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    • CommentAuthorTriassic
    • CommentTimeJun 12th 2015 edited
     
    The Energy Return on Energy Invested (EROI or EROEI) is the amount of energy acquired from a particular energy source divided by the energy expended, or invested, in obtaining that energy. EROI is an essential and seemingly simple measure of the usable energy or “energy profit” from the exploitation of an energy source, but it is not so easy to determine all of the energy expenditures that should be included in the calculation. Because EROI values are generally low for renewable energy sources, differences in these estimates can lead to sharply divergent conclusions about the viability of these energy technologies.

    Prieto and Hall used government data from Spain, the sunniest European country, with accurate measures of generated energy from over 50,000 installations using several years of real-life data from optimized, efficient, multi-megawatt and well-oriented facilities. These large installations are far less expensive and more efficient than rooftop solar-PV.

    Prieto and Hall conclude that the EROI of solar photovoltaic is only 2.45, very low despite Spain’s ideal sunny climate. Germany’s EROI is probably 20 to 33% less (1.6 to 2), due to less sunlight and less efficient rooftop installations.

    http://energyskeptic.com/2015/tilting-at-windmills-spains-solar-pv/

    Makes you wonder how efficient the UK s PV installations are?
    • CommentAuthorwoodgnome
    • CommentTimeJun 12th 2015
     
    I'm wondering the same thing regarding PV. Is it better to self install a small size array and use all the generated at home, for DHW and MVHR etc. Wonder how much cheaper self install is compared to MCS installed?.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 12th 2015 edited
     
    Or you can believe this from the other end of the spectrum.

    http://info.cat.org.uk/questions/pv/what-energy-and-carbon-payback-time-pv-panels-uk

    Another way to think about it is to make an estimate of the energy produced by the system over its life, say 750 kWh/kWp times 20 years, so that would be 15 MWh.
    Then look at the amount of energy needed to make the modules (4750 MJ.m^-2), 1319.5 kWh.m^-2 or about 2.11 MWh per module. Assuming 250Wp per module that will be 8.5 MWh.

    8.5 / 15 = 0.56, so just about 11 years return on the modules alone.

    If we assume that all the rest is worth about 5 MWh, that is then:

    (8.5 + 5) / 15 = 0.9 or about 18 years.

    So not brilliant, but a lot of assumptions there.

    It would be fair to say that new double glazing would have a similar embodied energy to PV modules. so if I put in new windows, about 10 m^2 in total, then the embodied energy would be somewhere around 13.2 MWh.
    If then reduce my usage by a quarter, that would save me about 0.056 MWh/year (being generous there)
    So over the 20 years that would be:

    1.12 / 13.2 = 0.084, or basically forever.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 12th 2015
     
    Posted By: TriassicEROI is an essential and seemingly simple measure of the usable energy or “energy profit”
    Not quite right to say it's 'energy profit' - in fact grossly misleading at low EROEI numbers.

    You can either say 'Energy Return on Energy Invested, or Energy Profit on Energy Invested. The EPOEI number is always 1.0 less than the EROEI number. Thus, EROEI 1.6 = EPOEI 0.6, and the break-point is EROEI 1.0, because it equals EPOEI 0.0, in other words for all the investment there's no profit, just a return that merely equals the investment.

    For EROEI less than 1.0, say EROEI 0.7, EPOEI is -0.3, in other words you're making a loss, investing more energy than you get out.
    • CommentAuthorEd Davies
    • CommentTimeJun 12th 2015
     
    Posted By: SteamyTeaThen look at the amount of energy needed to make the modules (4750 MJ.m^-2),…
    Where does this come from? It's over 5 times the 250 kWh/m² that CAT quote. There will be a lot of variation with different forms of production and over time and also depending on what gets counted but 5 times must cover pretty much the whole plausible range.
    • CommentAuthorbillt
    • CommentTimeJun 12th 2015
     
    I'd guess that Prieto and Hall have gone too far in the opposite direction from those that claim an energy return in 2 years.

    There are some paragraphs further down that page that highlight the problem.

