Tad Patzek's Home Page, GeoEngineering, Civil and Environmental Engineering, UC Berkeley
Can We Outlive Our Way of Life? Redwood City [2007 August 9]
The Disastrous Local and Global Impacts of Tropical Biofuel Production By Lucas J. Patzek and Tad W. Patzek in Energy Tribune, page 19-22 [2007 March]
"... the continuing push into the tropics by ... biofuel producers will only accelerate a potential ecological catastrophe. Vast tracts of Malaysian and Indonesian forest have already been lost, and the increasing demand for palm oil for biodiesel will cause further losses of tropical forests in these and other equatorial countries.
This deforestation will likely be devastating. And yet, despite the global push for biofuels, the potential damage – increased soil erosion, huge carbon dioxide emissions, biodiversity loss, and desertification – is largely being ignored.
Green Plants, Fossil Fuels, and Now Biofuels, by David Pimentel and Tad Patzek [2006 November]
"For 700 million years, green plants contributed to the formation of soil, oil, natural gas, and coal. As the human population increases, so too does the consumption of soil and fossil energy. If this trend continues unabated, humans will consume most of these precious resources within the next few hundred years."
The Biofuel Myths and Truths [2006 September 28]
Real Biofuel Cycles [2006 March]
- "The astronomic scale of energy consumption from fossil plants and the minute scale of energy production from new plants are fundamentally incompatible
- In engineered crop systems, we continuously apply fossil fuels and nutrients to replenish soil
- What Earth has produced over 400 million years cannot be produced in annual cycles
- If we ever attempt to do so, we will destroy the planet and ourselves
- The initial stage of planetary destruction is well under way
- We must pull back and use fewer resources"
"This paper analyzes energy efficiency of ... corn ethanol .. and switchgrass-cellulosic ethanol... From thermodynamics it also follows that ecological damage wrought by industrial biofuel production must be severe...
Thermodynamics of Corn Ethanol [2006 February 24]
"The energy efficiency of current cellulosic ethanol production is poorer than that of any other industrially produced liquid biofuel...
"Remark 5 ...The US has already squandered a lot of time, money and natural resources on pursuing the mirage of an energy supply scheme that CANNOT replace fossil fuels in aggregate... Instead, we should decrease consumption of these fossil fuels, increase the efficiency of our economy, while producing some biofuels for local consumption."
"In this paper I define sustainability, sustainable cyclic processes, and quantify the degree of non-renewability of a major biofuel: ethanol produced from industrially-grown corn.
Thermodynamics of Energy Production from Biomass with David Pimentel, in Critical Reviews in Plant Sciences, 24(5-6), 327-364, 2005 [2006 January 27]
"First, I demonstrate that more fossil energy is used to produce ethanol from corn than the ethanol’s calorific value. Analysis of the carbon cycle shows that all leftovers from ethanol production must be returned back to the fields to limit the irreversible mining of soil humus. Thus, production of ethanol from whole plants is unsustainable. In 2004, ethanol production from corn will generate 11 million tonnes of incremental CO2, over and above the amount of CO2 generated by burning gasoline with 115% of the calorific value of this ethanol.
"Second, I calculate the cumulative exergy (available free energy) consumed in corn farming and ethanol production, and estimate the minimum amount of work necessary to restore the key non-renewable resources consumed by the industrial corn-ethanol cycle. This amount of work is compared with the maximum useful work obtained from the industrial corn-ethanol cycle. It appears that if the corn ethanol exergy is used to power a car engine, the minimum restoration work is about 7 times the maximum useful work from the cycle. This ratio drops down to 2.4, if an ideal (but nonexistent) fuel cell is used to process the ethanol.
"Third, I estimate the U.S. taxpayer subsidies of the industrial corn-ethanol cycle at $3.3 billion in 2004. The parallel subsidies by the environment are estimated at $1.9 billion in 2004. The latter estimate will increase manifold when the restoration costs of aquifers, streams and rivers, and the Gulf of Mexico are also included.
"Finally, I estimate that (per year and unit area) the inefficient solar cells produce 100 times more electricity than corn ethanol. We need to rely more on sunlight, the only source of renewable energy on the earth."
Summary & Conclusions
Gigantic tree plantations could be designed to replace, say, 10% of the fossil energy used globally every year for 40-80 years. About 500 million hectares (a little more that 1/2 of the United States area) of new plantations would be needed. These plantations would be implemented in the tropics in good climate with plentiful water supply, apparently good soil, and easy access, i.e., along the ever-receding edges of natural tropical forests and along major rivers. Talk about developing industrial tree plantations for profit in degraded and sterile environments does not seem practical or convincing. Therefore, the new biomass-for-energy plantations will impact disproportionately many of the most important ecosystems on land and in shallow sea water. Will the global damage of tropical forest and clean water sources be beneficial in terms of saving other earth resources? The answer based on the work presented in this paper is a decisive no. In order to be profitable, a biomass-for-energy plantation must achieve a consistently high yield of dry wood mass. Trees that grow fast (e.g., Acacia mangium) use more water and nutrients than the slower-growing species. Consequently, these fast-growing trees damage soil and their wood is excessively wet after harvest.
