With this script energy sensor is in kWh. But Shellies reset this meter on every reboot. You can use power sensor, integration sensor and utility_meter:
sensor:
- platform: integration
source: sensor.shelly2_5b2604_power
name: 'Shelly Energy'
unit_prefix: k
round: 2
utility_meter:
energy_shelly2_monthly:
source: sensor.shelly_energy
cycle: monthly