Most home energy setups I read about here either bolt a commercial all-in-one unit to the wall or splice a used EV pack onto one small inverter and hope for the best. The CSTech went a different route: three salvaged Hyundai Kona packs, roughly 100 kWh of storage, driving a proper three-phase Victron system that keeps the whole house running with the utility completely down. That scale of storage behind a genuinely off-grid-capable three-phase setup is rare in DIY work, and in my view it puts this build in a different league from the usual single-phase garage installs.
The layout is AC-coupled: the Fronius grid-tie unit feeds into the AC output of the three MultiPlus-II inverters rather than hanging off the DC side. Solar modules land on both the Victron and Fronius gear, and three dedicated MPPT controllers add about 400 A of direct DC charging on top of the 140 A chargers built into the inverters. A Seplos BMS watches the packs, with communication running in a master-slave arrangement across the three banks and battery telemetry feeding straight into the central Victron monitoring hub.
The finish is what grabs me. Three battery cabinets on casters hold around 33 kWh each, each front carrying a red rotary disconnect, an LCD screen and dual RJ45 ports. The gray sheet-metal cabinets pack Schneider breakers on DIN rail, dual copper busbars behind clear acrylic, and bolt-down fuses labeled for each MPPT, inverter phase and battery. A rotary transfer switch labeled RETEA - 0 - SOLAR permits a full manual bypass of the solar side back to grid power for maintenance, and selector switches move the Fronius between the off-grid microgrid bus and the normal grid supply.
The one gap: the maker has promised a full breakdown and setup tips that have not appeared yet. Until then, how the mixed used EV modules behave long term stays an open question.
Project by The CSTech. Watch it on their YouTube channel: