As the person who came up with the term  EROI in the 1970s (but not the concept: that belongs to Leslie White, Fred Cotrell, Nicolas Georgescu Roegan and Howard Odum) let me add my two cents to the existing mostly good posts.   The problem with the "stacked " idea is that if you do that you do not deliver energy to society with the first (or second or third) investment --- it all has to go to the "food chain" with only the final delivering energy to society.  So stack two EROI 2:1 technologies and you get 4:2, or the same ratio when you are done.

The second problem is that you do not need just 1.1:1 EROI to operate society.  We (Hall, Balogh and Murphy 2009)  studied how much oil would need to be extracted to drive a truck including the energy to USE the energy.  So we added in the energy to get, refine and deliver the oil (about 10% at each step) and  then the energy to build and maintain the roads, bridges, vehicles and so on .    We  found you needed to extract three liters at the well head to use one liter in the gas tank to drive the truck, i.e. an EROI of 3:1 was needed.  

But even this did not include the energy to put something in the truck (say grow some grain)  and also, although we had accounted for the energy for the depreciation of the truck and roads,  but not the depreciation of the truck driver, mechanic, street mender, farmer etc: i.e. to pay for domestic needs, schooling, health care etc. of their replacement.    Pretty soon it looked like we needed an EROI of at least 10:1 to take care of the minimum requirements of society, and maybe 15:1 (numbers are very approximate) for a modern civilization.  You can see that and the implications worked out in Lambert et al.  below.  

I think this and incipient "peak oil" (Hallock et al. )   is behind what is causing most Western economies to slow or stop  their energy and economic growth.   Low EROI means more expensive oil (etc) and lower net energy means growth is harder as there is less left over after necessary "maintenance metabolism".    This is explored in more depth in Hall and Klitgaard book  "Energy and the wealth of Nations" (Springer).    

Charles Hall [email protected]

References:

Hall, C.A.S., Balogh, S., Murphy, D.J.R. 2009. What is the Minimum EROI that a Sustainable Society Must Have? Energies, 2: 25-47.

   Hall, Charles  A.S., Jessica G.Lambert, Stephen B. Balogh. 2014.  EROI of different fuels  and the implications for society Energy Policy Energy Policy. 64,: 141–              http://www.sciencedirect.com/science/article/pii/S0301421513003856?np=y      htt??//authors.elsevier.com/sd/article/S0301421513003856  

Lambert, Jessica,  Charles A.S. Hall, Stephen Balogh, Ajay Gupta,    Michelle Arnold  2014   Energy, EROI and quality of life.  Energy Policy Volume 64:           153-      http://authors.elsevier.com/sd/article/S0301421513006447

Hallock Jr., John L., Wei Wu, Charles A.S. Hall, Michael Jefferson. 2014.  Forecasting

           the limits to the availability and diversity of global conventional oil supply:

           Validation.  Energy 64: 130-153.   (Article 12 in: 

            http://www.sciencedirect.com/science/journal/03605442/64/supp/C     

       http://www.sciencedirect.com/science/journal/03605442/open-access 

The first hand waving explanation that comes to mind is that the energy economy has simultaneous energy outlays that accompany energy production and are not included in the EROI calculation.  In the numbers you use in your example, there needs to be a functioning economy maintained by the two 'free' units of EROI: supply chains, food production, finance, medicine, services, and so on. All of those activities require energy to operate.

Two free units are not enough, especially if you are investing some in further energy production: supply chains fail, panel production ceases because of those externalities; the problem compounds.

As I understand the argument, the energy producing part of the economy (renewable energy) uses 1 unit of energy itself while providing e.g. 2 spare units of energy for everything else. Ultimately the limitations work out in economics. Money spent on energy represents someone's time making it, plus someone else's time digging up the minerals to make it. The limiting resource is human time and depleting minerals which show up as ever decreasing quality of ores. The good news is that mining and manufacturing are becoming ever more automated. Ultimately we could have huge factories run by robots, fed with minerals dug up by self-driving diggers and dumper trucks, all running on solar electricity and hydrogen. So as Nils Ross says the EROEI could compound, if the system as a whole is energy-positive. I think there are enough alternative technologies out there that depletion of any one mineral will not be a problem as it will lead to the substitution of less scarce ones. We just need to make the transition quickly while we still have the fossil-fuel based economy to pump-prime it all. The bad news is that with an aging population, most jobs left in the economy will be looking after old people and serving frothy coffee while the tax rate will be very high, but that's another story...

Khalid, I know you use an EROEI of 3 for PV only of an example. But just to be certain that readers don't think that this is the definite value: in the literature values are found in the range of 3 to 9.

Many thanks for the responses Nils and John.

If I understand you correctly, if it were possible to come up with some comprehensive societal EROI figure (i.e. one that included not only energy input for all activities of the project, all material used by the project, but also an appropriate share of all energy required to sustain other activities related to the supply chain etc.) and this figure were greater than 1.0 then it should be possible to compound renewable resources.

For this to work in practice all of the energy input into all those processes would need to be PV (as discussed by John with his solar-powered self-driving diggers etc.) but for this question I'm just interested in the energy numbers.

Does this then mean that we can trade-off renewable energy density against external EROI? For example a 5m2 area could yield around 900kWh of energy (depending on location, tracking, etc.) per year at an external EROI of (say) 3.0, or 450kWh of energy per year at an external EROI of 9.0.

As I understand it this would be functionally similar to the extraction of tar-sands oil which is able to achieve relatively high external EROI, but a large proportion of the energy used in the extraction comes from the tar-sands themselves.

Jethro, many thanks for the comment. As you say, I am just using the figure for PV as an example. I understand EROI is difficult to calculate definitively, even if the inclusions/exclusions are consistent.

As the person who came up with the term  EROI in the 1970s (but not the concept: that belongs to Leslie White, Fred Cotrell, Nicolas Georgescu Roegan and Howard Odum) let me add my two cents to the existing mostly good posts.   The problem with the "stacked " idea is that if you do that you do not deliver energy to society with the first (or second or third) investment --- it all has to go to the "food chain" with only the final delivering energy to society.  So stack two EROI 2:1 technologies and you get 4:2, or the same ratio when you are done.

The second problem is that you do not need just 1.1:1 EROI to operate society.  We (Hall, Balogh and Murphy 2009)  studied how much oil would need to be extracted to drive a truck including the energy to USE the energy.  So we added in the energy to get, refine and deliver the oil (about 10% at each step) and  then the energy to build and maintain the roads, bridges, vehicles and so on .    We  found you needed to extract three liters at the well head to use one liter in the gas tank to drive the truck, i.e. an EROI of 3:1 was needed.  

But even this did not include the energy to put something in the truck (say grow some grain)  and also, although we had accounted for the energy for the depreciation of the truck and roads,  but not the depreciation of the truck driver, mechanic, street mender, farmer etc: i.e. to pay for domestic needs, schooling, health care etc. of their replacement.    Pretty soon it looked like we needed an EROI of at least 10:1 to take care of the minimum requirements of society, and maybe 15:1 (numbers are very approximate) for a modern civilization.  You can see that and the implications worked out in Lambert et al.  below.  

I think this and incipient "peak oil" (Hallock et al. )   is behind what is causing most Western economies to slow or stop  their energy and economic growth.   Low EROI means more expensive oil (etc) and lower net energy means growth is harder as there is less left over after necessary "maintenance metabolism".    This is explored in more depth in Hall and Klitgaard book  "Energy and the wealth of Nations" (Springer).    

Charles Hall [email protected]

References:

Hall, C.A.S., Balogh, S., Murphy, D.J.R. 2009. What is the Minimum EROI that a Sustainable Society Must Have? Energies, 2: 25-47.

