Due to the emerging need for the development of acceptance test codes for commercial concentrating solar power (CSP) plants, an effort is made here to develop a mirror reflectance model suitable for CSP applications as well as a general procedure to measure the average mirror reflectance of a solar field. Typically, a utility-scale solar field includes hundreds of thousands of mirror panels (if not more), and their reflectance is subject to many factors, such as weather and planned washing schedule. The newly developed mirror reflectance model can be used to characterize different types of mirror materials and can be directly used to perform optical performance evaluation of solar collectors. The newly proposed procedure for average solar field reflectance measurements includes a baseline comprehensive measurement and an individual factor measurement: the former allows a comprehensive survey of mirror reflectance across the whole solar field, and the latter can provide correcting factors for selected individual factors to further improve the accuracy of the baseline measurements. A detailed test case implementing the general procedure is applied to a state-of-the-art commercial parabolic trough plant and validates the proposed mirror reflectance model and average reflectance measurement procedure. In the test case, the plant-wide reflectance measurements at a commercial utility-scale solar plant were conducted and can shed light on relevant analysis of CSP applications. The work can also be naturally applied to other types of solar plants, such as power towers and linear Fresnel plants. (C) 2013 Elsevier Ltd. All rights reserved.