Archive for EROEI

Renewable Energy World Podcast: The Renewables Gap

As a long-time listener to the Stephen Lacey’s weekly podcast, I was happy to join in as he takes an in-depth look at the Renewables Gap: the question of where the energy is going to come from to power the necessary transition to a clean energy economy, an issue I looked at in Managing the Peak Fossil Fuel Transition.

I’m in great company on this podcast, so if you don’t tune in for me, you might want to know what Bill McKibben has to say about it.

You can download or listen to the podcast here.

Comments (2)

The ERoEI of Energy Efficiency

In previous articles, I’ve often claimed that the Energy Return on Energy Invested (ERoEI) for energy efficiency measures is much higher than the ERoEI for Renewable or fossil energy generation. This was based on the logic that a high ERoEI is needed to sustain the high financial returns from energy efficiency. Unfortunately, there are few studies of the energy return on energy efficiency, so most of my evidence was anecdotal.

No longer. I was just reading the 2009 Annual report for Green Building company PFB Corporation (PFBOF.PK.) PFB manufactures SIPS (Structural Insulated Panels) and ICFs (Insulated Concrete Forms) and in their sustainability report, they found that the energy saved by their insulation over 50 years would be approximately 130 times the energy used in its manufacture (see chart.)

Since ERoEI is a flawed measure, I also calculated the Energy Internal Rate of Return (EIRR), using both 25 year and 50 year lifespans… they worked out to be 262% and 264%, respectively. For comparison, the highest EIRR I’ve found for a energy generation technology is 205% for wood cofiring. The EIRR for a wind turbine is around 84%, and a combined cycle natural gas plant has an EIRR about 164%.

In otherwords, insulation is a slam-dunk when it comes to energy economics. That’s no surprise, but it’s nice to have some numbers, so we have a better idea of just how good a slam dunk it is.

Comments (11)

Energy Internal Rate of Return (EIRR) Numbers from a Literature Review

Jamie Bull at oCo Carbon Blog has conducted a literature review of Energy Return on Investment (EROI) for electricity generation technologies.

He also calculated Energy Internal Rate of Return (EIRR), a concept I promoted here and here to incorporate the timing of energy flows. Timing of energy flows is as important as total energy flows because renewable electricity generation typically requires almost all energy to be invested up front, while fossil generation technologies spread out this investment over the lifetime of the plant.

Jamie’s numbers make fossil generation technologies look much worse than mine did, but mine came from just one report and some simplifying assumptions, while his were based on a literature search. We’re still trying to determine the source of the discrepancy, but until we do, you should assume that his numbers are more accurate.

Comments (1)

A Little More On IRR and EIRR

For non-financial readers looking to understand Internal Rate of Return (IRR), which I used as the foundation for Energy Internal Rate of Return (EIRR) in my article Managing the Peak Fossil Fuel Transition, you can find a good discussion of IRR on Wikipedia.

In practical terms, IRR is nearly always calculated in a spreadsheet from a column of numbers indicating the directional cash flows (negative for investment, positive for returns.)

The Excel spreadsheet I used to estimate the IRRs of various generation technologies is available here.

Tom Konrad

Comments (3)

Managing the Peak Fossil Fuel Transition 

EROI and EIRR

by Tom Konrad, Ph.D.

Current renewable energy technologies must be adopted in conjunction with aggressive Smart Growth and Efficiency if we hope to continue our current standard of living and complex society with diminished reliance on fossil fuels. These strategies have the additional advantage that they can work without large technological breakthroughs. 

Energy Return on Investment

Energy keeps our economy running.  Energy is also what we use to obtain more energy.  The more energy we use to obtain more energy, the less we have for the rest of the economy.  

The concept of Energy Return on Investment (EROI), alternatively called Energy Return on Energy Invested (EROEI) has been widely used to quantify this concept.  The following chart, from a SciAm paper, shows the EROI of various sources of energy, with the tan section of the bar representing the range of EROIs depending on the source and the technology used.  I’ve seen many other estimates of EROI, and this one seems to be on the optimistic (high EROI) end for most renewable energy sources.