    "I was at a net energy conference at Stanford University the past two days. The hoped for outcome is a new net energy think-tank that would standardize net energy by having a specific way researchers must conduct their studies, which LCA or other data tables are most-up-to-date and should be used, what assumptions they must state, and so on. If researchers strayed from this format or added additional material, they’d need to say why.

    The reason this needs to be done is because policy makers don’t take EROI studies seriously. Nor should they since they’re too easy to game by proponents (i.e. not counting the energy to make steel because it is 100% recycled, cherry-picking the best performing wind or solar farms over the best performing time period, etc). Policy makers can’t be expected to make policy decisions or recommendations when EROI studies of a renewable ranges from 4 to 115."

    IOW you can't believe any of them.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 12th 2015 edited
     
    Was from wikipedia, I took the worse case.
    https://en.wikipedia.org/wiki/Embodied_energy

    They think that thin film can be done for 1305 MJ/m^2, or 362.5 kWh/m^2, which is about 27% of the mono ones.

    Someone would have to do a lot of research to find out why there is such a large difference. The active part is only a tiny amount of the mass of the module. I can't think they they are making massive energy savings on the glass and aluminium, transport and distribution.
    It could be that they based the energy on the CO2 emissions, which would make some modules made in some countries seem better.
    I am not sure.

    Glass has an embodied energy of 12.7 MJ/kg or 3.5 kWh/kg
    Aluminium is 170 MJ/kg or 47 kWh/kg
    So a m^2 of sheet of 6mm glass will weigh about 15 kg, or 52.5 kWh
    The frame will be about 3 kg or 141 kWh
    A rough total of 200 kWh/m^2 or 320 kWh/module.
    This leaves somewhere between 160 and 1120 kWh for the silicon.
    Single crystalline silicon has an EE of 4966 MJ/kg, 1380 kWh/kg
    Poly silicone wafer has an EE of 2000 MJ/m^2, 556 kWh/m^2
    https://et4407.files.wordpress.com/2013/11/embodied-energy-in-electronics-2.pdf

    A quick look back at the wikipedia figure for mono crystalline seem to imply that they have assumed the whole module is made from silicon.
    Silicone has a density of 2.3 tonne/m^3
    Assuming that the layer is 1mm, then the mass of the silicon is 2.3 kg with an EE of 3174 kWh
    This would make the worse case module have a total EE of 5720 kWh/module
    The best case ones 1530 kWh/module
    A module is about 1.6 m^2
    So 1530 to 5720 kWh/module

    I think.
    • CommentAuthoratomicbisf
    • CommentTimeJun 12th 2015 edited
     
    I'm dubious of this given how at odds it is with the figures published by respected sources such as the fraunhofer Institute. I wonder whether it really compares apples with apples. Because the further back you go, and the more tangential to the manufacture and installation of the PV you include, surely the closer to an EROEI of 1 you get?

    If you take the EROEI of say a hydroelectric power station and only take the energy used to make the concrete and steel, turbines etc, and then compare it with PV in which you add (to make it extreme) the energy used to grow the crops used to make the sandwich eaten by the engineer repairing the lift in the copper mine from which the PV factory gets its copper, then you could easily make PV look horrible. But you wouldn't be comparing like with like.

    Also I'm suspicious of the weight given to 'real life' yields from Spain, because I think this is the least difficult aspect and to the cynic just seems to have been added to give spurious credibility. After all, if we know the location, azimuth and angle of the panels, it's not difficult to calculate the annual yield with good confidence. Certainly compared with the difficulties of calculating the energy needed to produce them it's going to be very simple and accurate. It all smacks of appealing to those who have been taught to distrust 'theory' and rely on 'common sense'. For example the 'common sense' of Spain being a sunny country and Germany not, when in fact the difference between PV yield in those countries could well be much smaller than the difference between a PV factory using say electricity from coal or natural gas or hydro, or any of the non 'common sense' differences in manufacturing efficiencies.

    Ed
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 12th 2015
     
    Ed
    I think you are spot on there. I often hear that cars and turbines take more energy to make than they ever generate. Usually from old car fans and anti-turbine people.

