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Comment by armada651 | Hacker News Reader

> “The biggest challenge many people don’t realize is that even nature has no solution for the amount of energy we use,” said University of Chicago chemist Wenbin Lin. Not even photosynthesis is that good, he said: “We will have to do better than nature, and that’s scary.”

Aren't solar panels already more efficient at creating energy than photosynthesis?

It's true we haven't found an artificial method of photosynthesis that creates a fuel we can burn that is more efficient than nature, but do we want to?

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> Aren't solar panels already more efficient at creating energy than photosynthesis?

Solar panels convert light to electricity. Photosynthesis uses light to rebuild molecules into sugars.

Plants are about 1-2% efficient - https://en.wikipedia.org/wiki/Photosynthetic_efficiency

Modern solar cells easily hit 20% efficiency under decent conditions.

> It's true we haven't found an artificial method of photosynthesis that creates a fuel we can burn that is more efficient than nature, but do we want to?

If we want to use airplanes to quickly travel long distances, yes. Or if we want to haul loads to many arbitrary locations.

Photosynthesis covers the vast majority of land and ocean available on Earth while solar panels cover far less. So in a way, photosynthesis is more efficient - in a scalable way.

Yeah but that's a function of self-replication. If you could engineer a tuber or vine which did nothing but try to build up a huge H+ ion gradient between it's roots and it's tip, then we could just let that grow indefinitely and use it as a battery directly.

Similarly most models of "grey goo" would functionally be this: machines autonomously covering the biosphere in more efficient light harvesters.

That's not how you measure efficiency

How do you measure efficiency?

Per unit area or volume or mass

But efficient scaling counts too right?

In the reductive view, yes. But at some point one must also consider the entire ecosystem. Plants are very efficient in keeping the entire system running; fossil fuels are quite efficient in making it less hospitable to humans. That consideration goes beyond just talking about energy input or output per volume or mass (although in the end it cannot and should not divorce itself from those considerations lest it turns into pseudo-science like the many, many inane techno-scams are prone to do).

I would bet the the current yearly growth rate of energy harvesting is greater for solar panels than plants :) and plants have a billion year head start. (This is of course a silly argument)

Solar panels and photosynthesis drive different outputs, sure, but with the basically limitless electricity from the solar panels, we can then drive whatever output we want through applying the electricity to machinery or electrolysis

Electricity from solar panels is not "limitless" in any meaningful sense of the word. Solar panels deliver a limited amount of power per area. They require a non-zero area of land and non-zero resources for construction and maintainance, so you can't build and install an arbitrary amount of them.

Of course solar power is not limitless. Finite insolation, and finite land mass = finite resource.

But, you could generate the entirety of US energy usage from less than 100,000 square miles of solar panels, and quite possibly from less than 50,000 square miles, if you consider wind + solar. That's a lot of land, in one respect, but it's less than, e.g., the amount of land (circa 60,000 square miles) we currently use just to produce ethanol that accounts for less than 10% of just our energy use for small internal combustion engines. The challenge with solar/wind isn't limits on their production due to land, or even infrastructure, it's that they produce intermittently, and only produce electricity, and electricity is challenging to store for extended periods of time so you can match production to demand over time scales from hours to years.

It's limitless in that it's not outside the bounds of physics or economics if we really wanted to replace 100% of our energy with solar, night time/inclement weather storage notwithstanding

There's nothing but a lack of willpower preventing us from being on 100% solar and wind

It's limitless in that in a closed system not connected to the grid, it's not automatically a bad thing if you waste it. Waste some solar power, nothing happens. Waste some coal or oil and you either have a slick on the ground or a ton of new CO2 in the air

let me know when you can clone solar panels or when solar panels each produce thousands of solar panel seeds.

Solar fuels has a niche in that it allows us to make reduce the net CO2 released by carbon fuels. It would help blunt the level of changes needed to stave off worse climate disaster giving us more time to wean off of things like NG fired power plants and cars.

