To investigate the optical performance of the vertical single-axis (v-axis, in short) tracked solar panels as compared with fixed and full 2-axis tracked solar panels, a mathematical procedure to estimate the annual collectible radiation on fixed and tracked panels is suggested based on the monthly horizontal radiation. Calculation results showed that the yearly optimal tilt-angle of a v-axis tracked solar panel for maximizing the annual energy collection was almost linearly proportional to the site latitude, and the corresponding maximum annual collectible radiation on such tracked panel was about 96% of solar radiation annually collected by a dual-axis tracked panel. Compared with a traditional fixed south-facing solar panel inclined at the optimal tilt-angle, the annual collectible radiation due to the use of the v-axis sun-tracking was increased by 28% in the areas with abundant solar resources and increased by 16% in the areas with poor solar resources. An empirical correlation for a quick estimation of yearly optimal tilt-angles of v-axis tracked solar panels was also proposed based on climatic data of 31 sites in China. (c) 2010 Elsevier Ltd. All rights reserved.