environmentalresearchweb blog

« Green heat – district heating and energy storage | Main | New Royal Society president explores Climategate in documentary »

The EROI of algae biofuels

In an earlier blog post (“The Algebra of Algae…to Biodiesel”) I discussed if the US was to reduce its CO₂ emissions to 17% of those in 2005 (mimicking the ‘popular’ climate legislation from two years ago in 2009), then the US could produce 50 billion gallons of biodiesel from an algae feedstock. Aside from later being told that titling the blog “Algaebra” would have been much better (what I agreed with at the time), I have now discovered that the web is littered with discussions of brassieres made of algae. I’m glad I used my previous title!

But I digress, the caveat for my previous blog on algae biodiesel was is that to meet the CO₂ emissions limits there could be no other source of CO₂ emissions other than the power plants that would be capturing CO₂ and piping that CO₂ to the algae farms. There is also the possibility of using CO₂ directly from the atmosphere to grow algae, but most algae-facility designs assume a source of concentrated CO₂ to grow the algae feedstock. Clearly we need to understand the limitations of using ambient air, and the inherent CO₂ in the air, versus supplemental CO₂ from anthropogenic sources.

Over the last year a student (Colin Beal) at the University of Texas, Austin, has been characterizing the experimental set-up at the Center for Electromechanics for testing an algae to bio-oil process. The process stops short of converting the bio-oil into biodiesel, and he presented the results at a recent conference: Beal, Colin M., Hebner, Robert E., Webber, Michael E., Ruoff, Rodney S., and Seibert, A. Frank. THE ENERGY RETURN ON INVESTMENT FOR ALGAL BIOCRUDE: RESULTS FOR A RESEARCH PRODUCTION FACILITY, Proceedings of the ASME 2010 International Mechanical Engineering Congress & Exposition IMECE2010 November 12–18, 2010, Vancouver, British Columbia, Canada, IMECE2010-38244.

Colin counted the direct (electricity primarily) and indirect energy (nutrients, water, CO₂, etc) inputs into the process along with the energy content of two outputs: the biomass of the algae itself and the bio-oil extracted from the algae. He did not count the energy embodied in any capital infrastructure. What he found for this experimental, and very batch process was that the EROI of the experimental process was approximately 0.001.

This experimental EROI value for energy from algae must be kept in perspective of the stage of development of the entire technology and process of inventing new energy sources and pathways. It is important that we understand how to interpret findings “from the lab” into real-world or industrial-scale processes. To anticipate the future EROI of an algae to biofuel process, Colin performed two extra analyses to anticipate what might be possible if anticipated advances in technology and processing occur: a Reduced Case and Literature Model calculation.

The Reduced Case presents speculated energy consumption values for the operation of a similar production pathway at commercial scale. Many energy inputs are simply not needed or would be much smaller in a continuous flow process. The Literature Model provides an estimate for the EROI of algal biocrude based on data that has been reported in the literature. In this way the Reduced Case is grounded on one side by the sub-optimal experimental data and on the other side by the Literature Model, which is largely comprised of theoretical data (particularly for biomass and lipids production from optimal algae).

What Colin discovered was that the EROI of the Reduced Case and Literature Model were 0.13 and 0.57, respectively. This shows that we have much to learn for the potential of making viable liquid fuels. Additionally, Colin’s calculations for the experimental set-up (and Reduced Case analysis) show that 97% of the energy output resides in the biomass, not the bio-oil. For his idealized Literature Model, 82% of the energy output was in the biomass.

While these results seem discouraging, we do not have much ability to put these results into context of the rate of development of other alternative technologies and biofuels. How long did it take to get photovoltaic panels with EROI > 1 from the first working prototype in a lab? We have somewhat of an idea that it took one or two decades for the Brazilians to get reasonable EROI > 1 from using sugar cane for biomass and biofuel production (Brazilian sugar cane grown and processed in Sao Paulo is estimated near EROI = 8).

I believe we need to strive to quantify EROI for new technologies even they are still in the laboratory stage. Perhaps some very early technologies and processes are even too early for estimating or measuring EROI, but algae biofuels are clearly in the mainstream of research given the $500 m investment by Exxon-Mobil into genomics firms searching for the ideal strains of algae. These ideal strains of algae might simply excrete hydrogen, ethanol or lipids such that all of the capital infrastructure and direct energy requirements assumed for collecting algae and extracting the lipids even in Colin’s Literature Model can be largely unnecessary. Let’s hope others join in in trying to assess the EROI of their experimental and anticipated commercial processes for alternative energy technologies.

Posted by Carey King on January 23, 2011 2:35 AM | Permalink