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By Robert Rapier on Mar 28, 2006 with 1 response

Biodiesel: King of Alternative Fuels

OK, maybe not the king yet. But if we judge based on the merits, biodiesel is head and shoulders above ethanol. Let’s take a closer look at it.

Biodiesel has a couple of huge advantages over ethanol. First, it is not miscible in water, so you don’t have the huge input of fossil fuels that is required to separate ethanol from water. This makes the energy balance far better than that of ethanol. A poor energy balance is my primary objection to ethanol (especially grain-ethanol).

The second major advantage biodiesel has is that it has over 1.6 times the BTU value of the same volume of ethanol. A gallon of biodiesel contains approximately 121,000 BTUs/gallon (about the same as gasoline), versus approximately 75,000 BTUs per gallon for ethanol. Diesel engines also run 35-40% more efficient than spark-ignition engines (the kind that use gasoline or ethanol). That means that 1 gallon of biodiesel has the effective energy value of 1/0.65, or 1.5 gallons of gasoline. As shown in previous essays, 1 gallon of gasoline is worth around 1.5 gallons of ethanol on a BTU equivalent basis, so 1 gallon of biodiesel is effectively equivalent to (1.5*1.5) or 2.25 gallons of ethanol! The biodiesel group at UNH has done similar calculations if you want to get into greater detail (1).

Unfortunately, there are a couple of major disadvantages for biodiesel as well. The biggest is that most of us do not drive vehicles with diesel engines. It will take some time for a transition to diesels to take place. This is the most serious obstacle to wide-scale adoption in the short-term.

A second disadvantage that is often cited is that biodiesel has a much higher pour point and cloud point than petroleum diesel. This means that it will solidify at a much higher temperature, making it useless when the temperatures are cold. However, I can envision some easy engineering solutions for this problem. A vehicle could have a dual-tank, in which it is started up on petroleum diesel. The exhaust could pass through a heat exchanger through the biodiesel tank. There could be controls to regulate the temperature in the biodiesel tank so that it doesn’t get too hot. After the biodiesel warms up, a switch could automatically flip the fuel supply to the biodiesel tank. (If someone invents this, I want a cut!) Alternately, it can be simply cut with petroleum diesel, but the amount of biodiesel that can be added will be limited in cold climates.

Biodiesel from What?

Biodiesel can be produced from crops, such as soybeans. The reported EROI for biodiesel from soybeans is 3.2(2). Note that this is over double the EROI for ethanol, and that doesn’t even account for the higher efficiency of the diesel engine. Soybeans yield about 40 bushels per acre, which translates into around 60 gallons of biodiesel per acre. This is far short of the 350 gallons or more of ethanol that can be produced from an acre of corn, but we have to take into account the net energy produced. Given that the real energy return of grain ethanol is around 1.3, it took the energy equivalent of around 350/1.3, or 269 gallons of ethanol to make the 350. We netted out 81 gallons. For the soybeans, it took 60/3.2, or 19 gallons of biodiesel equivalent to produce the biodiesel, for a net of 41. But recall that 1 gallon of biodiesel is worth 2.25 gallons of ethanol when both are used in their respective engines, so the biodiesel yield is “worth” 2.25*41, or 92 gallons of ethanol. (Please note that these calculations are approximate. If I were going to try to publish this somewhere, I would convert everything into BTUs to calculate the net yields.)

However, I do not wish to make the argument that we should be making biodiesel from crops, unless we are doing so from by-products left over from food production. Production of biodiesel (or ethanol) from crops can’t make a significant dent in our current usage of motor fuels. Fortunately, there may be a better way. A couple of years ago, I ran across an article that really caught my attention. It was my Reference 1 below, a report by Michael Briggs at The University of New Hampshire. Briggs explained that biodiesel can be produced from algae, at yields as high as 15,000 gallons per acre! Briggs did a number of calculations of the feasibility and cost of replacing the entire motor fuel supply of the U.S. with biodiesel. I checked his calculations and read his references, and his analysis – based on experiments conducted by NREL – appeared to me to be spot on. In his own words, regarding the acreage that would be required:

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. To put that in perspective, consider that the Sonora desert in the southwestern US comprises 120,000 square miles. Enough biodiesel to replace all petroleum transportation fuels could be grown in 15,000 square miles, or roughly 12.5 percent of the area of the Sonora desert (note for clarification – I am not advocating putting 15,000 square miles of algae ponds in the Sonora desert. This hypothetical example is used strictly for the purpose of showing the scale of land required). That 15,000 square miles works out to roughly 9.5 million acres – far less than the 450 million acres currently used for crop farming in the US, and the over 500 million acres used as grazing land for farm animals.

It would be preferable to spread the algae production around the country, to lessen the cost and energy used in transporting the feedstocks. Algae farms could also be constructed to use waste streams (either human waste or animal waste from animal farms) as a food source, which would provide a beautiful way of spreading algae production around the country. Nutrients can also be extracted from the algae for the production of a fertilizer high in nitrogen and phosphorous. By using waste streams (agricultural, farm animal waste, and human sewage) as the nutrient source, these farms essentially also provide a means of recycling nutrients from fertilizer to food to waste and back to fertilizer.

