The idea is as follows. Cyanobacteria takes water as input and then gives oxygen and protons and electrons as output. So the idea is to genetically manipulate the Cyanobacteria so that the protons and electrons somehow collide to form hydrogen. Then with enough carbon, water and sunlight the Cyanobacteria population can grow to large enough to power a power plant. The idea behind the power plant is to use the heat from a hydrogen explosion to power a big turbine that can produce industrial quantities of power.