Domoticz

You are correct that if Power (expressed in W) is inserted once per hour, and stands for an hour, then the effective result is a same amount of Energy in Wh.
Would be interesting to check whether that matches the predicted Energy for that hour from forecast.solar.

Perhaps we should look with a different view, and just take the data from forecast.solar just as it is:
curious which type for Virtual Sensor is the most neutral, not adding anything to the received info.
Don't yet see anything better than "Custom Sensor, General" as applied in the other thread following this one.

Probably right, because if the Power (expressed in W) is set once per hour and stands for an hour, then the result is the same amount of Energy in Wh.
Should be interesting to check whether that matches the info from forecast.solar for the Energy-per-hour:
if that is true, then you do not need the Power-info from forecast.solar
If a difference, only guessing for the reason.

Probably best to take the data from forecast.solar as it is.
'Custom Sensor/ General' is the most neutral Virtual Device, as you have applied in the other thread followng this one.
For 'simple completenes' only need to add there a Watt-device as 4th Virtual Device for forecasted Power.