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Miguel R.L. (aka Lambda), ETH Zürich engineer
Time is fast running out to keep global surface temperatures below the 1.5°C limit we have set for ourselves. We are actually now headed for a catastrophic 2.7°C surface temperature rise by century’s end. There has been much written about decarbonizing ground transport such as cars, trucks, and increasing the proportion of renewables in electric grid. We also have the ability to increase building efficiency and significantly clean up many industries. The pace of change is both infuriating as well as shameful in this climate emergency, given the number of amazing technologies that are available.
In this article, we’ll primarily be looking at one sector in particular: the shipping industry. It emitted 2.5% global emissions. 880 million metric tons (Mt) of CO2 in 2019, the same as in which, for comparison purposes Germany produced 681 Mt of CO2. Although it is currently a small percentage of total GHG emissions at present, it is difficult to eliminate due to the long lives of large ships.25–35 years) and the need for a high specific energy storage medium.
We could end up choosing the most economically sound, environmentally-sound and technically feasible option. This could lead to us being locked into long-term, wasteful practices we cannot afford. It’s for this reason that we’ll compare the environmental, economic and engineering feasibility aspects of two of the most commonly considered contenders in this race: biofuels and green ammonia. We will make a distinction between the short and long-term time frames that are crucial to avoid rapidly degrading ecosystems, and destructive climatic change.
Hopefully, this will make it clear to the reader why I believe that ammonia will be the winner in the shipping sector. The following fuels will not be discussed in detail: (a.) hydrogen, (b.) liquefied petroleum gas (i.e. methane CH4, of fossil or renewable, and (c). Methanol. Hydrogen has storage and transportation issues that are unlikely ever to be resolved, but it could eventually replace ammonia. The fugitive methane emissions from LNG are difficult to eliminate and the LNG emits CO2 during its use. Methanol is carbon-neutral like all hydrocarbon synthfuels. It requires either CO2 direct, air capture (DAC), expensive CO2 or biogas. Conventional Liion batteries lack the required energy density to handle all shipping routes except the shortest. It is also unclear how long it will take for the commercialization of re-smeltable metallic-air batteries to become economically viable.
This article series will examine the implications of scaling biofuels and fully-renewable ammonia to large shares of shipping fuels. The sources will be available for readers to peruse at leisure. As this is an effort to identify the best solutions and make a small contribution in trying to get them implemented, constructive criticism will be welcomed. There will be numbers. Without them, this analysis would not be an opinion piece but an analysis. This first part will concentrate on scaling issues for biofuels in the foreseeable future. Part 2 will focus on the lifecycle emissions of biofuels, and solar ammonia. Part 3 will discuss the feasibility of cheaply synthesizing ammonia and distributing it using solar energy and electrolysis. Part 4 will conclude with a cost comparison between all relevant fuels.
Where do biofuels come form?
Biofuels, as they are currently produced, can be divided into two main types, bioethanol or biodiesel. First-generation (1G), biofuel feedstocks are derived from feed crops and edible oil. Second-generation (2G), biofuel feedstocks come from non-edible oil and waste oils and grease (biodiesel), as well as lignocellulosic resources (ethanol). As of 2020, third generation (3G) feedstocks will not be possible. their GHG emissions surpass those of fossil fuels.
Let’s look at the current origin of biofuel feedstocks. The EOCD-FAO Agricultural Outlook 2020–2029 report states:
“At present, about 64% of ethanol is produced from maize, 26% from sugarcane, 3% from molasses, 3% from wheat, and the remainder from other grains, cassava or sugar beets. Biodiesel accounts for 77%. It is made up of vegetable oils (37% rapeseed, 27% soybean, and 9% palm oils) or used cooking oil (23%). Advanced technologies based upon cellulosic biostocks (e.g. crop residues, dedicated energy crops, or woods) do not account for large shares of total biofuel production.”
The report also explains that advanced non-1G feedstocks won’t see a significant increase in their share over the next few years.
“Global biofuel production will continue to be dominated by traditional feedstocks, despite the fact that increasing sensitivity to the sustainability dimension of biofuel production is observed in many countries (Figure 9.3).”
At this point, we should note that the report’s definition of traditional feedstocks includes waste vegetable oils, which are usually classified as 2G feedstocks. It seems like a good idea, until you realize that waste oils only represent 23% of biodiesel fuelstock (see above). Despite this, there is a high demand for soybean oils in the biofuel industry. already pushing up soybean prices in the food industry.
The more important takeaway from the report, however, is the share of traditional feedstocks (91.4%), as well as the absolute energy generation from biological sources: 4340 PJ or 1’205’552 GWh. This number will be useful for later.
Area: A key measure
Let’s also investigate the space requirements of biofuel cultivation as it stands today. I encourage you to use more reliable sources to help me with this issue. The ones below should provide a reasonable estimate. I’ve compared with other lower-quality sources, and my numbers are within the ballpark; some are higher, some are lower. We’ll examine Brazilian bioethanol and biodiesel production, which is some of the most productive on Earth on a land area basis. Conversion of sugars from ethanol is easier and less expensive than biodiesel. The numbers are as follows(also refer to hereAnd here):
Now let’s compare the above power density figures with a couple of fairly recent utility-scale PV projects. Also included is a hypothetical PV project in Chile’s Atacama Desert, extrapolated from California’s numbers, using the same system-level solar-to-electricity efficiency:
Solar Star’s power density numbers may raise eyebrows if compared to the newer project in Egypt, but given the use of SunPower panels, which are some of the most efficient on the market, the above numbers should not be too surprising. Solar Star could have a higher ground coverage ratio (GCR), or the ratio of module area to land area.
