A non-deterministic uncertainty and global sensitivity analysis, based on the Sobol's method, is developed for a parabolic-trough direct steam generation plant for process heat applications. The objective of this work is to evaluate the robustness of the simulation-based design stage, identifying major modelling sources of uncertainty, as well as quantifying and ranking the relevance of its contribution to the system performance output uncertainty. An important finding obtained from the case considered in this work is that, although the complex characteristics of the direct steam generation two-phase regime introduces additional sources of uncertainty into the low-level modelling stage, the propagation and impact of this uncertainty to system level energy and economic-based design indicators is largely mitigated by higher-level input factors uncertainty. The economic design indicator uncertainty and global sensitivity analysis shows that the lowest relative output uncertainty is obtained by the levelized cost of energy with a coefficient of variation of 4.3%; followed by payback time with 12.1%. The largest contributors of input factors uncertainty to the levelized cost of energy uncertainty are the market discount rate and boiler efficiency, showing total sensitivity indices of 0.67 and 0.23, respectively. (C) 2014 Elsevier Ltd. All rights reserved.