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The real EROI of photovoltaic systems

Alternative Energy

Charles Hall is known for his multiple and important contributions in the field of sustainability, and in particular for having introduced the concept of Energy Return on Energy Investment, EROI or EROEI. He is now emeritus and still active in research; among other things as chief editor of the new Springer journal: “Biophysical Economics and Resource Quality, BERQ. Here, he intervenes in the recent debate on the EROI of photovoltaic systems, sending me this note that I am happy to publish.

by Charles Hall

The EROI of our various energy options, and its associated issues, may be the most important issues that will face future civilizations.  The present discussion tends to vacillate between people who accept (or advocate) very high EROIs for solar vs people who accept (or advocate) very low such EROIs.   I trust only one study, the one I did with Pedro Prieto, who has a great deal of real world experience and data. This study attempted to (conservatively) estimate all the energy used to generate PV electricity in Spain by following all the money spent (per GW) and using physical analysis where possible, and energy intensity of money where necessary. We found that the panels and inverters, which are the only parts measured in most studies, were only about a third of the energy cost of the system.  As noted in the responses to Ugo’s last post we estimated an EROI of 2.45:1 in 2008 assuming a lifetime of 25 years and at the juncture with the distribution system.   Studies that we think used more or less appropriate boundaries (Palmer, Weissbach) got similar results.

We recognize that subsequent studies to ours would probably have generated higher EROIs because of using panels of lower energy costs or higher efficiency.  But there are many ways that it might be lower too.  For example Ferroni and Hopkirk, who (despite, perhaps, some issues) have done us a good service by attempting to get actual lifetimes for modules, which were much closer to 18 years than infinity.  This agrees with what happened in Spain when, due to post-2008 financial turmoil, manufacturers did not honor their guarantees and legally “disappeared”, leaving broken systems unfixed.   (And what happened to all those “surplus” Chinese panels that were never used?   Should we factor in their energy costs, as we factor in dry holes for oil analysis?)  My point is that we need to include empirical, not theoretical, estimates of ALL the energy used to make these systems work.

This is what Prieto and Hall did, imperfectly I am sure, using conservative assumptions of energy costs, many of which now appear too low.  Mostly I do not see others doing this, so I mistrust their analyses. I do not know whether Bandhari et al. included only studies using appropriate boundaries, but I would guess that many are for just the panels (and maybe converters), not the whole system required to deliver the electricity.  Another way that we were conservative was to not include the (pro-rated) distribution system, as Ferroni and Hopkirk did (i.e. EROIpou, for point of use).  It seems to me that we should do this routinely, at least as sensitivity analysis. If you are really analyzing the EROI of solar you need to get the electricity to the factory, the gravel and panels to the installation site etc. etc,

There are at least three reasons that EROI estimates appear much wider than they probably really are:

1) They are often done by advocates one way or another, not by experienced, objective (and peer reviewed) analysts.

2) a common protocol is not followed.  Murphy et al. 2011  should be followed or good reasons given for not doing so. They recommend that all investigators generate a “standard EROI (EROIst) so that different studies can be compared, but then suggest that investigators may define in addition other criteria/boundaries as long as they are well defined and the reason for their inclusion given.    This protocol is being updated at this time to deal with various concerns.

3) Related to above appropriate boundaries are  often not used.  For a start “follow the money” as money is a lien on energy.  Where there is controversy (e.g. include labor or not, and how) this should be dealt with through sensitivity analysis.   Energy quality (e.g. electricity vs fossil) also needs to be considered, as Prieto and Hall did in their final chapter.

The largest problem with EROI studies is that although the concept has been around and even lauded since at least 1977 it has essentially never been supported by legitimate and objective funding sources such as the US National Science Foundation (which however has recognized this as a large failure and is starting a new program on EROI.)  As any investigator knows it takes money to do a good job, and this we have not had.  Most of the best work has been done on a shoestring or pro bono. This appears to be changing now, especially in Europe, and we hope to see some kind of objective, high-quality Institute/Program in the future.  We also need better governmental statistics on energy use and the development of appropriate energy I-O analyses to get a better handle on energy costs.  These had been done to high quality in the US 40 years ago but the official Bureau of Census energy use data has degraded, and we have ceased undertaking appropriate energy I-O analyses while the real experts have retired or died.

