Fronius Hybrid Inverters with Second-Life EV Batteries

Fronius is an Austrian manufacturer (Sattledt, founded 1945). Its Gen24 Plus and Verto Plus series accept a DC-coupled battery on a dedicated port and communicate over the Fronius Solar Battery interface — a CAN dialect derived from BYD Battery-Box HVS/HVM.

Short version. Four Fronius inverter families are relevant for second-life EV batteries: Primo Gen24 Plus (single-phase 3–10 kW), Symo Gen24 Plus (three-phase 6–10 kW), the older Symo Hybrid 3.0/4.0/5.0-3-S (three-phase 3–5 kW) and Verto Plus (commercial three-phase 15–33 kW). All Gen24 Plus units communicate over Modbus RTU (RS485) via RJ45 (NOT CAN, unlike most other hybrid inverters). The DC battery voltage window is up to 450 V (Primo single-phase) or up to 700 V (Symo three-phase), per dalathegreat Battery-Emulator wiki and Fronius operating instructions. BMS-EV emulates the BYD HVS/M (2020-25) battery model over Modbus RS485.

Supported Fronius families

Model family	Phase	AC power	Battery DC range	Max DC current	Battery interface
Primo Gen24 Plus 3.0–10.0	1-ph	3.0–10.0 kW	up to 450 V (per dalathegreat wiki)	25 A	Modbus RS485 (BYD HVS/M emulation)
Symo Gen24 Plus 6.0–10.0	3-ph	6.0–10.0 kW	up to 700 V (per dalathegreat wiki)	25 A	Modbus RS485 (BYD HVS/M emulation)
Symo Hybrid 3.0/4.0/5.0-3-S	3-ph	3.0–5.0 kW	120–460 V (Fronius Solar Battery 4.5/7.5/12.0)	16 A	Legacy CAN (Solar Battery only)
Verto Plus 15/20/25/27/30/33	3-ph	15.0–33.3 kW	200–800 V	40 A	Fronius Solar Battery (BYD HVM)

CAN protocol

Fronius GEN24 Plus uses Modbus RTU (RS485) on the battery-side RJ45 port (NOT CAN like most other hybrid inverters). BMS-EV emulates the BYD Battery-Box HVS/M (2020-25) Modbus register map. Cable: minimum CAT5, max 300 m Modbus / 20 m RS485. Terminating resistors on the last device: Modbus 1=0, Modbus 0=1. The critical frames are:

0x35E manufacturer name (ASCII "BYD")
0x35A alarm and warning bitmap
0x356 voltage, current, temperature
0x355 SOC and SOH
0x351 charge/discharge voltage and current limits
0x35F pack info (module count, firmware version)

The controller strips vehicle-specific frames from the EV pack, aggregates cell voltages and temperatures reported by the original BMS, then republishes the six BYD frames every 1 s.

Wiring topology

┌──────────────┐ ┌──────────────────┐ │ EV battery │ │ Fronius Gen24 │ │ pack │ │ Plus / Verto │ │ │ HV DC 150–530 V │ │ │ DC+ ────────┼───► fuse ─► contactor ┼───► BAT+ input │ │ DC- ────────┼───► shunt ────────────┼───► BAT- input │ └──────┬───────┘ └────────┬─────────┘ │ CAN (vehicle BMS) │ CAN (Fronius Solar Battery) │ │ └──► BMS-EV controller ──────────────────┘ (BYD HVS/M emulator over Modbus RS485)

DC voltage windowing

The Gen24 Plus family requires the battery window to lie inside 150–530 V. In practice:

Tesla Model 3/Y (350 V nominal, ~260–405 V operating) — inside window across full SOC range.
BMW i3 (355 V nominal, ~260–400 V operating) — inside window across full SOC range.
VW MEB (400 V nominal, ~310–450 V operating) — inside window across full SOC range.
Hyundai/Kia E-GMP 400 V mode (~300–410 V) — supported. 800 V mode is out of window and not directly compatible with Gen24 Plus.
Nissan Leaf 40/62 kWh (~300–400 V) — inside window; well-matched.
Porsche Taycan / Audi e-tron GT (800 V nominal) — Verto Plus (200–800 V) is the only Fronius option; Gen24 Plus is not compatible.

