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Concepts · Chapter 21

Coordinating PV surplus with the heat pump

Surplus solar into heat instead of the grid — via SG-Ready, EEBus or a HEMS. What actually works together.

Updated: 2 min read Deutsch →

When the sun delivers more than the house and battery currently need, you can steer the surplus into the heat pump — it then heats the buffer and hot water with your own power instead of exporting it cheaply. This is one of the most valuable automations.

The three ways to do it

  1. SG-Ready — the simple, universal option: a coarse "heat more now" signal (next chapter). Almost every heat pump understands it.
  2. EEBus — the more modern EU standard for communication between heat pump/wallbox and energy manager. Finer than SG-Ready, but still less widespread in home automation.
  3. A HEMS or Home Assistant — an energy manager that sees PV, battery and heat pump together and allocates the surplus deliberately.

The decisive question: do your brands talk to each other?

The PV inverter knows when there's surplus. The heat pump has to receive that signal. Whether that works across brands is the crux:

  • Some PV makers can output an SG-Ready or EEBus signal directly.
  • Otherwise a HEMS or Home Assistant does the bridging: it reads the surplus from the inverter and switches the signal to the heat pump.

That's why local controllability of both devices is so valuable — then you can build the coupling yourself, regardless of whether the brands match "out of the box."

What you can realistically automate

  • Hot-water priority on surplus: with lots of PV, heat the hot water a bit higher (a thermal store = a "free battery").
  • Buffer boost: run the heating buffer slightly warmer on surplus to save grid power later.
  • No dead-heading: the heat pump needs minimum flow — surplus heating means "more into the buffer," not "close the radiators."

The winter-reality limit

Honestly: in winter, when the heat pump needs the most, PV surplus is smallest. The coupling shines in the shoulder seasons and summer (especially hot water). In deep winter, efficiency and dynamic tariff help more — the battery-arbitrage lever from the last chapter.

In short: surplus coupling steers solar into buffer/hot water instead of the grid — via SG-Ready, EEBus or a HEMS/Home Assistant. The value appears when your brands (or your HEMS) bridge the signal. In winter the effect is small — there efficiency + tariff matter.

Next: steering the heat pump yourself — heating curve, setpoints, modes, without harming it.

In this section

Energy basics: kW, kWh, and what "kWp" actually means The single most common mix-up in offers and conversations, cleared up once — because everything else builds on it. How a PV system works From sunlight on the roof to power at the socket — the chain in four steps, and what actually drives yield. Understanding modules Mono or bifacial, cell quality, and the difference between product and performance warranty — without the marketing. Battery basics Nominal vs usable capacity, LFP vs NMC, depth of discharge, and sizing the battery to your array. How a heat pump works A fridge, thought about backwards — why a heat pump turns 1 kWh of electricity into several kWh of heat, without breaking physics.