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:


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.


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:


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:


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

18 thoughts on “Biodiesel: King of Alternative Fuels”

  1. The “start on something else and switch to congealing fuel when heat is available to make it flow” trick is already in use by people who burn “greasel” (unmodified waste cooking grease).

    – E-P, from the road

  2. You will have to tell me more about how that works when you get back. Waste heat from the exhaust seems to me like the ideal heat source, and it would heat up the fuel very quickly.

  3. It’s not exhaust heat that folks use. Most employ a system of copper tubing integrated into some sort of in-trunk tank. This tubing is plumbed into the vehicles radiator, so the hot coolant is carried to where the oil is stored. A dash switch hooked to a thermostatic gauge (of some sort, I’m not sure) “red lights” when you’re up to operating temp, and you switch over from petro- or biodiesel to the straight vegetable oil (SVO). At shutdown, you switch back for a minute or so to flush the system.

    From my research and discussions with local DC biodieselers, running on SVO can coke up the engine over time, but reports are conflicting. I think it depends on the operating RPM, injection pressures etc. I don’t own a car so I’m not too sure.

  4. Two Questions.

    Assuming there was an installed gas tank warmer to keep the fuel in liquid form, are there any harmful effects to the engine if you were to just put biodiesel into your 18 wheel truck? –like seals wearing out differently, or engine life reduction or anything like that?

    Second. I’m estimating that a 2000 acre project next to a coal power plant would equal 810 hectares. $80,000 per hectare equals a little under $65,000,000 to set up the production ponds. Add to that an operating cost of $10,000,000 equals $75,000,000 to set up, and run the show for a year. According to this post it would produce 40,000,000 gallons of biodiesel and 50,000,000 gallons of ethanol. Even at $1/gallon for each that would yield 90 million dollars of revenue. If those numbers are anywhere close to reality, this is a financial no brainer.

    So the second question… is my math wrong?

    Third question. Why isn’t everybody talking about this?

  5. Jay,

    My understanding is that biodiesel is better for engines because it has a higher lubricity. The primary disadvantage right now is that biodiesel is currently produced mostly from soybeans, and that is more expensive to produce than regular diesel.

    I think the only thing that might be wrong with the math is that the 15,000 gallons is a maximum theoretical yield. I am not sure what their actual yields are at this time.


  6. What about feedstocks? Is that a limiting factor? If we were to convert all our municipal sewage waste over to growing biodiesel algae, combined with CO2 waste from coal burning power plants (ignoring the fact that they’re probably not next to each other)…. Is there enough feedstock to actually grow this algae?

  7. One of the unfortunate side effects of ethanol is that it is highly corrosive and can not be transported via pipelines. As a result it must be trucked, which is more expensive, both in terms of dollar cost as well as energy.

    Supposing that the algal biodiesel production numbers are correct, is distribution feasible? Does biodiesel have the same corrosive effects? What effect might the coagulation problem have on distribution?

  8. You can pump biodiesel without problems. The only real problem is that it gels in cold weather. The rememdy to this is to blend with conventional diesel, or design future vehicles with some kind of fuel system heater for cold weather.

  9. I found this article to be phenomenal, but evenmore is its content. What an ingenious idea to use algea as a fuel source and as a carbon dioxide net. I hope that adiquate funding is provided for such projects, I can’t see why any one wouldn’t want to invest in this. I for one have decided to be an activist towards the goal of converting this nations main fuel source to biodiesel.

    To answer your first question, biodiesel can be mixed at any ratio with petro-diesel. Therefore it can be used at any time on a diesel engine, however, it is recommended that after a short use of biodiesel you replace the filters for there might be some gunk that has built up by the cleaning that biodiesel provides to the system. Also vehicles made before 1992 will have rubber hoses and gaskets which are destroyed by biodiesel, so obviously it would have to be used in a vehicle that has Viton hoses.

