https://community.home-assistant.io/t/templates-how-to-deal-with-unavailable-inputs/554306/3
- name: "Solarertrag heute"
unique_id: solar_daily_yield
unit_of_measurement: 'kWh'
icon: mdi:solar-panel
state: >
{% if states('sensor.battery_day_charge_1')|is_number and
states('sensor.battery_day_discharge_1')|is_number and
states('sensor.daily_yield_1')|is_number and
states('sensor.daily_yield_2')|is_number
%}
{{ states('sensor.daily_yield_1') | float(0) + states('sensor.daily_yield_2') | float(0) + states('sensor.battery_day_charge_1') | float(0) - states('sensor.battery_day_discharge_1') | float(0) }}
{% else %}
{{ this.state }}
{% endif %}
device_class: energy