The PTC system operates at a higher temperature than the ETC system and with a higher evaporation pressure in the ORC.
Although this results in a higher instantaneous power production, the operation of the PTC system is more intermittent because the greater decrease in the solar collector fluid enthalpy through the ORC evaporator (with its associated increased heat input to the cycle) cannot be sustained by the collector at the temperature required.
Thus for short periods the collector fluid must recirculate within the solar array, bypassing the ORC, while it recovers to the required temperature, before being sent back to the ORC evaporator.
The ETC system also displays intermittent operation for a large part of the day, but is able to sustain longer periods of continuous operation during the peak solar hours. With its tracking capability the PTC system is also shown to operate across a slightly longer portion of the day due to its ability to collect irradiance when the sun is low on the horizon. However over the course of the day, the total accumulated work output for the two systems is almost identical.