During the SFERA-II project, the measurement accuracy of a facility called KONTAS-Cp consisting of a bypass with electric heating, temperature difference measurement and a Coriolis mass flow sensor to measure thermal heat capacity (Cp) of heat transfer fluid (HTF) is enhanced and an additional Coriolis mass flow sensor is included. The bypass is portable and can be coupled to practically any test facility using thermal oil. Such coupling enables the measurement of the heat capacity of the heat transfer fluid contained in the facility and also the calibration of installed mass flow sensors. Among others, mass flow and specific heat capacity are key measurands to carry out energy balance studies / efficiency measurements in thermal collector assessments. The enhancement of the accuracy of heat capacity measurements is necessary because of insufficient data quality regarding the specific heat capacity of used thermal oils in parabolic trough applications, especially at elevated operation temperatures in the range of 200 to 400 °C. The objective of this work is to reduce the in-situ measurement uncertainty of the specific heat capacity. The uncertainty in Cp was reduced to 1.0%. The Cp-measurement bypass in combination with the inclusion of a highly accurate mass flow sensor lead to a high measurement accuracy of thermal performance tests of CSP components and systems. Thus, European research centres are enabled to offer a more reliable service to users from industry and research.