If these issues can be resolved, which is not too difficult at least in principle, and if the protocols are followed, then I think we will narrow the range of published EROI estimates considerably.  In the meantime I have done a fair amount of sensitivity analysis (e.g. Guilford et al 2011; Prieto and Hall 2012) that suggest that at least for the studies I have been involved with the range of uncertainty is well within plus or minus 25 percent (except when using the assumptions of using the energy cost of the full salary of labor or electricity is multiplied by a quality factor of three, in which case the range is two to three).   At this time, we do not recommend either of those two factors for general use.   This range of uncertainty is much less than the EROI range among the different technologies, as shown in Euan Mearns most recent post.

Cassandra’s legacy by Ugo Bardi

67 Comments on "The real EROI of photovoltaic systems"

  1. PracticalMaina on Fri, 27th May 2016 10:39 am 

    true but that is less than the loss that would be experienced converting 120 ac down into a 12 dc…I believe, or at least fairly similar. That’s a good sized house for Europe correct? I am talking bare bones end of days, camper or yurt sized living.

  2. GregT on Fri, 27th May 2016 1:08 pm 

    My trailer has 160W of PV, a 1750W pure sine inverter, hooked up to two large golf cart type batteries. If in full sun, it will provide continuous power for LED lighting, a 22″ LED TV, a small stereo system, a water pump, and limited use of a small microwave. If not in full sun the batteries will last about two evenings of light use, without the microwave. The system without batteries costs around $2000, and the batteries were about 600 dollars a piece. All totalled, including installation and taxes, the system came in just shy of $4000.

    It is a great source of lighting and entertainment as long as the sun is shining, and has allowed us to camp for up to a week without shore power. Without enough sun, we recharge the batteries through the charging system on the truck, or plug in somewhere to an AC source. Even with the solar system, we are still reliant on propane for refrigeration, cooking, and heating.

  3. GregT on Fri, 27th May 2016 1:45 pm 

    Sorry, somewhat misleading. When I say continuous, I mean lighting in the evening, a couple of hours of TV/DVD, and a few hours worth of stereo usage. The water pump turns on and off as needed. The microwave would drain the batteries very quickly if used for more than a few minutes.

  4. ghung on Fri, 27th May 2016 1:58 pm 

    Homepower figured all of this stuff out decades ago; charts, graphs, wire sizes, formulas for calculating losses, schematics…. BTW, aluminum wire is frowned upon in the low voltage DC world; even considered dangerous.

    Anyway, the debate seems a bit moot considering that so many of us have been living with both AC and DC for whatever uses are suitable. This PC is running off of the 24 volt battery set which is maybe thirty 12 ga. wire-feet away. Of course, it could still be running from AC inverted from DC, converted back to DC in a standard PC power supply with its losses and silly cooling fan.

    It all depends on application. DC LEDs are available that will operate fine on anything from 10 volts – 30 volts, and they’re cheaper than 120 VAC LED bulbs. Who cares about a little line loss when your lighting or PC only use a few watts and aren’t creating a lot of heat via conversions?

  5. ghung on Fri, 27th May 2016 2:01 pm 

    BTW, Greg; what kind of golf cart batteries cost $600 a piece? I’m looking at top-of-the-line Rolls/Surrette 500AH L-16 types for under $400.

  6. ghung on Fri, 27th May 2016 2:04 pm

  7. GregT on Fri, 27th May 2016 2:43 pm 


    I’m probably incorrect when I refer to them as golf cart batteries. They are 6V, the same approximate dimensions as an average car battery, but 20 inches long. Also, keep in mind that I am in Canada. A $400 US battery would equate to around $625 CAD, after exchange, taxes, and environmental levies. A 550AH Rolls/Surrette runs about $600 CAD. After taxes and levies that would be closer to $700.

  8. numbersman on Fri, 27th May 2016 4:15 pm 

    Where are the rest of the comments? Only 7 of the 57 are visible….

  9. peakyeast on Fri, 27th May 2016 4:20 pm 

    @ghung: Why is alu wire considered dangerous?

  10. peakyeast on Fri, 27th May 2016 4:26 pm 

    @ghung: I think the fear of alu wiring comes from old times when solid one core alu wiring was used.

    Alu is probably more susceptible to breakage from bending or temperature variations.

    But with multicore and the price difference one can today buy a better alu cable than copper (both resistance wise and amperagewise).

