Several readers have asked us to evaluate some recent innovations in algae extraction processes. These technologies play some role in concentrating the algae after harvest and/or extracting the biofuel precursors.  Unfortunately, evaluating these processes is difficult because only incomplete energy requirements are usually provided.  This is often due to minimizing what are clearly significant energy inputs or simply not providing them at all.  Whether this is the result of obfuscation or bad science I leave up to the reader.

Any publicizing of new innovations should include a discussion of the energy balance achieved by the new technology.  Short of that, there should be enough information for the reader to derive the energy balance themselves. 

So what is an energy balance? By definition, “an energy balance (physics) is the arithmetic balancing of energy inputs versus outputs for an object, reactor, or other processing system; it is positive if energy is released and negative if it is absorbed.”  In short, do you get more energy out of the algae than you expended processing it?

One of the most illustrative ways to present an energy balance, particularly for commercial processes, is in terms of cost.  For example, the energy contained in the average algae is around 0.005 kWh/gram, if lipids, carbohydrates and proteins are all considered.  The “value” of this energy is the cost to purchase it; for example, electricity in Nevada (at commercial rates), currently sells for $0.1059/kWh.  If you grow and harvest 10,000 grams of algae, the energy value is 50kWh (10,000g x .005kWh/g x $0.1059/kWh), or $5.30.

The energy balance is positive if you can extract $5.30 worth of lipids, carbohydrates and proteins for less than that.  Depending on the technology, costs can include materials, electricity, heat, water and chemicals.  When chemicals and materials are considered, their costs reflect the energy required for their manufacture and transportation.

It should not be surprising that costs add up quickly.  The Department of Energy (DOE) in its draft National Algal Biofuels Technology Roadmap (2009) recommends that 1st generation extraction processes consume no more than 15% of the energy value of the algae.  For future generations of extractors, the energy requirements become even more stringent.

Thus, evaluating any proposed extraction process SHOULD be very easy.  We can quickly estimate the energy value of any given quantity of algae.  And if we have enough information, we can calculate the cost of processing that quantity of algae for any publicized extraction process.  If the costs are less than 15% of the energy value of the algae, buy their stock.  But if the costs are greater—or if they provide insufficient information on which to calculate an energy balance—caution and skepticism are warranted.