Last decade marked a dramatic increase in renewable energy assets investment around the world and a substantial increase of global renewable energy consumption. To enhance investment decisions in renewable energy generation involves optimization studies that can show the expected renewable energy generation in consideration of numerous constraints, while reduced downtime, enhanced safety and reliability margins of the renewable energy generation plants will reduce the operating cost and increase profitability. To prevent the escalation of maintenance costs resulting from unidentified (and lately identified) ageing degradation mechanisms requires proactive techniques to forestall the effect of different stressors, on the renewable energy generation plant. This paper explores investment decision models for optimising renewable energy generation and different types of ageing mechanisms and their effects on renewable energy generation. Whereas the decision models provide insight on different optimization models for renewable energy generation, the area of application and the constraints considered in the study, the ageing management framework helps in managing ageing related stressors for established renewable energy plants. Since ageing stressors are induced by components interactions, environmental factors and human errors in design, manufacturing, installation and maintenance, Deming PLAN-DO-CHECK-ACT cycle was used for designing a systematic ageing management framework that stipulates early setoff of ageing management program through a systematic procedure that uses multidisciplinary team of plant assets management personnel to monitor material degradation, spare parts obsolesce and human errors. Proper implementation of this framework can result in safe, reliable and cost effective renewable energy generation since operating cost can be reduced with minimized downtime.