There is a relationship between product durability and the effect the product has on the environment and economy. One approach that impacts this dynamic involves a circular economy. The idea of a circular economy is gaining more traction as some businesses have begun to shift toward a product as a service model in which they, the businesses, maintain ownership of the product. One example of this business model is emerging in the energy sector. Given this shift, the life of the product becomes more important as it directly impacts the bottom line of the business. This gives rise to the marginal cost of durability (MCD) metric. The MCD determines the cost of the product in relation to the life of the system. For longer life, the design generally necessitates more cost-intensive measures to ensure durability. In the context of sustainable design, system life is particularly important for renewable energy systems that promote sustainable living. These large structures often require a high volume of materials and the end-of-life disposal for those materials. The design requirements for material also increase as the design life increases. The additional materials provide a safeguard against failure phenomena, such as fatigue. The MCD metric has been used in previous studies. However, there is no formal method for determining the MCD. This article examines a method for measuring the MCD for the commercial class of wind energy production systems. A metamodel of the damage response is built in lieu of expensive computational models. Design optimization is used to search for the design parameters having fatigue damage as a constraint. This process is repeated for a set of system life values, yielding a set of designs. Curve fitting is used to find a mathematical relationship between life and cost. An example of this method is applied to the study of a wind turbine tower life. The study indicates that the wind turbine tower design for 80 years has 34% more mass and cost than a 20-year design. The results from the proposed method provide information that can be used to determine the design life of a system.