how do I format the above so it can go

[cobalt vale]

You don't - that's a new style template sensor and doesn't go under sensor:

You could do

template: !include template.yaml

and then template.yaml would be:

- sensor:
    - name: Grid Import Power
      state_class: measurement
      icon: mdi:transmission-tower
      unit_of_measurement: W
      device_class: power
      state: >
        {{ [0, states('sensor.envoy_SERIALNUMBER_current_power_consumption') | int - states('sensor.envoy_SERIALNUMBER_current_power_production') | int ] | max }}
    - name: Grid Export Power
      state_class: measurement
      icon: mdi:transmission-tower
      unit_of_measurement: W
      device_class: power
      state: >
        {{ [0, states('sensor.envoy_SERIALNUMBER_current_power_production') | int - states('sensor.envoy_SERIALNUMBER_current_power_consumption') | int ] | max }}

[sacred oasis]

thank you, I think I was getting closer.
I had
template:

• sensor: !include sensor.yaml

then

• name: Solar Power Corrected
  state_class: measurement
  icon: mdi:solar-panel
  unit_of_measurement: W
  device_class: power
  state: >
  {% set value = states('sensor.envoy_xx_current_power_production') | int(0) %}
  {% if value <= 5 -%}
  0
  {% elif is_state('sun.sun','below_horizon') %}
  0
  {%- else -%}
  {{ value }}
  {%- endif %}

[ashen robin]

To format your text as code, enter three backticks on the first line, press Shift+Enter for a new line, paste your code, press Enter again for another new line, and lastly three more backticks.
```yaml
example: here
```
Don't forget you can edit your post rather than repeatedly posting the same thing.

[sacred oasis]

which I think is fine until later in the sensor.yaml when I start trying to specify platform:

[cobalt vale]

Yeah, you can't mix different formats

[sacred oasis]

thank you for your help I'll implement how you suggested

[cobalt vale]

Your approach will be fine, as long as you don't duplicate sensor: in sensor.yaml