Abstract
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.
Highlights
A novel smart, thermochromic solar absorber has been developed
The determined solar absorptance and thermal emittance values are used to predict the thermal performance of the thermochromic flat plate solar 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
Summary
A novel smart, thermochromic solar absorber has been developed. Its particularity lays in the ability to change its optical properties with temperature. At normal operating temperatures the thermochromic absorber exhibits a high solar absorptance and low thermal emittance, while at high operating temperatures the thermal emittance is increased drastically. In this fashion, it provides a passive overheating protection of the solar collector. The perfectly reversible transition occuring at 68°C, with a transition temperature adjustable by doping, makes VO2 a promising choice for solar thermal applications.[1] Through the thermochromic transition, the optical properties of the film change markedly – especially in the near and mid-infrared spectral region – and a thermal emittance modulation of ~25 – 30% has been reported for individual thermochromic films deposited on Al substrates[2]
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