Our Photovoltaic Future: the Next Five Billion Years

Cassandra's Legacy:

"Life is nothing but an electron looking for a place to rest," is a sentence attributed to Albert Szent-Györgyi. It is true: the basis of organic life as we know it is the result of the energy flow generated by photosynthesis. Sunlight promotes an electron to a high energy state in the molecule of chlorophyll. Then, the excited electron comes to rest when a CO2 molecule reacts with hydrogen stripped away from an H2O molecule in order to form the organic molecules that are the basis of biological organisms. That includes replacing degraded chlorophyll molecules and the chloroplasts that contain them with new ones. The cycle is called "metabolism" and it has been going on for billions of years on the earth's surface. It will keep going as long as there is sunlight to power it and there are nutrients that can be extracted from the environment. 

But, if life means using light to excite an electron to a higher energy state, there follows that chlorophyll is not the only entity that can do that. In the figure at the beginning of this post, you see the solid state equivalent of a chlorophyll molecule: a silicon-based photovoltaic cell. It promotes an electron to a higher energy state; then this electron finds rest after having dissipated its potential by means of chemical reactions or physical processes. That includes using the potentials generated to manufacturing new photovoltaic cells and the related structures to replace the degraded ones. In analogy with the biological metabolism, we could call this process "solid state metabolism". Then, the similarities between the carbon-based metabolic chain and the silicon-based one are many. So much that we could coin the term "stereosphere" (from the Greek term meaning "solid.") as the solid-state equivalent of the well known "biosphere". Both the biosphere and the stereosphere use solar light as the energy potential necessary to keep the metabolic cycle going and they build-up metabolic structures using nutrients taken from the earth's surface environment.

Cont....