Short answer
A PV inverter converts solar, a hybrid inverter adds a battery, and a PCS is the power conversion system on the battery and grid side of larger sites. What decides it for HUBCORE is whether per-phase measurements can be read and active/reactive power limits written over a documented interface that also works without the vendor cloud.
Types and coupling
AC coupling joins solar and battery on the AC side — easier retrofit, more conversion steps. DC coupling joins them on the DC side — lower losses, tighter dependency on a single device. Single-phase suits small sites; three-phase is a precondition for serious load management and phase balancing.
| Aspect | AC coupling | DC coupling |
|---|---|---|
| Retrofit | Easy, existing PV stays | Often requires inverter replacement |
| Losses | More conversion stages | Fewer conversion stages |
| Control | Devices controllable separately | One device, one interface, one point of risk |
Grid-following, grid-forming and islanding
A grid-following inverter needs existing grid voltage and follows it. Grid-forming can create voltage and frequency itself, which is a precondition for islanding and black start. Emergency power supply (EPS) is a separate function — it requires correct switching, clear anti-islanding protection and agreement on which loads stay powered at all.
Islanding and backup power touch personal safety and grid operator requirements. They must not be promised as a sales argument before a site-specific design and approval.
Control: P, Q and phase data
Useful control means being able to set an active power (P) limit or setpoint, where needed reactive power (Q) or cos φ, and to read back the actual state per phase. Without per-phase data you cannot balance load or prevent overloading a single phase.
- Setpoint acceptance time and ramp speed
- Behaviour on comms loss (fail-safe limit, not full power)
- Measurement resolution and timestamping
- Scaling: several units in parallel under one shared limit
Interfaces and cloud dependency
HUBCORE uses only protocols the manufacturer documents — typically Modbus TCP/RTU, SunSpec, REST or MQTT. We do not run reverse-engineered or undocumented interfaces in production. If critical control only works through the vendor cloud, we treat that as an architectural risk.
HUBCORE implication
Every protocol claim is verified against the documentation of the specific model and firmware version, including roles, credentials and fallback on comms loss. Country-specific grid-code compliance is evidenced per project.
Red flag: if a vendor does not document the interface or requires its own cloud for critical control, HUBCORE cannot guarantee the device's behaviour on site.
Cyber security and certification
A controllable power device is a security asset. We require authenticated access, scoped permissions, encrypted traffic, a firmware update path and logs. Country-specific compliance (grid codes, connection conditions) must be evidenced per market and per model — we never assume a device approved in one country is approved in another.
HUBCORE minimum inverter requirements
Before an inverter or PCS can be part of a HUBCORE-controlled site, these points must be covered in writing.
- Public interface documentation with registers/endpoints
- Local control without the vendor cloud
- Per-phase measurements in the readback
- P limit and defined behaviour on comms loss
- Authenticated access and a firmware update path
- A clear owner for service and liability
HUBCORE fit filter
- Controllability — Can the device be safely limited, started and stopped through a documented interface?
- Measurability — Do we get trustworthy measurements (power, energy, phases, state, faults) at sufficient resolution?
- Integrability — Is the interface publicly documented (e.g. Modbus, SunSpec, REST, MQTT, OCPP) and versioned?
- Local operation — Do critical control and safety keep working when the vendor cloud or internet is down?
- Security — Is access authenticated, are rights scoped, is traffic encrypted and firmware updatable?
- Serviceability — Is it clear who owns maintenance, spare parts, firmware and fault resolution?
- Scalability — Can the solution grow (more points, kWh, sites) without redesigning the architecture?
HUBCORE's position
For HUBCORE, choosing an inverter is first of all choosing an interface. A high-efficiency but closed device is worth less in our ecosystem than an average device whose control is open, local and predictable.
Not yet verified
- How broadly and completely is SunSpec actually supported by models available in Estonia?
- Which grid-forming solutions are realistic at apartment-building scale?