Plants have very low sunlight conversion efficiency compared to solar farms. If you need chemical fuel instead of electricity, it would still be more efficient to use solar electricity to turn carbon dioxide and water into simple liquid fuels like methanol (usable in spark ignition engines) or dimethyl ether (usable in diesel engines).
Solar panels have a manufacturing cost, though, while you could imagine a renewable plantation of diesel trees that needs no raw ingredients other than a handful of seeds. It could even be self-seeding, though there are some good reasons we don't usually produce GE crops with viable seeds.
I'm sure the economics don't work out for it: solar panels are already cheap, the land could grow other crops, etc. But photosynthesis being lower-yield than photovoltaic generation isn't enough to rule it out. Perhaps as science fiction, on a future mission to an Earthlike planet that doesn't have the right resources to produce semiconductors at scale.
Biodiesel is an oil plus an alcohol (usually 80% vegetable oil + 20% methanol) reacted using an alkaline catalyst like lye.
Methanol is also known as "wood alcohol", and can be made at ~40% yield by cooking down wood ("destructive distillation") in a specific fashion, or made from too-cheap-to-meter natural gas if you've got it. Anything you can do with natural gas can also be done with anaerobically fermented methane. You can also use ethanol (fermented from any carbohydrate crops) instead of methanol, creating a biodiesel with slightly different but still usable properties.
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Sunflower, rapeseed, and soybean oil have very well-established agricultural workflows which require very little labor input.
Palm oil is substantially higher yield, but more labor intensive and is associated with tropical rainforest destruction.
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You don't necessarily even need to react your vegetable oil. The original Diesel Cycle demonstration engines ran on straight peanut oil, and there are some truck engines out there (like the 12 valve Cummins) that will happily run on filtered waste fryer oil all day long. It's just a matter of tuning, viscosity, compression ratios, seal materials, and the like, being slightly different from petrochemical diesel fuel. Reacting vegetable oils into fatty acid esters ("biodiesel") does attain some modest engine benefits, but mostly it's to match compatibility with petrochemical diesel grades so that you don't, eg, need to replace your fuel lines & pumps with different diameter fuel lines & pumps.
Depends on the context? Could be used in facitilies to produce biochar for production of terra preta/black earth/chernozem which counts as carbon-sink and is very productive soil. Doubly dual-use, so to speak. On-demand. Either biochar, or wood gas. Maybe even both.
You wrote it like „diesel trees” would be working in a way where you simply chop it down and put it in your gas tank.
Making and then using „diesel trees” would definitely require special equipment and manufacturing pipelines that might be the same cost or more than those for solar panels.
It's my science fiction story, so I'm going to say the tree we engineered for this was the sugar maple: you can put a tap in it and collect highly pure diesel fuel with a pre-Columbian level of technology.
> Plants have very low sunlight conversion efficiency compared to solar farms.
Measured how? If nothing else, they seem to be good at carbon capture. And I don't see how you it could account for engineered for plants engineered to store more of their energy as oil.
Measured by the fraction of incident sunlight that gets transformed to usable energy. Solar farms generate about 30 times as much power per hectare as corn farms, assuming that you can use electricity directly:
"Ecologically informed solar enables a sustainable energy transition in US croplands"
As a rough estimate, you'd lose 2/3 of that energy if the electricity had to be turned into liquid fuels. That would still mean 10 times greater usable energy produced per acre.
Plants genetically engineered for fuel production might be somewhat more efficient in the future, but future solar farms are also probably going to be more efficient.
For anyone wanting to learn more - the holy grail of Ag engineering would be to increase the efficiency of rubisco, which is the rate-limiting enzyme in photosynthesis - so understandably there’s a ton of research at doing just that.
A somewhat less (but still!) ambitious project is to retrofit C4 photosynthesis into rice. It's something like 50% more efficient, and has evolved independently dozens of times, so it's probably a lot more feasible.
If you had a widely applicable improvement, you’d be able to grow fruit trees in Canada or have two harvests in one season for food crops, or grow much denser species of wood, much more quickly for construction lumber. It would be massively world changing — but it is a 4 billion year old enzyme so is pretty entrenched..
Oh interesting! Is photosynthesis the main thing limiting growth speed?
I would have expected there to be multiple processes with similar or aligned timings, or some built in limiting mechanism or something... it's not like giving humans higher calorie food makes them become adults faster.
Improving rubsico would be more along the lines of improving your metabolism so that you can process 4,000 calories per day with the loose analog of supplying more CO2 being the ‘higher calorie food’. It’s the single largest bottleneck in photosynthetic efficiency. TBH, it would likely take several more breakthroughs for plants to make use of an improved rubisco but it’s still a massive target for ag research.
Either a perennial with oily fruit (someone mentioned palm oil down below), or something where you can relatively easily use the entire plant. The idea I keep coming back to is algae bred or engineered for oil content, but I'm not actually sure how feasible that is.
> Mayali says that growing phytoplankton outdoors with natural light and finding a less energy-intensive method of powering production would help microalgae-based diesel compete.
I'm sorry, were they measuring the carbon footprint of growing algae by what it takes to grow it inside with artificial light?
