In general, the roundtrip-efficiency is not a fixed quantity but a value that changes and depends on many factors (e.g. operation point). For some applications like electric mobility, constant efficiency works well enough. However, for other use-cases such as hot water production and storage, the efficiency depends strongly on the outside temperature.

For that reason, it would be a great feature to let users define the field roundtrip-efficiency as a time series. Following the work in PR #897 , this feature could use the field QuantityOrSensor and the utility function get_continuous_series_sensor_or_quantity.