April 07, 2011
Skepticism On Algae Biodiesel Yields
Kansas State University researchers claim that optimistic projections of algae biodiesel production are not realistic.
"We found that phycologists -- algae scientists -- maintain that some popular estimates of producing 200 to 500 grams of algae per square meter of open pond per day weren't feasible because there's simply not enough sunlight coming through the atmosphere to do so," Pfromm said. "Unless we can change the sun, such production is physically impossible -- and the hard numbers prove that. Most economists wouldn't necessarily recognize this as an issue in a business plan because it's dictated by physics, not finances."
The team used a more realistic, yet still optimistic, production number -- 50 grams per square meter per day. They determined it would take 11 square miles of open ponds making 14,000 tons of algae a day to replace 50 million gallons of petroleum diesel per year -- about 0.1 percent of the U.S. annual diesel consumption -- with an eco-friendly algae alternative.
The cheaper open pond approaches face problems with water evaporation rates (big underground water reservoirs are already getting depleted), invasion by organisms that eat algae, and invasion by algae species that can out-compete any species ideal for oil production, whether natural or genetically engineered.
Natural algae produce oil best when they are nitrogen-starved.
"Algae don't make oil out of the kindness of their hearts. They store energy as oil when they are starved for nitrogen so they can make more algae in the future," Pfromm said. "The end result is the yield isn't that high because we can either stress the algae to produce more oil or let them reproduce very efficiently -- not both."
Lots of selection for higher production crops amounts to selecting away overhead aimed at protection against predators and competitors. The same will apply to genetically engineering algae for higher oil production. So methods to keep out other species will need to be developed for algae oil ponds that are open. I think this is a very hard set of problems to solve.
This is not surprising. I know a guy who researched this around 1981. Biology is not very efficient at producing hydrocarbon fuels. Its better to make it thermally using nuclear power as the heat source.
My estimate is 8.64703056844E-7 kg/s/m^2 = 74.7103 gm/day/m^2 for a closed photobioreactor.
Of course, I've been telling the oil from algae (as opposed to the protein from algae) guys they've been barking up the wrong tree for over 5 years:
If the government were at all serious about getting to the bottom of this oil from algae noise, they'd fund the oil prize.
But algae is not the only plant that can provide oil. There is also Jatrhopa which is already shown to be suitable for jet fuel and biodiesel.
Separately, genetically engineered new plants can also be useful for dramatically increased cellulosic alcohol production.
Some types of hybrid poplar trees can grow from 6 to 10 feet per year.
Another idea is to create various low grade genetically engineered plants just for the purpose of burning as fuel in power plants, just to generate electricity, with zero carbon emissions since the plants absorb carbon dioxide to grow. But to develop such innovations and inventions, we need a Manhattan Project.
DM, and anyone else quantitatively so-deluded, click through the numeric link I gave you and follow the arithmetic and its supporting cites. It makes VERY short work of this whole debate.
There's also the problem of supplying the algae with enough carbon. Corn fields already become limited by CO2 mass transfer on sunny calm days, and they have much more surface area than a pond. Bubbling CO2 from a fossil fuel plant through the pond means you're not really replacing fossil fuels, just extending them a bit.
To make this work, they'd need to get algae that grow in extremely alkaline conditions, and spray some of that solution into the air to grab CO2. If the salinity is high enough it might retard evaporation sufficiently. There are algae that grow in soda lakes (notably in Africa) that might be suitable. To combat invasive species, we'd probably have to engineer the algae to be tolerant of some horrible broad spectrum poison, then load the ponds up with that as well.
"Another idea is to create various low grade genetically engineered plants just for the purpose of burning as fuel in power plants"
You mean like ... wood? Corn ethanol? How is that working out?
Algae Biodiesel has been portrayed as a great hope for biomass energy. I am skeptical. Jatropha's really besides the point of my post.
Still, I'm curious about jatropha. Is there enough land to grow enough jatropha to contribute a substantial amount toward world liquid fuels consumption? How many gallons per acre?
If the economics of jatropha start to make sense then food prices are headed even higher. What's the current production cost of jatropha fuel per gallon? Or is this some sort of long term research project?
Insolation is the ultimate limiter for all solar powered schemes. You can't get more power than is in the sunlight. That the top of Earth's atmosphere that about 1,336 W/m2, the atmosphere attenuates that to about 1,000 W/m2, clouds dust, night, seasonal angles of incidence, reduce it further, then whatever the scheme's efficiency is.