   Hall, Charles  A.S., Jessica G.Lambert, Stephen B. Balogh. 2014.  EROI of different fuels  and the implications for society Energy Policy Energy Policy. 64,: 141–              http://www.sciencedirect.com/science/article/pii/S0301421513003856?np=y      htt??//authors.elsevier.com/sd/article/S0301421513003856  

Lambert, Jessica,  Charles A.S. Hall, Stephen Balogh, Ajay Gupta,    Michelle Arnold  2014   Energy, EROI and quality of life.  Energy Policy Volume 64:           153-      http://authors.elsevier.com/sd/article/S0301421513006447

Hallock Jr., John L., Wei Wu, Charles A.S. Hall, Michael Jefferson. 2014.  Forecasting

           the limits to the availability and diversity of global conventional oil supply:

           Validation.  Energy 64: 130-153.   (Article 12 in: 

            http://www.sciencedirect.com/science/journal/03605442/64/supp/C     

       http://www.sciencedirect.com/science/journal/03605442/open-access 

Many thanks for the response and the references Charles.

I'm still struggling a little bit with gaining an intuition of why it is not possible to stack/compound EROI. If I understand your response correctly part of the problem is that while society is waiting around for energy from one project to be fed into a second project (etc.) society needs to continue to operate (otherwise it'd all be a bit pointless!) and this has a high energy overhead.

I understand that with oil it is possible to achieve higher external EROI by using some of the oil as the main source of energy for extraction/processing. Obviously this means less oil is delivered to the outside world, but it is delivered at a higher EROI which is more useful. I don't understand why a similar gearing is not possible with renewables.

Is it something to do with the timing of the input energy required VS the timing of the energy which the project will deliver over its life?

Khalid

Indeed if you update the QUALITY of the energy you can come out "ahead" .  My PhD adviser Howard Odum wrote a lot about that, and I am deeply engaged in a discussion about the general meaning of Maximum Power (a related concept) with several others.  (Send me your email to [email protected] and I will send you a paper. So you can willingly turn more coal into less electricity because the product is more valuable.   Probably pretty soon (if we are not already) we will be using coal to make electricity to pump out ever more difficult oil wells....

I have also been thinking about EROI a lot lately and about what should the boundaries of analysis be.   One of my analyses is available in the book "Spains PV revolution: EROI and.. available from Springer or Amazon for I think $40.   ALso I just write this paragraph for other purposes but I am including it for you to think about.  It might help you think about the issue of stacking: 

"To me the issue of boundaries remains critical. I think it is proper to have very wide boundaries. Lets say we run an economy just on a big PV plant. If the EROI is 8:1 (which you might get, or higher, from examining just the modules) then it seems like you could make your society work. But lets look closer. If you add in security systems, roads, and financial services and the EROI drops to 3:1 then it seems more problematic. But if you add in labor (i.e. the energy it takes to make the food , housing etc that labor buys with its salaries, calculated from national mean energy intensites times salaries for all necessary workers) it might drop to , lets say, 1:1. Now what this means is that the energy from the PV system will support all the purchases of the workers that are building/maintaining the PV system (let's say 10 percent of all workers, as may be the case for the energy workers in US now) they will be taken care of, BUT THERE WILL BE NO PRODUCTION OF GOODS AND SERVICES for the rest of the population. TO me this logic is why we should include salaries of the entire energy delivery system (although I do not because it remains so controversial). I think this concept, and the flat oil production in most of the world, is why we need to think about ALL the resources necessary to deliver energy from a project/technology/nation."  

Khalid, I am certainly not the expert Dr. Hall is on this, so I also find it confusing. In my mind, the difficulty I encounter (and it sounds like perhaps you do as well) is one of accounting and defining the start and end points.  I think this is similar to or at least related to the issues of boundaries that Dr. Hall is interested in.

