This site uses cookies. By continuing to use this site you agree to our use of cookies. To find out more, see our Privacy and Cookies policy.
Skip to the content

[IOP] A community website from IOP Publishing

Tag Archives: biofuels

Carbon accounting policies for biofuels

In a recent post. Not all biofuels, however, have the same carbon footprint. How can biofuels for transport and their life-cycle greenhouse gas emissions then be effectively regulated?
As pointed out in the corresponding paper are insufficient for not accounting for a series of general equilibrium effects. The European Commission, in fact, is currently reviewing its stance, and may review the FQD in this summer. But what kind of measure can improve the biofuel conundrum?
The twin paper by Flachsland et al. studies a potential role of emission trading also for the transport sector. Now, this is an effective measure in terms of bringing a level-playing field across all fuels. In fact, if a cap is global in scope, and covers all relevant sectors, we could sleep quietly: wherever emissions appear they will be accounted for, and it is not relevant whether they are induced by biofuels or not. It matters only that they get a price tag, and that people try to reduce emissions.
However, a global cap is not in sight, and an inclusion of agricultural emissions also seems utopian currently. Hence, we are still stuck with the GHG accounting problem for biofuels (and potentially relevant general equilibrium effects for other fuels such as electricity) when transport is included in the European Emission Trading Scheme.
One possibility is to treat biofuels by default as having at least gasoline-equivalent emissions (see DeCicco, 2009 and processing emissions, gaining credits if certified. This would reverse the burden of proof. Properly implemented, it can be seen as an implemented precautionary principle – better safe the forests and its carbon stock then being sorry big time.

Posted in Sustain to gain | Tagged | Leave a comment | Permalink
View all posts by this author  | View this author's profile

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 in Energy the nexus of everything | Tagged , , , | Leave a comment | Permalink
View all posts by this author  | View this author's profile

The Algebra of Algae … to Biodiesel

Over three decades ago the US government, through the then-known and newly-established Solar Energy Research Institute (SERI), established a Biofuels Program that included the Aquatic Species Program (ASP) to explore the ability to develop biofuels from microalgae. Today, SERI is known as the National Renewable Energy Laboratory (NREL), and in 1998 they concluded the ASP as the progress had slowed and there was a belief that advances in biological control and genetic engineering of algae were required to create a valid algae-based biofuel industry. Aside from carbon sequestration, NREL reports that: “Algal biodiesel is one of the only avenues available for high-volume re-use of CO2 generated in power plants. It is a technology that marries the potential need for carbon disposal in the electric utility industry with the need for clean-burning alternatives to petroleum in the transportation sector.” [Sheehan et al., 1998]

Furthermore, NREL states: “…we believe that biodiesel made from algal oils is a fuel which can make a major contribution to the reduction of CO2 generated by power plants and commercial diesel engines.” [Sheehan et al., 1998]

Finally, the NREL closeout report reads: “When compared to the extreme measures proposed for disposing of power plant carbon emissions, algal recycling of carbon simply makes sense.” [Sheehan et al., 1998]

If we combine these statements made in 1998 with proposed legislation in 2009 for greenhouse gas (GHG) reductions, we can pose the question regarding the viable size of an algal-based biofuel industry in the United States. The most popular climate bill in the current Congress is the American Clean Energy and Security Act of 2009 (ACES Act) by Henry Waxman and Edward Markey, and it discusses reducing GHG emissions by 83% of 2005 levels by 2050.

In 2005, the US carbon dioxide (CO2) emissions were 6,030 million metric tons (MtCO2). The electricity sector accounted for 2,510 MtCO2 and the transportation sector accounted for 1,980 MtCO2. In accordance with popularly discussed proposed legislation, 17% of 2005 US CO2 emissions are approximately 1,000 MtCO2. For simplicity of this analysis, we’ll assume that total CO2 emissions, rather than more generally all GHG, will need to be reduced to the target 17% by 2050.

