Without very much publicity or fanfare at all, it seems
that a new range of fuels are sprouting beneath our feet. The Committee on Climate Change (CCC)
predicts that bioenergy consumption could more than double to 15% of the UK’s
energy supply in 2050 (CCC, 2018), and BP is raising the bar for large energy companies
by planning to increase its bioenergy production nearly five-fold this decade
alone (Doyle, 2020). Clearly bioenergy is set to be a major feature of the
energy system of the future, but nevertheless, it doesn’t seem to awaken the
same enthusiasm amongst green-minded members of the public as solar and wind
do. In the US, bioenergy is often left off of opinion polls about renewables (Fernando,
2013) and in general we don’t see it on fancy PR infographics such as this one publicising renewables as much as we see solar and wind, indicating a difference in attitude. Are
we deliberately having our attention shifted away from this soon-to-be giant of
a sector? Does bioenergy hold as much potential as these other sources of clean
energy, or is there a less photogenic side to it?
Let us begin with the problems. Every proposed solution to the future energy question has a host of issues and it turns out that, unfortunately, bioenergy is far from an exception. Let us examine them in detail.
Can't See the Wood for the People
Unlike energy sources such as offshore wind power, that don't necessarily consume valuable space, energy from trees and crops at scale almost necessarily becomes a problem the more people you have to feed, and the more land becomes uninhabitable due to rising sea levels, soil erosion and other challenges our food-producing land is set to face in the years to come.
Producing bioenergy (we shall exclude the promising research into biofuels from algae that could be grown in lower-footprint operations) consumes land, and lots of it. While the most optimistic energy yield per year for a square metre of land with bioenergy is about 1 W/m^2, with solar we can get up to almost 14 W/m^2. What's more, this is mitigated by the fact that solar panels can be used within developed land, for example on rooftops and car parks (check out Solar Roadways), whereas bionergy requires dedicated farmland (Wysession, 2016).
As the population grows and sea levels rise to cover more and more of our land, the optimal use of that land is going to matter like never before.
Just as an extreme example, if we tried to supply all of the US energy demand (about 3 TW) with biofuels, it would consume so much land that they'd have to import all of their food. World food prices would soar. In fact, growth of bioenergy production in the US has already rendered corn so expensive now that Mexicans, who count the food as a staple of their cuisine, can no longer afford it. Solar on the other hand, could power the whole US within 256 km^2, just under 3% of the total 9147590 km^2 owned by the US! (Wysession, 2016).
In a world where people could increasingly resort to fighting over land, water and other natural resources, this tremendous gap simply cannot be ignored.
It is all the more worrying, then, that agriculture (and by consequence, bioenergy) will become increasingly resource-intensive as the decades continue.
Seeds of Doubt
In natural ecosystems, resources such as minerals and carbon are kept in balance by restorative cycles. For example, nitrogen, a key element for plant health and productivity, is removed from the soil when plants assimilate it and are eaten by animals, and is returned to the soil when animals die or release their waste onto the soil (in addition to the key role of nitrogen-fixing microorganisms). However, to meet the huge demands on agriculture we create today, these systems simply can't keep up, and we are forced to add fertilisers to the land. These fertilisers take energy to produce, part of the explanation for our low figure of 1W of bioenergy per m^2.
Unfortunately, though, the costs of using more fertilisers - were we to rely on bioenergy on a much larger scale - do not stop there. Fertiliser use can pollute natural waterways via a process called eutrophication, leading to large dead-zones where only algae survive. Yet another harsh reality stares us in the face in that fertilisers on farmland can release N2O (a greenhouse gas with 298 times the warming power of CO2) into the air, damaging the potential of this energy source to provide a solution to global warming! (IPCC, 2018).
In addition to fertilisers, the production of plants for bioenergy consumes water. With the change in rain patterns from climate change and the rise in demand for water from population growth, South Africa, the US, China, a large proportion of the Asia-Pacific region (3w Market Reports, 2020), and the Middle East and North Africa (World Bank Group, 2017) will all become increasingly dependant on water desalination. This process consumes large amounts of electric power to process salt water into fresh water.
We are thus met with another problem. If we seek to produce energy to meet our needs with biofuels, it is not exactly helpful that we need to add so much energy.
Not Carbon Neutral
There are growing fears around bioenergy's carbon neutrality. Obviously if this technology causes a net increase in atmospheric CO2 levels, it is not a green technology. The ideal application of biofuels is where they are produced by plants which draw their carbon directly from the same atmosphere into which the biofuel combustion-products are released, closing the loop.
The worry arises when we consider the fact that bioenergy isn't produced at the point of consumption and needs extensive work to harvest, dry, and transport it to the next stage in the value chain. For example, Drax, the largest producer of electricity from wood pellets in the UK, receive these wood pellets from forests in the US. The fuel is transported by ship, consuming a huge amount of energy in the process. Until all of these technologies are decarbonised completely, and this is easier said than done, bioenergy might not reach carbon neutrality.
