Predicting the thermal performance of thermochromic flat plate solar collectors

A thermochromic vanadium dioxide (VO2) based absorber coating is proposed. The optical response of the multilayered absorber is first simulated, then, the spectral reflectance of the deposited absorber is measured. The determined solar absorptance and thermal emittance values are used to predict the thermal performance of the thermochromic flat plate solar collector. The corresponding stagnation temperature is estimated to be ~25°C lower than that of a standard collector. This is mostly due to the increase in emissivity over the thermochromic phase transition and, partially, to a lower solar absorptance than in standard absorbers. However, a concurrent increase of the solar absorptance over the phase transition limits the overheating protection abilities of the thermochromic collector. Alternative scenarios based on thermochromic absorbers with assumed, constant solar absorptances and the same temperature dependent thermal emittance as determined for the measured sample, are considered. The corresponding thermal performances and stagnation temperatures are predicted and discussed.