Utilizing renewable energy (RE) is an important part of the design and development of green buildings. However, it is unreasonable to assess renewable energy utilization (REU) only with the net ratio of end-use energy provided by the renewable energy system to a building's total energy consumption, but ignoring the system efficiency of REU with the necessary extra conventional energy consumption, such as electricity. In this paper, the energy quality coefficient (EQC) is introduced to describe the quality of energy, while the energy conversion coefficient (ECC) is applied to evaluate energy system efficiency. The indexes and their expressions were developed based on exergy analysis. Based on these two indexes, an effective substitution ratio (ESR) was developed for the evaluation of REU. Furthermore, the ESR of utilizing RE to substitute for single type and multiple types of conventional energy is discussed. Finally, case studies were conducted and some conclusions were drawn from the results for application of RE in buildings. (c) 2007 Elsevier Ltd. All rights reserved.