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Life on Earth learned through billions of years of evolution to make do with renewable energy. Evolution discovered early on that the sun light is an excellent renewable energy source. To harvest sun light, many different types of biological solar batteries are used. One of the simplest ones is found in so-called purple bacteria. Their cells contain about hundred bulbous invaginations of the cell membrane, pointing into the cell. The spherical bulbs contain six different kinds of proteins adding up to a total of about 250 proteins. The primary function of the bulbs is to absorb sun light and electrically charge their spherical membrane, the charge being then used to synthesize fuel for the bacterium's energy needs. The structures of the individual proteins were determined earlier through X-ray crystallography. In a recent paper, a team of experimental and computational biologists report the atomic level architecture of the entire bulb. The team used atomic force microscopy on flattened bulbs to measure the height profile of the proteins, reconstructing from the data the bulbous protein assembly. The result is a detailed picture of the bulb, showing over 4000 chlorophyll molecules being held in the bulb, absorbing sun light, and transferring its energy to reaction centers that convert the sun light into an electrical membrane voltage. Indeed, the team could calculate, using quantum and thermal physics, from the architecture the amazing efficiency of the bacterial solar battery. More on chromatophores of purple bacteria can be found here.