The general trend is clear: the energy of the future will have lower EROI than the energy of the past.  Low carbon fuels such as natural gas, nuclear, photovoltaics, wind, and biofuels have low EROI compared to high-carbon fuels such as coal and (formerly) oil.   

The graph also clearly shows the decline in the EROI over time for oil.  Other fossil fuels, such as coal and natural gas, also will have declining EROI over time.  This happens because we always exploit the easiest resources first.  The biggest coal deposits that are nearest to the surface and nearest to customers will be the first ones we mine. When those are depleted, we move on to the less easy to exploit deposits.  The decline will not be linear, and new technology can also bring temporary improvements in EROI, but new technology cannot change the fact that we’ve already exploited all the easiest to get deposits, and new sources and technologies for extracting fossil fuels often fail to live up to the hype.

While there is room for improvement in renewable energy technologies, the fact remains that fossil fuels allow us to exploit the energy of millions of years of stored sunlight at once.  All renewable energy (solar, wind, biomass, geothermal) involves extracting a current energy flux (sunlight, wind, plant growth, or heat from the earth) as it arrives.  In essence, fossil fuels are all biofuels, but biofuels from plants that grew and harvested sunlight over millions of years.  I don’t think that technological improvements can make up for the inherent EROI advantage of the many-millions-to-one time compression conveys to fossil fuels.

Hence, going forward, we are going to have to power our society with a combination of renewable energy and fossil fuels that have EROI no better than the approximately 30:1 potentially available from firewood and wind.  Since neither of these two fuels can come close to powering our entire society (firewood because of limited supply, and wind because of its inherent variability.) Also, storable fuels such as natural gas, oil, and biofuels all have either declining EROI below 20 or extremely low EROI to begin with (biofuels). Energy storage is needed to match electricity supply with variable demand, and to power transportation. 

Neither hydrogen nor batteries will replace the current storable fuels without a further penalty to EROI.  Whenever you store electricity, a certain percentage of the energy will be lost.  The percent that remains is called the round-trip efficiency of the technology, shown on the vertical axis of the graph below, taken from my earlier comparison of electricity storage technologies. (Click to enlarge.)

Storage Technology Comparison

Round trip efficiency (RTE) for energy storage technologies is equivalent to EROI for fuels: it is the ratio of the energy you put in to the energy you get out.  You can see from the chart, most battery technologies cluster around a 75% RTE.   Hence, if you store electricity from an EROI 20 source in a battery to drive your electric vehicle, the electricity that actually comes out of the battery will only have an EROI of 20 times the RTE of the battery, or 15.  Furthermore, since batteries decay over time, some of the energy used
to create the battery should also be included in the EROI calculation, leading to an overall EROI lower than 15.

The round trip efficiency of hydrogen, when made with electrolyzers and used in a fuel cell, is below 50%, meaning that, barring huge technological breakthroughs, any hoped-for hydrogen economy would have to run with an EROI from energy sources less than half of those shown.

Taking all of this together, I think it’s reasonable to assume that any future sustainable economy will run on energy sources with a combined EROI of less than 15, quite possibly much less. 

It’s Worse than That: The Renewables Hump

All investors know that it matters not just how much money you get back for your investment, but how soon.  A 2x return in a couple of months is something to brag about, a 2x return over 30 years is a low-yield bond investment, and probably hasn’t even kept up with inflation.

The same is true for EROI, and means that users of EROI who are trying to compare future sources of energy with historic ones are probably taking an overly-optimistic view.  For fossil fuels, the time we have to wait between when we invest the energy and when we get the energy back in a form useful to society is fairly short.  For instance, most of the energy that goes into mining coal comes in the digging process, perhaps removing
a mountaintop and dumping the fill
, followed by the actual digging of the coal and shipping it to a coal plant.  Massey Energy’s 2008 Annual Report [pdf] states that "In 2008… we were able to open 19 new mines, and ten new sections at existing underground mines."  This hectic rate of expansion leads me to believe that the time to open a new mine or mine section is at most 2 years, and the energy cycle will be even quicker at existing mines, when the full cycle between when the coal is mined and when it is burnt to produce electricity requires only the mining itself, transport to a coal plant, and perhaps a short period of storage
at the plant.  Most coal plants only keep a week or two supply of coal on hand.