It is possible to achieve higher power density numbers. For example, the Echuca solar farm in AustraliaThis December 2019 project, which was completed, does not include a tracking system. Instead it plasters ground in a manner that is reminiscent of an extended accordion. I believe that solar modules are so cheap that even though each solar module produces less power than in a single axis tracker configuration the savings in installation labor, time, tracker costs and land costs start to accrue. If this configuration, deployed by Australia’s 5B, is expected to be good enough for the 10 GW, $20 billion Australia–Singapore Power Link project, it ought to be sufficient for any potential solar farm in Atacama as well.
For the upcoming map, I nonetheless assumed the more conservative numbers and extrapolated Solar Star’s numbers to Atacama (Echuca would halve the required area). Solar Star makes 20.1% efficiency modules. LONGi was created in 2021. world’s largest PV companyBy sales revenue and market value, the company has achieved a c-Si cell-level efficiency of 26.3%October 2021. It is likely that we will soon have 23% efficient cSi modules. This is especially true when we consider that companies like SunPower or Kaneka have already achieved 24% efficiency in small prototype modules. A switch like this would reduce the area needed by 14%.
The summary of the above tables is that solar in the best locations is easily 30× as power dense as the most efficient of biofuel crops. Using Echuca numbers and newer solar modules would raise this figure to about 60× the power density. Accounting for realistic solar-to-ammonia synthesis inefficiencies (which will be analyzed in Part 3), we still achieve a power density that is 20–40× as great. This figure does NOT include the 15–20% yield increases estimated possibleFrom tight PV-electrolyzer Integration, the type that can avoid multiple lossy power transformations. Although it would not reduce the amount of synthesis energy required, such integration would certainly lower the cost and the area required.
Let me rephrase for maximum clarity: on an equal chemical energy basis, the best solar ammonia synthesis installations today occupy about 2.5–5% the area that sugarcane ethanol does. If we substitute bioethanol for biodiesel, the gap will widen even further.
These numbers are bad enough for biofuels on their own. But they get even worse when you consider what type land area is being converted to energy production. This could be biodiverse cerado that could aid in fighting climate change or sun-scorched deserts of great beauty, but low in biodiversity. Unfortunately, human-induced desertification will only increase the likelihood of the former, while stressing the survivability and viability of the latter.
Scale matters
Let’s now look at scaling up biofuels to worldwide shipping and aviation consumption. Shipping was consumed in 2019, the year prior to the pandemic. 221 million metric tons of oil equivalent (Mtoe), or approximately 2.57 million GWh. The global 2019 biofuel production is only 47% of the world’s shipping energy demand.
That is, all the world’s biofuel production provides less than half of the global shipping fleet’s energy consumption. Scaling up to worldwide demand would require about 536’000 km2Productive, frost-free, drought-free farmland that is comparable to Romania and Oman (or slightly smaller than Botswana).
With aviation’s energy density requirements being even stricter than those of shipping, we will again require energy dense fuels, at least for the foreseeable future. In 2019, the aviation energy consumption of both OECD and non-OECD countries was 3.74 million GWh. Liquid biofuels energy production is only 19.1% of the current combined aviation and shipping demand. However, the aviation energy market is expected to grow. from about 13 quadrillion BTUs (quads) in 2019 to about 29 quads by 2050.
While battery electrification is certain to reduce some of the fuel demand, the exact amount remains uncertain. The battery electric aircrafts like the Heart Aerospace’s400 km (250 mi), E19, or Wright Electric’sThese developments are welcome and will be crucial to electrify short-haul flight in the future. They cover 1290 km (800 mi), Wright 1. With commercialization planned for 2030 and 2026, respectively, short-haul commercial passenger flight under 1500 km will only be accounting for. about a third of aviation’s emissions, batteries will have a minor impact in denting aviation’s emissions for at least the next decade. Similar reasons explain why the shipping battery electrification share is estimated to be about 5%. 5% by 2040 by some sources. IRENA projects an approximation of halving of shipping’s energy intensity by 2050 [figure 30]The overall energy demand is still about flat. Let’s look at these areas graphically, by representing the areas with countries and superimposing the outlines over Brazil:
For comparison purposes, let’s also graphically juxtapose the predicted energy use in 2050 for both industries put together:
An image is worth a thousand words, isn’t it? These figures assume sugarcane ethanol production. Only. It is even more difficult to produce the biodiesel needed for aviation. We also ignored any embodied energy in the fertilizer used to grow the crops, as well any energy required for farming machinery or fuel processing, such as the approximately. 0.1 kg of methanol required per liter of biodiesel. Some might point out that the figure does not compare PV electricity with chemical power. That’s actually not true. The following areas are represented by Togo, Iceland, and North Macedonia. AfterScaling the actual PV area with the electricity conversion loss to ammonia. In other words, chemical energy is compared to chemical energy.
There you have it. In this first part, we’ve established that biofuels, if scaled to actual consumption figures, would create huge monoculture wastelands that we could be returning to nature. The second part will briefly address alternative forms of biofuel production and dispel any doubts regarding biofuel emissions superiority. Part 3 will examine the feasibility of cheaply synthesizing solar ammonia and transporting it. It will show that neither electrolyzer capital cost nor capacity factors are a problem. Part 4 will compare solar ammonia costs to both biofuels as well as bunker fuel, and summarizes the discussion.
Featured image by Valentin SchönposFrom Pixabay
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