For the first time, I live in a house with an electric heat pump (natural gas boilers are still the most common here in Italy).
As I always do when I have some kind of new machinery I immediately leaf through the manual. Note: this does not apply to software, for which I read the documentation only after several failures 😅.

Inside the manual there’s a section called Smart Grid Ready. The idea is to simply tell the heat pump when there is free electricity or when the electricity is cheaper, to raise the set point temperature.
I imagined this as a thermal battery where the house stores energy when it’s convenient and releases it when necessary.

Smart Grid Ready Manual Section Smart Grid Ready pinout on the heat pump manual. I used the Switch-on recommendation contact.

For once, a smart feature seemed really smart, so I decided to make it work with my solar panel system.
I have a SolarEdge inverter and after a quick search, I found it supports Modbus communication over TCP. There exist libraries on GitHub to read real-time data directly from the inverter.
Unfortunately, my inverter is connected to the network via WiFi instead of Ethernet, and SolarEdge disabled Modbus over WiFi for some firmware versions. So I had to use the SolarEdge APIs, making http requests to their cloud platform.

This is a sketch of how it works:

Diagram of the project

I wrote a program in go that runs on the Raspberry. It’s available on my GitHub. It requests the current power flow to SolarEdge and controls a relay connected to the Smart Grid input of the heat pump.
SolarEdge only offers 300 daily requests to their APIs. Running the script only during daylight I can collect a sample every 2 minutes, enough for my goal.

My heat pump uses up to 2 kW when producing domestic hot water, so I used this value as the threshold to consider the power surplus enough for the smart grid toggle.

I also attached a LED semaphore to the Pi:

  • 🔴 Red: no production at all
  • 🟡 Yellow: production, but not enough
  • 🟢 Green: enough free electricity, smart grid ON 🤟


Here’s a picture of the Raspberry with the semaphore and the relay, running inside a cotton buds plastic case on top of the heat pump internal unit:

Photo of the Raspberry Pi


Using the smart grid input I was able to move some spikes of consumption from the night to the day. I’m still evaluating if the pattern is consistent.

Production and consumption before and after the smart grid input


Here’s some improvements I may try in the future:

  • update the inverter firmware to enable Modbus over TCP and get data from the inverter, avoiding their cloud service;
  • read from the Raspberry if the heat pump is actually active or not, to improve the algorithm.


That’s all! 👋