Electricity goals around the world tend to focus on increasing social benefit through one of two avenues: (1) increasing overall system sustainability or (2) increasing access to electricity. These goals guide the transition of the power system. In pursuit of these goals decision makers will need modeling tools that can inform decisions, in a way that is flexible enough to include a wide range of preferences and goals. It is clear that the future generation mix of the power system will change, but the most sustainable solution, will change based on a country's goals. This dissertation will explore the various options for power grid expansion in disparate electricity systems. We present three essays that focus on evaluating the sustainability of different electricity futures to allow decision makers to understand impacts and trade-offs between various combinations of power generating technologies. The first two essays are focused on evaluating the sustainability of generation mixes for New England. In the first essay we take a multi-model approach, first determining the reliability of the system overall, then evaluating different generation portfolios based on seven sustainability criteria. In the second essay we expand this work by implementing pumped hydro storage into the model. The sustainability of the system with and without storage capabilities is presented and evaluated. The third essay focuses on the UN Sustainable Development Goals, and electricity access in developing countries. Here we present a model that can be used by decision makers in developing countries to determine the best method of grid expansion to meet electricity access goals