Michael E. Salassi, Kayla L. Brown, Michael A. Deliberto and Kenneth A. Gravois

Renewable energy research and development are expanding in size and scope across the United States as the focus has shifted from the relatively simple process of producing ethanol from grain to producing a variety of biofuels through advanced cellulosic processes. The Renewable Fuels Standard, passed by Congress as part of the Energy Independence and Security Act of 2007, establishes biofuel production target levels for the coming years, and much of the growth in production is projected to be in cellulosic biofuel.

Cellulosic biofuel is produced from lignocellulose, a structural material that comprises much of the mass of plants. The advantage of this type of biofuel production is that a wide variety of plants can be used as feedstocks. Much of the production and economic research being conducted in this area is seeking to identify crops that can produce high levels of plant material per acre at an economically feasible production cost to be used as a viable feedstock for biofuel production.

Louisiana has the potential to play a major role in the development and production of cellulosic biofuel. One of the leading crops being considered as a feedstock is energy cane. Energy cane is similar to sugarcane – but with major differences. Energy cane has a lower sucrose content and higher fiber content than sugarcane varieties grown in the state, and most importantly, it has higher expected yields in terms of tons of plant material per acre.

Initial results from research conducted by the LSU AgCenter show the potential for energy cane production in Louisiana, expected crop yields and projected variable production costs.

Renewable energy

Renewable energy sources can be defined as those sources of energy that are naturally replenishing and flow-limited. This means that renewable energy sources are virtually inexhaustible over a long time period but are limited in the amount of energy available at any one time. Sources of renew able energy that have been used for decades include solar, hydroelectric, geothermal and wind. In 2011, renewable energy accounted for approximately 12 percent of total U.S. domestic energy production.

Bioenergy technologies use renewable biomass feedstocks to produce an array of energy-related products, including electricity; liquid, solid and gaseous fuels; heat; chemicals, and other materials. Bioenergy is the leading source of renewable U.S. energy production and accounts for 48 percent of total renewable energy production and 5 percent of total U.S. energy production. The term “biomass” generally refers to any organic, non-fossil material of biological origin constituting a renewable energy source, including dedicated energy crops, other agricultural crops, agricultural crop wastes and residues, wood wastes and residues, aquatic plants, animal wastes, and municipal and other wastes.

Energy cane yields

The LSU AgCenter has recently begun evaluating varieties of energy cane as part of several research projects to identify the feasibility of using energy cane as a biofuel feedstock. Production research is evaluating the yield potential (tons of plant material per acre) and stubbling ability (years of harvest) of energy cane. Economic research is evaluating the projected cost to a grower of producing energy cane.

Yield estimates of energy cane varieties for the first three years of harvest (plant cane, first stubble and second stubble) conducted by the LSU AgCenter at the Sugar Research Station in St. Gabriel from 2009 to 2011 are shown in Figure 1. These energy cane varieties were developed by the U.S. Department of Agriculture-Agricultural Research Service Sugarcane Research Unit in Houma, La., and are being evaluated by the AgCenter as part of a multistate Sun Grant Project. Plant cane yields ranged from 25.5 to 44.2 tons per acre at a field harvest weight (wet tons). First-stubble yields were similar, ranging from 24.4 to 47.0 tons per acre. Second-stubble yields, however, were higher, ranging from 50.7 to 72.4 tons per acre.

Because energy cane varieties are known to have longer stubbling ability than traditional sugarcane varieties, energy cane yields are expected to increase over time to some maximum level and then decline for a period of years. Current research continues to evaluate the yield potential and stubbling longevity of alternative energy cane varieties.

Energy cane production costs

To estimate the cost of using energy cane as a biofuel feedstock, yields beyond second stubble were projected under alternative stubbling assumptions. Production costs were estimated for the various planting, cultivation and harvest operations required, and then feedstock costs were estimated on a dry ton basis. Cellulosic processes produce biofuel by first drying feedstock to low moisture levels and then using a chemical process to convert the dry biomass to biofuels.

Energy cane yields through second stubble were used to project yields through fourth-, fifth- and sixth-stubble crops based on a yield-decline pattern similar to sugarcane but applied later in the crop cycle. Fiber content from energy cane trials, ranging from 17.8 to 28.7 percent, was used to convert yields to dry-matter content. An approximation of dry matter content (dry matter yield) can be obtained by multiplying the weight of field harvest yields by the percent dry matter content. Variable production costs per dry ton of plant material, excluding charges for land and equipment, were estimated to be in the range of $52 to $67 per dry ton and are shown in Figure 2. These production cost estimates, with additional charges for land and equipment, will form the basis of future biofuel feedstock prices paid to crop producers.

Other research projects in the AgCenter are focusing on reducing the conversion rates of dry matter feedstock to units of alternative biofuels. The production of advanced biofuels from agricultural crops offers tremendous potential for Louisiana, both in the agricultural production sector as well as the biofuel energy production sector.

Michael E. Salassi is the Fairbanks Endowed Professor, Kayla L. Brown is a graduate research assistant, and Michael A. Deliberto is a research associate in the Department of Agricultural Economics & Agribusiness. Kenneth A. Gravois is the Graugnard Professor at the Sugar Research Station, St. Gabriel.

(This article was published in the winter 2013 issue of Louisiana Agriculture magazine.)