Sometimes the content on Green Chip Stocks is driven by what our readers are asking. That's the case with today's blog.
I recently received the following question from reader identifying himself only as Dwayne:
I just read your article on growing algae to produce bio-diesel. I was wondering about the relative amounts of CO2 input/output, i.e. has anyone done the math to figure out how much CO2 algae take in to produce a gallon of diesel fuel, compared to the amount of CO2 produced when that same gallon is burned. If the amount released from burning is equal to or less than the amount algae consume, then this is a win/win situation. If the amount released by burning is greater than the amount consumed, then we have a problem.
Perhaps you could address this in another article?
Thank you.
At first glance this can seem like a complex question. Honestly, it took me a few seconds to wrap my head around it.
In reality, the answer is very simple and, in my opinion, further strengthens the case for mass-adoption of algae biofuels.
With all biofuels, the amount of carbon dioxide released when burned is equal to the amount of carbon dioxide consumed when the feedstock was grown.
That means for corn-based ethanol, the amount of CO2 released when one gallon is burned is about the same amount of carbon absorbed by the plants that grew the corn to make that one gallon.
Verbose, I know.
For algae, it takes about one ton of CO2 to make two tons of algal material. It's difficult to say how much biodiesel or ethanol two tons would make because different companies are achieving different results.
Taking average conversion numbers, about 190 gallons of fuel (both biodiesel and ethanol) can be made from those two tons of algae.
When burned, those 190 gallons will emit about 10.5 pounds of CO2 each. This is better than the 20 pounds that comes from each gallon of gas burned in an internal combustion engine. http://www.fueleconomy.gov/Feg/co2.shtml
So the short answer is: algae biofuel, when burned, releases the same amount of CO2 that was used to grow it, which is still less than burning gas. So it's a winner already.
Enter Complexity
But because the CO2 used to grow algae can come right from power plant combustion, that 10.5 pounds of carbon is the result of more than just the liquid fuel being burned, greatly lowering the carbon intensity.
If you have an algae cultivation system attached directly to a coal-burning power plant, emissions can be reduced by some 40%. So the resultant emissions when the algae biofuel is burned come not only from powering the car, but also from burning coal to produce hundreds of thousand of kilowatt-hours.
This effectively makes algae a carbon sink.
Of course, the exact numbers depend on numerous factors, such as the conversion rate of algae to fuel and exactly how much electricity was produced relative to the CO2 absorbed by the algae.
No matter the exact carbon intensity for algae biofuels, their ability to absorb CO2 from other energy production operations makes it one of the best to date. No other feedstock can absorb more carbon dioxide from external sources during the growth cycle.
Hope this answers the question,
—Nick
Subscribe to
your reply to your reader is incorrect. The low of conservation of mass would in the ideal sense be neutral since you must account for all the carbon that is inputted to make and grow the algae and then subsequently burned. There is no net accumulation or sink of carbon, otherwise many laws of physics that we know would not work. Since there is no such thing as a perfect system, the is a net production of carbon because algae do not consume nor give us 100% yield of diesel. In addtion, to set up the farm and pump the water and nutrients to the algae comes from an outside energy source such as a fossil fuel plant. If you do a global balance on the entire process you will see that it consumes more carbon than if you did not even grow the algae. The only way to reduce carbon emissions is to use a fuel that does not contain carbon and whose process to make it does not use carbon. The people at Genesys, LLC, www.genesys-hydrogen.com, have it right when they came up with a technology that uses two resources that are cheap and plentiful, heat and water to make hydrogen. The heat can come from solar or geothermal origins and the water could be waste or seawater. They make higher valued products such as hydrogen and oxygen without any carbon in the technology.
I suspect Dwayne was more interested in the question whether the biodiesel produced from algae contains more energy than is needed to run the process (Energy Return on Energy Invested: EROEI). There's very little data on that in the scientific literature for algae, but what's there suggest: NO, or perhaps a little. This is similar to bioethanol from corn or wheat: it doesn't make sense.
It's generally ignored that growing the algae is expensive (100 times forest biomass in open systems, 1000 times in closed systems). There's a lot of gray energy in the construction of ponds or photobioreactors, and a lot of energy is needed to run the systems (paddle-wheels, pumps, cooling, gas-exchange), to harvest the algae (flocculation, centrifugation, drying), to extract the lipids, to convert the lipids to biodiesel. Until this has been calculated through green scum may just as well be a green scam.
I suspect Dwayne was more interested in the question whether the biodiesel produced from algae contains more energy than is needed to run the process (Energy Return on Energy Invested: EROEI). There's very little data on that in the scientific literature for algae, but what's there suggest: NO, or perhaps a little. This is similar to bioethanol from corn or wheat: it doesn't make sense.
It's generally ignored that growing the algae is expensive (100 times forest biomass in open systems, 1000 times in closed systems). There's a lot of gray energy in the construction of ponds or photobioreactors, and a lot of energy is needed to run the systems (paddle-wheels, pumps, cooling, gas-exchange), to harvest the algae (flocculation, centrifugation, drying), to extract the lipids, to convert the lipids to biodiesel. Until this has been calculated through green scum may just as well be a green scam.