In contrast, Nuclear and Renewable energy (with the exception of biofuels and biomass) present an entirely different picture.  A wind farm can take less than a year to construct, it will take the full farm life of 20 years to produce the 10 to 30 EROI shown in the graph.  Solar Photovoltaic’s apparent EROI of around 9 looks worse when you consider that a solar panel has a 30 year lifetime.  Only a little of the energy in for Nuclear power comes in the form of Nuclear fuel over the life of the plant: most is embodied in the plant itself.   

Jeff Vail has been exploring this concept on his blog and the Oil Drum.  He refers to the problem of the front-loading of energy investment for renewable energy as the Renewables Hump.  He’s also much more pessimistic than the above chart about the actual EROI of most renewables, and found this chart from The Economist which illustrates the up-front nature of the investment in Nuclear and Wind: 

In terms of EROI timing, those technologies for which the cost of generation includes more fuel have an advantage, because the energy used to produce the fuel does not have to be expended when the plant is built.

In a steady state of technological mix, EROI is the most important number, because you will always be making new investments in energy as old investments outlive their useful lives and are decommissioned.  However, in a period of transition, such as the one we are entering, we need a quick return on our energy investments in order to maintain our society.  Put another way, Jeff Vail’s "Renewables Hump" is analogous to a cash-flow problem.  We have to have energy to invest it; we can’t simply charge it to our energy credit
card and repay it later.  That means, if we’re going to keep the non-energy economy going while we make the transition, we can’t put too much energy today into the long-lived energy investments we’ll use tomorrow.

To give a clearer picture of how timing of energy flows interacts with EROI, I will borrow the concept of Internal
Rate of Return (IRR)
from finance.  This concept is covered in any introductory finance course, and is specifically designed to be used to provide a single value which can be used to compare two different investments with radically different cash flow timing by assigning each a rate of return which could produce those cash flows if the money invested were compounded continuously.

Except in special circumstances involving complex or radically different size cash flows, an investor will prefer an investment with a higher IRR.

Energy Internal Rate of Return (EIRR)

I first suggested that IRR be adapted to EROI analysis by substituting energy flows for investment flows in early 2007.  I called the concept Energy
Internal Rate of Return, or EIRR
.  Since no one else has picked up the concept in the meantime, I’ve decided to do some of the basic analysis myself.

To convert an EROI into an EIRR, we need to
know the lifetime of the installation, and what percentage of the energy cost is fuel compared to the percentage of the energy embodied in the plant.  The following chart shows my preliminary calculations for EIRR, along with the plant lifetimes I used, and the EROI shows as the size of each bubble.

 EIRR

The most valuable energy resources are those with large bubbles (High EROI) at the top of the chart (High EIRR.)  Because of the low EIRR of Photovoltaic, Nuclear, and Hydropower, emphasizing these technologies in the early stage of the transition away from fossil fuels is much more likely to lead to a Renewables Hump scenario in which we don’t have enough surplus energy to both make the transition without massive disruption to the rest of the economy.

How to Avoid a "Renewables Hump"

Note that the three fossil fuels (oil, gas, and coal) all have high EIRRs.  As we transition to lower carbon fuels, we will want to keep as many high EIRR fuels in our portfolio as possible. 

The chart shows two renewables with EIRRs comparable to those of fossil fuels: Wood cofiring, and Wind.  Wood cofiring, or modifying existing coal plants to burn up to 10% wood chips instead of coal was found to be one of the most economic ways of producing clean energy in the California RETI study. The scope for incorporating biomass cofiring is fairly limited, however, since it requires an existing coal plant (not all of which are suitable) as well as a local supply of wood chips.  Some coal plants may also be converted entirely to wood, but only in regions with plentiful supplies of wood and for relatively small plants.  The EIRR for this should fall somewhere between Wood cofiring and Wood Biomass, which is intended to represent the cost of new wood to electricity plants.

