LAUSR

Abstract Although achieving efficient solar-thermal conversion with nanofluids (NFs) plays an important role in developing photothermal technologies, full-spectrum energy usage is still challenging currently. In this work, dimensionless methods of designing NFs are proposed in complex permittivity ( e ) space, to make the most of solar energy. Firstly, an effective regime Ω ′ for each size parameter x is determined, in which an ideal photothermal efficiency can be guaranteed if only the NPs’ permittivity falls into this area. Besides, on the other hand, by introducing a dimensionless parameter Q i , our methods also allow to actively chose properties of NFs with a desirable solar-to-thermal efficiency, including volume concentration of NPs ( f v ) and thickness of NFs (L). Based on the proposed principles, results show that SiO2@Ni and SiO2@TiN NFs perform better with efficiency 15–30% improved than other widely used materials, such as SiO2@Ag(Au, Al) counterparts. Further, genetic algorithms are employed to verify the above results. Consistently, it suggests that near-perfect full-spectrum photothermal efficiency of SiO2@Ni or SiO2@TiN NFs can be obtained, reaching to 99% under certain conditions. In addition, regarding these two superior NFs, appreciable performance can also be protected with considerably small values of f v and L, which helps to reduce costs and is attractive in practice. The proposed principles offer a powerful tool to actively design optimized NP-related NFs for achieving perfect photothermal conversion, which will also potentially stimulate the development of other advanced photothermal technologies.