As I understand your comments, you envision the problem as such: Start with one unit of energy  to make PV panels that produce 2 units of energy.  I then invest those 2 units entirely to make 4 units.  I can then invest those entirely to make 8 units, and then do the same to make 16 units.   At this point you provide the output to the economy.  From this point of view then your initial 1 unit of electricity is now providing 16 units to the economy. A second option is to look at the conversion at each stage.  At stage you only achieve a 2:1 gain (2:1, 4:2, 8:4, 16:8 etc.).  Taking this further, it seems to me there is a third possible way you could look at the problem. You can sum the energy at each stage (1+2+4+8 =15) and compare it to the output.  That is you invested a total 15 units of energy to build a device which yields on 16. 

Judging by his initial answer to you, Dr. Hall seems to indicate that the way to approach the problem is the second.  I think the reason for this is the boundary conditions/end state of the scenario.  Where I (and perhaps you) think I get off track is in thinking about this in the transitional period.  I.e. at the current time, one can envision using coal or oil etc. to be the initial investment (the 1 unit in the scenario) and that also drives the world while you are ramping up.  During this period the stacking math you propose somewhat makes sense to me.  However, once you replace enough of the fossil (or high return) capacity with the 2:1 for example  (i.e. you scale to a large enough point where most of your capacity is 2:1) you reach a tipping point where you can no longer grow because your average return over the economy is closer to 2:1 than 20:1.  As  I think you agree, 2:1 is not enough to run the economy much less run the economy and have excess to divert to the multiplication/stacking effort.  I.e. as you move closer to making a complete transition, you reach a limit in the size of the energy economy and (maybe?) the third type of math looks more like where you are.  Then as things age and come off line you are in big trouble.  Of course one thing that isn't considered here is the possibility of improvements in efficiency etc. that could significantly increase the return for the (currently) low technologies. 

Hope that's helpful and at least close to being somewhat coherent and correct.  As i said I am not the expert Dr. Hall is in the subject, but i thought my own struggles with sorting through this might be of use.

Many thanks once again for the detailed responses Charles and James. I am getting much closer to understanding and accepting this now.

I will try and come up with a concrete example where I think EROI-gearing should work (with made-up but plausible numbers) and if I can't poke holes in it myself will post it here for criticism. I realise now that my original question was a little bit vague and it would be helpful for me to consider a concrete (if fictional) proposal, as this should clarify the issues surrounding boundaries (of both scope and in terms of start/stop effects) which I think I'm struggling with.

Khalid

Hmmm, maybe I see your point.   I suppose over time you could do this, but why are we not already doing this with our 10 or 20:1 resources:  10:1 --> 100:1  --> 10,000:1.   I think it has something to do with the entire economic activity associated with generating energy.   Here is a response I had about the boundaries that might be used in EROI,  WHile itis not exactly addressed to your question it is close enough:

To me the issue of boundaries remains critical. I think it is proper to have very wide boundaries. Lets say we run an economy just on a big PV plant. If the EROI is 8:1 (which you might get, or higher, from examining just the modules) then it seems like you could make your society work. But lets look closer. If you add in security systems, roads, and financial services and the EROI drops to 3:1 then it seems more problematic. But if you add in labor (i.e. the energy it takes to make the food , housing etc that labor buys with its salaries, calculated from national mean energy intensities times salaries for all necessary workers) it might drop to , lets say, 1:1. Now what this means is that the energy from the PV system will support all the purchases of the workers that are building/maintaining the PV system (let's say 10 percent of all workers, as may be the case for the energy workers in US now) they will be taken care of, BUT THERE WILL BE NO PRODUCTION OF GOODS AND SERVICES for the rest of the population. TO me this logic is why we should include salaries of the entire energy delivery system (although I do not because it remains so controversial). I think this concept, and the flat oil production in most of the world, is why we need to think about ALL the resources necessary to deliver energy from a project/technology/nation.

I will need to think about your cascading EROI somemore.  At a mimimum you would have to wait a long time for this to play out and probably your workers would starve!  But let me think some more. 

Hi,

I finally got around to doing a bit more thinking about this and I have come up with the attached by way of a thought experiment. My conclusions from this very simplistic analysis is that EROI-gearing which we've discussed above is not that important.

