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> I don't know of any algae, anywhere, that are more concentrated sources of carbon than existing trees. Even if we had to grow both sides, algae are still prob

> I don't know of any algae, anywhere, that are more concentrated sources of carbon than existing trees. Even if we had to grow both sides, algae are still problematic, since separating them from water is apparently quite a difficult problem. Again, we're talking about land use for the energy you get, not the carbon it stores. Algae have a distinct advantage when it comes to metrics with land use in the denominator, since they don't use any land. ...and pulling algae from water is significantly easier than pulling biomass out of forests. I'm not sure what you're getting at there. > Yield of rapeseed in the US in 2020 was 2.16 tonnes/hectare/year. Yields of lignocellosic biomass (dry mass) in the US (miscanthus, eucalypt) is almost an order of magnitude higher. Yup, the other stuff is much heavier per hectare for sure. That doesn't make it a better source of fuel. Having more mass just means it takes more energy to move it. Step 2 is you extract fuel from it.

pfdietz 4y ago
No, I was talking about the temptation of mining existing biomass. The focus on yield was a change of subject. But even then, algae is greatly overhyped, for a number of reasons. First, as I mentioned, separating it from water is something of a showstopper (and no, it's not easier than cutting down trees). Second, it rapidly reproduces, with a generation time much shorter than a growing season, so keeping out undesirable wild species is difficult. Third, high yields require a lot of CO2, to the extent that simply absorbing CO2 into a pond isn't enough; instead bioreactors with an external source of CO2 are needed. That vastly increases capital cost over a simple field (and if the CO2 is from combustion of fossil fuels, then that's a fraud not a zero CO2 source of fuel.) Evaporation of water will be a big negative. Algae might work if one can get species that grown in extremely alkaline conditions, with water that can be sprayed into the air and recovered to scrub CO2 into the solution from the air. There are algae that grow in suck alkaline lakes. To get around the wild contamination problem would likely require engineering the algae to survive some kinds of poisons, then filling the water with those poisons as well to kill everything you don't want there. This wouldn't be very environmentally friendly. You still have the water separation problem, now made harder by the water being alkaline and toxic. > Yup, the other stuff is much heavier per hectare for sure. That doesn't make it a better source of fuel. Having more mass just means it takes more energy to move it. Step 2 is you extract fuel from it. The huge problem with biomass is the land requirement. That yield for rapeseed would be crippling for that crop as a fuel source for an economy.
- cbsmith 4y ago
  > No, I was talking about the temptation of mining existing biomass. I clearly missed a step then. So when you say: "I think the biggest argument against biofuels is that if they achieved large scale use, it would encourage people to mine biomass from existing forests instead of growing it." So, I drew from that a conclusion that if biofuels were prevalent, you believe there's an incentive to mine forests to create biofuels, rather than the grow new biofuels. In my mind, that means going into wild forests, ripping trees and other biomass out of the ground, slicing it up and transporting it to some kind of a processing plant, where you'd separate out the useful bits and turn it in to biofuel. The incentive comes from the profits yielded from selling the biofuel after paying the costs of creating it. I don't disagree that there are challenges growing and harvesting of algae, but it is something that is done, at an industrial scale, already (largely for the harvesting of pigments). They don't produce CO2, but they do pump in a lot of fresh CO2 (and pump out O2) to ensure good yields. It's just not done for purposes of creating biofuel, because there's no demand to justify the costs involved. In a world you're envisioning where there is much more of an incentive to produce biofuels, it seems eminently reasonable those incentives would apply to algae as much as anything else. > Second, it rapidly reproduces, with a generation time much shorter than a growing season While there are challenges related to this, this does largely mitigate the turn around time advantage that existing wild forests might have. > The huge problem with biomass is the land requirement. That yield for rapeseed would be crippling for that crop as a fuel source for an economy. Rapeseed is currently produced on an industrial basis in places where the HEAR derived from it already yields more profits than say, growing soybeans. It's not a popular crop, because the demand for edible canola products is much higher than the demand for biofuels, but if that demand were to shift... Where we agree is that I don't see biofuels being a viable strategy, at least for the foreseeable future. I just don't see a future where they become viable, but the incentive to mine existing forests for biofuels becomes significantly more significant than extant incentives to mine forests.

pfdietz 4y ago

No, I was talking about the temptation of mining existing biomass. The focus on yield was a change of subject. But even then, algae is greatly overhyped, for a number of reasons. First, as I mentioned, separating it from water is something of a showstopper (and no, it's not easier than cutting down trees). Second, it rapidly reproduces, with a generation time much shorter than a growing season, so keeping out undesirable wild species is difficult. Third, high yields require a lot of CO2, to the extent that simply absorbing CO2 into a pond isn't enough; instead bioreactors with an external source of CO2 are needed. That vastly increases capital cost over a simple field (and if the CO2 is from combustion of fossil fuels, then that's a fraud not a zero CO2 source of fuel.) Evaporation of water will be a big negative. Algae might work if one can get species that grown in extremely alkaline conditions, with water that can be sprayed into the air and recovered to scrub CO2 into the solution from the air. There are algae that grow in suck alkaline lakes. To get around the wild contamination problem would likely require engineering the algae to survive some kinds of poisons, then filling the water with those poisons as well to kill everything you don't want there. This wouldn't be very environmentally friendly. You still have the water separation problem, now made harder by the water being alkaline and toxic. > Yup, the other stuff is much heavier per hectare for sure. That doesn't make it a better source of fuel. Having more mass just means it takes more energy to move it. Step 2 is you extract fuel from it. The huge problem with biomass is the land requirement. That yield for rapeseed would be crippling for that crop as a fuel source for an economy.

cbsmith 4y ago
> No, I was talking about the temptation of mining existing biomass. I clearly missed a step then. So when you say: "I think the biggest argument against biofuels is that if they achieved large scale use, it would encourage people to mine biomass from existing forests instead of growing it." So, I drew from that a conclusion that if biofuels were prevalent, you believe there's an incentive to mine forests to create biofuels, rather than the grow new biofuels. In my mind, that means going into wild forests, ripping trees and other biomass out of the ground, slicing it up and transporting it to some kind of a processing plant, where you'd separate out the useful bits and turn it in to biofuel. The incentive comes from the profits yielded from selling the biofuel after paying the costs of creating it. I don't disagree that there are challenges growing and harvesting of algae, but it is something that is done, at an industrial scale, already (largely for the harvesting of pigments). They don't produce CO2, but they do pump in a lot of fresh CO2 (and pump out O2) to ensure good yields. It's just not done for purposes of creating biofuel, because there's no demand to justify the costs involved. In a world you're envisioning where there is much more of an incentive to produce biofuels, it seems eminently reasonable those incentives would apply to algae as much as anything else. > Second, it rapidly reproduces, with a generation time much shorter than a growing season While there are challenges related to this, this does largely mitigate the turn around time advantage that existing wild forests might have. > The huge problem with biomass is the land requirement. That yield for rapeseed would be crippling for that crop as a fuel source for an economy. Rapeseed is currently produced on an industrial basis in places where the HEAR derived from it already yields more profits than say, growing soybeans. It's not a popular crop, because the demand for edible canola products is much higher than the demand for biofuels, but if that demand were to shift... Where we agree is that I don't see biofuels being a viable strategy, at least for the foreseeable future. I just don't see a future where they become viable, but the incentive to mine existing forests for biofuels becomes significantly more significant than extant incentives to mine forests.