Natural Gas

To avoid a Renewables Hump, we will need to emphasize high-EIRR technologies during the transition period.  If domestic natural gas turns out to be as abundant as the industry claims (there are serious doubts about shale gas abundance,) then natural gas is an ideal transition fuel.  The high EIRR of natural gas fired generation arises mostly because,
as shown in the chart "it’s a gas" most of the cost (and, I assume energy investment) in natural gas generation is in the form of fuel.  Natural gas generation also has the advantage of being dispatchable with generally quick ramp-up times.  This makes it a natural complement to the variability of solar and wind.

However, I think it is unlikely that we’ll have enough domestic natural gas to both (1) rely much more heavily on it in electricity generation and (2) convert much of our transportation fleet to natural gas, as suggested by T Boone Pickens.  We’re going to need more high-EIRR technologies to manage the transition.  Fortunately, such technologies exist: the more
efficient use of energy.  

Energy Efficiency and Smart Growth

I have been unable to find studies of the EROI of various efficiency
technologies.  For instance, how much energy is embodied in insulation, and how does that compare to the energy saved?  We can save transportation fuel with Smart Growth strategies such as living in more densely populated areas that are closer to where we work, and investing in mass transit infrastructure. 
The embodied energy of mass transit can be quite high in the case of light rail, or it can be very low in the case of better scheduling and incentives for ride sharing.

Many efficiency and smart growth technologies and methods are likely to have much
higher EIRRs than fossil fuels.  We can see this because, while the
embodied energy has not been well studied, the financial returns have. 
Typical investments in energy efficiency in utility run DSM programs cost
between $0.01 and $0.03 cents per kWh saved, much less than the cost of new fossil-fired generation.  This implies a higher EIRR for energy efficiency, because part of the cost of any energy efficiency measure will be the cost of the embodied energy, while all of the savings are in the form or energy.   This relationship implies that higher IRR technologies will generally have higher EIRRs as well.  

Smart growth strategies also often show extremely high financial returns, because they reduce the need for expensive cars, roads, parking, and even accidents [pdf.]

Conclusion: Brian or Brawn

The Renewables Hump des not have to be the massive problem it seems when we only look at supply-side energy technologies.  By looking at demand side solutions, such as energy efficiency, conservation, smart growth, and transit solutions, we need not run into a situation where the energy we have to invest in transitioning from finite and dirty fossil fuels to limitless and clean renewable energy overwhelms our current supplies.  

Efficiency and Smart Growth are "Brain" technologies, as opposed to the "Brawn" of traditional and new energy sources.  As such, their application requires long-term planning and thought.  Cheap energy has led to a culture where we prefer to solve problems by simply applying more brawn.  As our fossil fuel brawn fades away, we will have to rely on our brains once again if we hope to maintain anything like our current level of economic activity.

Comments (16)

A Hard Look at the Ethanol Industry

My weekly column for AltEnergyStocks again doubles as part of my study for the second CFA(R) exam.  The Equity valuation part of the curriculum contains a chapter by Michael Porter on analyzing competitive pressures in an industry.  I decided to apply it to the corn based Ethanol industry, and, as often is the case, it changed my way of thinking about the industry.  I’ve never been bullish, because I worry about a classic commodity squeeze: both ethanol and the main feedstock (corn) are commodities, and are subject to forces outside the industry which effect their prices.  For instance, if corn harvests were to be poor because of drought or pests, at the same time that oil prices fell, many ethanol producers would be forced out of business because their costs exceed their selling prices.

I also went on a little rant about the typical measures of Energy Payback and Energy Return on Energy Investment (ERoEI) often used in the industry.  These measures are often used to criticize ethanol, but it is a weak criticism, because they do not take into account the time value of energy: namely that a kWh of electricity today is a lot more useful than a kWh produced 30 years from now.  We should instead be thinking in terms not only of how much energy we have to use to get energy out, but also in terms of how soon we get that energy.

I propose a couple measures, of Energy Net Present Value (ENPV) and Energy Internal Rate of Return (EIRR) which I think would give us a clearer view of the undying energy economics (and hence the potential economic profitability) of various energy production technologies.  But that is a column for another week.

This week, here are my thoughts on competition in the corn Ethanol industry, and how it might affect your investments.

