How much land surface would it require to replace petroleum with biofuel in the US?

[bascule]

So claims the always-correct Wikipedia:

 

http://en.wikipedia.org/wiki/Algae_fuel

 

The United States Department of Energy estimates that if algae fuel replaced all the petroleum fuel in the United States, it would require 15,000 square miles (40,000 square kilometers), which is a few thousand square miles larger than Maryland.[8] This is less than 1/7th the area of corn harvested in the United States in 2000.[9][10]

 

They cite a Washington Post story:

 

http://www.washingtonpost.com/wp-dyn/content/article/2008/01/03/AR2008010303907.html

 

Algae, like corn, soybeans, sugar cane and other crops, grows via photosynthesis (meaning it absorbs carbon dioxide) and can be processed into fuel oil. However, the slimy aquatic organisms yield 30 times more energy per acre than land crops such as soybeans, according to the U.S. Department of Energy. The reason: They have a simple cellular structure, a lipid-rich composition and a rapid reproduction rate. Many algae species also can grow in saltwater and other harsh conditions -- whereas soy and corn require arable land and fresh water that will be in short supply as the world's population balloons

 

Sounds doable...

[CaptainPanic]

I'll reply only to the wikipedia link about algae, which is crap.

Unfortunately, they use several assumptions which aren't proven on big scale, or just wrong:

 

1. Efficiency on sunlight. Estimate is much higher than realistic.

2. Algae need constant mixing (they need light-dark-light-dark-light-dark etc), which requires a serious pump to keep the liquid turbulent.

3. Algae need CO2, and produce O2. These two gases need to be added to and removed from the water. This requires one enormous gas compressor for the CO2, and a complicated system for O2 removal (because oxygen is actually toxic to algae, believe it or not).

 

Therefore, the yields described have been achieved on lab scale, where power input was neglected, and where artificial lights provided the energy for photosynthtesis. I absolutely disbelieve (and I'll prove you why) that algae can be that efficient.

 

1. Claim: "algae can produce 100,000 gallons of oil per acre".

100,000 gallons = 378,000 liter = 300,000 kg

Heat of combustion of vegetable oil = 40 MJ/kg

Total energy per acre / yr = 300,000*40E6 = 1.2E13 J/(yr acre)

That is equal to 1.2E13 / 4,046.8564224 = 2.96E9 J/(yr m2) (finally, it's all in SI units!!)

Total insolation on 1 m2 in a warm, sunny place is about 250 W/m2, or 250 J/(s m2). That's the 24 hrs average for a place in the south of Spain.

Therefore in 1 yr, we get 250 * (3600*24*365) = 7.88E9 J/(yr m2)

 

At this point, it's worth noticing that the total insolation (7.88E9 J/(yr m2) is only a bit larger than the total energy which is supposedly captured in the algae's oil (2.96E9 J/(yr m2), algae growth itself not even included!!). The very best algae on earth can convert 10% of the sun's energy into biomass (not: oil). Of that biomass, only a part is oil.

 

Therefore, a more realistic number would be:

7.88E9 J/yr m2 total insolation

7.88E8 J/yr m2 converted to biomass

3.94E8 J/yr m2 converted to oil

9.85 kg/yr m2 converted to oil

Total yield per acre = 40000 kg/acre, or 10500 gallons / acre (why did I convert it back to gallons / acre? dammit!)

Note: this is the best case scenario!!!!!! 10 times lower than the myth that's found on wikipedia

 

Points 2 and 3 only reduce the efficiency, because a gas compressor that will bubble CO2 through water needs serious power. The CO2 is likely not pure (it costs a lot of energy to purify CO2, and not many sources actually produce pure CO2 - perhaps ethanol factories?).

 

Then you still need to recover the oil. The algae are wet, and you need to separate the oil from the rest (which needs to be recycled to recycle the nutrients)... probably you need to dry and burn the algae, which (because it's so wet) does not necessarily provide a lot of energy.

