This is a diy project for building a smart water heater powered by the sun using cheap iot material and open source software.
- a working Home Assistant installation with esphome plugin installed
- a Sonoff 4CH device (~30 EUR)
- a THERMIS Heating Element 3000 W or similiar (~60 EUR)
- a smart meter connected to Home Assistant, e.g via edl21
- a temperature sensor connected to Home Assistant, e.g. DS18B20
The Thermis water heating element with 3000 Watts consists of three independent heating elements with 1000 watts each. This should be sufficient for a normal 3-4 person household. With the Sonoff 4CH they can be switched independently with three different relays. Connected to a smart power meter the esphome flashed Sonoff 4CH is able to switch the relays independently depending on available PV power. The temperature of the power-to-heat device can be set in a thermostat device directly in home-assistant. The esphome powered Sonoff 4CH device will then automatically adjust the water temperature.
The power-to-heat device is set up to constantly receive the total_system_power sensor value of the edl21 integration via home-assistant. This sensor value is transmitted every 1-2s. Therefore the power-to-heat device can switch the heating elements on/off if the heating power exceeds the available PV is power. The power-to-heat device turns the heating elements successively off or back on if other devices draw energy or not.
In case you worry about hours when the PV is providing less than 1000 watts: if would generally be possible to further control one heating element with a power control device. In my opinion, I tried it out, it is not worth the effort. Ignore it and size the PV accordingly to have more hours with more than 1000 watts.
Definitely, but this is a lot easier to build, cheaper and serves you with warm water more than six months a year.
The MIT License (MIT).