It just so happens that a few days after that NPR report on jatropha came out, Energy for Sustainable Development (one of my favorite bioenergy-relevant journals) released an issue with not one, not two, but three articles on jatropha bioenergy. Here’s a quick run-down of the studies for those of you who might be curious:
- An analysis model for small-scale rural energy service pathways — Applied to Jatropha-based energy services in Sumbawa, Indonesia. This study examines the energetic and economic performance of jatropha-fuelled cooking, lighting, and mechanical power generation systems at a variety of scales from a lifecycle assessment perspective. The conclusions are generally unfavorable for household-scale systems due to high conversion costs and inefficiencies encountered and for commercial-scale systems due to logistical hurdles, though the study does identify village-scale mechanical-power projects as a potential goldilocks compromise with positive potential.
- Human energy requirements in Jatropha oil production for rural electrification in Tanzania. This paper highlights the fact that mechanized equipment for harvesting and de-hulling jatropha is still in development, and that the labor burden associated with the current practice of performing these operations by hand can be a fundamental limitation. The authors examine a decentralized electricity system in Tanzania and estimate that it takes a 220-meter length of jatropha hedgerow to produce 1 kg of jatropha oil, with 7.5 hours of labor required to harvest and de-hull that crop by hand. Combined with local jatropha seed market prices, the resulting income to the laborer is only $0.90/day (low even by most developing-country standards); thus the electricity produced in such a system would be generally unaffordable to those whose labors helped produce it.
- Jatropha curcas L. and multifunctional platforms for the development of rural sub-Saharan Africa. This paper gives a review of the jatropha bioenergy concept, highlighting the failure of large-scale liquid fuel production operations but emphasizing the potential viability of small-scale distributed energy systems. Interestingly, the authors posit that smaller-scale systems might also have better environmental performance, as the jatropha is more likely to be cultivated as hedgerows or on marginal lands as opposed to in large biodiversity-suppressing monocultures on prime lands that minimize yield risks for large commercial operations. However, they highlight land availability as a hurdle for such systems, estimating that at worst case a total of 8 hectares of land may be required to supply even a small mutilfunctional platform based around a 10 hp engine (though they acknowledge that estimates of yields and conversion efficiencies in the literature vary widely, and in the best-case scenario the land requirement drops to a fraction of a hectare).
All of the articles acknowledge that large-scale jatropha plantations have so far been a bust, and highlight the significant hurdles associated with a viable jatropha bioenergy operation. However, there is much work being done to improve system performance. After the previous past, we got a comment from a jatropha breeder based in Ghana, working to develop lines that maximize yields and pest resistance while minimizing toxicity (analogous to the development of oil palm from a wild plant into a commercial crop over the last several decades). Check out their blog highlighting these ongoing efforts here:
Finally, I have to round this post out with a plug for jatropha-based cooking systems as another example of down-scaling so-called ‘modern’ bioenergy technologies to fill ‘traditional’ bioenergy niches. Jatropha can potentially be leveraged as a clean-burning fuel for domestic cooking through one of two difference conversion technology pathways:
- the direct combustion of jatropha oil in plant-oil stoves (video), or
- the gasification of jatropha seeds (typically considered a waste biomass) in semi-gasifier cookstoves (video)
So despite the criticisms, research on jatropha bioenergy systems continues on multiple fronts. Like most other bioenergy systems, positive economic and environmental outcomes remain elusive, and will likely be dependent on careful system design coupled with continuing feedstock development. On the other hand, the prospect of clean, locally-produced renewable bioenergy as a tool for sustainable development is enticing enough to justify continued efforts.