 

Conclusion

The estimate of 100000 gallon / acre is totally unrealistic, and probably won't even be reached if you place the whole algae reactor on the sunniest place of the galaxy: planet Mercury. In addition, the power requirements to make the whole thing run are huge. You need enormous pumps and compressors, and the investment is also significant.

Edited June 16, 2009 by CaptainPanic
not only breaking down Wikipedia's numbers, but also giving a realistic (high) estimate

[SH3RL0CK]

Sounds doable...

 

I've always been a big proponent of bio-ethanol. Considering we already produce very nearly 10% of our gasoline this way (and we aren't trying all that hard at it...yet), I agree this can probably be acheived.

 

In a previous thread, this issue was discussed: http://www.scienceforums.net/forum/showthread.php?t=28991&highlight=ethanol&page=4

 

While good points were brought by both sides, what I find encouraging (for corn; algae has even greater potential) is the following (if I may quote myself):

 

Here is a study on the potential within the USA:

 

http://www.brightsurf.com/news/headl...ependence.html

 

 

90 billion gallons of ethanol could be sustainably achieved by 2030 within real-world economic and environmental parameters.

 

Note the word "sustainable." In the context of the paper, this means the production does not interfere greatly with food production or the like. Now 90B gallons equates to something like 246 million gallons a day.

 

It is interesting to note that today the USA consumes about 230M gallons of gasoline daily (http://wiki.answers.com/Q/How_much_g...rica_use_daily) , so assuming cars become efficient enough to overcome the natural demand growth in gasoline (should be easily acheivable as hybrid-electric vechicles alone DOUBLES the efficiency) then biofuels is a sufficient answer to our liquid fuel requirements. Keep in mind an engine specifically designed for ethanol is as fuel efficient as todays engines designed for gasoline (that and we can also create bio-butanol instead of ethanol).

 

The other uses for crude oil will require other solutions however.

 

Of course as POM later pointed out, this is potential, not a certainty. We will need to do a considerable amount of work before bio-ethanol will be able to replace our petro-generated gasoline.

Edited June 16, 2009 by SH3RL0CK

[Mokele]

The very best algae on earth can convert 10% of the sun's energy into biomass (not: oil).

 

Yes, but that's per algal cell, right? If there are multiple layers of cells, any sunlight missed by the top cells can be picked up by the next layer, and the next, and the next, and so on.

 

We also don't know the conditions used - perhaps they used clear tubes of algae and water (thereby allowing more surface area)? A continuous flush of water should be easy by just pumping water through the pipes, controlling O2 & CO2. Vanes in the pipe can induce any level of turbulence desired (though I'm not sure you're right on this point - I've seen the greatest algal growth in stagnant conditions).

[D H]

Considering we already produce very nearly 10% of our gasoline this way (and we aren't trying all that hard at it...yet), I agree this can probably be acheived.

Citation needed, please. This looks like cooking of the books, and doubly so. E10 gasoline, for example, contains 10% alcohol. The 90% of E10 that is gasoline does not count as alcohol. It counts as gasoline. Not all of the alcohol added to gasoline is bioalcohol. Some (I don't know the proportion) of that alcohol is produced from fossil fuels.

[SH3RL0CK]

Citation needed, please. This looks like cooking of the books, and doubly so. E10 gasoline, for example, contains 10% alcohol. The 90% of E10 that is gasoline does not count as alcohol. It counts as gasoline. Not all of the alcohol added to gasoline is bioalcohol. Some (I don't know the proportion) of that alcohol is produced from fossil fuels.

 

Ethanol is alcohol. Therefore the E10 gasoline you are buying is 10% ethanol...therefore 10% of our gasoline supply is ethanol. As far as where the ethanol comes from, only 5% of all ethanol comes from petroleum; basically it comes from sugar cane, corn, or other plant material.

 

http://en.wikipedia.org/wiki/Ethanol_fuel

 

Creation of ethanol starts with photosynthesis causing a feedstock, such as sugar cane or corn, to grow. These feedstocks are processed into ethanol.

 

About 5% of the ethanol produced in the world in 2003 was actually a petroleum product.