If you have a subscription, there’s also an excellent article in the NYTimes on ethanol in Hawaii.  I think it ties in well to this one, and the one I wrote last July about renewable energy in Maui.

Comments off

Vision of a sustainable energy future

I’ve been meaning to write an article outlining a vision of a sustainable energy future, where biomass is converted into fuel and electricity through pyrolysis and the waste product, carbon is used as a fertilizer a-la terra preta to produce more biomass.  The good news is I don’t have to.  The Engineer Poet did, and it’s just part of a much broader vision you’ll find here.   He also goes into a great discussion of transportation technologies and efficiency which would never have made it into the article I’d write.  I like it when other people crunch numbers, so I don’t have to.

Give yourself a half hour to read the whole article.  It’s worth it.

( Terra Preta: I got a comment from Erich J Knight on terra preta here that went into a lot of depth, but I deleted it by mistake.  Forturnately, he says pretty much the same thing in his blog.  I first heard about terra preta from Ron Larson, chair of the American Solar Energy Society, who is very active in the local (Denver) renewable energy scene.  If you haven’t heard about terra preta, and are concerned about globabl warming or soil fertility without fertilizers from fossil fuels, it’s worth looking into.)

Read the rest of this entry »

Comments (4)

Good Ethanol

I wrote a blog a couple months back talking about how environmentalists should avoid lumping all ethanol together as “bad” renewable energy because the Energy Return on Energy Investment (EROEI) is very low.  First of all, new ethanol plants being built today do have a net energy gain on a well-to-wheels basis (the critics are using decade old data), and so long as the energy inputs come from renewable sources, ethanol looks like a decent way to turn other forms of renewable heat energy into something we can put into our tank and drive around with.

E3 Biofuels is doing just that with a 25 million gallon “closed loop” ethanol plant in Mead Nebraska.  The distiller’s grain byproduct of the ethanol production is fed to cattle at an adjacent feedlot.  This saves energy by avoiding having to dry the grain and transport it to where the cattle are.  The manure from the feedlot is passed into an anaerobic digester which not only produces 100% of the energy necessary for the ethanol distillation process in the form of methane, but it also helps solve the nasty environmental problems caused by the massive supply of manure feedlots produce.  It was runoff from cattle manure that caused the problems with our spinach supply recently.

Other benefits are that by running the manure through the digester, odor is reduced, and methane from the manure decomposition does not escape into the atmosphere.  Methane is a much more potent greenhouse gas than is CO2.

If you believe the promoters that “This plant will make ethanol more than twice as energy-efficient as any other method of producing ethanol or gasoline,” I estimate that the well-to-wheels EROEI is between 2 and 4 (probably closer to 2.)  It’s not the great EROEI’s we get from Wind and geothermal, but it’s a liquid fuel we can use in our existing vehicle fleet (either as E85 in Flex-Fuel vehicles, or as E10 or E20 in standard gasoline engines.)

Without liquid fuel, we’re in great danger of economic disruption due to peak oil, but unless we get that liquid fuel in a manner less carbon intensive than conventional corn ethanol, we’ll be up to our ears in melted icecaps.

Obviously, what we really need is much more energy-efficient cellulosic ethanol which does not compete with our food supply for feedstock, and it will be great if that process is powered by renewable heat (methane form digesters, or solar thermal) but given that we’re unlikely to stop eating beef anytime soon, this is an elegant, closed process.

Comments (1)

There’s Ethanol and then there’s Ethanol

In the renewable energy community, Ethanol has a bad rap, due to some often-quoted, seldom checked studies on energy payback.

It’s received wisdom that ethanol from corn has an energy return on energy invested (EROEI) of somewhere between 0.8 and 1.0; i.e. you get less out than you put in.  The persistence of this idea is possibly due to some great cartoons.  I’m probably going to undermine my whole argument here, by including this one…

Then again, I expect that my audience is highly intelligent, and not easily distracted.  If you weren’t, you probably wouldn’t still be reading my extremely dense and often-tortured prose.  You deserve a good cartoon every now and then…

Back in the world of ethanol, times have changed.

Even though cellulosic ethanol is still very much in its technological infancy, a lot of companies and people are doing a lot of interesting things with corn ethanol to make the process more efficient, and, get those energy inputs in the form of “free” waste heat from some other process, or from renewable sources such as cow manure or landfill gas.

