  The realm of latent heat storage has witnessed emergence of optical charging
as a promising route of solar thermal latent heat storage. However, it is still
in its initial stages of development and warrants further investigations to
take it to the next level i.e., realization of optical charging based
real-world systems. Engineering efficient optical charging process in turn
necessitates efficient photo-thermal energy conversion, transfer as well as
storage of the incident solar radiant energy. The present work is a determining
step in deciphering, quantifying, and understanding the aforementioned steps
involved in the optical charging process. In particular, experiments have been
designed carefully to investigate optical charging of composite-PCMs (particles
laden organic PCMs) with and without thermochromism assistance.
Spatial-temporal temperature distribution curves reveal that temperature spread
(in the liquid phase) in case of optical charging of non-thermochromic
particles (carbon soot nanoparticles) laden PCMs is significantly high (as high
as approximately 24 {\deg}C) relative to that observed in case of thermochromic
particles (microcapsules) laden PCMs (approximately, 4 {\deg}C). The magnitude
of the temperature spread (being representative of the deviation from
thermostatic optical charging) clearly points out that opposed to
non-thermochromic laden PCMs, nearly thermostatic optical charging can be
achieved in case of thermochromic particles laden PCMs. Furthermore, in case of
optical charging without thermochromic assistance, the temperature spread, peak
temperatures and the melting rates increase with increase in particles
concentration. Whereas, in the latter case, although the temperature spread and
peak temperatures are nearly independent; the melting rates do depend on the
particles concentration.