  11. peakyeast on Fri, 27th May 2016 4:32 pm 

    @numbersman: This site was made by a noob and not maintained by new noobs.

    Look at the URL – change the last part “comment-page-x” to the page you want.

    It also works in those articles where there is more than 50 comments, but for some strange reason the URL stops before the “comment-page-x”. There you just add it.

  12. GregT on Fri, 27th May 2016 4:43 pm 

    Aluminum wire tends to oxidize at points of termination peaky. Not so much a problem with the wire itself, as an incompatibility with the metals used in switches, receptacles, etc.

  13. peakyeast on Fri, 27th May 2016 4:55 pm 

    @GregT: The outer layer of alu wiring is oxidized. Pure aluminium doesnt survive for long in our atmosphere, but the oxidized aluminium coating effectively prevents oxygen from “burning” all the aluminium.

    So perhaps you mean it causes other metals to oxidize? Which I could believe.

    I could also believe that aluminium – if heated enough would burn very nicely. But then we are already in a serious fault condition.

  14. peakyeast on Fri, 27th May 2016 4:57 pm 

    @GregT: Sorry – that is what you said about switches e.t.c.

    You are, of course, correct in that respect.

  15. peakyeast on Fri, 27th May 2016 5:00 pm 

    But I still think that those problems are of older date given the level of knowledge and materials used today.

    Aluminium wiring is very common. Gold plating contacts is also – which should prevent oxidation of the contacts in a switch as long as its still there.

  16. shortonoil on Sat, 28th May 2016 9:59 am 

    Harquebus quoted on page 1 of these comments

    “Whenever somebody with a decent grasp of maths and physics looks into the idea of a fully renewables-powered civilised future for the human race with a reasonably open mind, they normally come to the conclusion that it simply isn’t feasible.”

    We are completely convinced that the above statement is true, but that does not mean that renewables can not be of significant use to modern society. It is not that they can replace fossil fuels, but they could considerably extend their useful life span. That could be as much as a century. At the world’s present consumption rate the oil age will be ending in 13 years, and society will have to pay a very high price to get it there. We are now witnessing the bankruptcy of the Petro-States, and much of the Western world’s petroleum industry. Over the next five years it will become very apparent as to what is happening.

    Geothermal, wind, tidal power, small hydroelectric, and in some cases solar can replace much of the electricity production of the world. Electricity that is now being supplied from our rapidly depleting fossil fuels. More than 90% of auto trips are less than 25 miles round trip. Well within the range of EV’s. Most of our internal combustion engine usage can be replaced. ICs could be used only for longer trips, and larger vehicles.

    The amount of petroleum that can be economically converted to finished fuels is now less than 300 Gb, and falling rapidly. The ERoEI of petroleum is now 8.7:1, and at 6.9:1 it will no longer be economically viable to convert the average barrel into finished fuels. The world’s petroleum industry is now attempting to increase production to compensate for its declining ERoEI. It is referred to as maximizing cash flow, when in reality it is because of depletion their barrels can no longer command a price high enough to pay for themselves. The problem lies in the quarterly outlook of business. A geothermal plant may not be economical today, but in five years it is likely to become more than competitive with fossil fuel powered electrical production. But that plant will have to be built BEFORE the fossil fuels needed to construct it have become completely depleted out. It could then save millions of boe to be used for construction of more plants.

    Over the next decade society will have to provide $trillions to keep the petroleum industry operating. Maybe by then it will begin to recognize that the present state of business is not sustainable in a depletion ravaged fossil fuel world. Then again maybe it will continue to stubble along until it falls into its own self dug hole.

  17. Davy on Sat, 28th May 2016 11:40 am 

    I doubt general attitudes and lifestyles can be changed in time and if ever. In a world of competitive cooperation that turns into dysfunctional compromise usually per a market based settlement little can be achieved until there is a serious existential crisis. A serious existential crisis is already too late. It is likely already too late so what you see is what you get because in less than a decade the status quo will fly apart with normality front loaded and the tail being the really destructive change. We can call this the collapse curve. We are just entering the curve.

    We know some place will adapt better than others so it will be a mix of time and location. Anything that can be done now should be done because of leverage. A little now is worth a lot later. What we can do now is so much more than what we can do latter because of destructive change and economic abandonment will bleed the economic life blood out of our global system. Time is the key variable now. Time wasted can never be replaced.

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