Regarding the costs, he writes:

In “The Controlled Eutrophication process: Using Microalgae for CO2 Utilization and Agircultural Fertilizer Recycling”, the authors estimated a cost per hectare of $40,000 for algal ponds. In their model, the algal ponds would be built around the Salton Sea (in the Sonora desert) feeding off of the agircultural waste streams that normally pollute the Salton Sea with over 10,000 tons of nitrogen and phosphate fertilizers each year. The estimate is based on fairly large ponds, 8 hectares in size each. To be conservative (since their estimate is fairly optimistic), we’ll arbitrarily increase the cost per hectare by 100% as a margin of safety. That brings the cost per hectare to $80,000. Ponds equivalent to their design could be built around the country, using wastewater streams (human, animal, and agricultural) as feed sources. We found that at NREL’s yield rates, 15,000 square miles (3.85 million hectares) of algae ponds would be needed to replace all petroleum transportation fuels with biodiesel. At the cost of $80,000 per hectare, that would work out to roughly $308 billion to build the farms.

The operating costs (including power consumption, labor, chemicals, and fixed capital costs (taxes, maintenance, insurance, depreciation, and return on investment) worked out to $12,000 per hectare. That would equate to $46.2 billion per year for all the algae farms, to yield all the oil feedstock necessary for the entire country. Compare that to the $100-150 billion the US spends each year just on purchasing crude oil from foreign countries, with all of that money leaving the US economy.

I spent a lot of time reading through his references (some are very long reports), and I could not understand why we weren’t massively funding this research. It turns out that NREL stopped funding the program in 1996. The reason remains unclear to me, but this concept had given me hope that there might be a viable alternative out there after all that didn’t require us to turn all our forests into farmland. I spent a lot of time wondering just how I could involve myself in this area and contribute. I did e-mail Michael Briggs and we had a nice discussion, and I came away convinced that he knew what he was talking about. So why on earth weren’t we all over this? Frankly, I still don’t know the answer to that.

Biodiesel Plus Carbon Dioxide Recycle

Fast forward to 2006, and newspapers across the country picked up the story that Isaac Berzin, of MIT, is using algae to quickly recycle carbon in carbon dioxide rich exhaust stacks from power plants (3). What a brilliant, brilliant idea! Why didn’t I think of that? By doing this, he is able to double up on the benefits. First, the carbon dioxide gets converted back into plant material instead of going directly into the atmosphere. This would be a way of sequestering the carbon, provided the algae was properly disposed of. The story reports:

Fed a generous helping of CO2-laden emissions, courtesy of the power plant’s exhaust stack, the algae grow quickly even in the wan rays of a New England sun. The cleansed exhaust bubbles skyward, but with 40 percent less CO2 (a larger cut than the Kyoto treaty mandates) and another bonus: 86 percent less nitrous oxide.

That alone is incredible. But that isn’t all:

After the CO2 is soaked up like a sponge, the algae is harvested daily. From that harvest, a combustible vegetable oil is squeezed out: biodiesel for automobiles. Berzin hands a visitor two vials – one with algal biodiesel, a clear, slightly yellowish liquid, the other with the dried green flakes that remained. Even that dried remnant can be further reprocessed to create ethanol, also used for transportation.

One key is selecting an algae with a high oil density – about 50 percent of its weight. Because this kind of algae also grows so fast, it can produce 15,000 gallons of biodiesel per acre. Just 60 gallons are produced from soybeans, which along with corn are the major biodiesel crops today.

Now that’s ethanol I can live with. Finally:

For his part, Berzin calculates that just one 1,000 megawatt power plant using his system could produce more than 40 million gallons of biodiesel and 50 million gallons of ethanol a year. That would require a 2,000-acre “farm” of algae-filled tubes near the power plant. There are nearly 1,000 power plants nationwide with enough space nearby for a few hundred to a few thousand acres to grow algae and make a good profit, he says.

I hope this guy is extremely successful and makes a billion dollars. He has the potential here to make a contribution to society that most of us only dream about. As he himself said “This is a big idea, a really powerful idea.” I couldn’t agree with those sentiments more.


Biodiesel has a much greater energy content than ethanol, and diesel engines are more efficient than spark ignition engines. The energy return for biodiesel is over double that of ethanol. One the downside, most of us don’t drive vehicles with diesel engines, and there is a technical problem (minor, in my opinion) that biodiesel will solidify in cold weather. But the most amazing thing is that biodiesel can be produced from algae that have been used to reduce carbon emissions from the exhaust of power plants, in yields as high as 15,000 gallons per acre. This is 2 orders of magnitude higher than biofuel yields from crops. Biodiesel produced from algae is the only theoretically feasible alternative energy solution that could actually replace our current fuel demand. Combined with an aggressive conservation program, success in large scale biodiesel production from algae could ultimately lead to energy sustainability. The one thing we lack here is a good analysis of the energy balance. The group at UNH reports that the EROI is likely to higher than the 3.2 reported for soybeans, but I would still like to see a rigorous analysis.


1. Wide-scale Biodiesel Production from Algae

2. Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus

3. Algae — like a breath mint for smokestacks

4. Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus

  1. By Alternative Fuel on September 18, 2011 at 10:32 pm

    That is right! Advanced diesel vehicles using EPA-mandated ultra-low sulfur diesel (ULSD) fuel are among the most fuel-efficient vehicles available today.

    In fact, The Navy hopes to have completed testing and approved a biofuel for use in their fighter jets by 2013 and is looking to do the same for its ships in the same time frame.

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