It may sound strange or even retrograde, but isn’t that what the first Homo sapiens did when they used fire? The carbon-carbon and carbon-hydrogen bonds of wood-forming polymers stored enormous amounts of energy, which, when combusted by the action of a comburent (oxygen) and ignition, led to the release of water, CO2, and heat/light energy. This clearly implies a recirculation of the CO2 that had been fixed in the plant biomass through photosynthesis, biomass that served as an energy store. However, it is precisely this indiscriminate use of organic material combustion forces us to stop artificially releasing this CO2 that had naturally been fixed. But the interesting thing about this point is that everything we pollute is susceptible to being reversed if we re-fix it in the biomass that once burned and use it as a storage of chemical energy transmutable to other types of energy – in a similar way to a battery.

Pioneer approach: biomass CAES

In 2005, ideas about using biomass as energy storage were boiling in many universities, as its potential is not trivial. One example is the idea of Paul Denholm, who wanted to bring together several processes involving biomass gasification. In this system he devised, he intended to generate electricity by combining wind power, compressed air storage, and gasification. It so happens that this technology required polluting gases, extracted from natural gas deposits or similar. Replacing this with synfuel from biomass gasification would solve this CO2 emission problem.

Is the biological battery close by?

As we have been saying, ideas on this subject have been developing for the last two decades. Many projects have failed, but many others have prospered, incorporating important changes in the biomass paradigm. Current efforts are focused on identifying new forms of biomass, more efficient and robust as a form of storage; exploring new ways of converting this biomass into carbon stacks that achieve greater thermochemical performance; and researching carbon nanostructures. Agricultural fields have already benefited from recycling their waste into energy. Although this is promising, the mechanisms for transforming biomass into batteries or carbon anodes remain to be fully understood. Battery scientists will have to join forces with biomass transformation engineers to achieve this. Real large-scale practical applications are still on the horizon.

Understanding the concept of biomass

We can argue that biomass does not have a defined chemical structure. While this is true – as both the origin and processing of biomass is different – it does not mean that we cannot define this concept. In fact, it can be understood from two different fields. From physiology and ecology, important scientific areas, biomass corresponds to the total weight of organic structures synthesized by living beings in a given geo-temporal context. In other words, the mass of all living things in an ecosystem at a given time. From an energetic point of view, biomass is nothing more than the useful fraction of these compounds manufactured by living beings. Some of these compounds are small and not very heavy, so their energy yield is low. They usually correspond to living matter and its metabolites. Others are polymeric, long, highly branched chains of carbon and hydrogen, which usually serve as a support or annex to living matter, although they are essentially inert organic compounds. It is from this type of material that most useful energy is extracted, so we usually use as biomass the products derived from plants, which grow very heavy and large structures such as suber, very rich in polymers such as celluloses, hemicelluloses, phenolic compounds such as lignin; starches, proteins or lipids.

Current State & Start-ups

Many initiatives are starting to emerge, and in almost all of them we can see words like “renewables” or “microgrids”. Mavericks Renewable Energy uses recycled biomass through biodigesters. Then there are many others that sell themselves as “biomass power generation”, such as Cool Energy or Rapid Renewables.

The Future

There is still no great winning horse due to the complexity of the problem to be solved. However, we can all understand that our situation has changed since hominids domesticated fire. The range of possibilities is beginning to widen, and as of today, there is no firm verdict on how far we can go in harnessing this natural store of atmospheric CO2. Initiatives such as Elon Musk’s contest to fix 1 ton of CO2 per day could be the final push for a global effort to achieve the long-awaited prize: taming the planet’s climate drift.