WC Archive

Obviously, algae based fuels can be a truly renewable energy source. In this type of process you basically need only tubes, pumps, filters and sensors. Float your algae tubes out in the middle of the ocean. It should be easy to highly automate, you don't pay for land, you can ship the product by boat, if you float your tubes near the equator you insulate yourself from many of the impacts of climate instability. If you divert some of the carbon from the algae into long lasting plastic consumer goods, we can harvest our materialistic desires to create a carbon sink.

Occam -- Algae farms in saltwater oceans, under a noonday sun? Fully automated? I'd love to see it.

It would be nice to get a smokestack multiplier count and a solid estimate of how many pounds of fuel one can produce in a given year (minus energy spent on upkeep)

Still, for as long as we are expanding old-style energy supplies, we run afoul Jevons Paradox.

Contraction of supplies equals gains in effiency, as long as they aren't too severe.

The article should have mentioned non-coal plant related algae farms. There are many heavy emitters of CO2... Natural Gas Plants, manufatures of steel, glass, lumber etc. Why just coal? Also you quote 15,000 gallons per acre in one paragraph but the following quote from Berzin figures out to 45,000 gallons per acre.

It seems impressive when you say you can generate 4-12 gallons of fuel/year per square meter but the same area covered in 10% efficient solar panels would generally generate over 180 kWhs/year and displace in excess of 150 kg of CO2 by skipping the coal plant altogether. Solar panels don't smell either.

My money is on PV to EV but good luck with the algae thing.

Well, if the biofuels substitute for petrol, there is a net reduction in emissions (in that the petrol isn't being burned) - so this is still a real abatement. And given that the problem with biofuels seems to be having enough land area to produce them (and energy input, given US farming methods), this seems to be a good way of producing them.

What about algae at the exhaust end of cars - collecting CO2 to use again? Maybe solar panels on cars aren't worth it but if you could use the sun hitting them to turn emissions into biodiesel it's got to be doubly effective in terms of delaying CO2 atmospheric pollution.
P.S like the floating farms idea too!

Perhaps we should expand our view of the problem. We have two very large impacts on the planet, one from our energy use and the other from our agriculture. Our agricultural land use may be an even-larger impact than our energy systems. If CO2 from fossil-fuel plants can be used to encourage the growth of algae, it may be interesting not to use the algae for biofuels, but instead as a soil amendment. Increasing the organic matter of soils serves as a mid-term CO2 sink and has numerous benefits to agriculture. Just a thought.

Regardless of what scheme we use, the demand for energy seems, for all practical purposes, inexhaustible. If one provides another form of energy in the form of algae, for example, total demand will just expand to negate the postive impacts of that algae. We need to sequester the algae or use it as a soil amendment, as suggested above. Otherwise, the algae will not be a substitute for fossil fuels but an addition to fossil fuels. If we simply increase our energy use, there will not be a net reduction in energy use.

While the use of algae could be a positive contributor to the reduction of greenhouse gases, this is only true if we impose enforceable global constraints on greenhouse gases.

The problem with the algae scheme is that if you use them in open ponds (the "real green" option) they are very unstable cultures.

Research has indicated that yields are disappointingly low in real circumstances (not more than 20 to 30 MT of dry matter, which comes down to around 5 to 7 MT of oil, and a bit less if used for ethanol). Several ordinary tropical plants have higher yields, and are less dangerous qua contamination of waterbodies.

http://www.biodieselamerica.org/site/downloads/articles/Biodiesel%20from%20Algae.pdf

So unless some bioengineerd kind of algae with much more stable and robust characteristics is found, the algae scheme isn't perhaps that viable.

Before we get too excited about the algae biofuel, what is the the EROI (Energy return on investment) for this system? Would this system require pumps, water systems, heaters, feeding? What is the fuel input required in terms of digging the reservoirs, pumping water to the pools and converting the little buggers to fuel? Finally, what is the ecological footprint for these things? I like the idea of carbon neutral systems and this is a great way to "store" energy for later use. I agree that PV and EV will be more efficient in the long run, but this is a good system to store energy for when we need it later.

There are some interesting numeric posts at The Oil Drum today:

http://www.theoildrum.com/story/2006/1/16/155759/653

One other non-numeric reminder I could make is that the planet is mostly covered in one giant salt pond (the oceans), and despite it's awesome size, and amosphere surface transfer area, it has not provided a sufficient CO2 sink to hold down global atmospheric increases.

