This work proposes an indirect adaptive nonlinear control scheme based on a recurrent neural network and the output regulation theory. The neural model is first trained off-line, being further improved by means of an on-line learning strategy using the Lyapunov and nonlinear observation theories. The regulation problem is solved by an iterative strategy, formulated as an eigenvalue assignment problem, ensuring the convergence of the regulation equations. The strategy was tested on a distributed collector field of a solar power plant (Plataforma Solar de Almeria, Spain). Experimental results, collected on the solar power plant, show the effectiveness of the proposed approach. (c) 2010 Elsevier Ltd. All rights reserved.