Bioenergy crops in the desert??

There is some concern that bioenergy crops are more trouble than they're worth. They may produce a lot of biomass, but doesn't that come at a cost of lots of added fertilizer and water? Are fertile, midwestern climates the only suitable locations for growing crops, for food or fuel? For some plants, that may be true. But different plants are well-adapted to arid & semi-arid landscapes.

One group of plants with a fairly long history of cultivation includes various Agave species. Agave plants are succulents with a special type of photosynthesis (a process plants use to convert sunlight into energy) called CAM (Crassulacean acid metabolism) that increases water-use efficiency relative to most other plants. Traditionally, Agave varieties have many different uses: they have been used for production of fibers like sisal, for honey/sugar substitutes (agave nectar), and the flowers and stalks are edible. The most well-known use for agave is the fermentation & distillation of the sap to make mezcal, one type of which is tequila.

In addition to these uses, the leaves are also good sources of biomass that can be used as feedstock for conversion into biofuels. Although Agave farms may not produce as much biomass (in terms of tons per hectare) as Miscanthus or Sugarcane (see table below), Agave plants can be productive with as little as 12% of the water needed by these large grasses.

Table: Estimated productivity, rainfall, and nitrogen requirements of current or potential bioenergy crops (see article by Somerville et al. 2010. Science 329:790-792 for references).

Crop	Average productivity (MT ha–1 year–1)	Ethanol yield (liter ha–1)	Seasonal water requirements (cm year–1)	Tolerance to drought	Nitrogen requirements (kg ha–1 year–1)
Corn		3800 (total)	50–80	low	90–120
Grain	7	2900
Stover	3	900
Sugarcane	80 (wet)	9950 (total)	150–250	moderate	0–100
Sugar	11	6900
Bagasse	10	3000
Miscanthus	15–40	4600–12,400	75–120	low	0–15
Poplar	5–11	1500–3400	70–105	moderate	0–50
Agave spp.	10–34	3000–10,500	30–80	high	0–12

There is a lot of interest in producing energy sustainably in this country. Water is a particularly valuable resource, particularly in the western U.S. Using excessive irrigation or groundwater to grow crops in arid regions is not a responsible use of this resource. However, many plants, such as Agave, are naturally adapted to climates that experience little and/or erratic rainfall. By planting and harvesting climatically-appropriate energy crops, even the more extreme regions of this diverse country could become good producers of bioenergy.

Re: funding innovation

I recently attended the Philomathia Foundation Symposium at Berkeley on "Pathways to a Sustainable Energy Future," which had a number of amazing speakers. I was particularly impressed with Arun Majumdar, the director of ARPA-E (Advanced Research Projects Agency-Energy, sponsored by the Dept. of Energy. ARPA-E's mission is explicitly bold: to fund potentially revolutionary technologies that are too risky for industry to fund. Another mission is to re-assert the United States' technological leadership.

I naively assumed that the U.S. is already at the top of their game technologically, but Majumdar pointed out that the majority of the leading "green" energy companies (solar companies, electric car manufacturers, advanced rechargeable battery manufacturers) are foreign. This may be because, as Manumdar says, "The U.S. spends more on potato chips than on Energy R&D." It seems we are addicted to what is bad for us (see previous post on oil addiction). I agree that we should rediscover some national pride in ingenuity and technology and re-assert our technological leadership. Promising research results can have a high impact commercially, ideally in the form of smart, socially and environmentally responsible capitalism (a source for another blog post: the academic-industry partnership).

Even though it is probably not enough, I am really excited by the government's commitment to fund these "big ideas." Although it's considered risky, I think we live too much in a society that is scared to take risks, scared to innovate, because of the chance of failure. Sure, most of these ventures won't pan out, but even if just a single innovative, pie-in-the-sky idea works, it could make today's technology obsolete.

Coping with the "blend wall"

Part of the problem with biofuels gaining any momentum in our current car-driven, fossil fuel based economy is that our engines are built to run on gasoline..which can be blended with 10% ethanol. If the U.S. uses ~140 billion gallons of gasoline a year, then the demand for ethanol is about 14 billion gallons annually. Apparently we already produce about 12 billion gallons of corn ethanol per year (with even more capacity in idled biorefineries)...so we have basically reached what is referred to as the "blend wall," with no market for cellulosic ethanol.

How to cope with this dilemma?

One option would be to replace all corn-based ethanol plants with cellulosic biofuel pruduction plants, which would be an expensive, short-term fix, essentially tearing down something fully functional. And the "blend wall" problem would remain, with a maximum market of 14 billion gallons.

Another option is to increase the required amount of ethanol in blended fuels to 12% or 15%, something the EPA is considering. This is the most likely scenario, as it's technically and politically safest. But truthfully, this option will not do a whole lot to encourage use of biofuels in the long-term. I think of this option as a baby step, not covering much ground, but better than nothing.

A third, bolder option would be to make the leap to flex-fuel car engines, such as those that run on E85 ethanol (a fuel blend of 85% ethanol & 15% gasoline). Most of the cars in Brazil are built to run using some level of blended fuel, up to 100% ethanol. Since Brazil generates all of their own ethanol from sugarcane refineries, they have attractively achieved energy security (a topic for a future blog). Estimates of the cost of producing all future car engines to be flex-fuel lays around $100/car. If the average cost per new car in 2009 sold in the U.S. (according to the National Automobile Dealers Association) is $28,400, this minor change would amount to less than 1% of the value of the car. Although flex fuel contains its own controversies, it seems like a bold alternative way forward that would encourage both greater energy security and economic stability for the cellulosic biofuels market.

Power density--why oil tastes so good..

As Americans, we are addicted to things that are bad for us. French fries, hot dogs, chips, sodas & cookies. All these foods contain loads of sugar & fat--essentially rich sources of energy for our bodies. The trouble is, we really don't need these rich sources of energy or "nutrients" in excess. One cheeseburger probably takes care of all of our daily caloric needs.

Same is true for oil. It is densely packed with energy. Nothing (other than coal and other petroleum products) comes even close to oil in terms of power density (the amount of energy produced per square meter of Earth's surface). Solar and wind facilities provide 1-2 orders of magnitude less power per square meter than oil, and biomass plants (based on corn ethanol) are even less dense...providing 1% (or less) of the energy per area compared to oil--see figure below from article in Science 329:780 (2010).

Source of data in figure: upper left and bottom--DOE; upper right--V. Smil, Energy Transitions, Praeger (2010)

Yikes! That's sobering news & tough to compete with. To soften the blow somewhat, it is worth pointing out that the full cost of energy should also include the cost of extraction, transport, storage, AND environmental risks (including CO2 output)...which is where renewables have the potential to come out ahead.

Can we learn anything from our unhealthy food addiction that can be applied to our unhealthy oil addiction? A good start is educating people on the scope of the problem, benefits & disadvantages to different forms of energy. But the truth is, most people do not want to change their lifestyles. An oft cited poll by The New York Times/CBS News (released 20 June 2010) found that although 90% of respondents agreed that "U.S. energy policy either needs fundamental changes or to be completely rebuilt," only 49% supported new taxes on gasoline to fund new and renewable energy. Seems to me that we should stop subsidizing oil and instead subsidize renewables, AND impose Greenhouse Gas taxes (on energy companies!!) that penalize for catastrophic environmental risks (such as drilling for oil) and emitting CO2 at any phase of the production. That might help level the playing field.