV — up to the discharge limit BMW BMS reports.

Is 22 kWh, 33 kWh or 42 kWh i3 best?

The 33 kWh (94 Ah) is best value for money — highest availability and 25–29 kWh usable at typical SoH.

How is Solar.web configured?

Standard installer flow. Add the Gen24 Plus with BYD battery selected. SoC, charge/discharge power and total energy are visualised without additional setup.

Does emulation limit charge/discharge power?

Not below Fronius Gen24 Plus limits. The 10 kW Symo can charge/discharge at up to 10 kW subject to BMW i3 current derating at low SoC and low temperature.

Order a BMW i3 + Fronius BMS-EV controller

Pre-configured BYD Premium HV firmware

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Last updated: 2026-09-18

Current firmware: 15.0.14

Technical author: BMS-EV engineering team (Clima Boost sp. z o.o., Poland)

Reviewer: Jakub Lipiński, founder/lead engineer BMS-EV

Revision: 2026-09-18 — aligned with firmware 15.0.14, SOFAR 180–800 V DC verification, Kia EV6 + SOFAR HYD 15KTL case study reference