Concepts · Chapter 23
SG-Ready in depth
Two contacts, four states — what SG-Ready really is, who sends the signal, and where its limits are.
"SG-Ready" (Smart-Grid-Ready) sounds high-tech but is mechanically very simple. Understanding what it can — and can't — do helps you judge offers and control options correctly.
What it literally is
SG-Ready is two contacts (terminals) on the heat pump that read the state of two switches. Two switches give four combinations — and each has a meaning:
| State | Mode | What the heat pump does |
|---|---|---|
| 1:0 | Block | Switched off (brief utility block, max 2 h) |
| 0:0 | Normal | Runs normally, no signal |
| 0:1 | Recommend on | A soft nudge — heat a bit more |
| 1:1 | Start command | A strong "on" — actively heat up |
That's all it is: a 2-bit signal — block / normal / soft boost / strong boost.
Who sends the signal
The heat pump only reads the contacts. Something else has to close them:
- Your PV inverter, when it detects surplus.
- evcc / Home Assistant via a relay (your own logic: "power cheap now / PV flowing → boost").
- The grid operator (§14a), triggering the block at peak times.
So the heat-pump maker only provides the terminals — the signal comes from elsewhere.
The limit: it's coarse
SG-Ready can't say "run 43 °C flow" or "charge the tank to exactly 52 °C." It can only do the four coarse states. What "boost" concretely means is decided by the heat pump's controller (usually: raise the target temperatures by a preset amount).
When SG-Ready is enough — and when not
- Enough if you want a simple PV-surplus boost and your heat pump has no open data interface. It's universal and cheap (often just a relay + wiring).
- Too coarse if you want fine, data-based control. Then Modbus (if the heat pump supports it) is the better route — full setpoints and modes instead of four states.
The hidden trade-off point
The wiring of the SG-Ready contacts often falls between trades (heating says "electrician," electrician says "heating"). Clarify explicitly in the offer who wires the contacts and to which signal source.
In short: SG-Ready = 2 contacts, 4 states (block/normal/soft/strong). The signal comes from PV, evcc/HA or the grid operator — not the heat-pump maker. Universal and simple, but coarse; Modbus is the finer route where available. Clarify who wires the contacts.
As the last pro topic, the honest question: cooling with the heat pump — what really works in a radiator house.
In this section