The Ergosphere
Friday, December 01, 2006

It comes almost too fast to keep up

Evidence accumulates that the biofuel recycling step in Sustainability is not only feasible, but here today:  Greenfuel just announced production of commercial-quality biofuels from CO2 scavenged from an Arizona powerplant (h/t:  Cervus @ GCC).

Further, they mentioned that the CO2 capture efficiency is as high as 80% during daylight hours.  This is astounding, and it strongly suggests that a closed-loop system is feasible:

So long as the volume of the greenhouses is large enough to store CO2 and supply oxygen overnight, this requires no exhaust to the atmosphere; it can turn all biomass input into electricity PLUS liquid biofuels.  It could even burn its own biofuels to make carbon-free electricity, cycling the carbon in a closed loop.  We don't need fuel cells right away; we can start with small gas turbines and work up from there.

What are we waiting for?

You might want to send your paper to the management of Greenfuels. That might open up some opportunities for you.
they mentioned that the CO2 capture efficiency is as high as 80% during daylight hours. This is astounding

I got real excited about this part, but then I read the press release, where they say

“We estimate that this process can absorb as much as 80 percent of CO2 emissions during the daytime at a natural gas fired power plant,”

The key word, unfortunately, is estimate. Theoretical performance, not actual performance. Still, this is a big step forward, if only because they have managed to engage the utility generator and get their technology taken seriously in that context. But let's be careful about overselling their acomplishment.
Don't look now but old physics codger Robert Bussard claims he can build a fusion power plant demo for about 200 million.

People in the know about physics says his physics and his credentials seem sound but are skeptical about the results he reported from his last experiment which "blew up". And they're also skeptical that he's really solved the gridless inertial electrostatic confinement problem as he claims. Given that he's hardly published anything over the last 11 years he was funded by various parts of the DOD, the skeptics may have a point. But Bussard claims that his approach is viewed with hostility by the establishment that has pursued various expensive Tokamak designs.

I read one description of his design that claims there's nothing thermal about it. It goes from fusions straight to electricity.

If he's right then game over. I've seen his lecture on google video. I think some billionaires or vc's out there should risk about 10 or 20 million on him to demonstrate the viability of his approach. It's seem so little and the worst it could do is advance what we know about iec physics which seem so much cheaper than the tokamaks.
Here's what you need to do... arrange a meeting with Ah-nold and dazzel him to the point that he makes tou Califirnia Energy "Tzar".

I'm only half joking... getting the ear of someone like that could really amplify your scheme.
Were you able to find out any more info on the gallons per acre question on the algal biodiesel?

I also recall something like 150,000 gal/acre on GCC (I specifically remember thinking that that basically solved a lot of problems).
Question re. algae biodiesel: what happens to yield-per-acre if you don't have flue gas CO2 available? As would be the case if you used the biodiesel in cars (where collection of CO2 would, AFAIK, be much more difficult than at a power plant).

Obviously one can grow algae using CO2 from the atmosphere (it happens in nature all the time); but how would this affect yields?

As for using algae biodiesel in a powerplant setting, as EP suggests, would it not be simpler just to set up a photovoltaic array?

Algae biodiesel is commonly quoted as having a potential yield of 15000 gal/acre; taking 35.7 MJ/L as the energy content for biodiesel, this yield-per-acre comes out to 5.18 TJ/ha. Average daily insolation in the US ranges from 150-250 W/m2, which works out to 47.3 to 78.8 TJ/ha annually. Result is a net efficiency (from solar insolation to biodiesel energy content) of 6.6-10.9%.

This efficiency is comparable to the solar cells EP mentioned here:

...particularly when conversion efficiencies from biodiesel to electricity are taken into account. Of course, if your goal is process heat or storable energy it's a different story.

I'm not trolling; I ask these questions out of genuine curiousity. FWIW, I see algae biodiesel as one of the more promising biomass candidates.
The figure of merit we should be looking at isn't efficiency of conversion of sunlight to power, but dollars per watt (plus dollar value of storage).  It would take more acres of algae than silicon to do the job, but what can you get for the same money?

If you can get 5000 gallons of veggie oil and another 5000 gallons of ethanol per acre per year, that's something like 639 million BTU of product per year.  Converted to electricity at 40% efficiency, that's about 75000 kWh.  You might have to replace greenhouse covers every few years (at 10¢/ft^2/year, that's $4400/acre/year) which would run about 6¢/kWh.  You'd have to multiply this cost by about 4 to equal today's cost of PV, and the capital expenses are a small fraction of PV's; this allows systems to be installed and paid off very fast.

IMO, this is the sort of thing we need:  it gets the ball rolling but doesn't have the huge sunk costs which prevent us from moving on when better technology arrives.  Further, it can switch between electricity and liquid fuels depending which is in demand.
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