First published in Cleantech Infocus: Algae Biofuel, November 2008. Copyright Cleantech Investor Ltd. 2008
Could algae, the most basic of plants, represent the solution to the world’s energy needs? They may be small, but the credentials of these one cell plants are impressive. As with all plants, algae use photosynthesis to harness sunlight and CO2. Energy is stored in the algae cells as lipids (oils) and carbohydrates – which can be converted into biodiesel or other fuels. What’s more, algae are the fastest growing plants in the world.
No arable land is needed to cultivate algae, which means they do not compete with commodity food crops. They do not need fresh water – indeed they can grow in brackish water or even waste water. Furthermore, the cultivation of algae can potentially absorb CO2 from smoke stacks, thereby contributing to the reduction of GHG emissions.
It’s no wonder, therefore, that companies hoping to harness algae as a biofuel feedstock are attracting growing levels of investment funding. Dr Al Darzins, Director of the Research Center for Biofuels at the US National Renewable Energy Laboratory (NREL), estimates that $280 million was invested in algae by US venture capitalists in the first half of 2008, of which $84 million went to back research projects. There have been further investments during the second half of this year, including September’s high profile $100 million financing of Sapphire Energy which was led by Cascade Investment LLC (owned by Bill Gates).
These companies are working on a host of different strains of algae, different approaches to cultivation – and different end products. The end products include biodiesel, but also bioethanol and what is described as ‘green crude’.Research into the fuel production capability of algae has a long history. The seminal field study was the NREL’s Aquatic Species Program (ASP), which was conducted between 1978 and 1996. The programme was responsible for major advances in algae science – both in terms of the manipulation of the metabolism of algae and the engineering of microalgae production systems.
The ASP tested the feasibility of large scale open pond algae production in various locations over six years. At Rosswell, New Mexico, tests proved that outdoor ponds could be run with high efficiency of CO2 utilisation (over 90% of injected CO2) and the researchers concluded that, on the grounds of cost, there was little alternative to open pond designs. However, the debate about whether open ponds or bioreactors are the best solution is still a live one.
There are many challenges which must be overcome before algae biofuel can be produced economically. These include both engineering challenges and biological challenges – and both are important. There is much research into strains of algae with high lipid production, but improving oil production is only part of the story. For example, algae produce lipids under stress, but increased oil content does not necessarily correlate with overall productivity of oil since higher levels of oil may be offset by lower rates of cell growth.
Marc van Aken of SBAE Industries suggests a check list for investors which might include the following:
Contamination (In open ponds there is a threat to an algae strain from other photoplancton.)
Nutrient depletion (When the algae population grows exponentially, then there is a danger of a crash in population.)
Photic inhibition (the danger of overstressing the mechanism for photosynthesis).
Self shading (If algae cultivation is very successful there is a danger of a negative feedback loop and no more light.)
Harvesting (Algae require a great deal of water, the pumping and processing of which consumes lots of energy; a litre of water typically contains only a few grams of algae—less than one-half of 1% by weight.)
Van Aken believes that, if all of the above concerns can be dealt with, then there is a potentially scalable process. SBAE is working with the aquaculture industry, which has much experience in growing algae, to try to resolve some of these challenges.
Cary Bullock of GreenFuel Technologies points out that the capital investment being undertaken at present, especially US Government funding, is no longer focusing on engineering, but primarily on biology – to locate the most productive strains. The ASP focused on identifying algae strains with the potential to produce high volumes of oil – and also to grow in stressful conditions (extremes of temperature, pH and salinity). A collection of over 3,000 strains of algae from all over the US was narrowed down to 300 of the most promising species.
The ideal choice of algae strain in any particular location will depend upon the feedstock, the availability of CO2, accessibility to nutrients (the make-up of the water), the climatic conditions – and whether the algae is being grown for fuel or for other purposes (such as nutraceutical production or for the sequestration of CO2).
Equally, these factors will also influence the ideal choice of growing system. Open pond systems, based on the NREL model, have been adopted by many companies, including Livefuels, Petrosun and Aurora Biofuels. However, others are working on alternatives including a variety of photobioreactor designs and dark feeding systems. Vertical bioreactor technology is championed by Valcent, while companies such as Algenol are working on algae to ethanol technologies, and Solazame focuses on dark feeding solutions. There are positive and negative aspects to all of these approaches.
There are many types of photobioreactors, including systems which utilise artificial light. The cost of the energy to create the artificial light makes these a less economical (and less environmentally friendly) solution at present, but the economics may change as new technologies emerge – for example, those technologies which make the use of natural light possible in enclosed environments.
Carbon sequestration from algae
GreenFuel Technologies is an example of a company which takes as its starting point the recycling of CO2 emissions: it has undertaken research into the interaction between algae and flue gases in various different environments. According to Cary Bullock , the company’s research concludes that of the c12,300 power industry CO2 emitters in the US, only around 1,500 have the required criteria for algae harvesting – namely CO2 insulation. Bullock believes the numbers will drop further when the economics of installation of an algae farm are assessed. Even after the uneconomic projects are removed, according to Bullock it is a reasonable assumption that, using hybrid systems, algae might be used to recycle 20% of power generation CO2 emissions.
So what is possible?
The photosynthetic efficiency of normal crops is around 1%: but algae, under cultivation, are generally agreed to have a photosynthetic efficiency of up to 5%. Indeed, some in the industry, such as Belgium based SBAE, claim that photosynthetic efficiencies of between 10% and 14% can be achieved in optimum conditions.
What currently seems clear, however, is that the photons from the sun can be converted into either oil or volume – not both. There are high oil content strains of algae, which yield oil content as high as 60% – or even 80%. The challenge remains to grow high oil content strains of algae in high volumes.
Algae has a low footprint in terms of land. This makes the yield estimates for biofuel from algae look very impressive: reported yields range from 5,000 to 15,000 gallons per acre. The key to success in high volumes, however, will be to reduce the cost of production – ultimately the price per gallon will need to be competitive with the price of equivalent fossil fuels and biofuels from other feedstocks.
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