Here’s how we charge our EV during the summer. It takes a bit of effort to get things set up – up to you if you think it’s worth it. We do.

It needs to be really easy to plug the ‘granny’ lead into the car – it’s something you are going to need to do many times. We leave the charging lead permanently plugged into a smart plug in the garage. The cable and charging connector loop over a ‘hook’ right by where the car charge socket is when parked. Walk to the front of the car, open the charge door and plug in the lead. Press the on switch on the smart plug and charging starts. From getting out of the car to charging takes takes 15 seconds. There’s a real world picture below – you can see the smart plug, the charging lead control box on the shelf and the ‘sophisticated’ hangar for the charge lead. It doesn’t have to look good – it just needs to be quick and easy to use.

Second make sure scheduled charging is disabled on the car – its usually set for the cheap overnight electricity times but we are going to be charging in the day. Many cars have a ‘charge now’ button to overrule the schedule but it’s easy to forget. Most fast chargers (7kW home charge points) have a schedule set from their app. Set that schedule up for cheap overnight and you have best of both worlds – a scheduled fast charge overnight when you need it and anytime charging from the granny lead.

We started out using the timer in the smart plug app to turn off the charge. Easy to do and a sure way of making sure the home battery doesn’t run out charge. Depending on the time of day we’d put it on for two or three hours getting around 18 or 27 miles into the car. It did require thought though to set the timer – remember we want to keep enough charge in the home battery to get the house through the evening and night without using any grid electricity. In summer that needs around 50 – 60% in our home battery when the solar fades – sounds a lot but 20% is reserved for grid outages so it’s around 4 kWh to last around 14 hours including cooking dinner and perhaps heating some hot water.

It would be much easier to monitor the home battery charge level and turn off the EV charging at 50-60%. Enter Home Assistant (HA). HA has a Powerwall integration that delivers battery charge level (and a whole lot more information into HA). It’s straightforward to set up an automation in the HA user interface to turn the smart plug off when the battery reaches a preset level. For more flexibility we wanted to be able to set the minimum battery charge level – see screenshot below.

In HA you can define ‘Helpers’ to allow you to interact with the system. ‘Min battery charge’ is such a helper – it shows a slider you can adjust to set a number. Then the automation can use that number to compare to the battery charge. Here’s how the automation looks when set up – it’s all done in the HA UI, no coding needed.

Yes, the smart plug is named ‘Christmas’ – never got around to changing it!

The ‘Approx miles added today’ is a bit more complicated to set up – all it does is multiply the total energy today reported by the smart plug by four – our EV does around 4 miles per kWh. To set it up the following needs to be added to the HA configurations.YAML file.

template:
  - sensor:
    - name: "miles_added"
      unit_of_measurement: "miles"
      state: >
        {% set nrg = states('sensor.christmas_today_s_consumption') | float %}
      
        {{ (nrg * 4) | round(0) }}
    

The Notifications action sends an email telling us that the charging has been turned off and how many miles were added. Again has to be set up in the configurations file – sensitive data replaced with ***. We set up a dedicated gmail account to send mails from Home Assistant – we never look at it!

notify:
  - name: "NOTIFIER_NAME"
    platform: smtp
    server: "smtp.gmail.com"
    port: 587
    timeout: 15
    sender: "stephen*******@gmail.com"
    encryption: starttls
    username: "stephen*******@gmail.com"
    password: "************"
    recipient:
      - "steve@**********.me.uk"
    sender_name: "Home Assistant"

The contents of the mail are defined in the automations .YAML file

service: notify.notifier_name
    data:
      title: Solar ev charging switched off
      message: 'EV charging has been switched off

        Approx {{ states(''sensor.miles_added'') }} miles added today'

Yes, the HA set up is a bit hard work – check out the Home Assistant community for help. We generally try to find something close and modify it to get where we want to be. It’s much easier if you don’t want to bother with the email but for us the mail really helps especially when getting things set up.

There’s lots of good, high quality Home Assistant resources on the web. Worth seeking out the most recent ones as HA has been around for a while and has developed over that time. Many refer to the ‘Supervisor’ which confused us as there was no Supervisor anywhere in our HA installation – it had been replaced by the comprehensive ‘Settings’ menu several releases ago.