What seems to be more important is to have a means of deploying renewable energy that is truly sustainable, in that it can deliver net energy to society, whilst also internally providing all energy required for indefinite operation (given some up-front investment of energy).

This feels a bit like the EROI equivalent of a perpetual motion machine, but I don't think it violates any laws of thermodynamics (it still relies on a massive net input of energy from the sun). Rather than the elaborate system of self-replicating robots suggested above and in the attached, we could consider instead a genetically modified tree which outputs a liquid fuel, and thrives and survives without conventional (energy intensive) agricultural inputs such as irrigation and fertilizers (like the joule energy concept).

Criticism expected and welcomed, although I'd prefer if we didn't dwell on the fact that a lot of the technology used in the attached doesn't exist yet. My main interest is whether the relatively low EROI of renewable energy sources fundamentally limits the complexity of a society that can be fueled by them.

http://www.jouleunlimited.com/

Khalid

Perhaps the easiest way to think about this is historical:certainly we had lots of sunshine and clever minds in the past.  But we did not have  a society with many affluent people until the industrial revolution, based on millions of years of accumulated net energy from sunshine. AN affluent king, living a life of affluence less than most people in industrial societies now, was supported by the labor of thousands or millions of serfs harvesting solar energy.  The way to get rich was to exploit the stored solar energy of other societies through wear (see Plutarch or more recently Joe Tainter's the collapse of complex societies).

Your PV example implies (I Think) an EROI of 20:1. Of course if you can get that good for you, and that leaves 19 to deliver to society. SO then your plan would work I think. Better than oil now.

But in fact most renewable energy (good hydropower is an exception) are low EROI or else seriously constrained by indeterminacy.  If you want to see this in detail I suggest you read the small book "Spain's PV revolution" (Prieto and Hall, $40 from SPringer).  Look at all the stuff required to support "free" solar energy.   WE (and Palmer and Weisbach independently) found EROIs of about 3:1 at best when all costs are accounted for. 

The lower the EROI the larger the investment needed for the next generation: that is why fossil fuels with EROIs of 30 or 50 to one have led to such wealth : the other 29 or 49 have been deliverable to society to do economic work or can be invested in growth of the fuel.  If the EROI is 2:1 obviously half has to go into the next generation for the growth and much less is delivered to society.   One can speculate or fantasize about what one can do with some future technology but having been in the energy business for 50 years I have seen many come and go.  Meanwhile we still get about 75-80 percent of our energy from fossil fuels (with their attendant high EROI).   Whether this is changing is of course of great interest. 

I suppose intensive palm oil or jatropha  comes as close as anything to what you suggest, but I think they are both pretty energy (including labor) intensive.   Brazillian sugar can an make ethanol at an EROI of  8:1 but often causes soil degradation.   So I am not holding my breath,  but keep at it.   I am happy to be proved wrong.  

ps. could you please send the Melbourne link you included to me at [email protected].  I could not open it. 

Charlie

Hi Khalid,

 It was this one I could not download. I was confronted by a University of Melbourne account log-in page:

http://www.sciencedirect.com.ezp.lib.unimelb.edu.au/science/article/pii/S0301421513006447).

I suspect that Charles had the same problem.

I was interested in the argument that a complex society requires a greater EROEI than a simple society. It is a question of the range of jobs that people do in a society with lower EROEI. Do the energy inputs also require man/woman-hours input and thereby prevent people from doing other jobs?

 Thanks for the cartoon. I can see the trade-off between gearing ratio and time. Perhaps another way of seeing this is by considering the original self-replicating solar gatherers, i.e. living plants and animals!

In a hunter-gatherer society, the population density is very low but there is lots of gearing and very low human maintenance in order to turn lots of solar power into a few edible fruits, nuts, roots and hunted animals. The pay-back time is the regeneration time after hunting and gathering, and is rather long.

