The Azimuth Project
Carbon negative energy (Rev #21)

Contents

Idea

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

If you can think of other sources of carbon negative energy, enter information about them here! There are many other technologies with carbon negative effects, such as carbon capture and storage, energy storage, and load balancing?. However, these are best discussed elsewhere. What’s a good name for a page on ‘reducing carbon dioxide in the atmosphere’? If you know, create this page! Then we can link that to pages on particular strategies.

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.

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.

Enhanced weathering

One of the main long-term mechanisms that removes carbon dioxide from the ocean and atmosphere is the natural weathering of rocks. We can vastly accelerate this process by digging up suitable rocks, crushing them into powder and spreading them around. The rock dust then ‘weathers’ by reacting with carbon dioxide. This method of carbon capture and storage is called enhanced weathering.

Since this reaction is exothermic — that is, heat-producing — it can even serve as a source of carbon negative energy. However, it is difficult to harvest this energy, since the reaction is slow.

For more details, see Enhanced weathering.

Coal bed methane extraction

Disused and uneconomic coal mines continue to emit methane. They can also be used to sequester carbon dioxide. Coal has a stronger affinity for CO2 than methane. So, putting CO2 in mine shafts displaces the methane, which can be captured and used as it rises to the surface. This idea is called coal bed methane extraction. It may constitute a source of carbon negative energy.

See:

category: carbon, energy