The current thermoelectric solar tower plants demand the measure of high solar irradiance on the receiver. Its measure would facilitate the operation of the plant and would contribute to a greater receiver security. Currently, solar tower plants do not have a flux measurement system in their receiver as it is not considered in their design. The inclusion of the flux measurement system in its design phase would facilitate its incorporation and correct operation. Instead, infrared temperature measurement systems are used to infer the irradiance on the receiver. This procedure is not suitable since the delay between the irradiance and the temperature in the receiver can reach a few minutes depending on the materials, the transfer fluid, the operating conditions and the meteorological variables. Traditional flux measurement methods, used during the evaluation of small solar receiver prototypes, turn to moving parts that do not extrapolate to large receivers of commercial solar tower plants due to scaling problems. On the other hand, the use of mobile elements, which interact with the concentrated solar radiation directed towards the receiver, would negatively affect the daily operation of the plant. This work presents a simple method that allows characterizing a large target and quantifying its degree of homogeneity and diffusivity. With favourable information about receiver diffusivity, a way of proceeding to measure directly high solar irradiance on the surface of the receivers of solar tower plants without including moving parts is presented. This measurement system would consist of a digital camera and a radiometer. (C) 2019 Elsevier Ltd. All rights reserved.