Engineering education is undergoing a restructuring driven by the needs of an increasingly multidisciplinary engineering profession. At the same time, power systems are transitioning toward future smart grids that will require power engineers with skills outside of the core power engineering domain. Since including new topics in the existing curriculum while maintaining the existing requirements is difficult, this paper proposes a project-based cooperative learning approach to promote soft skills in an engineering course. This paper then shows how to construct a realistic open-ended multidisciplinary problem whose solution requires a wide range of skills, which is not a trivial task. The design and technoeconomic viability assessment of a small-scale photovoltaic battery system is used as a case study. The effectiveness of the approach and students' satisfaction were assessed over two years. Survey results after the first year revealed that the students did not feel sufficiently prepared for multidisciplinary work. After appropriate adjustments in the second year, the survey results improved noticeably. Statistical analysis reveals that the project teaches skills that are complementary to the core domain skills, which confirms the validity of the approach.