SIMULATION OF THE PERFORMANCE OF PV/T (PV-PCM) SYSTEMS IN TRANSIENT STATE

Carlos Armenta-Deu

Abstract

The paper describes the analysis of the thermal performance of a PCM unit attached to a PV panel configuring a PV/T system. Thermal performance has been analyzed from the transient process point of view considering the temperature evolution of the PCM with time dependent on ambient temperature and solar radiation. A specific algorithm for determining the time evolution of the PCM temperature has been developed. The model uses the DERIVE software to solve the proposed algorithm, considering that the influence of ambient temperature on the thermal performance of the PCM can be neglected if compared with the effects of the solar radiation changes. The model has been simulated for solar radiation from 350 W/m2 to 1 kW/m2 that corresponds to current daily values in a standard clear sky day. Simulation has been run up to the point where steady state is reached, but paying especial attention to the transient period. Transient time for the PCM temperature has been correlated to a polynomial function within 99.6% accuracy, allowing determining the time at which the PCM reaches the melting zone. Melting zone has been defined as the target working zone since the system operates at constant temperature, and the PV panel works at constant efficiency. Simulation results have proven that the PCM operates at the melting zone from 10 am to 2 pm, solar time, what represents 2/3 of the daily power generation. The simulation has shown that steady state considerations are not suitable for PV/T system including PCM units in the configuration, since the time constant of the PV/T is much longer than the one for the solar radiation, what means the PCM operates at the transient state all the day, so the PV/T does.

Abstract

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