Improve some stats so they can be used in statistics graph

[cz1497]

Hi All,

First, thanks for the integration it's excellent and so much more informative than the foxess cloud app.

I noticed that some of the stats are not available to the statistics graph in HA with the default configuration.yaml. For example I like a chart like this one that shows current solar plotted over time (without having a gauge that you click on)

I got it to work by adding state_class: "measurement" in my configuration.yaml which seems to work although I'm a noob to HA so not sure if this is the best way to go about it.

  - name: "PV Power Now"
    device_class: "power"
    state_class: "measurement"
    unit_of_measurement: "kW"
    state: >
          {{ (states('sensor.pv1_power') | float(default=0) + states('sensor.pv2_power') | float(default=0) ) * 1 }}

Thoughts?

Cheers
Dave