There is much interest in using renewable energy sources, such as wind, wave and solar, to generate electrical energy. Unfortunately, such energy sources are intermittent, and, therefore, conventional sources must still be available to meet the demand during quiescent periods. Hence, the reliability and economic assessment of these novel sources cannot be made using standard capacity-replacement-based methods; instead, energyreplacement methods are required. The paper extends the loss-of-energy-expectation method to evaluate the generation reliability including novel energy sources. These results are then used to calculate the economic benefits of such sources. The approach is illustrated using the IEEE reliability test system. Although the paper concentrates on wind energy sources, the technique and approach are applicable to a generation system containing any type of intermittent energy source.