  10. Good article, Robert!

    For more on using straight waste grease in a diesel car, and using exhaust heat to melt the grease, see There are also others, as Google will testify…

    The key missing ingredient to the current energy debate (if one can even call some of the bone-headed ideas floating around a debate) is the basics. I would phrase it as two questions:
    1. What would the ideal “fuel of the future” look like?
    2. What would serve as an ideal feedstock to making that “fuel of the future”?

    The answer to Q1 IMHO is this: as close to the fuels we use today as possible. This may disappoint many people who are looking for the next great thing. But let’s face it, liquid fuels have many advantages over gaseous fuels (as any chemical engineer would be aware of), with apologies to the hydrogen crowd.

    This is part of why biodiesel is better than ethanol. Biodiesel blends better with diesel than ethanol blends with gasoline (BX i.e. B5, B10 etc. can be pumped just like diesel, unlike EX where the ethanol has to be shipped separately, at cost).

    Even better than biodiesel would be renewable hydrocarbons, like TDP/TCP40 and BTL. These would avoid the gelling problems of biodiesel. They would also be easier to produce, avoiding the rather tedious transestrification step required for biodiesel production.

    The answer to Q2 is waste. A DOE/USDA report, Billion Ton Vision found that the US could potentially produce 1.3 billion tons per year of biomass, which could replace 33% of transportation fuel use.

    Of course, 33% is not 100%, but it is a huge step forward. There are many side benefits to like cleaning up the environment, the potential to recycle nutrients, reducing landfill waste, etc.

    Once we approach full use of this source, we would need to look at other sources. This is where algal systems that you have been discussing would fit in.

  11. Re biodiesel and running on vegetable oils:
    I have been running my diesel on waste canola oil for the past 15 months, done 28,ooo kms at a cost of 10 cents per litre (we’re metric here, 5 litres = 1 US gallon). I use the radiator pipes to heat the oil and a spare diesel tank to start up and flush the injectors on shut down. This is standard practice, thousands of people have these kits. There’s no problems with gunking up injectors. I add a biocide to stop bugs in the fuel, maybe (ironically) the sort of bugs in algal biodiesel?
    But I think biodiesel is the way to go long term, particularly algae production. Volumes are much higher, companies can set up their own plants and sell to themselves (cutting out retail, transport costs and decentralising power-based retail chains), it’s very sustainable, environmentally friendly and cost effective.

    Anyone know where you get the algae from?

  12. I have been running my diesel on waste canola oil for the past 15 months

    Does it smoke much, or has it given you any other problems of note?

    Anyone know where you get the algae from?

    NREL has a “library” of high oil algae, but it takes a lot of turn that algae into biodiesel. It is technically feasible, but complex and finicky.

    Cheers, Robert

  13. As a grad student at MIT, I’ve seen the greenfuels installation and heard the numbers quoted for biodiesel production from algae. I’m wondering if you’ve given any thought to the consequences of using methanol in the production of biodiesel, since it is derived mainly from natural gas. As I understand it, a mole of methanol is required to produce a mole of transesterified fatty acid (biodiesel)… I suppose ethanol could be used, but I don’t think you’d be a huge advocate of that.

  14. For the future: if we’re plugging our cars in overnight to charge them up anyway, plug-in biodiesel hybrid could easily have a small heater connected to the fuel tank, right? A small timer either in the car or at the socket-end could warm up the fuel tank an hour before you need to leave in the morning.

    I don’t know how common block heaters are in the US, but they’re common here in Canada. Similar concept, I would think.

  15. hey,

    Great post, and I was wondering if you or anyone elese would be interrested in submitting renewable energy related articles to, while promotign your website by placing up to 3 links back to your site?

    I hope some of you will take up this opportunity, I hope to create a trusted community of authors with a great deal of interest in energy.


  16. one fueltank of biodiesel is equal to enough rice to keep an african male human alive for 1year…

    is it all that great?
    I say go thorium power plants.

  17. Very cool, I build biodiesel processors which turn waste vegetable oil into biodiesel. It is really amazing how simple the process is, as well as saving the customer $2-3 per gallon at the pumps. Algae biodiesel looks even more promising. As the other poster said, we just need to keep moving in the right direction.

Comments are closed.