Development of a wind farm project includes a lot of interconnected steps and one of the most important ones is the proper energy yield assessment. Wind energy yield assessment is typically based on wind measurements on a measurement mast that are later used in one of the wind flow software models. In cases where there are multiple wind measurements on the potential wind farm site, a question arises on how to optimally use all the available data. This paper shows a method of using such data through the application of the portfolio theory, a well-established theory in economics and frequently used in other scientific disciplines. The method shown is very flexible in terms of input data and software models, and the results of its application show that it is possible to increase accuracy and reduce uncertainty of energy yield assessment. The key result of the method is the possibility to achieve better quality of input data for the energy yield assessment without spending additional resources. The method opens up a wide space for further research and improvements, all with the objective of achieving better results of energy yield assessment and finally, better prepared wind project. (C) 2014 Elsevier Ltd. All rights reserved.