The Azimuth Project
Carbon negative energy (Rev #6)

Carbon negative energy refers to any form of usable energy whose production reduces the amount of carbon dioxide in the Earth’s atmosphere.

Biofuel versus biochar

Photosynthesis can take carbon out of the atmosphere and provide useful fuel. If all the carbon taken out is returned to the atmosphere when this fuel is burnt, this process is roughly carbon-neutral. This is an oversimplification of the actual story. On the one hand, it takes energy to grow and process vegetation into usable fuel; if this energy comes from fossil fuels there may be a net gain of CO2 in the atmosphere. On the other hand, not all the carbon is returned to the atmosphere: some stays in the ground, at least for a while, in the form of roots, humus, etcetera.

We need detailed figures here! What is the overall carbon footprint of biofuels? People have done research on this already, and the results should probably go in a page on biofuel. — John Baez

Ignoring these subtleties, we may very roughly say that fossil fuels are carbon-positive while biofuels are, at best, approximately carbon-neutral. On the other hand, biochar offers the possibility of strongly carbon-negative energy production: significant long-term reduction in atmospheric CO2 combined with the production of significant amounts of energy. The idea here is to create some usable fuel from plant material, while also creating large amounts of charcoal which can be buried to sequester carbon. Unlike rotting vegetable matter, buried charcoal can sequester carbon for centuries or even millennia.

For more, see biochar.

If you can think of other sources of carbon negative energy, enter information about them here! — John Baez

The reaction

2CO2 + MgSiO4 = 2MgCO3 + SiO2

or in words

carbon dioxide + olivine = dolomite + silica

is exothermic but slow. It doesn’t seem practical today, but it may be one day. There is more information in the Wikipedia entry on olivine.

Isn’t this what is being suggested in some of the clean coal schemes? They all pretend to be ‘permanent’ but some actually are. I’d thought that it needs moisture for appropriate rock to absorb the CO2.

Energy storage and load balancing both have carbon negative effects.