[philipkglass]

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).

[dmurray]

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.

[tekno45]

what goes through my mind is the fact plants aren't low maintenance, the land has to be tended.

growing the fuel plant is probably easy.

How do you get it OUT of the plant?

Solar panels just sit there (they do need cleaning i admit) and produce electricity that we can manipulate very cheaply already.

What machine collects diesel from plants? Can you safely dispose of the plant matter?

[mapt]

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.

...

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.

...

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.

[tekno45]

Thanks! very interesting space that i barely understand lol. hope it didn't come off as know it all, just questions.

[aaronblohowiak]

I’d rather farm food where plants grow well and put up panels where they don’t..

[motorest]

> I'd rather farm food where plants grow well and put up panels where they don’t..

False dichotomy. There are places where food does not grow at all and can be used to grow fuel crops. Say, the ocean.

https://en.wikipedia.org/wiki/Algae_fuel

[Tade0]

No need for diesel trees when there's wood gas, which was successfully used to power vehicles:

https://en.wikipedia.org/wiki/Wood_gas

It's wildly inefficient though and not worth the trouble compared to solar panels and batteries.

[LargoLasskhyfv]

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.

[ozim]

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.

[dmurray]

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.

[arghwhat]

No no, you integrate the pump directly into the tree. Skip the farms, just plant the trees at the station in place of the current pumps.

[anvandare]

Forest fires would definitely get a lot more exciting.

[ozim]

Maybe that's quite the reason why we didn't do it :)

[andrewflnr]

> 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.

[philipkglass]

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"

https://www.pnas.org/doi/full/10.1073/pnas.2501605122

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.

[mikeyouse]

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.

https://en.m.wikipedia.org/wiki/RuBisCO

[JumpCrisscross]

Strongly recommend for one of the light-dependent reactions from before that enzyme: https://youtu.be/WhCczIqADuI

[murderfs]

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.

[rendaw]

Why do we need more efficient photosynthesis in plants? Is it for indoor cultivation?

[mikeyouse]

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..

[rendaw]

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.

[melagonster]

Plants get more energy, so they generate more food.

[andrewflnr]

Ok, yeah, if your reference for biofuel is corn, where you can only use a tiny fraction of the plant, no kidding it'll look bad.

[andsoitis]

Which plant do you estimate is a much better pick?

[andrewflnr]

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.

[KnuthIsGod]

https://hakaimagazine.com/news/biofuel-made-from-algae-isnt-...