Smidge204 said:
GRA said:
AThe short version is that it looks like this will produce about 0.01L/day/m2, or a power density of around 4W/m2. Not great, but better than most wind farms, assuming they can produce it commercially at that, that it's affordable, and it makes sense to do so.
Don't forget to consider distribution and end-use efficiencies. The oil substitute they produce can be used with maybe 20% efficiency when all is said and done, while electricity is around 80% efficient in most cases.
=Smidge=
Yes, my original post which had all the math (and which disappeared into its electrons) stated that the 4W/m2 considered only the gross output, and not all the embodied energy in growing, harvesting, refining, transporting etc. And like Dave, I want to know what the water usage is.
Oddly enough, the book I've been reading this week before this topic popped up is "The Biofuel Delusion: The Fallacy of Large Scale Agro-Biofuels Production":
http://www.amazon.com/The-Biofuel-Delusion-Agro-Biofuels-Production/dp/1844076814" onclick="window.open(this.href);return false;
This is undoubtedly the most tedious reading I've done this year. The book appears to have been written by academics for academics, and most of the first four or five chapters is incredibly dry and abstruse, primarily dealing with the methodology used in calculating metrics like Energy Return on Investment (EROI), Exo-somatic Metabolic Rates etc. Starting from chapter 5 and especially chapter 7 on, you finally get to the meat. Let's just say that it doesn't look good for biofuels, although (as far as I've gotten) they don't specifically cover algae-based biofuel.
They do calcs for US corn ethanol and Brazilian sugar-cane. The data for both is bad, the US case particularly so. IIRR, to replace just 10% of the oil used for transportation in the US by sustainably-produced corn-ethanol would require 48% of the US. population to be involved in agriculture, versus <2% now, and
would require something like 5-7 times (I don't have the book handy and my memory is hazy. It might well be higher) the 175M hectares of land now under cultivation in the US FOR ALL PURPOSES for its production. I guess we can just import all our food (from where?).
The Brazilian case is a bit better, but not all that much, and has its own energy, population, land, environmental and socio-economic constraints.
I have no idea if algae-based biofuels would make sense and lack the ability to determine that myself, but everything I've read to date suggests the answer is no, and that at least with crop-based biofuels, rather than transform them into liquid fuel it's more efficient just to burn them.
Edit: I've now retrieved the book, and I find that I considerably understated the amount of land required in the section above I bolded. Here's the full quote, with my explanations in square brakets:
"Using the 11/1 ratio [calculation previously shown by authors] between gross and net energy supply of [corn] ethanol, we calculated that the net supply of 3 EJ of ethanol [10% of US transportation oil requirement] - a net flow of 140 billion litres - would translate into a requirement of gross production of 33 EJ - 1540 billion litres. This gross production would require:
- 148 Ghours of labour in biofuel production (almost 48 per cent of the labour supply that could be provided by the US workforce after absorbing all the unemployed!). This would require half the US workforce to agree to go back into farming and rural activities; and
- 5500 million hectares of arable land (More than 31 times the 175 million hectares of arable land in production in the US in 2005).
"Also in this case, we find a total lack of feasibility in using a self-sufficient corn-ethanol system aimed at reducing the dependence on fossil energy - 10 per cent of the transportation fuels - and generating zero CO2 emission. This lack of feasibility clearly indicates that the actual production of ethanol in the US is only possible because such a production
is powered by fossil energy fuels!" [Emphasis in original]