Check controllability: the HEMS & Home Assistant checklist

If your goal is local control without cloud lock-in — PV, battery, heat pump, and later the EV from one system you own (ideally Home Assistant) — then a few concrete specs decide whether that's actually possible. The biggest lock-in trap is an inverter/HEMS that only exposes data through the manufacturer's cloud.

This page is the checklist. For each capability: good / acceptable / red flag.

Reading and controlling the system locally

Local Modbus TCP/RTU — the gold standard for Home Assistant. If the inverter exposes Modbus on the LAN, HA can read PV, battery SoC, grid flow and often write setpoints (charge/discharge, export limit) — with zero cloud. Good: documented local Modbus register map, read + write. Acceptable: read-only, or via a dongle. Red flag: no Modbus, cloud API only.

Open local API vs cloud-only — a documented LAN/REST/MQTT interface means no dependence on the vendor's servers (which can change, charge, or shut down). Good: local REST/MQTT/Modbus, documented. Acceptable: local but undocumented. Red flag: cloud-only, terms forbid scraping.

Home Assistant integration maturity — some systems have native or well-maintained community (HACS) integrations: SMA (native + Modbus), Sungrow (excellent HACS integration, read + write), Huawei, Fenecon/OpenEMS, RCT. Many cloud-only brands are read-only or unstable. Good: mature (HACS/native), read + write. Acceptable: community, read-only. Red flag: cloud-polling only.

EEBus — an emerging EU standard for device ↔ energy-manager communication, especially heat pumps and wallboxes ↔ HEMS. The modern successor to SG-Ready. Less HA-native than Modbus today, but strategically important.

Coordinating PV + heat pump + grid (the actual goal)

Dynamic-tariff readiness — to buy power when it's cheapest (Tibber/aWATTar/Rabot) you need a smart meter (iMSys) + a controller that can shift battery charging and heat-pump runtime into cheap/green hours. Worthless if the system can't act on a price signal.

PV-surplus heat-pump control — steer surplus PV into the buffer/hot-water tank instead of exporting it cheaply — via SG-Ready, EEBus, or a HEMS that controls both. Whether YOUR PV brand can talk to YOUR heat-pump brand is the key cross-vendor question.

Battery setpoint control — can an external system (HA) command the battery to charge/hold/discharge at a target power? This unlocks tariff arbitrage and your own logic. Sungrow and Huawei allow it via Modbus write; many cloud systems don't.

Emergency power (backup) — single-phase Ersatzstrom vs automatic 3-phase Notstrom/UPS. For whole-home backup you need a 3-phase backup-capable hybrid + backup box, correctly wired.

Smart meter (iMSys/MID) — a grid-point meter (increasingly a certified iMSys) is required for dynamic tariffs and for the HEMS to see true import/export.

EV / V2H readiness — provision now (cable, load budget, 3-phase) for an 11 kW wallbox with PV-surplus charging; longer term, bidirectional charging (V2H/V2G) is coming.

The control hierarchy (for Home Assistant, the inverter brand is decisive)

• Tier 1 (local Modbus read + write, mature HA integration): Sungrow, SMA, Huawei, Fenecon/OpenEMS, Sigenergy, RCT.
• Tier 2 (workable): GoodWe, SolaX (needs the right dongle).
• Avoid for a local-control goal: Felicity, EcoFlow, EV.cockpit, Viessmann (cloud-leaning/closed).
• Heat pumps: the Stiebel/Tecalor platform (Stiebel ISG) gives the best mix of R290 efficiency AND open local control. Buderus/Bosch is the most closed (HomeCom cloud; local only via the community EMS-ESP bridge).

Rule of thumb: for Home Assistant the inverter brand is decisive, not the HEMS name in the brochure. Before buying, ask: documented local Modbus (read + write)? mature HA integration? And will Modbus control be enabled at commissioning (some brands need an installer account for it)?

Controllability and software support change with firmware — verify the details for your specific model at the time of purchase.