My solar system also only reads its full power usage without seeing what power is going direct to the geysers. In my case, I’m using a Hall sensor with an Efergy cloud based system to read the power that is still being drawn from the grid.
In the USA, most smart meters send data along the ISM band, in a protocol called Encoder Receiver Transmitter, by Itron corporation. This applies to electric, gas, and water meters. Said protocol has a variety of message formats, but they’re all fairly easy to work with. The meters generally have a barcode or similar tag on them, usually near the word/logo for “Itron”, with an 8 digit numeric ID.
A Software defined radio (SDR) can be put to good use though to read this data into Home Assistant though. This project explains how that can be done.
See https://pdx.su/blog/2024-03-17-reading-my-electric-meter-with-rtlsdr/