 

http://en.wikipedia.org/wiki/Ethanol#Production

 

Ethanol for use in alcoholic beverages, and the vast majority of ethanol for use as fuel, is produced by fermentation. When certain species of yeast (e.g., Saccharomyces cerevisiae) metabolize sugar they produce ethanol and carbon dioxide.

Edited June 16, 2009 by SH3RL0CK

[D H]

I don't know about you, but I can still buy E0 gasoline.

 

2007 US motor gasoline consumption: 9,286,000 barrels/day

(Source: http://www.eia.doe.gov/basics/quickoil.html)

 

2007 US alcohol fuel consumption: 4,748,395,000 gasoline-equivalent gallons/year

(Source: http://www.eia.doe.gov/cneaf/alternate/page/atftables/attf_c1.html;

the above number is the sum of the "Ethanol in Gasohol" and "E85" lines)

 

This is 3.3%, not 10%, of the total motor gasoline consumption. There is still some fudging of numbers. Not all of the alcohol added to gasoline is biofuel. Some comes from coal, for example.

[CharonY]

The space calculation for algae is imo not very informative for a simple reason: the bioreactors can come in a lot of different forms and shapes, in fact there are numerous possibilities to increase surface area, while reducing or maintaining the overall footprint. However, the results I have seen from recent large bioreactor tests indicate that the yield is somewhat low and the costs relatively high.

[SH3RL0CK]

I don't know about you, but I can still buy E0 gasoline.

 

2007 US motor gasoline consumption: 9,286,000 barrels/day

(Source: http://www.eia.doe.gov/basics/quickoil.html)

 

2007 US alcohol fuel consumption: 4,748,395,000 gasoline-equivalent gallons/year

(Source: http://www.eia.doe.gov/cneaf/alternate/page/atftables/attf_c1.html;

the above number is the sum of the "Ethanol in Gasohol" and "E85" lines)

 

This is 3.3%, not 10%, of the total motor gasoline consumption. There is still some fudging of numbers. Not all of the alcohol added to gasoline is biofuel. Some comes from coal, for example.

 

 

I'm surprised you are able to still get E-0. Notice that in recent legislation something else is required: http://en.wikipedia.org/wiki/Gasoline

 

This law (Energy Policy Act of 2005) will require all auto fuel to contain at least 10% ethanol.

 

http://en.wikipedia.org/wiki/Energy_Policy_Act_of_2005

General provisions

...

Increases the amount of biofuel (usually ethanol) that must be mixed with gasoline sold in the United States to 4 billion gallons by 2006, 6.1 billion gallons by 2009 and 7.5 billion gallons by 2012[1]...

 

 

Your second reference is from 2007...due to the above legislation, perhaps things have changed since then? Nevertheless, as you say it is probably true that bio-ethanol blended into our fuel is somewhat less than 10% of the total today...that said, I don't see why bio-fuels will not eventually replace fossil fuels for our liquid fuel needs.

[Mokele]

One nice thing about algae for fuel is that it grows just about anywhere. In contrast, fossil fuels are where they are, and you have to build all your mining equipment there (no matter how precarious the situation, as in offshore drilling), then transport all of that fuel to its destinations. The cost of physically moving large amounts of liquid from A to B are not insubstantial (trucks run on gas, trains have limited reach, ships are expensive, and pipelines even more expensive).

[CaptainPanic]

Yes, but that's per algal cell, right? If there are multiple layers of cells, any sunlight missed by the top cells can be picked up by the next layer, and the next, and the next, and so on.

 

No, the 10% is an overestimation of the realistic (big scale) value of the overall efficiency.

Algae in a normal pond will do about 1-2% efficiency (overall, not per cell)... or less.

Algae in super-mega-fancy-bling-lab-reactors can do 13% efficiency on light (which is specific LED-light I tihnk). That's the highest number I've heard. (Citation needed )

 

Since measurements on a single cell aren't possible, due to the fact that the really high efficiency requires incredibly turbulent mixing, the numbers are always the overall efficiency.

