When I first got into the renewable energy space, Robert Rapier was one of the first people to whom I reached out, as he’s been around this industry quite a while. I recall that he was quite gracious with me; we had a long and interesting chat on the phone.
Here’s Robert’s take on the enterprise of cellulosic ethanol, which, for what it’s worth, aligns 100% with my own: it won’t scale.
If it is to offer real value, a biomass to energy project needs to involve a feedstock that has a negative value to society, like municipal solid waste, manure, waste tires, etc. But growing plants for this purpose, with the financial and ecological costs of planting, irrigation, fertilization, harvest, and processing, appears to be a loser.
The reason: simple thermodynamics. What percentage of the sun’s energy that was incident on a certain plant becomes available as a biomass energy source? An extremely small portion. Life forms are not here because they store tons more energy than they need to perform their biologic functions; in fact, they’re evolved specifically so that doesn’t happen.
I believe that, under absolutely optimal circumstance, algae has the highest efficiency of any plant in converting solar energy to stored biomass energy. That efficiency is ~3%.
We were doing better than that with PV solar back in the 70′s. Now we can get an order of magnitude more efficiency than that. So I wholeheartedly agree: if the goal is to collect energy from a plot of land, then there are much more efficient ways of doing so.
Exactly. I’m reminded of a guy I ran into at the American Chemical Society conference a couple of months ago, who was explaining his work in microbial fuel cells. When I speculated that the power density must be miserably small, he acknowledged that it indeed was. Of course, this suggests the question: Then why are you doing it, when we have real-world problems to solve? But I didn’t confront on the subject.
LOL.
It would have been hilarious had you asked your question, but I understand why you couldn’t at the time.
Sadly… the answer probably would have been the classic: “Because that’s where the money is”.
If we fund it, someone will work on it, no matter how silly.
Btw, that’s exactly right. When I told your dad about the conversation, he told me that ARPA-E had funded that. I was astonished — and revolted at the same time.
While I agree biomass does not scale, I disagree that farming biomass is of lower economic value than PV. The difference is capital intensity, and the potential for carbon sequestration in root systems.
Biomass farms can be much less capital intensive than PV (so long as the land is not a premium cost. Think of farming the medians of interstate highways for biomass: you might not want to put PV there, since it might be run over by a semi going off the road, but a mix of native grasses and prairies plants, harvested a couple times a year might produce useful biomass for fuel, sequester carbon in growing root systems, and provide habitat for birds or small mammals.
Biomass has a role to play… we should not aim for a PV monoculture, just because it is more “efficient.”
A point well made. Good to hear from you again, Tom.
I believe making corn ethanol has 0 efficiency. What about sugarcane ethanol like Brazil makes? Is it net energy positive?