So now we might see why there is not so much excitement around bioenergy as there is for solar, wind, hydro and the like. But still, the fact is that bioenergy is growing and we are forecasted to become only more reliant on it with the passage of time. Is this a mistake? Will we suffer the consequences?
I don't think so. Bioenergy doesn't look like a good candidate as a basal energy source to power our civilisation, but there are specific applications where it is set to be essential.
Rethinking Our Chemicals
The areas in which bioenergy really impresses are exactly those areas where mainstream renewables can't help us. The developed world has been reliant on fossil fuels for so long, we've constructed a vast variety of applications for these resources that electricity alone cannot always necessarily replace. Even if they are inefficient to produce, as long as we have enough renewable energy, a world without fossil fuels would be a world where it is nevertheless worthwhile to produce bioenergy.
- Transport Fuels: The needs of the shipping and aviation sectors are hard to meet with electricity in a number of ways but it all comes back to energy density. Carrying enough mass of electric batteries in planes and ships consumes weight and space allowances that render them crippling to these forms of transport. In addition, the thrust generated in a planes' jet engine is not comparable to that of an electric propeller. Commercial flights rely on this power. Bioenergy is a potential candidate to replace jet fuel in future aviation industries. (National Grid, 2019).
- Chemical Feedstocks: The chemical industry has grown to rely on petrochemicals as a feedstock. It provides molecules which serve as a carbon chain for processing into other organic chemicals, such as pharmaceuticals and, critically, plastics. Chemical plants such as SABIC are already using biofuels to replace this unsustainable resource.
- Negative Emissions: Some industries are simply not ready to decarbonise yet, such as the cement industry. One way to deal with this is to offset these emissions with afforestation - planting trees to absorb the emissions. However, operations like these cost money. Afforestation could create entire new value chains, though, if the resulting biomass is used as an energy source, but obviously this releases the emissions again.
The real potential of this idea is when bioenergy is combined with Carbon Capture and Storage. Bioenergy Carbon Capture and Storage (BECCS) can lead to the negative emissions we are searching for whilst also acting as an energy source. It is easier to apply CCUS to energy plants than to more diffuse emissions-sources such as soil degradation and melting permafrost.
Conclusion
Bioenergy is not as clean and attractive as the other members of the renewables family, but we will be needing it for a wide range of applications. These applications are mostly failures in the versatility of other renewables, and where specific chemicals are needed.
Some countries may even have enough rain that they can grow biofuels very efficiently. They will have an advantage in this area which could be useful in trade.
I ask that you forgive me for this image, (we are engineers, not waiters!) but my favourite potential method of using bioenergy is in anaerobic digestion of faecal sludge. Humans strip huge quantities of nutrients from the soil in producing and harvesting our food, and we flush them out to sea every agricultural year. Soil depletion is a frighteningly imminent threat. If we don't want to use artificial fertilisers and risk polluting the natural environment, we should be excited about a technology that recycles the nutrients in a way that mimics natural returning of nutrients to the soil by animals.
We can use bacteria to convert our sewage sludge into biogas, a valuable, zero carbon, transportable and energy-dense fuel. The residues they leave behind can be processed into dry fertilisers to allow us to grow the food we need.
I think the reason bioenergy is not as celebrated as the other renewables is because its applications are more specific and less aesthetic. But make no mistake, bioenergy is going to change our world, fancy infographics or not!
References
Committee on Climate Change, 2018. Biomass in a
low-carbon economy. [Online]. Available from: https://www.theccc.org.uk/publication/biomass-in-a-low-carbon-economy/
Doyle. A, 2020. BP reveals strategy to reach net zero. [Online].
The Chemical Engineer. Available from: https://www.thechemicalengineer.com/news/bp-reveals-strategy-to-reach-net-zero/
Fernando. R, 2013. Public attitudes to biomass cofiring. [Online].
IEA Clean Coal Centre. Available from: https://usea.org/sites/default/files/012013_Public%20attitudes%20to%20biomass%20cofiring_ccc214.pdf
IPCC, 2018. SPECIAL REPORT: GLOBAL WARMING OF 1.5 ºC. [Online] Chapter 2. Available from: https://www.ipcc.ch/sr15/
National Grid, 2019. 2019 Future Energy Scenarios. [Online]. Available from: https://www.nationalgrid.com/uk/gas-transmission/insight-and-innovation/future-energy-scenarios-fes
World Bank Group, 2017. Beyond Scarcity: Water Security in the Middle East and North Africa. [Online]. Available from: https://www.worldbank.org/en/topic/water/publication/beyond-scarcity-water-security-in-the-middle-east-and-north-africa
3w Market News Reports, 2020. DESALINATION SYSTEM MARKET 2020-2024. [Online]. Available from: https://3wnews.org/uncategorised/2869144/desalination-system-market-2020-2024-latest-industry-updates-projections-consumption-analysis-investment-cost-profits-data-forecast-to-2024/
Wysession. M. E, 2016. The Science of Energy. [Online] The Great Courses and Audible. Available from: https://www.audible.co.uk/pd/The-Science-of-Energy-Audiobook/
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