could not convert string to float: 'unavailable'

[woopstar]

Sometimes, some of the sensors become unavailable. This results in the following error in the log:

2024-09-23 09:09:33.136 ERROR (Recorder) [homeassistant] Error doing job: Task exception was never retrieved (None)
Traceback (most recent call last):
  File "/config/custom_components/ev_smart_charging/coordinator.py", line 770, in update_sensors_new
    await self.update_sensors(
  File "/config/custom_components/ev_smart_charging/coordinator.py", line 820, in update_sensors
    self.solar_charging.update_grid_usage(float(new_state.state))
                                          ^^^^^^^^^^^^^^^^^^^^^^
ValueError: could not convert string to float: 'unavailable'

There should be a check for this in the code.