After my first positive experiences with ESPhome, I had a closer look into the documentation and found out that deepsleep is also implemented.

I had some soil moisture sensors connected to an ESP8266 to detect if irrigation is necessary. The device is powered by an 18650 cell. It wakes up every 30 mins, switches on the power to the sensor, reads the sensor, sends the measured value via MQTT and goes back to deep sleep. It was not too difficult to implement it in ESPhome:

esphome:
  name: eh-bodenfeuchte3
  on_boot:
    - switch.turn_on: Sensor_Vcc
    - delay: 1s
# Terrassensensor

esp8266:
  board: huzzah

# Enable logging
logger:

# Enable Home Assistant API
api:
  password: ""

ota:
  - platform: esphome
    password: ""

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Eh-Bodenfeuchte3"
    password: "EfGXNoIANTV5"

captive_portal:

deep_sleep:
  run_duration: 12s
  sleep_duration: 30min
  id: ds

switch:
  - platform: gpio
    pin: GPIO14 #D5
    id: Sensor_Vcc

binary_sensor:
  - platform: homeassistant
    id: no_deep_sleep
    entity_id: input_boolean.no_deep_sleep

mqtt:
  broker: 192.168.2.204
  discovery: false
  discover_ip: false

sensor:
  - platform: wifi_signal
    name: "WiFi Signal Sensor"
    update_interval: 10s

  - platform: adc
    pin: A0
    name: Terrassenfeuchte
    samples: 10
    update_interval: 8s
    id: terrassenfeuchte
    filters:
      - multiply: 1000
    on_value:
      - mqtt.publish:
          topic: "ESP/H2O/Sensor3"
          payload: !lambda |-
            return to_string(int(1*id(terrassenfeuchte).state));
          retain: true
      - if:
          condition:
            binary_sensor.is_on: no_deep_sleep
          then:
            - deep_sleep.prevent: ds
#            - logger.log: "No sleep!"
          else:
            - deep_sleep.allow: ds
#            - logger.log: "Let's snooze!"

Each time it wakes up, the **on_boot**-section is carried out. There I switch on the voltage for the sensor. As it does not draw much current, I power it directly from a GPIO.

The implementation in ESPhome allowed me even to add a switch to HA to prevent the device from going to deep sleep again after the next time it wakes up again. This allows easily flashing OTA without opening the waterproof housing. A feature which I did not have before.

I put the device into the soil in April and remove it at the end of October. I charge the cell at the beginning of August to be sure that it lasts. That's good enough for me.