Energy Economics
Applied Optimization

Humpty Dumpty and “Renewable Fuels”

“When I use a word,” Humpty Dumpty said, in a rather scornful tone, “it means just what I choose it to mean – neither more nor less.”


        — “Alice in Wonderland,” Louis Carroll


Some of HD’s most skilled disciples work in public policy.  In their efforts to apply to the making of public policy his powerful insight on the uses of language, HD’s disciples sometimes create misrepresentations of fact.  One of these misrepresentations is that “renewable fuels” exist, are potentially abundant, and are “green” (i.e., low-carbon) alternatives to gasoline and diesel fuel.  


These popular misconceptions are the basis for the Renewable Fuel Standard (RFS) of the Energy Independence and Security Act of 2007 (EISA).  The RFS requires that U.S. transportation fuels contain annually increasing volumes – reaching 36 billion gallons per year (bgy) by 2022 – of “renewable fuels”.  Most of the bio-fuel now being produced in the effort to meet this mandate is ethanol – mainly corn ethanol, augmented by some bio-diesel.  Perhaps in the future, some cellulosic ethanol will be produced as well.      


EISA defines renewable fuel as “fuel . . .produced from renewable biomass [italics added] and . . . used . . . in a transportation fuel.”  Unfortunately, EISA doesn’t say what renewable biomass is.  For a definition, one must look elsewhere.        


According to the U.S. Energy Information Administration, renewable biomass is one of many renewable energy resources.  These are defined as “. . . energy resources that are naturally replenishing [italics added] but flow-limited [italics added]. . . virtually inexhaustible in duration but limited in the amount of energy available per unit of time.  Renewable energy resources include biomass, hydro, geothermal, solar, wind, ocean thermal, wave action, and tidal action.”   In other words, renewable energy resources are essentially inexhaustible but capable of producing energy at only low rates per unit of land area.


Biomass is plant material, vegetation, or agricultural waste used as a fuel or as a feedstock in the production of a fuel.  Hence: renewable biomass is biomass produced in a manner such that is naturally replenishing, and hence flow limited.       


Biomass is fundamentally different from the other renewable energy resources (e.g., solar, wind, etc.) in that biomass is naturally replenishing only under certain circumstances.


Biomass is naturally replenishing – therefore “renewable” – only if it is produced entirely through natural processes and not through on-purpose cultivation (i.e., farming).   


Biomass produced through natural processes includes materials such as manure, wood slash and brush (used as domestic fuels in developing countries), and non-food plants (such as trees and switchgrass) that grow on uncultivated land.  


Biomass is not naturally replenishing if it is produced on purpose, as through the industrial agriculture that is practiced in the U.S. and elsewhere.  


Biomass that is produced on-purpose by industrial agriculture – corn, for example – is not renewable.    


On-purpose production of biomass requires the consumption of non-renewable resources – mainly fossil fuels (for fertilizer, pesticides, and fuel) and fertile soil (lost through erosion and exhaustion).  These non-renewable resources are indispensable to on-purpose biomass cultivation.  They relax the flow limitation – that is, the limited production potential per unit of land – inherent in all naturally replenishing processes. The non-renewable resources thereby permit achievement of economically useful yields of biomass per unit of land dedicated to its production (e.g., bushels of corn/acre).  Without these non-renewable resources, farmers would have no economic incentive to produce either corn or ethanol derived from corn.


Conversion of biomass to bio-fuel (e.g., corn to corn ethanol) and transportation of bio-fuel to the end user consume still more fossil fuels.  Whether or not the bio-fuel has positive net energy (i.e., yields more energy when consumed than the energy required to produce it) is immaterial to the question of what is a renewable resource.  Biomass whose production requires consumption of non-renewable resources is not renewable.  This applies not only to corn ethanol but also to sugar cane ethanol and to cellulosic ethanol.  


Truly renewable fuels that can be produced in volumes of public policy interest or even commercial interest do not exist, certainly not in the U.S.  Bio-fuels that are truly renewable (naturally replenishing) cannot be produced in large volumes because all natural processes for producing biomass are severely flow-limited.  For example, corn grown naturally, without cultivation, yields » 10 bushels/acre.  By contrast, corn grown by means of industrial agriculture, yields » 150 bushels acre – but through the consumption of non-renewable resources required to overcome the flow limitation of natural processes.  


None of this is a commentary on whether or not the Renewable Fuel Standard, and the consequent introduction of large volumes of ethanol into the U.S. gasoline pool, is good public policy.  On that, time and facts will tell.  However, one wonders whether Congress would ever have enacted the Renewable Fuel Standard if its members had understood that – whatever their other benefits may be — the bio-fuels whose production they were mandating are fact not renewable.