I understand that there are some important differences between a closed algae growth system and the oceans ... but can a few acres of tubes really beat 64 million square miles of open water?

LOL, I google'd and snatched a number (64 million) ... but that's just for the Pacific.

Odo: I could see how algae could work more efficiently if they were applied at the source of CO2. When is it going to be easier to trap the gas -- when it's just been emitted in concentrated form, or after it has had time to diffuse and mix evenly with all the other atmospheric gases? At the source all the carbon is still in one place, and we just have to cycle it through the algae until it's gone.

The Jevon's Paradox issue is more worrisome to me.

Note algae ponds could also help to clean up wastewater. If you use (partly) wastewater as support, they will use the ammonia and urea.

For CO2 sources, power plants are not the only ones possible. Natural gas treatment, ethanol production (CO2 is a byproduct of alcoholic fermentation), cement kilns, hydrogen manufacturing, various chemical processes all yields more or less pure CO2 streams, most of whom are for now vented into the air.

I agree Richard, that on an equal square foot basis an engineered solution might win, but you know ... consider the largest algae tube farm you can imagine, and then consider its relative size to the oceans.

It would be HUGE to get a tube farm going with an effective square mile of growth media (subracting out are taken by racks, pipes, etc.). The oceans are 100 million times bigger than that.

Are the tubes 100 million times more efficient?

BTW, there are those old proposals for dumping iron in the oceans to increase their CO2 fixing ability:

http://news.nationalgeographic.com/news/2004/06/0609_040609_carbonsink.html

Odo: In fact, that factor of 100 million doesn't seem too far off to me. Googling for a few numbers gives me the following:

The diffuse concentration of CO2 in the atmosphere is about 0.03%. The NREL report that Lorenzo posted said that the flue gas emissions of coal plants can be as high as 13%. There's a factor of about 2000 already: if the CO2 is a thousand times more concentrated, it should be a thousand times easier for a given alga to pick it up, all other things (like photosynthetic efficiency) being equal.

Then you have the concentration of algae in the oceans. This link shows that chlorophyll concentrations are low in the equatorial area and high up near the poles. That probably depends on many factors, such as overall sunlight levels, ocean currents, temperatures and so on. But let's suppose for the sake of argument that chlorophyll concentrations trace biomass of algae, and let's say the surface-averaged concentration is about 0.3 mg/m3. This site says algae are about 1.5% chlorophyll by weight, so this gives about 20 mg/m3. The NREL report quotes a number in mass per unit area per unit time, so we need to estimate a depth to which algae will grow. This link is for lakes, but it gives us some idea; just for giggles let's assume the beasties grow to a depth of 10 m, and that the useful light gives out there. That means we've got 0.2 g/m2 averaged over the Earth's surface.

In contrast, the NREL guys are claiming densities of 50 g/m2 per day. That's like the most algae-sludged lake you can imagine growing. I admit ignorance about how quickly algae grow in the oceans, but I would be surprised if the whole population turned over multiple times per day. So you're looking at maybe another factor of 100-1000 from the densities of algae.

So you have a factor of a million. Then if you allow one square-mile pond per gigawatt power plant, and you have a thousand such plants currently in operation around the world, the numbers begin to look competitive. I'm not claiming they're dead on -- just trying to show that it's not as large a discrepancy as a factor of 100 million.

Note, however, that this is not a plan to sequester CO2 already in the atmosphere; it's intended to prevent new CO2 from entering the atmosphere, or (if we use it for fuel and not fertilizer) at the very least to increase our energy return per carbon atom released.

Nor are the NREL guys saying anything about pipes; their proposal is all about open ponds using local species of algae. There are evaporation issues to consider, but who knows? Presumably the emission gases would be piped down from the stacks and then dissolved into the pond; that's a lot less infrastructure than the closed bioreactors you seem to be talking about.

Anyone have more details which might make my estimate more accurate or reasonable?

Those are some interesting numbers. I'll have to give it some more thought. The critical questions seem to be how much faster cultivated plants (algae or for that matter trees) can grow in high CO2 environments, and then how large such cultivation efforts can scale.