Physically Optimal Solar Resource Efficiency in Giant Clams

Living photosynthetic systems can be near-perfectly efficient at solar energy conversion at small length- and time-scales. However, they are very inefficient (~3%) at the scale of crops or ecosystems. Is it physically possible to realize the near-perfect efficiencies of photosynthesis at a small scale over large land areas? Answering this question is crucial for reducing economic reliance on fossil fuels. We created a simple model of a "solar transformer" that was inspired by the geometry of symbiotic giant clams that host single-celled algae in their tissues. We found a straightforward, general mechanism to achieve a photosynthetic light-use efficiency of 67% of the solar radiance in an average tropical day. Remarkably, living clams may exceed this efficiency, and we describe the mechanical mechanisms that may allow this.