Tom Wayburn's idea is interesting, though I am not
the person who can help him with these questions.
Tom, do remember some other energy sources for the
Earth-atmosphere-biosphere system:
Heat generated within the Earth by rqadioactive decay
and friction under moving crustal plates produces
volcanoes, earthquakes, and hydrothermal vents that
probably support most of the world's biomass without
(much) benefit from photosynthesis. There is (I think)
still a little heat left over from the gravitational
compression of the Earth.
Then there is the energy (re-)introduced to the system
by electricity generation, fossil fuel burning, etc....
Jon Greenberg
Science Editor/Curriculum Developer
Agency For Instructional Technology
jon@ait.net