Then in an animal-based pastoral society there is a higher population density but more manual input terms of animal husbandry and a shorter regeneration time.

Then an arable farming society is able to support an even higher population density but with lots of manual input and an even shorter regeneration time.

We now have high-tech intensive agriculture with lots of other energy input (fuel) but relatively few people employed in agriculture. At the moment, if we were to grow the extra fuel using other land, the system just would not work – the EROEI of intensive agriculture is too low for the amount of land available.

 So the question is whether it is possible to have high gearing and low manual input but within the available land that we have, and sustainably? It appears to me that our current best hope is mass-produced solar PV, mass produced batteries and electricity used for everything it can do. I think it works provided the energy inputs for raw materials is low enough. That might mean moving away from lithium and cobalt towards sodium and aluminium. See for example Faradion batteries but that's just one of several promising technologies.

 I am skeptical about Joule Unlimited. It is limited by the supply of concentrated CO2, and by the area-efficiency of photosynthesis, even if it is more efficient than most agriculture.

 Best Regards,

John

Khalid/John

Obviously we could have some kind of culture with labor intensive , low energy input systems if people were willing to take a large drop in their life style.  I fear the problem might be that people would rather go to war than accept a decline in life style. 

Lee's assessment of the traditional  !Kung hunter gatherer life style implies an EROI of 10:1 and lots of leisure (except during droughts--which is the bottleneck).  Past agricultural societies obviously had a positive EROI based on human labor input -- otherwise they would have gone extinct.  But it required something like a hectare per person.  According to Jared Diamond cultures became more complex with agriculture vs hunter gatherer ..probably associated with an increase in EROI in fertile areas although we have no real ability to make that calculation. 

The best assessment I have about EROI and  quality of life possible is in:

Lambert, Jessica, Charles A.S. Hall, Stephen Balogh, Ajay Gupta,

Michelle Arnold 2014 Energy, EROI and quality of life. Energy Policy Volume 64:

153-167

http://authors.elsevier.com/sd/article/S0301421513006447

It is open access.  Also our book:  Hall and Klitgaard, Energy and the wealth of nations.   Springer

At the moment the EROI of contemporary agriculture is 2:1 at the farm gate but much less, perhaps one returned for 5 invested  by the time the food is processed, distributed and prepared.

Hamilton A , Balogh SB, Maxwell A, Hall CAS. 2013. Efficiency of edible agriculture in  Canada and the U.S. over the past 3 and 4 decades. Energies 6:1764-1793.

As you can see from these studies to get numbers with any kind of reliability requires a great deal of work. 

Dr. Halls,

Would it be possible to meet the EROI goal of, say for example 10:1, in order to maintain our current life style by mixing wind, solar and hydro? Can we have an energy system various renewable energy sources of different EROI to give a net EROI of 10:1?

Sourabn

Good question.  

First of all I am not sure that we can maintain our current life style on an EROI of 10:1, but lets assume we can (see our papers in Energy Policy about a year and a half ago --see below). 

We would need liquids of course for tractors , airplanes and ships -- I cannot quite envision running those machines on electricity.  But lets ignore that issue for the moment.

The problem with wind is that it tends to blow only 30 percent of the time, so we would need massive storage.  To the degree that we can meet intermittentcy with hydro that is good, although it is tough on the fish and insects below the dam.  The energy cost of that would be huge, prohibitive with respect to batteries, huge with respect to pumped storage, and what happens when the wind does not blow for two weeks, as is often the case?    

Solar PV may or may not have an EROI of 10:1 (I assume you know of the three studies that came up with about 3:1: Prieto and Hall, Graham Palmer, Weisbach -- but there are others higher and certainly the price and hence presumed energy cost is coming down --but you should also know that many structures are lasting only 12 , not 25 years) -- -- this needs to be sorted out ).  But again the storage issue will be important.   (Palmer's rooftop study included storage). 

These are all important issues --  except to research funders who seem to be only promotion of this or that,  but not good analyses.  

