Turn on immersion heater via smart switch when exporting power

[Will]

The best way of diverting solar surplus solar generation into hot water is to use an Eddi or iBoost device but there are cheaper, easier ways to reuse your exisiting immersion heating element to heat up hot water from surplus solar generation.

I'm using a Frient smart cable device inline to the immersion which is a smart switch and energy monitoring device https://frient.com/products/smart-cable/

This combined with a simply Home Assistant automation turned on the water heater when the export feedin power is over 2kW for more than 5 minutes and turns the water heater on for 1 hour.

An Eddi or Iboost is a far nicer solution as it can very the amount of power going to the heating element but my cheap and cheerful solution has been working flawlessly since I set it up.

Keen to hear all your thoughts on how you use your surplus solar generation.

[xBoris]

I had a similar thought a while back and setup mine via a Shelley EM.

It did the job but I decided to uninstall it.

Despite being rated for 16A, it got very hot under the load of the immersion heater. On some occasions it would reach the device's safety cut out at around 95C. Too dicey for me.

Has the frient device been any better in this regard?

[Will]

Has the frient device been any better in this regard?

Yes, 100% than a shelly, the frient doesn't even get warm and it has internal safety measures including temp sensing to protect it so I sleep well knowing it's a solid bit of kit.

[xBoris]

Thanks for the info Will.

[Homer]

Waiting for my Eddi and batteries to be installed in the meantime I hooked up a dehumidifer via a smart switch.

Home Assistant switches it on an off depending on the amount of spare power. When its running its consumes around 300W's and is working as an effective background heater lessening the load on my central heating and earlier in the week I stuck it in front of a clothes rack and dried the washing instead of using the tumble drier. Anything is better than giving my excess power away for free

[Will]

yep, good idea. Best to use the power than give it away!

[SolarJunkie]

I haven't delved too deep into this, as I bought an iBoost, but there are DIY PWM projects available, which might be worth investigation, in addition, I've noticed another company "Solic" making a cheaper diverter, at a current price of around £225 (I'm not affiliated) this would give you a ROI in half the time of an iBoost.

[Ched]

As we have just had our system installed and are waiting for paperwork I though we could use any export to the grid to power a small heater.
I tried using the visual editor and it looks similar to the example at the top of the thread but it doesn't seem to work.

Here is my YAML code:

Code: Select all

alias: Turn heater On IF batt Full and 100w to Grid
description: ""
trigger:
  - platform: numeric_state
    entity_id: sensor.feed_in_power
    for:
      hours: 0
      minutes: 0
      seconds: 0
    above: 100
condition:
  - condition: numeric_state
    entity_id: sensor.battery_charge
    above: 95
action:
  - type: turn_on
    device_id: 2696e8290a414bbcb310060e51cfd9d8
    entity_id: switch.beer_fridge
    domain: switch
  - delay:
      hours: 0
      minutes: 1
      seconds: 0
      milliseconds: 0
  - type: turn_off
    device_id: 2696e8290a414bbcb310060e51cfd9d8
    entity_id: switch.beer_fridge
    domain: switch
mode: restart

It's only set to 100 watts to grid as a test. The 'beer_fridge' is a Kasa smart plug that was used to control the beer fridge before being moved
Any ideas where I am going wrong?

Thanks for any help.

[pdw]

I thought I'd share my solution to this, which is to use a T-Smart immersion heater thermostat (https://www.tsmart.co.uk/). These are fairly inexpensive (I paid around £90) and if you have a heater with a swappable thermostat, very easy to install. It also gives you access to the water tank temperature in HA.

I created a custom integration for this (https://github.com/pdw-mb/tsmart_ha) which is now available through HACS. This exposes the thermostat as a climate entity so you can set target temperate and mode, and also gives you the state of the relay so you can calculate energy consumption.