We find that sustainable generation of electricity and/or Fischer-Tropsch (FT) diesel fuel from wood pellets produced in remote tropical plantations is impossible, unless sun-drying of raw wood and improved soil management are widely implemented. In our opinion, the scale and rate of wood processing necessary to replace a substantial fraction of automotive fuel and electricity demand on the earth makes the widespread sun-drying of wood impractical or impossible. The gigantic tropical sugarcane plantations on mostly agricultural land suffer from the similar weaknesses. Their shaft work output from burning cane-ethanol in the efficient internal combustion engines is insufficient to cover the cumulative free energy consumption in producing this ethanol.
The only option that gives a marginal benefit is the conversion of the sugarcane ethanol to hydrogen used in 60%-efficient fuel cells to produce electricity (Deluga et al., 2004), but such cells do not exist, see Appendix A.
In particular, for the tree plantations, we reiterate the following:
- Biomass-for-energy plantations are environmentally costly and inefficient engineered systems, and their long-term high yields are uncertain and questionable.
- Locally-produced electricity from biomass seems to be the best option that could make a prolific acacia and sugarcane plantation “sustainable,” if their immediate environments were not degraded by the toxic ash and air emissions.
- The Fischer-Tropsch automotive fuel from biomass is not as good an option, and the plantations producing it are not sustainable.
- Ethanol from tree biomass seems to be an especially poor choice.
- The anhydrous ethanol automotive fuel from sugarcane stems is a better option, yet it is unsustainable too, even when burned in efficient hybrid cars.
- Plant residues, called “trash” by those who do not understand their vital importance to the long-term survival of plantation soils, should be kept on the plantations and allowed to decompose.
- Plant “trash” cannot be a significant source of biofuels, and it is not independent of parent ecosystems.
- The most desirable product of dedicated industrial tree-for-energy plantations may be wood pellets produced in very efficient central facilities close to the plantations. Production of these pellets requires 33-41% of the high heating value of the wood.
- Excellent site characterization by Mackensen et al. (1999; 2000; 2003), enabled us to use two average stands of acacias and eucalypts in a freshly established, prolific plantation in Indonesia as the examples of generic industrial tree plantations in the tropics.
- Our example acacia and eucalypt stands were the first tree rotations, and received small fertilizer treatments of 100 kg NPK/ha. The plantation trees were mostly depleting the initial store of nutrients in the plantation soil, i.e., the environmental low entropy (Georgescu-Roegen, 1971; Patzek, 2004).
- We have calculated the minimum restoration work of nonrenewable natural resources depleted by the example tree stands, and compared it with the maximum useful work obtained from the plantation wood pellets as (a) electricity generated in an efficient power station, (b) the FT diesel fuel burned in a 35%-efficient car plus cogeneration electricity, and (c) wood-ethanol burned in a similarly efficient car.
- If this useful work is larger than the minimum restoration work, the example stands are “sustainable” under our assumptions, otherwise they are not.
- To calculate the long-term restoration work, we have assumed fertilizer treatments equal to the amounts of soil nutrients (N, P, K, Ca, and Mg) depleted during a single tree rotation and site preparation that follows each harvest.
- We have assumed that fertilizer application efficiency is 100%, i.e., 30-90% of the various nutrients are provided by natural (management-independent) fluxes.
- We have neglected the cumulative exergy consumption in sea transport of wood pellets and their storage costs.
- Under the conservative assumptions in this paper, it is possible to show that even an exceptionally prolific stand of Acacia mangium (22 odt/ha-yr), see Figure 5, is not “sustainable” with respect to Options (a) and (b) above, unless the cumulative exergy consumption in wood drying and chipping is cut in half. In view of Item 1 above this cannot be done, unless sundrying of raw wood is employed, which in turn may be impossible when wood is processed at a very high rate.
- Conversion of acacia wood pellets to ethanol that powers the same efficient car, Option (c), is never sustainable.
- The example stand of Eucalyptus deglupta is not “sustainable” with respect to Options (a)- (c), with or without sun-drying of wood, because its net productivity is only 5 odt/ha-yr, close to the average productivity of tropical forests, see Figure 5.
- After several tree rotations, the progressively damaged soil may not support the consistently high biomass yields from the two tree stands.
- In the long run, therefore, increased fertilizer, herbicide, and insecticide treatments are inevitable, and their inherent high exergy costs and negative environmental impacts will increase the degree of unsustainability of these two stands.
- Plantation management and average biomass yield are highly site-specific, and it is diffcult to make sweeping generalizations from an analysis of the two example tree stands.
For the sugarcane plantations we conclude that
- An average sugarcane plantation in Brazil is as efficient in sequestering solar energy as the prolific acacia plantation (all acacia slash must be left on the plantation to decompose, but only some sugarcane slash is left), and its maintenance costs a little more free energy than that of the acacias.
- Ethanol production from sugarcane is driven by burning the cane leftovers, bagasse and parts of attached cane tops, and converting their heat of combustion to steam, electricity and shaft work. Sugarcane stem crushing, juice extraction and fermentation, and ethanol distillation consume almost exactly the same free energy as wood pellets from the acacia stems and bark.
- We have calculated the free energy consumed to clean the sugarcane distillery wastewater; it is non-negligible, and requires extra fossil fuel and grid electricity.
- Despite efficient sequestration of solar energy, the prolific sugarcane-for-ethanol plantation in Brazil is not sustainable according to our strict criteria, unless its ethanol powers 60%-efficient fuel cells. The problem is that such cells do not exist, see Appendix A.
- The sugarcane slash and attached tops sequester a significant amount of solar energy, and deplete significant amounts of nutrients from the soil. The attached tops and leaves are burned in the distillery. The detached leaves and slash should be left to decompose and improve structure of the plantation soil.