The heat transfer and flow characteristics of a multiple V-shaped rib roughened solar air heater were numerically investigated. Calculations were performed for different geometrical parameters of the channel and rib, focused on their detailed effects on the maximum heat transfer enhancement. The multiple V-shaped ribs greatly enhanced the heat transfer, and the maximum thermohydraulic performance factor was found to be 2.35 in the studied ranges. Increasing the spanwise rib number produces two opposing effects on the heat transfer performance, resulting in an optimal spanwise rib number giving the maximum thermohydraulic performance factor. The geometrical parameters of the rib and channel influence the optimal spanwise rib number by changing the affecting factors of the thermohydraulic performance factor. The optimal spanwise rib number decreased with an increase in the channel height, rib attack angle, and relative rib pitch, whereas it first increased and then remained constant with an increase in the relative rib height. (C) 2018 Elsevier Ltd. All rights reserved.