EBI study concludes potential contribution of microalgae biofuels in US will be modest due to resource constraints and cost
Even with necessary advances in biology and process efficiencies, the resource potential of microalgae biofuels will always be modest mainly due to the lack of sites having all the needed resources, in particular available CO2, according to a new detailed assessment from the Energy Biosciences Institute (EBI) in Berkeley. However, the report concludes, over the long-run, algae oil could make a vital, even if modest, contribution to a US biofuels industry.
The study, “A Realistic Technology and Engineering Assessment of Algae Biofuel Production” is based on a detailed techno-economic analysis of five microalgae biofuel production scenarios based on technologies that currently exist or are expected to become available in the near-term, including raceway ponds for microalgae cultivation; bioflocculation for algae harvesting; and hexane for extraction of algae oil.
|“The main conclusion from this report is that oil production with microalgae will be expensive, even with relatively favorable process assumptions (e.g. low cost system designs, high productivity algae cultivation, high oil content, low cost harvesting and processing).”|
In all five cases, water and nutrients (N and P) are supplied by municipal wastewater, which also provides some of the carbon needed for algae growth. Additional CO2 is supplied by flue gas from a natural gas-fired power plant. The cases differ in three main ways: (1) primary process objective (either biofuel production or wastewater treatment); (2) biofuel outputs (either biogas only or biogas plus oil); and (3) farm size—growth ponds covering either 100 or 400 hectares (250 or 1,000 acres).
Engineering designs and cost analysis for the various cases were based on projecting current commercial microalgae production and wastewater treatment processes at much larger scales. They assumed higher productivities due to plausible technological advances. The estimated capital costs for a 250-acre biofuel production system emphasizing oil production were about $21 million, with annual operating costs at around $1.5 million, to produce about 12,300 barrels of oil, giving a break-even price per barrel of oil of $330 (based on an 8% capital charge). Increasing the scale of the system to 1,000 acres reduced the break-even price to about $240 per barrel. These prices considered wastewater treatment credits, which reduced costs about 20%. Other facilities that maximized wastewater treatment produced fuel at lower cost due to greater treatment revenue. However, the availability of wastewater would greatly limit the national scale of this lower-cost fuel production.
Sale of algae co-products, such as pigments or animal feeds, could improve the economics of algae biofuel, but it is not considered in this analysis because the higher value co-product markets would likely become saturated before significant biofuel quantities were produced, while commodity animal feed co-production would likely not have a decisive effect on biofuels production costs without other production improvements in addition.—Lundquist et al.
The major technical assumptions for all five cases are:
- 25% recoverable triacylglyceride content in algae biomass;
- 22 g/m2-day (80 mt/ha-yr) annual average total biomass productivity, of which 20 g/m2-day is harvested;
- Oil yield of about 20,000 liters/ha-yr (2,100 gal/acre-yr);
- Individual ponds are 4 hectares (10 acres) in size (690 m by 60 m, with 30m wide channels) and mixed with paddle wheels at a nominal water velocity of 25 cm/sec;
- Hydraulic residence time in the ponds is 3 to 5 days, depending on season; and
- Flue gas CO2 is supplied by countercurrent sumps within the ponds to eliminate any carbon limitation on the algae growth rate.
The results of the present study, based on a detailed de novo analysis, project high costs for microalgae biofuels produced by facilities designed primarily for biofuels production. Even with low capital charges, it is not possible to produce microalgae biofuels cost-competitively with fossil fuels, or even with other biofuels, without major advances in technology.
All techno-economic assessments of algae biofuels are necessarily based on assumed processes for harvesting and oil recovery, as well as microalgae biomass productivity and oil content. These are the assumptions that R&D has to address...the major area for long-term cost improvements is in biology: the goal being to at least double biomass and oil productivity through strain selection and genetic modification. These strains must then be cultivated reliably in the outdoor ponds and harvested cheaply—major challenges that may require a decade’s effort or longer to become practical.
Additional cost reductions will need to come from engineering improvements in essentially all system components, such as in reactor construction, harvesting, dewatering, and oil recovery. Such advances must be proven in pilot-scale (~10 ha) production systems. The favorable economics of microalgae production for biofuel in conjunction with wastewater treatment could allow for practical, near-term development of engineering, technological, and human resources in this field.—Lundquist et al.
The algae biofuels industry is still in its early stage, the report notes. Although well over 100 companies in the US and abroad are now working to produce algal biomass and oil for transportation fuels, most are small and none has yet operated a pilot plant with multiple acres of algae production systems. However, several companies recently initiated such scale-up projects, including several major oil companies such as ExxonMobil (which a year ago announced a $600-million commitment to algae biofuels technology), Shell (with a joint venture project, Cellana, in Hawaii), and Eni (the Italian oil company, with a pre-pilot plant in Sicily).
|“Only through intensive, continuous, eventually large-scale research with outdoor ponds can we hope to achieve progress in any reasonable time frame: Intensive in terms of data collection, including both biotic and environmental parameters. Continuous means every day, every month, multiple years, and multiple locations; and large-scale in terms of the numbers of ponds and their sizes.”|
The US Department of Energy has funded several R&D consortia and pilot projects, and one 300-acre demonstration project in New Mexico, by Sapphire Energy, Inc. The US Department of Defense is supporting several fast-track projects. In the United Kingdom, the Carbon Trust has initiated a 10-year effort to develop algae oil production, engaging a dozen universities and research laboratories, while the European Union recently funded three 25-acre pilot projects.
Most of these projects use the raceway, open pond-based algal production technologies, which were analyzed in the EBI report. These projects hope to show that it is possible to mass culture algae with current or near-term technology within the technical and economic constraints required for biofuel production.
Once the technologies are developed, global resource availability will be a major controller of algae production, the report states. Four key resources (suitable climate, water, flat land and carbon dioxide) must all be available in one location for optimal algal biomass production. The authors state that despite the need for all four resources, algal oil production technology has the potential to produce several billion gallons annually of renewable fuel in the US However, achieving this goal, particularly at competitive capital and operating costs, will require further research and development.
It is clear from this report that algae oil production will be neither quick nor plentiful—ten years is a reasonable projection for the R&D to allow a conclusion about the ability to achieve relatively low-cost algae biomass and oil production, at least for specific locations. Indeed, this is a short time frame, only possible because of the fast growth rates of algae. Rapid growth is one of the few fundamental advantages of microalgae compared to other sources of biofuels, as it suggest the ability to rapidly progress in the cultivation research (a week of algae cultivation is equivalent to over a whole year of growing a higher plant crop). This will accelerate both the research and also the ability to implement any results.—Lundquist et al.
The project is one of the more than 70 studies on bioenergy now being pursued by the EBI and its scientists at the University of California at Berkeley, the University of Illinois in Urbana-Champaign, and Berkeley Lab. BP is supporting the Institute with a 10-year, $500-million grant.
Tryg Lundquist, Ian Woertz, Nigel Quinn, John Benemann (2010) A Realistic Technology and Engineering Assessment of Algae Biofuel Production. Energy Biosciences Institute Report, October 2010