Jatropha curcas is a non-edible plant that grows in arid regions. The oil produced from its seed can be used as a biofuel that can be mixed with petroleum diesel. Already it’s been used twice this year in combination with algae to fuel test flights of commercial airlines.
While corn-based ethanol seems a lost cause propped up by government support, many think there is potential for jatropha to provide a viable source of fuel. Because the plant can grow in deserts or otherwise infertile land, it doesn’t contribute to a rise in food prices, the way corn ethanol has been accused of doing. Like many alternative sources of energy, though, it’s yet to be tested on large-scale basis. R-Squared Energy digs into whether or not jatropha could provide a renewable fuel solution:
R-Squared: Consider the potential for displacing 10% of the world’s distillate demand of 1.1 billion tons per year with jatropha oil. To replace 10% of the world’s distillate demand will require 110 million tons of distillate to be replaced. Jatropha, with about 10% less energy than petroleum distillates, will require 122 million tons on a gross replacement basis (i.e., not considering energy inputs). On marginal, non-irrigated land the yields will likely be at the bottom of the range of observed yields. At a yield of 0.146 tons per hectare (the lower range of yields), this would require 836 million hectares, which is greater than the 700 million hectares currently occupied by permanent crops.
An estimated 2 billion hectares of land is considered to be degraded and perhaps suitable for jatropha cultivation (Oldeman et al. 1991). There are also an estimated 1.66 billion hectares in Africa that are deemed suitable for jatropha production (Parsons 2005). This could provide a valuable cash crop for African farmers. But, until an estimate is made of the energy inputs required to process and distribute the jatropha-derived fuel on a widespread basis – especially on marginal land – the real potential for adding to the world’s net distillate supply is unknown. Jatropha seed yields can vary over a very large range – from 0.5 tons per hectare under arid conditions to 12 tons per hectare under optimum conditions (Francis et al. 2005). However, if marginal land is to be used, then yields in the lower range will probably by typical. Makkar et al. determined that the kernel represents 61.3% of the seed weight, and that the lipid concentration represented 53.0% of the kernel weight (Makkar et al. 1997). Therefore, one might conservatively estimate that the average oil yield per hectare of jatropha on marginal, non-irrigated land may be 0.5 tons times 61.3% times 53.0%, or 0.162 tons of oil per hectare. Jatropha oil contains about 90% of the energy density of petroleum diesel, so the energy equivalent yield is reduced by an additional 10% to 0.146 tons per hectare. While this is substantially less than the oil production of soybeans, rapeseed, or palm oil, the potential for production on marginal land may give jatropha a distinct advantage over the higher-producing oil crops.
…Jatropha has one significant downside. Jatropha seeds and leaves are toxic to humans and livestock. This led the Australian government to ban the plant in 2006. It was declared an invasive species, and ‘too risky for Western Australian agriculture and the environment here’ (DAFWA 2006).
While jatropha has intriguing potential, a number of research challenges remain. Because of the toxicity issues, the potential for detoxification should be studied (Heller 1996). Furthermore, a systematic study of the factors influencing oil yields should be undertaken, because higher yields are probably needed before jatropha can contribute significantly to world distillate supplies (see Calculation 1). Finally, it may be worthwhile to study the potential for jatropha varieties that thrive in more temperate climates, as jatropha is presently limited to tropical climates.