Algae production requires CO2. And because algae and grow in aquatic environments instead of on land, the surface area of the algae that are exposed to the air, which contains CO2, is more limited than terrestrial biomass. Therefore, to grow algae biomass on industrial scales (e.g. profitable scales) CO2 is pumped into the algae-bearing water at much higher concentrations than in the atmosphere. Estimates for the amount of CO2 that are required for making biodiesel from algae are approximately 0.02 +/- 0.004 tons of CO2 per gallon of biodiesel (tCO2/gal). For example, NREL reports an example that 60 billion gallons (Bgal) of biodiesel would require 900 – 1,400 MtCO2. This quantity of CO2 is 36%-56% of total US power plant emissions.

So to get a maximum limit of how much biodiesel could be produced per year under the carbon restriction of the ACES Act, we can assume that all CO2 emissions come from transportation only. The figure below plots a simplified trajectory of US CO2 emissions (left axis) under the ACES Act, along with emissions from the electricity and transportation sectors. On the right axis, I’ve plotted the amount of biodiesel from algae that can be produced assuming that 100% of power plant emissions are captured and used for growing algae to make biodiesel (clearly an over estimate). This inherently assumes that (1) there will be absolutely no net CO2 emissions from any other industrial process, industry, or combustion of any hydrocarbon aside from burning the biodiesel in vehicles and (2) that no technology will feasibly exist for re-capturing the CO2 from combustion of biodiesel in the vehicle itself.

AlgebraOfAlgae_image.jpg
AlgebraOfAlgae_image.jpg

The plot shows that in 2050 50 Bgal/yr of biodiesel from algae would be the maximum amount allowed. Compare this to the 2008 US consumption of approximately 138 Bgal of gasoline and 61 Bgal of diesel. About half of the diesel was for freight trucks. Therefore, in 40 years, for the US to meet the ACES Act carbon reductions, we could produce 50 Bgal of biodiesel from algae, with 1,000 MtCO2 coming from fossil fueled power plants (assumed) if and only if no other fuel or economic sector had a net emission of CO2. Thus, if the CO2 supplied for algae came from coal power plants, then we would essentially be producing electricity from coal with CO2 capture, but not geologic or other storage systems, in the quantity of approximately 1,000 TWh or 50% of today’s coal powered generation. This does not mean that additional coal or natural gas power plants could not operate, but each would have to capture and sequester 100% of the CO2 emissions – a practical impossibility, but a sufficient assumption for this back-of-the-envelope analysis.

So what are some implications or conclusions from this quick analysis?

To drive as many miles as we do today (2.7 trillion/yr by cars and light trucks only) on 25%of current liquid fuels consumption, we need our transportation sector to be 400% more “liquid fuel” efficient in the range of 80 MPG of biodiesel to leave 16 Bgal for freight (about half the fuel for today’s freight)

This is not entirely difficult to imagine for light duty vehicles that currently have a fleetwide average of approximately 21 MPG. By creating plug-in hybrids and making cars lighter, the capability of meeting this fuel economy has been demonstrated. Imagining the implications for freight trucks may be more difficult, as they would still have to get over twice as efficient as today, and increasing freight travel by rail could help get goods around the country with less fuel. There are other possibilities, but knowing what we have to work for in terms of a carbon balance can prevent a “algae to biodiesel” bubble while still moving us to a lower-carbon future.

Posted in Energy the nexus of everything | Tagged , , | 3 Comments | Permalink
View all posts by this author  | View this author's profile

More Water-Energy Nexus: Biofuels Dominate US Water for Transportation

A recent paper from the University of Minnesota, by Sangwon Suh and others, estimates the change in embodied water in corn ethanol from 2005 to 2008 (see: Water Embodied in Bioethanol in the United States; http://pubs.acs.org/doi/abs/10.1021/es8031067?prevSearch=water+ethanol+suh&searchHistoryKey).

This paper indicates that the state with the highest quantity of embodied water per corn ethanol is California – strangely higher than Arizona and New Mexico, both of which are estimated to be both growing corn and producing ethanol from it. The range of consumptive water embodied in corn ethanol is 5 to 2,140 liters H2O per liter ethanol. The high end of the range translates to a higher value as compared to my previous study on the water intensity of transportation, likely due to a different assumption regarding how much irrigation water is consumed. Suh assumes that all withdrawn irrigation water is consumed, whereas I used United States Geological Survey data for estimating consumption by subtracting how much withdrawn irrigation water is returned to the source.