 

We also don't know the conditions used - perhaps they used clear tubes of algae and water (thereby allowing more surface area)? A continuous flush of water should be easy by just pumping water through the pipes, controlling O2 & CO2. Vanes in the pipe can induce any level of turbulence desired (though I'm not sure you're right on this point - I've seen the greatest algal growth in stagnant conditions).

You're partially right on the liquid pumps: the liquid pumps are relatively efficient. Obviously, inducing extra drag using vanes will cause problems:

 

1. You increase drag. You increase the pressure drop per m of pipe. Therefore either you use shorter pipes, or your pressure behind the pump is higher (meaning your pipe system must withstand higher pressures).

We're talking about several bars of pressure here.

2. Algae and other stuff will get stuck behind the vanes, and you will spend all your income on cleaning and maintenance.

 

However, O2/CO2 pumping systems are the real big one. These will consume a significant portion of the energy produced. Gas compression requires much more energy than liquid pumps... and we're dealing with incredible amounts of gas. The gas flow is likely to be several times higher than the product (algae) flow.

 

To achieve the really high production rates, the algae need constant mixing.

However, I don't see any future for the algae bioreactors. I think the best way is to simply have a racetrack pond, which does not require any input of energy other than a small amount for a rather insignificant liquid flow.

[bascule]

I'll reply only to the wikipedia link about algae, which is crap.

 

Perhaps you can point out a flaw in the original papers from the US Department of Energy:

 

http://www.ott.doe.gov/biofuels/pdfs/biodiesel_from_algae_ps.pdf

http://www.ott.doe.gov/biofuels/pdfs/biodiesel_from_algae_es.pdf

 

Unfortunately, they use several assumptions which aren't proven on big scale, or just wrong:

 

1. Efficiency on sunlight. Estimate is much higher than realistic.

2. Algae need constant mixing (they need light-dark-light-dark-light-dark etc), which requires a serious pump to keep the liquid turbulent.

3. Algae need CO2, and produce O2. These two gases need to be added to and removed from the water. This requires one enormous gas compressor for the CO2, and a complicated system for O2 removal (because oxygen is actually toxic to algae, believe it or not).

 

Therefore, the yields described have been achieved on lab scale, where power input was neglected, and where artificial lights provided the energy for photosynthtesis. I absolutely disbelieve (and I'll prove you why) that algae can be that efficient.

 

1. Claim: "algae can produce 100,000 gallons of oil per acre".

100,000 gallons = 378,000 liter = 300,000 kg

Heat of combustion of vegetable oil = 40 MJ/kg

Total energy per acre / yr = 300,000*40E6 = 1.2E13 J/(yr acre)

That is equal to 1.2E13 / 4,046.8564224 = 2.96E9 J/(yr m2) (finally, it's all in SI units!!)

Total insolation on 1 m2 in a warm, sunny place is about 250 W/m2, or 250 J/(s m2). That's the 24 hrs average for a place in the south of Spain.

Therefore in 1 yr, we get 250 * (3600*24*365) = 7.88E9 J/(yr m2)

 

At this point, it's worth noticing that the total insolation (7.88E9 J/(yr m2) is only a bit larger than the total energy which is supposedly captured in the algae's oil (2.96E9 J/(yr m2), algae growth itself not even included!!). The very best algae on earth can convert 10% of the sun's energy into biomass (not: oil). Of that biomass, only a part is oil.

 

Therefore, a more realistic number would be:

7.88E9 J/yr m2 total insolation

7.88E8 J/yr m2 converted to biomass

3.94E8 J/yr m2 converted to oil

9.85 kg/yr m2 converted to oil

Total yield per acre = 40000 kg/acre, or 10500 gallons / acre (why did I convert it back to gallons / acre? dammit!)

Note: this is the best case scenario!!!!!! 10 times lower than the myth that's found on wikipedia

 

Well again, it's not just "Wikipedia", you are saying a peer reviewed research paper published by the US Department of Energy is wrong. That's a bit more audacious of a claim.

 

I do not have the expertise required to poke holes in your assessment. So perhaps you can do me a favor and evaluate the calculations found in the original paper and point out the flaws?