We have, but it's not a single process. We can convert light to electricity quite cheaply and efficiently with solar PV panels and then use that electricity to electrolyze hydrogen from water and capture CO2 from air(or seawater). Then there are a variety of processes, such as the Sabatier reaction, to convert the hydrogen and carbon into a hydrocarbon. I believe Prometheus Fuels is combining the hydrogen electrolysis and CO2 capture into a single step. Terraform Industries is also working on this problem, but is focused on driving down capital costs of electrolysis so that carbon neutral fuel producers can afford to have electrolyzers sitting around unused 75% of the year and only working when solar electricity is so abundant that it's practically free. Electrolysis and carbon capture takes a lot of energy, but assuming that all electricity comes from solar panels, it is far more space efficient than biofuels. An acre of corn or sugarcane can produce about 400-700 gallons of ethanol per year, or about 36-64 gigajoules of fuel. An acre of solar panels (laid nearly flat to maximize space efficiency) that is converted to methane at 30% efficiency (efficiencies around 50-60% are very normal and state of the art is around 75%, but 30% is much easier and cheaper) can produce about 350 gigajoules of fuel per year.

There's also some research on converting hydrogen and CO2 to edible carbohydrates, either chemically or through hydrogenotrophic or methanotrophic bacteria. That will be a huge revolution for either increasing the carrying capacity of the planet or decreasing humanity's impact on the planet. It will also be a huge boon for countries without much arable land to be able to feed their people without relying on imports. Electricity to food is not quite ready for scaling up yet, but synthetic fuels are absolutely ready to go as soon as solar electricity prices drop just a bit more or fossil fuel prices rise a bit more.

> We have, but it's not a

> single process.

Technically, biological photosynthesis consists of two different major processes. You’ve got a membrane complex called „photosystem“ (of which they are two types) and an enzyme called Rubisco. The former drives the light reactions oxidizing water into hydrogen and oxygen (and thereby creating reducing agents and a proton gradient). The latter drives the dark reactions reducing CO2 into various forms of sugar.

In some plants CO2 fixation runs at night and, hence, at a different time than the light reactions. In others, it happens in different cells and, hence, physically separated from the light reactions. CAM and C4 plants, respectively, are more efficient in hot or dry biotopes.

I'm not sure what they mean anyway. The amount of solar energy hitting earth is a lot larger than human energy utilization. Like by a factor of 10000 (tens of terawatts vs ~100 petawatts).

Well first of you'd have to reduce that by the efficiency of our panels, so we're down to 20 petawatts

And then you'd have to factor in the fact that basically none of the planet can be covered in solar panels

And then the fact that you wouldn't be able to efficiently transport the energy to where we need it

So yes in theory you put a couple hundred sqkm of solar panels in the Sahara and you're golden, in practice it's much more complex

Exactly. Our best ornithopters still aren't as good as birds and probably will never be. I guess air travel is doomed.

Its a ridiculous statement. Nature, if that's what you want to call it has to all intents and purposes infinite energy.

Our ability to release energy from matter is what we have built upon.

We can just store the fuel for carbon capture in that case, right?

Sure, but if carbon capture is the goal there are easier methods than artificial photosynthesis. The point of artificial photosynthesis is to create a fuel you can eventually burn again.

Re-using the CO2 in the atmosphere certainly beats simply adding to it, I'm guessing that's the point here.

For it to be truly sustainable the carbon needs to be stored in a way that humans wouldn't get at out of greed ever again. So it would need to be in some useless form like maybe diamonds or something.

A ton of CO2 is produced by about $150 worth of fuel (oil). So if you can do carbon capture for less than $150/tCO2 it would make more sense to sell the fuel and capture more carbon.

> So if you can do carbon capture for less than $150/tCO2 it would make more sense to sell the fuel and capture more carbon.

How does this math work?

If it's $149 to recapture, who's paying for this $149? Is the person buying $150 worth of fuel now paying for it also, at ($150 + recapture cost)/gallon?

I believe the idea is to sell captured carbon to be used as fuel. So we are net 0.

That would be valid once we stop extracting carbons from other sources (oil, gaz, coil…). Since that won’t happen at a global scale soon, burning the captured carbon won’t stop the carbonification of the air/water.

The $1 profit goes towards paying for capturing carbon. Every 150 barrels of captured fuel you sell, you make $75 profit you could spend on either not selling a barrel, or some more efficient way of reducing our climate impact like maybe buying a solar panel or sponsoring a windmill.

Or what the sibling suggests, you keep the money as profit / funds for growing the business so you displace traditional oil and you prevent the increase of CO2 in the atmosphere that way.

In terms of energy, you'll always need more to recapture than burning that fuel will give you (cuz entropy)

So if money = energy (which is a wrong assumption), buying that barrel would always be a loss

Unless that barrel is a higher value to you than the energy required to create the barrel would otherwise be.

If you capture the carbon for example as carbon dioxide instead of methane "cuz entropy" need not apply.

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