I’ve been educating myself a lot about this reading C. Scott Miller’s Bioconversion blog.  I admit I’m having to do a lot of catch up on this, because I was one of those people who believed ethanol was a total government subsidized boondoggle until recently.

All that said, even at an EROEI of 1.25 to 1.8, ethanol is not much of an energy “source.”  Sure, we’re getting a little energy out of the process, but one way to think about EROEI is how much effort it takes to get our energy. 

As a rough illustration, at an EREOI of 2, there has to be one person working to get energy for every person doing something else.  So if civilization were to exist one out of every 2 people would have to be employed in the energy sector… the other 50% would then have the energy they needed to do other useful things, like be doctors, politicians, soldiers, engineers, builders, investment advisers, bloggers, artists, manufacturers, scientists, psychologists, food farmers (as opposed to energy farmers), talk show hosts, etc.

 You might argue that some of those professions aren’t very useful (investment advisors and politicians perhaps), but even if we eliminate all those “useless” professions, I think the more useful professions like talk show hosts and artists might start finding themselves a little squeezed.

There is a reason that the human race was 95%+ farmers or hunter gatherers for most of of our history: the energy sources we were using were not powerful enough, with too low EROEI to sustain higher forms of civilization, such as talk show hosts.

If you don’t believe me, read this great article on “Peak Wood,” the cause of the iron age.

Back to ethanol: it’s not going to solve our world energy problem.  It’s a useful way to turn non-liquid fuels (manure, biogas, or coal) into something you can put in your car, but if we in the U.S. are  looking for a domestic source of energy that will wean us off the Middle Eastern oil teat, we can do it, only if we want to be a nation of farmers, witha much smaller population and lower standard of living than we have now.

Ethanol is big business these days, and it will make a tiny dent in our oil addiction, so all the investment is probably doing some good.  I predict that the biggest beneficiaries will be the farmers, and considering how hard farming is, that’s not a bad thing.  It’s probably better than out-and-out farming subsidies.

Basically, I’m no longer worked up about ethanol subsidies and mandates.  There are a ton of better ways we could be spending the money, but it’s hardly the stupidest thing our government does with our money.   I’d even be happy about it if they’d simply replace the money spent on all farm subsidies with subsidies for farm based energy.

I just don’t want it to distract from the important work we have to do to deal with the twin probems of peak oil and global warming:

  1. Improve energy efficiency (especially of our vehicle fleet.)
  2. Develop high ERoEI energy technologies: Wind, Solar concentrating, Geothermal.  PV will probably make it on this list as the technology improves.
  3. Displace some of that oil in transport with renewable electricity, via plug-in hybrids.  (Economic fuel cells are still too far away to make hydrogen a viable transportation fuel in the next 20 years)

Comments (8)

John Turner’s Renewable Energy Future; renewable technologies compared.

When you want an informed, but unbiased opinion, it’s usually best to ask someone John A Turnerwhose livelihood does not depend on coming back with the “right” answer.  When it comes to comparing different renewable energy technologies, one of the best experts I’ve heard from is John Turner.   Dr. Turner is a principal scientist for the Center for Electric & Hydrogen Technologies & Systems at the National Renewable Energy Laboratory (NREL), in Golden, Colorado.

The Hydrogen economy is that long hoped for world in which one day our cars will fill up at the corner hydrogen station, and combine that fuel with oxygen in the air, a process which will create electricity for the car’s motor, and with the only emissions being water.  It all sounds wonderful, but to reach that nirvana of zero emissions, the hydrogen itself needs to be produced with non-emitting technology.  That is because, contrary to oversimplified hype from politicians, hydrogen is not an energy source, but rather an energy carrier.  Like a battery, it has to be produced (charged) before it can be used.