Known limitations

Firmware pairing. Fronius firmware ≥ 1.28 is required for stable BYD HVS handshake. Earlier firmware misinterprets the alarm bitmap and forces the inverter into "battery service" mode.
Single battery cluster per inverter. Gen24 Plus does not accept parallel battery clusters. Verto Plus accepts up to three clusters — BMS-EV can present multiple EV packs as separate clusters, but each pack needs its own controller.
No AC-coupled operation. Fronius inverters treat the battery as strictly DC-coupled. If your existing PV is on a different inverter, retrofit as a hybrid AC+DC bus is required.
Contactor precharge. Fronius closes its internal BAT contactor without external precharge; the BMS-EV controller must complete precharge on the pack side before signalling ready in frame 0x35A.

Recommended EV battery pairings

EV battery	Nominal V	Usable capacity	Best-fit Fronius model
Tesla Model 3 SR+ (55 kWh)	350 V	50 kWh	Symo Gen24 Plus 8.0/10.0
Tesla Model 3 LR (75 kWh)	355 V	70 kWh	Symo Gen24 Plus 10.0 or Verto Plus 15
BMW i3 33 kWh	355 V	27 kWh	Primo Gen24 Plus 4.0–6.0
BMW i3 42 kWh	355 V	37 kWh	Primo Gen24 Plus 6.0–8.0 or Symo Gen24 Plus 8.0
VW ID.3 58 kWh (MEB)	400 V	52 kWh	Symo Gen24 Plus 8.0/10.0
VW ID.4 77 kWh (MEB)	400 V	72 kWh	Symo Gen24 Plus 10.0 or Verto Plus 15
Hyundai Kona 64 kWh	356 V	60 kWh	Symo Gen24 Plus 8.0/10.0
Nissan Leaf 40 kWh	350 V	36 kWh	Primo Gen24 Plus 5.0/6.0
Nissan Leaf 62 kWh	350 V	56 kWh	Symo Gen24 Plus 8.0/10.0
Porsche Taycan 93 kWh (800 V)	800 V	84 kWh	Verto Plus 20/25 (only 800 V-compatible)

FAQ

Which Fronius model do I need if I have both PV and a battery?

Gen24 Plus is the standard choice — it is a true hybrid inverter with both PV MPPTs (two on Primo, three on Symo) and a battery port on the same unit. The older Symo Hybrid works but is being phased out (spare parts and firmware updates only). Verto Plus is only justified above 15 kW AC.

Can I put two EV batteries on one Fronius Gen24 Plus?

No. Gen24 Plus supports one battery cluster on its BAT port. To parallel two EV packs you either need a Verto Plus (three cluster inputs) or two separate Gen24 Plus units, each with its own pack and BMS-EV controller.

Does the Fronius Solmetric monitor read cell voltages?

Fronius Solar.web reports pack-level SOC, voltage, current, temperature and alarm state — the values BMS-EV forwards from the original vehicle BMS. Individual cell voltages are not published by the CAN protocol; they remain visible only via the vehicle BMS's own diagnostics port.

Is the older Symo Hybrid worth using with an EV pack?

Only if you already own one. Its DC window (120–460 V) is narrower and its Solar Battery CAN dialect predates BYD compatibility. Gen24 Plus is a significantly better match for second-life packs and is still current-production.

What happens on a Fronius firmware update?

Fronius firmware updates arrive over the internet and reboot the inverter without notice. BMS-EV controllers survive this because the BYD HVS handshake is stateless on the battery side — the controller retries frame 0x35E every 100 ms until the inverter re-establishes the session, typically within 60 s.

Can I use Fronius with an 800 V Porsche Taycan pack?

Only the Verto Plus family (200–800 V input) is compatible. Gen24 Plus is capped at 530 V. Verto Plus 20 kW and 25 kW are the practical choices for a 93 kWh Taycan pack in home storage.

Does Fronius require a specific fuse rating on the battery side?

Yes. Fronius specifies a gPV DC fuse on the battery positive rail sized for the maximum battery current (25 A for Gen24 Plus, 40 A for Verto Plus). Use a rated HV DC fuse holder (Bussmann or Siba PV-series). Do not substitute an AC-rated fuse — DC arc extinction requires a different design.

Order a Fronius-compatible BMS-EV controller

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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

Parameter	Value	Source
Communication protocol	Modbus RTU (RS485) via RJ45, NOT CAN	dalathegreat/Battery-Emulator Fronius wiki, Fronius GEN24 operating instructions
Primo Gen24 Plus (1-ph) max battery voltage	up to 450 V	dalathegreat Fronius wiki
Symo Gen24 Plus (3-ph) max battery voltage	up to 700 V	dalathegreat Fronius wiki
Emulated battery model	BYD HVS/M (2020-25)	dalathegreat Fronius wiki setup guide