A small scale solar tracking concentrated photovoltaic-thermal (CPV-T) system was investigated to enhance the energy efficiency of photovoltaic systems. The experimental measurement was firstly done to obtain the environmental parameters and on site efficiencies of the system. A novel Non-Dimensional Lattice Boltzmann Method (NDLBM) was then developed to simulate the transient fluid flow and heat transfer of the CPV-T receiver. This NDLBM establishes a whole set of dimensionless form of lattice Boltzmann equations and boundary conditions with dimensionless governing parameters in both macroscopic and mesoscopic length scales. The relaxation time is expressed in form of the mesoscopic Reynolds number instead of the viscosity, making the relationship between the mesh size and simulation range clearer. The present physics-based dimensionless inlet/outlet flow and heat flux boundary conditions make it possible to simulate the present high solar irradiance, large temperature difference, and high velocity mixed convection heat transfer problem. The effects of the flow rate, inlet flow temperature and distributions of the inlet/outlet on the heat transfer are obtained with NDLBM simulations over a wide range of Reynolds number, Rayleigh number, and Richardson number. The results provide a full understanding of the mechanics of the efficiency enhancement of the CPV-T system due to water cooling. © 2014 Elsevier Ltd.