Today energy is directly related with progress or growth of any country and every event requires a huge amount of energy. In today’s global competitiveness, demand for energy is very high and India is facing a problem of very poor energy supply. So, researchers and planners are worried about very poor productivity of thermal power plant and the most critical cause for this problem is high capacity waste at these plants. This paper focuses on causes of capacity waste and for this, DMAIC approach is adopted. The study also clears some myths of Six Sigma compatibility at process industries (thermal power plant) for performance improvement. After implementation of the first phase i.e. “Define”, the study confirms the competence of Six Sigma in defining the issue of capacity waste.