    If a module cost about £125, that would translate to about 2 MWh of energy (at 6p/kWh). And they are made from more than just energy.
    From my quick scout around it is very hard to find a definitive answer to this.
    • CommentAuthorCWatters
    • CommentTimeJun 12th 2015
     
    Interesting..

    https://en.wikipedia.org/wiki/Energy_returned_on_energy_invested

    "In regard to fossil fuels, when oil was originally discovered, it took on average one barrel of oil to find, extract, and process about 100 barrels of oil. That ratio has declined steadily over the last century to about three barrels gained for one barrel used up in the U.S."

    So US oil has an EROEI of about 3. Not that different to PV?
    • CommentAuthorringi
    • CommentTimeJun 12th 2015
     
    Is also the type of energy 1kwh of gas is worth less then 1kwh of electric...
    •  
      CommentAuthorfostertom
    • CommentTimeJun 12th 2015
     
    Posted By: atomicbisfsurely the closer to an EROEI of 1 you get?
    Spot on - it's the real deep question - on a really honest all inclusive accounting, can we really afford (western scientific/industrial) civilisation at all? !t may well be operating at an EROEI of barely above 1.0. Maybe the definition has to be widened - a RRORI (Resource Return on Resource Invested) of barely above 1.0. In fact, now below 1.0.

    Not quite the same thing but from
    http://www.footprintnetwork.org/en/index.php/GFN/page/earth_overshoot_day
    "In less than 8 Months, Humanity exhausts Earth's budget for the year"
    "August 19 is Earth Overshoot Day 2014, marking the date when humanity has exhausted nature’s budget for the year. For the rest of the year, we will maintain our ecological deficit by drawing down local resource stocks and accumulating carbon dioxide in the atmosphere. We will be operating in overshoot."
    "We maintain this deficit by liquidating stocks of resources and accumulating waste"
    1972 was I believe the year that the world went into overshoot; before 1972 we operated within the planet's capacity to reprocess our activities. Since 1972 Earth Overshoot Day has crept ever earlier. If you sum up all those Overshoot periods, it means the earth would take about 20yrs (and rising exponentially) to make good the deficit, if humans stopped all their activity. Likely?

    It need not be so. Development, even Growth, need not equal Overshoot/deficit. A simple matter of humans really getting it (or rather, rediscovering) that we are not just optional live-alongside neighbours with nature, not even dependent on nature, but that we ARE nature, and when we harm nature we cut off our own right hand.

    Then every material recycling plant, every product manufactured, every building or city built, every grand infrastructure project, would be urgently designed to not merely fractionally minimise its contribution to ever-accumulating global damage, but rather to actively assist nature in clearing up the mess that we (this unconscious fraction of itself) has made.

    In the hope of acheiving that clearup in a matter of 1000s or 100s of years, rather than 10,000s of years if nature's processes are left to do it unaided. Because the human race won't survive 10,000s of years amid the compounding mess (which has barely kicked in yet) - maybe 100s.
    • CommentAuthorEd Davies
    • CommentTimeJun 12th 2015 edited
     
    Posted By: SteamyTeaIf a module cost about £125, that would translate to about 2 MWh of energy (at 6p/kWh). And they are made from more than just energy.
    Exactly the approach I was thinking of.

    Say panels cost 70p/W. I was going to go for cheaper energy for production - something more like what Chinese industrial electricity prices might be - say 3.5p/kWh so 20 kWh/W or 20'000 full-sun operating hours. At 800 hours/year in the UK that'd be 25 years payback.

    That's more or less an upper bound as most energy is likely to be more expensive (though it wouldn't surprise me if bunker oil for a container ship was less) and, as Steamy's said, energy is only a fraction of the cost of manufacture.

    [Edit to add: actually it seems bunker oil is about $600/tonne and 40 MJ/kg (i.e, a bit less than diesel fuel or petrol, which are around 42 MJ/kg, which makes sense) which works out at 8.64 p/kWh. That's surprisingly high - it's easy to see why Britain doesn't have much oil-fired grid generation these days.]
    • CommentAuthoratomicbisf
    • CommentTimeJun 12th 2015
     
    Hi, that's not what I meant about approaching an EROEI of 1. What I meant was that as you include things further and further from the actual production and installation of the solar PV (the engineers sandwich etc) the energy invested becomes greater and greater while the energy returned remains the same. Once it's expanded to the whole of society/the whole world economy, the energy 'invested' must be the same as the energy 'returned', but that simply sshows that the whole concept becomes meaningless when expanded so far.