So I would say the answer seems to be no, although it might work well for lets say half of our energy use.   As time goes on that percentage might increase (or decrease).  

Maybe you can figure this out!  Good luck. 

Charlie

 Hall, Charles  A.S., Jessica G.Lambert, Stephen B. Balogh. 2014.  EROI of different fuels   and the implications for society Energy Policy Energy Policy. 64,: 141-151          http://www.sciencedirect.com/science/article/pii/S0301421513003856?np=y      htt??//authors.elsevier.com/sd/article/S0301421513003856  

Lambert, Jessica,  Charles A.S. Hall, Stephen Balogh, Ajay Gupta,    Michelle Arnold  2014       Energy, EROI and quality of life.  Energy Policy Volume 64:           153-      http://authors.elsevier.com/sd/article/S0301421513006447

An interesting contribution to the discussion about EROEI can be found here:

http://bountifulenergy.blogspot.de/2015/05/six-errors-in-eroei-calculations.html

http://bountifulenergy.blogspot.de/2010/09/eroi-doesnt-matter.html

http://bountifulenergy.blogspot.de/2014/07/renewables-have-higher-eroei-than.html

@Charles Hall: You make some statements that are somewhat inaccurate and could easily mislead the less well informed:

Windturbines produce electricity during 70 to 90% of the time. You seems to have confused capacity factor with relative time of operation.

Using a single number for the capacity factor is also not so accurate. Depending on the location and design choices the capacity factor can vary from 20% to over 50%.

With the lifetime of PV systems you seem to have confused the inverter with the system as a whole. The practice has shown that PV modules last much longer thatn the 25 years garantueed by the manufacturer. In Oldenburg we have a system from 1976 that is still producing electricity and shows little degradation loss [1]. Inverters are the weak point of the system and sometimes need to be replaced. Ofcourse, this would need to be considered in an EROEI calculation. But this is something different than what you state.

[1] http://www.presse.uni-oldenburg.de/download/einblicke/54/parisi-heinemann-juergens-knecht.pdf

Jethro

I resent your statement that I am misleading anyone.   I write as clearly, accurately and honestly as I can, almost entirely in peer reviewed publications,  and always have. I include sensitivity analysis while acknowledging legitimate uncertainty (for example p. 115 ff in Prieto and Hall).  Some people do not like my conclusions. But no one has shown with explicit analysis that Prieto and Hall is in any important way incorrect.  At least three other peer reviewed papers) (Palmer 2013, 2014; Weisbach et al. 2012  and Ferroni and Hopkirk (2016)  have come up with similar conclusions on solar PV.    I am working on the legitimate differences in technique with legitimate and credible solar analysts with whom I have some differences , e.g. Marco Raugei.   All of this will be detailed in a new book from Springer in January on EROI.

First I would like to say that the bountiful energy blog post is embarrassingly poor science and totally unacceptable. As one point the author does not back his (often erroneous) statements with references. The importance of peer review is obvious from this non peer-reviewed post.

Second I do not understand your statement about wind energy producing electricity 70-90 percent of the time.  In England, for example, it is less than 30 percent (Jefferson 2015) .

Third your statement on the operational lifetime of actual operational PV systems is incorrect. Of course one can find PV systems still generating electricity after 30 years.  But actual operational systems requiring serious maintenance (and for which we do not yet have enough data) often do not last more than 18-20 years,

For example Spain's "Flagship " PV plant (which was especially well maintained) is having all modules replaced and treated as "electronic trash" after 20 years :

http://renewables.seenews.com/news/spains-ingeteam-replaces-modules-at-europes-oldest-pv-plant-538875

Ferroni and Hopkirk found an 18 year lifespan in Switzerland.

Dr. Hall,

Apologies for thread necromancy (I've been told not to do that). Do you know of any studies that attempt a similarly expansive (you call it 'extended' in your papers) system boundary for non-PV sources similar to what you did with the Spain studies?

-Gabe Susca-Lopata