The difference in the methods of Suh and myself are not that important, and Suh does us a favor by tracking the changes from 2005 to 2008. During this time period he estimates that the embodied water in corn ethanol has increased 46% and the total consumptive water use has increased by 68%. This implies that more marginal lands, with worse climates for corn agriculture, and being used to grow corn, for food or fuel. This tendency is of course the fear of many that we will be using irrigated agriculture for biofuels on marginal lands even though many are assuming annual crops or perennial grasses on these lands will not be irrigated. In many regions, such as over the Ogallala Aquifer, industrial agriculture has already been overexploiting groundwater resources. It is important to know that the vast majority of the water embodied in corn ethanol is from farming, and thus it is farming corn in general that impacts the water resources, and not necessarily the push for corn ethanol. The Renewable Fuels Standard simply creates another marker for corn, and exacerbates the situation.

Recent work we’ve done at the University of Texas at Austin‘s Center for International Energy and Environmental Policy together with members of the Bureau of Economic Geology shows that in 2005 the water embodied in light duty vehicle transportation fuels in the US accounted for approximately 2.5% of the total water consumption. By 2030, we estimate this could be up to 10%, mainly due to increasing ties in the nexus of energy and water in the form of biofuels. This consumption of nearly 14,000 billion liters holds for a vastly different diversity in the number of miles driven on different fuels from 23% – 71% based upon petroleum – quite a spread! So we have many ways to use our water resources for creating new fuels for transportation … or food, but that’s another story.

Posted in Energy the nexus of everything | Tagged , , | 2 Comments | Permalink
View all posts by this author  | View this author's profile

Water and Transportation Nexus: US Domestic Water for Imported Oil?

Energy and water are inextricably linked. If we consider food as energy, which we should since it is the substance that powers our bodies, then the energy-water nexus is perhaps the most important in the agricultural sector. When we use agriculture to grow crops for biomass that is later converted to liquid fuels, then the energy-water nexus is even more apparent. I calculated how much water is used for driving light duty vehicles (cars, vans, light trucks and sport utility vehicles) and published the results in Environmental Science and Technology (10.1021/es800367m). Results are also summarized in a commentary in Nature Geoscience volume 1.

The results vary from 0.1-0.4 gallons of water per mile (0.2 – 1 L H2O/km) for petroleum gasoline and diesel, non-irrigated corn for E85 vehicles, and non-irrigated soy for biodiesel. Additionally, driving on electricity from the US grid consumes near 0.2-0.3 gallons of water per mile (0.5 – 0.7 L H2O/km). The reason is that water is used to cool off the coal, natural gas, and nuclear power plants on the grid. However, if irrigated corn is used to make E85 ethanol in the United States, then the water consumption jumps by one to two orders of magnitude to 10-110 gallons of water per mile (23-260 L H2O/km), with an average of 28 gallons of water per mile driven. Keep in mind that only about 15-20% of corn bushes are irrigated to any extend in the US.

This information is only an introduction to the energy-water nexus, but the US government is looking at it more closely recently due to research showing how constraints on one side can create problems for the other. This is typified by potential legislation proposed by Senator Bingaman: The Energy and Water Integration Act of 2009. This bill use similar language as in my Env. Sci. and Tech. paper in measuring the life cycle impact of water for transportation in terms of water consumed per distance traveled. Hopefully, research, industry, and government efforts can minimize impacts on water resources and use them wisely for our energy future.

The concept of using water resources sustainably, especially for growing biomass for liquid fuels, makes one wonder about water embodied in imports and exports in general. Is it better for the US to import biofuels from Brazil that are grown from sugar cane that might not stress water resources as much as corn agriculture does in the US? The US has a tariff on imported ethanol, but not imported oil. If the US has an energy policy goal of reducing imports from the Middle East, then it seems like the tariffs would be switched since the US has friendly relations with the Brazilians. So it seems the current US energy policy is to literally trade domestic water for foreign oil. I guess it could be worse.

Posted in Energy the nexus of everything | Tagged , , , , | Leave a comment | Permalink
View all posts by this author  | View this author's profile