Plasmonic nanoshell-based nanofluids have recently been demonstrated to be promising candidates for efficient solar thermal conversion. During the nanoshells' fabrication processes, more often than not, only part of the dielectric core is covered by metals. However, there are few reports on how these particle defects affect the solar thermal conversion. In this paper, we find that the coverage defects of TiO2/Ag nanoshells, instead of deteriorating, may enhance the solar absorption of nanofluids. The underlying mechanism mainly lies in the redshift of the symmetric localized surface plasmon resonance from the visible region for perfect nanoshells to the near-infrared in the presence of particle defects. The poor absorption of perfect nanoshells based nanofluids in the near-infrared is thus improved. The redshift can be quantitatively predicted and understood by an effective medium approach. This work opens a new route to enhance the solar thermal conversion of nanofluids by mediating the resonance absorption of composite nanoparticles via defects, and helps to deepen the understanding of plasmonic absorption properties of non-perfect nanoshells. (C) 2017 Elsevier Ltd. All rights reserved.