 

NREL's research showed that one quad (7.5 billion gallons) of biodiesel could be produced from 200,000 hectares of desert land (200,000 hectares is equivalent to 780 square miles, roughly 500,000 acres), if the remaining challenges are solved. In the previous section, we found that to replace all transportation fuels in the US, we would need 140.8 billion gallons of biodiesel, or roughly 19 quads (one quad is roughly 7.5 billion gallons of biodiesel). To produce that amount would require a land mass of almost 15,000 square miles.

[CaptainPanic]

Ok, let's see:

NREL's research showed that one quad (7.5 billion gallons) of biodiesel could be produced from 200,000 hectares of desert land (200,000 hectares is equivalent to 780 square miles, roughly 500,000 acres), if the remaining challenges are solved. In the previous section, we found that to replace all transportation fuels in the US, we would need 140.8 billion gallons of biodiesel, or roughly 19 quads (one quad is roughly 7.5 billion gallons of biodiesel). To produce that amount would require a land mass of almost 15,000 square miles.

7.5 billion gallons = 28.4 billion liter = 22.7 billion kg, which is equivalent to 9.1E17 J (assuming biodiesel has a heat of combustion of 40 MJ/kg).

 

Surface area: 200,000 ha, or 2.0E9 m2.

 

So: the "NREL energy production" equals 9.1E17 / 2.0E9 = 4.55E8 J/m2 per year

 

Now, let's compare that to my realistic (but still very high) numbers:

Therefore, a more realistic number would be:

7.88E9 J/yr m2 total insolation

7.88E8 J/yr m2 converted to biomass (10% = high!)

3.94E8 J/yr m2 converted to oil (50% oil, 50% biomass = high!)

9.85 kg/yr m2 converted to oil

 

I conclude that the number NREL calculated is incredibly high, because it is higher than my really optimistic estimate... but not as unrealistic as the other wikipedia value... In addition, NREL claim that they place their entire reactor in the desert, which may be more sunny than my assumption (which was southern Spain). Still, everything has to be absolutely perfect to achieve this number...

 

I am sure however that none of the process energy requirements are included. And cooling will be a major issue in the desert too.

 

Therefore, I don't believe that the NREL number is realistic.

[Mokele]

You're using european values for insolation? Why? Latitude matters.

 

For much of the US, insolation exceeds that in Europe by over 50%, and in some areas, by over 100%. European values correspond to southern Alaska.

[bascule]

The New York Times just published an article arguing that biofuel produced from algae would cost $1/gallon

 

And just for the record, I am not Johnny-come-lately to this idea

[CaptainPanic]

You're using european values for insolation? Why? Latitude matters.

Mostly for practical reasons - I didn't have didn't look for other values.

For much of the US, insolation exceeds that in Europe by over 50%, and in some areas, by over 100%. European values correspond to southern Alaska.

First of all, I used not "just" a European number, but I used southern Spain, 250 W/m2. That's not Alaska in latitude, but more like Oklahoma and Kansas (for latitude) and New Mexico (for the type of weather).

 

I did a quick check on insolation in New Mexico (which we can hopefully agree is one of the sunnier places of the USA?).

 

[...]Winter and summer solar monthly collector capacity, for tilt of 35°: in January, the average daily insolation [3] is 5.3 kWh/m2/day, corresponding to a monthly energy availability of 11090 kWh assuming a collector efficiency of 30 % and 225 m2 of collectors online at any given time. In August, the average daily insolation [3] is 6.9 kWh/m2/day [...](source)

Taking the high value (August):

6.9 kWh/m2/day = 24840000 J/m2/day = 287.5 W/m2.

I used a value of 250 W/m2 for the year-round average. I therefore conclude that it's reasonable.

I know they included a tilt, so this conclusion isn't 100% waterproof, but I hope you can accept that the error is less than 100%.

 

In addition, I was discussing issues that will not be solved by 100% more sunlight. I attempted to show that more fundamental problems are found in the estimates of algae production.

 

Please note that I don't think that algae are a bad idea. I am just stating that the production is often overestimated by incorrect extrapolations.

Edited June 30, 2009 by CaptainPanic