Microbial solar cells (MSCs) are recently developed technologies that utilize solar energy to produce electricity or chemicals. MSCs use photoautotrophic microorganisms or higher plants to harvest solar energy, and use electrochemically active microorganisms in the bioelectrochemical system to generate electrical current. Here, we review the principles and performance of various MSCs in an effort to identify the most promising systems, as well as the bottlenecks and potential solutions, for "real-life" MSC applications. We present an outlook on future applications based on the intrinsic advantages of MSCs, specifically highlighting how these living energy systems can facilitate the development of an electricity-producing green roof.