    Ed
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 12th 2015 edited
     
    Bit about environmental accounting here:
    http://www.bbc.co.uk/programmes/b05xqbml
    •  
      CommentAuthorfostertom
    • CommentTimeJun 12th 2015
     
    Posted By: atomicbisfWhat I meant was that as you include things further and further from the actual production and installation of the solar PV (the engineers sandwich etc)
    which is absolutely right and proper and the only way to not deceive ourselves - but of course beware of double-counting - and all easier said than done.
    Posted By: atomicbisfthe energy invested becomes greater and greater while the energy returned remains the same. Once it's expanded to the whole of society/the whole world economy
    as it should be
    Posted By: atomicbisfthe energy 'invested' must be the same as the energy 'returned'
    maybe that's so with pure point-of-use energy, but there's an immense flywheel of stored energy, both fossil and nuclear potential, that's in the pipeline at various stages, and we are approaching the point of investing that faster than 'profit' energy come out the other end for useful use by us (meaning other than by the energy industry). That can be so supremely profitable in money terms that its resource-terms bankruptcy can be overlooked for decades. In fact, recast the issue into Resources-in-general terms, rather than just the Energy resource, and we're already well over that line.
    Posted By: atomicbisfbut that simply sshows that the whole concept becomes meaningless when expanded so far.
    On the contrary, that's when reality kicks in at last.
    • CommentAuthorEd Davies
    • CommentTimeJun 13th 2015
     
    Posted By: atomicbisfthe energy used to grow the crops used to make the sandwich eaten by the engineer repairing the lift in the copper mine
    The energy cost of the spare parts, etc, for the lift should be included in the embodied energy of the copper.

    The sandwich is a bit more difficult. If the alternative is to leave the engineer to starve then it should be included; if they're going to eat anyway then not. Whatever, the PV should be assessed on the embodied energy of the copper as it arrives at the factory gate. AIUI, that's pretty well established.

    Posted By: atomicbisfBecause the further back you go, and the more tangential to the manufacture and installation of the PV you include, surely the closer to an EROEI of 1 you get?
    Why? Right now the human race has a lot more energy in store (energy which has been returned by previous investments which is yet to be expended on further investments or end use) than it had when Cnut became king of England so our EROEI over the last millennium must have been greater than one. Even more so for longer periods - the first replicator probably only had microjoules more energy than the similar atoms around it but we've picked up a few more since then.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 13th 2015
     
    Posted By: atomicbisfthe energy 'invested' must be the same as the energy 'returned'
    Wouldn't that mean 100% efficiency in the energy industry?
    • CommentAuthorYanntoe
    • CommentTimeJun 13th 2015
     
    Hang on!

    All this very interesting but isn't the argument a different one?

    Over a period "x" I will consume an amount of energy.

    I can get this from a variety of sources, whether "green" or not.

    The important question is how do the EROEI of the various choices compare?

    (Clearly more complex when I don't actually need to buy a refinery to use oil etc, but it is true, nevertheless, that this is the real question.)
    Would it not be a gift to the "global warming deniers" , to undermine the use of solar PV without the comparison to the use of eg oil using a similar methodology, and then compare the outcomes?

    I suspect that what we should be investigating is the technology which does the least harm, comparatively, and then continuing to argue for usage reduction overall or the need for a new technology.

    Or have I again missed something?
    Ian
  1.  
    Not sure I have properly understood how to use EROEi when choosing if green building technologies are 'worth having'..?

    Is the EROEI for PV one-tenth that of coal as Wikipedia suggests? And if so, should I choose PV for my house, or a coal fire, or both/neither?

    1kWh of PV electricity has many more uses than 1kWh of coal energy (lights, TV ...), and 1kWh coal has more uses than 1kWh of warm water. EROEI doesn't seem to account for this, treats all energy as being equal?

    1 kWh of PV electricity can be useful several times, eg the same kWh that powers my computer, also heats my house. Does that double its EROEI?

    How about some other ratios :

    EROCE - energy return on carbon emitted

    EROEI - energy return on effort invested - more commonly called 'convenience'

    ERORI - energy return on resources invested - more commonly called 'cost'!