Dr. Turner’s goal is to guide us to the hydrogen economy with as few missteps as possible, with missteps in his mind being the used of unsustainable technologies to get there.  Since he wrote his visionary 1999 article in Science, outlining a path to a “Renewable Energy Future” in which hydrogen serves as portable energy storage for an economy fueled solely by renewable sources of power.  The weak link in this chain is fuel cell technology.  Fuel cells are used to efficiently convert hydrogen and oxygen to electricity and water.  They have been around for well over a century, but are still too expensive for use in cars, although they are practical in some military and larger scale civilian operations.  A similar problem exists for hydrogen storage.

In contrast, hydrogen as a storage medium for electricity from intermittent power sources such as wind is a technology whose time has come. Norsk Hydro is currently doing a trial run of a wind/hydrogen combination system on a small Norwegian island, powering 10 homes.

What is most interesting to me about his presentation, is his unbiased comparison of different renewable technologies, along with nuclear, and Internal Gasification Coal Combustion (IGCC) with carbon sequestration.

He compares these technologies for robustness: the ability to meet our future energy needs; for expense, and for Energy Payback.  Energy payback and the related measure EREOI (Energy Return on Energy Invested) give us an idea of how much of our energy will have to be devoted to making more energy.

Here’s the run-down (with some additions of my own):

Technology

Energy Payback/ EROEI Robust? Price per kWh (approximate 2003 prices) Long term?
Wind

3-4 months; 20-30x

Yes

5-8 cents

Yes

Solar PV

3-4 years; 8x

Very

21-24 cents

Yes

Concentrating Solar

5 months; 40x

Very

8 cents

Yes

Biomass

varies

No

7 cents

Yes

Geothermal

varies by source

No

4-7 cents

Yes

Nuclear

1 year, not counting waste disposal. <20x

Yes

13-18 cents

?

Coal (w/ carbon sequestration)

16% of energy required for sequestration.

For now

5-6 cents

70 yrs, at current growth rates.

Energy efficiency

months; 50x +

Can never get all energy from efficiency

1-2 cents

Yes

(Items with links are from linked sources)

We’ll need all these energy sources, but Wind and concentrating Solar (CSP) stand out as near-term, robust, economical solutions, while Energy Efficiency and Geothermal will give us the most bang for our buck as we try to get started down the road.

Comments off

Ethanol vs. Biodiesel

A new study from the university of Minnesota comparing the lifecycle energy costs and emissions of corn ethanol to soy biodiesel is all over the press this morning. 

The results are no surprise to any of us who follow the industry: corn ethanol yields 25% more energy than it takes to produce it; while soy biodiesel yields 93% more.

The numbers for ethanol ar not new: people have been arguing about the EROEI (Energy Return on Energy Invested) for ethanol for years, and the numbers have slowly risen with improving technology from about -10% to today’s 25%.  What are new, are the EREOI numbers for soy biodiesel.  I had only heard one number for the EREOI of “biodiesel” before – and no mention of the feedstock was made, nor was I able to trace it back to a reputable source… I suspect it was a back of the envelope calculation by a biodiesel advocate.  That number was a 220% return, quoted to me twice, once by management at Blue Sun Biodiesel, and once by the person manning the booth for the International Center for Appropriate and Sustainable Technology, both of whom do good work, but who have an incentive to believe this highest number they hear.  Disclaimer: I too have an incentive to believe the highest number I hear because I have a Jeep that I use biodiesel in to minimize my carbon emissions.   Using the new numbers, my Jeep Liberty has about the same carbon footprint as my 2002 Prius, when running on B100.  On B20, which I use in the winter, the Prius still looks much better.   I’m pining for a plug-in hybrid diesel.

But I’m very happy to see reality injected into the whole biofuels debate.  Neither ethanol not biodiesel (nor both together) is going to save the US from having to import petroleum: if our entire corn and soybean output were shifted to these biofuels, that would only replace about 12% of gasoline demand, and 6% of diesel demand… are we ready to start talking about massively investing in increasing the efficiency of our vehicles yet?

One other new note in the article, which I like given my affection for biodiesel, is that soy is a much less fertiliser intensive crop than corn, and so growing it has fewer local environmental impacts. I hope these authors continue their work, and expand the study to include other feedstocks for both ethanol (sugarcane, cellulostic) and biodiesel (canola, algae, recycled oil).

Comments (3)

Follow

Get every new post delivered to your Inbox.

Join 142 other followers