Experimental Methodology for the Heat Losses Estimation in TES tanks

What is it about?

The present work introduces an indirect approach for the estimation of the heat losses in TES (Thermal Energy Storage) tanks. Heat losses are calculated taking into account the fact that in steady state condition they are equal to the heat input provided by electric heaters. The proposed methodology has been tested in the TESLAB (Thermal Energy Storage LABoratory) tank which is equipped with two electric heaters simulating the heat input from solar irradiation. Heaters' operation is controlled by an industrial PID (Proportional Integral Derivative) controller regulating their duty factor to achieve the desired set temperature. Total electric power is calculated as the summation of the contribution of each heater, which is equal to the product of the duty factor and the measured electric power. Heat losses for the TESLAB tank are compared with the measured losses during the cooling process satisfactorily. The proposed methodology could be also applied for the measurement of the heat losses of larger tanks, receivers and even CSP (Concentrated Solar Power) plants under operation without solar irradiation. Preliminary testing at the CSP-DSW (Concentrated Solar Power-Desalinated Sea Water) plant of The Cyprus Institute at PROTEAS (Platform for Research, Observation and TEchnological Applications in Solar energy) is quite promising.

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Why is it important?

The characterization of each subsystem of a CSP (Concentrated Solar Power) plant is necessary for its efficient operation. In a TES (Thermal Energy Storage) tank the knowledge of the temperature distribution and heat losses is required in order to predict potential freezing locations, cool down times and tank's contribution to the overall efficiency. In this paper an indirect experimental approach for the measurement of the heat losses in TES tanks is presented. The temperature distribution and heat losses in the pilot tank of The Cyprus Institute in the TESLAB laboratory are given. Heat losses then are compared to the heat losses during the cool down procedure of the tank. The satisfactory agreement between both methods shows the potential of the proposed methodology.