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Comment by dahfizz | Hacker News Reader

What's the efficiency of using actual plants to produce fuel? Either through refining e.g. corn oil directly or using plants to feed bacteria that produce a fuel. That's a carbon neutral way to convert sunlight to fuel.

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Algae and Cyanobacteria tend to be substantially more efficient than whole plants (6-8% [1]). There are some caveats though. Generally the industry has found it hard to grow algae at commercial scale cost-effectively for several reasons including (but not limited to):

- Contamination by outside organism kills your algal culture

- If you create a closed system, the algae will stick to the glass, fouling the surface and reducing light transmission

- Extraction of materials from the algae is hard, you end up with a lot of water weight you need to get rid of somehow

There are also some counterintuitive aspects in that apparently dropping the efficiency of the antennae (light collection) actually makes the overall culture more productive because excess light makes it past the initial cell layer and therefore other cells can benefit from the light. Otherwise the initial cells grab all the light they can, and waste whatever light energy they don’t need.

I think it’s an interesting field, but so far it’s been a hard road to make it actually work at scale cost effectively.

[1] https://www.sciencedirect.com/topics/chemistry/photosyntheti...

Since lichen are a symbiosis with algae, cyanobacteria, or both, it's possible that we could create lichen-like habitat for both or either and extract the sugars for fuel.

Just a few years ago we realized a pretty profound misunderstanding of how lichen function, which partly explains why we have trouble propagating them in a lab. Perhaps there's enough new information there to warrant some more research.

During the dot-com boom there were people cooking biodiesel from algae but I suspect they couldn't get the embodied cost of the system down. Either materials, or maintenance. I'll bet microbial mats in particular foul the system over months if not weeks.

Edit to add:

Whereas the earlier work was on 'digesting' algae and extracting the lipids, within a symbiotic structure (lichen, coral, root nodules, mycorrhiza) the host is exchanging sugars for minerals. You wouldn't have to 'crack open' anything to get to them, if you can find a way to collect them, which I suspect puts us deep into nanomaterials territory.

I worked on phycology for an algae biofuels startup for the better part of a year.

Just chiming in to say that this is a good post, and I don't even have much to add to it.

I quit once I realized that paving over desert ecosystems with huge raceway ponds filled with glyphosate, wasn't solving any problem I wanted solved.

If we don't switch fuels, there will soon be no shortage of desert ecosystems no matter how many we pave over...

I don't want to speak for anyone else, but the point might have been that there may be other ways to get energy which accomplish the goal without requiring that sacrifice.

Correct, and while I work on developer tools these days, I had a satisfying stint at a battery-analytics company after transitioning to software development.

Raceway ponds full of glyphosate in the desert; sounds like Sapphire Energy?

For what it's worth, I think we'll be able to dispense with the glyphosate if we're more flexible about what algae we're growing, and fuzzily select ecosystems rather than strains. That way we're better able to tolerate invaders & other stresses. But that means we're not operating at peak efficiency, which means a larger footprint.

I'm more concerned about how we source fertilizer.

(For context, I'm between jobs, but my last job was as an algae cultivation technician.)

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

  Quoted values sunlight-to-biomass efficiency

  Plants, typical     0.1% [3], 0.2–2% [4], 3.5-4.3% [5]
  Typical crop plants 1–2% [3]

Solar cells can turn about 10% of incoming sunlight into electricity (cells are more efficient, but they don’t cover the whole ground, typically aren’t kept optimally oriented, etc)

Plants are much easier to recycle as well.

Biodegradable by definition.

The maintenance is much more expensive and time consuming though. Most solar panels are install and forget for their lifetime measured in decades, with some small failure rate in the meantime. Plants however typically require maintenance multiple times a year and most have usable lifetime measured in months, not decades.

There are more types of plants than just corn. Trees are much easier and cheaper to establish than solar for example.

Trees are the lowest of that low range that start at 0.1% efficiency.

And if you collect only the wood, it's a couple of magnitude lower than it.

But delivering the energy from those trees to consumers is harder and more expensive than for solar cells.

Also, if your desired output is electrical power, you’ll lose more energy converting your trees to electricity.

On the plus side for trees, storing the energy they stored is cheap, and can be done for centuries.

The net effect is that PV cells are more economically viable than using photosynthesis to catch solar energy (at least for now; there’s work being done on improving photosynthesis; I don’t see that beating PV soon, though, certainly not because PV cells keep improving fairly rapidly)

Trees are often turned into heat and energy. Obviously they have very different requirements from PV cells and overall probably aren't as good they are certainly viable in some places (e.g Italy).

Somehow it just doesn’t feel right to burn trees to produce clean or green energy. It might work on a small scale but not sure about doing it on an industrial scale.

It might be renewable but it still makes air pollution. On certain nights when everyone in the neighborhood decides to have a fire the air quality is terrible - almost as bad as during summer forest fire season.

and plants are not only energy storage. They are great water storage, air cleaners, area temperature regulators. Not even counting as habitat for rich fauna fungi...life.

Still waiting to hear a politician running on the platform of more plants.

Plants are enormous consumers of water. The water argument is strongly in favor of PV.

There is a lot more to water than consumption. Overall trees usually have a positive effect on water flows.

Solar cells are more efficient and last longer, but don't grow themselves from seeds produced by the previous generation. That makes it much more expensive to cover large areas with them.

I spent a couple of years doing USDA/DOE research into oilseed biofuels. The short answer to your question is 'it depends'. Part of our work involved doing a LCA (life cycle assessment) on the oilseeds as a biofuel.

There are several considerations to be had here. Firstly, are you farming on marginal or primary farmland? Marginal land is generally marginal for a reason and will have typically lower yields. How are you farming? What intensity? Where do you have to move the product to for processing? What is the energy mix going into the processing workflow? Do you have to move the fuel again after you process it?

The relatively easy answer to solving for the above issues, is that in some circumstances, it can make sense for some farmers to generate some oilseed for the purposes of making their own biodiesel.

you tend to spend nearly the same energy to produce biofuel as you get. that could improve some but it doesn’t appear to be a real solution, at least not with 9 billion to feed too.

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