    Help please!
  2.  
    I guess the alternative to PV is a bare roof, which has an EROEI of zero? So PV is a good idea.

    Or, the alternative to PV is a bare roof and £5k unspent, which i can spend on something else with a higher EROEI, such as buying power from a hydro generator.. So then PV is a bad idea?

    Help please!
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 14th 2015
     
    When using EROEI should be not look at the amount of energy from the Sun, which is the energy source, like coal is (that is just stored solar energy), rather than the energy used to make the kit.

    We had a thread about this before, I was highly critical of the methodology then.
    There should be a distinction between the capital expenditure and the running expenditure.
    • CommentAuthorYanntoe
    • CommentTimeJun 14th 2015
     
    Are there not many costs involved with energy production, inter alia; production ("kit"), extraction, distribution, profit, opportunity cost (eg loss of alternative usage of land), pollution (often uncosted), decommissioning and also subsidies. There may also be socio-political cost (eg "supporting" unfriendly regimes like Mr Putin or ....)

    I guess the only way to decide whether PV is a good idea is to have transparency of all of the above and then do the maths

    Not something I can do, I'm afraid, but I don't think that PV will fare badly versus most of the rest, and I guess if I put a 4meter Square solar roof on the barn that's an addition to the generating capacity making the UK more energy secure, and does not increase our dependency on Mr Putin. It may even provide financial benefit, in 7 or 20, or 21 years or whatever it might be, so could be considered to be a useful pension top up one day.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 14th 2015
     
    Most of our gas comes from our own reserves, Norway, Finland, Netherlands and some shipped in from USA and Wales (but it is Qatar gas).

    The Russians are already suffering more than us due to low gas prices (another good reason to keep energy prices high).

    If you start to think too much about EROEI, it just gets silly. Should you take into account the service costs of a gas boiler, maybe the higher embodied energy compared to an electrical element, how about removal of pollutants at the refinery, are 'secondary products' like plastics or fly ash building blocks a credit or a debit.

    And does it really matter if you can use PV to supply all your energy needs, and a bit more to make a few more modules.

    I think it really comes down to resource depletion.

    The stone age did not end because we ran out of stones.
    • CommentAuthorEd Davies
    • CommentTimeJun 14th 2015
     
    Posted By: SteamyTeaWhen using EROEI should be not look at the amount of energy from the Sun, which is the energy source, like coal is (that is just stored solar energy), rather than the energy used to make the kit.
    If that “be” should be “we” then, no, we shouldn't worry about the energy from the sun except as an opportunity cost - e.g., if we're discussing whether to use PV or solar thermal and only have a limited amount of roof space.

    Should you take into account the service costs of a gas boiler,
    Yes.

    …maybe the higher embodied energy compared to an electrical element,
    Yes.

    …how about removal of pollutants at the refinery,
    Yes.

    …are 'secondary products' like plastics or fly ash building blocks a credit or a debit.
    A credit. Allocation of the embodied energy between the oil and the plastic is a bit harder but so long as you're consistent it should be OK.

    And does it really matter if you can use PV to supply all your energy needs, and a bit more to make a few more modules.
    Yes, it does matter if you could have supplied all your energy needs directly from the resources used to make the modules in the first place. E.g., if the manufacture of your PV panels caused more emissions (CO₂ and others) from a Chinese coal plant than you would have caused by using grid electricity in the UK then the panels are worse than useless. That's the fundamental question here which everybody is making too complicated.

    The OP's quoted source is an outlier, though. Most of the other studies seem to say that PV pays back much quicker.

    The stone age did not end because we ran out of stones.
    I've never quite understood what this quote is supposed to mean. Just that sometimes technologies are replaced because something better comes along rather than because they stopped working? How profound! Or am I missing something?

    Whatever, it's well worth remembering that at each stage we bootstrap new technologies off old ones. Timber was needed to start coal mining. Coal was needed to extract oil (e.g., to make steel). And so on. There's a PV plant in Texas that gets half its energy from an adjacent PV field. Quite likely it's possible to move forward to a completely solar-based economy (counting wind as indirect solar) but it's probably only really practical if the Triassic's source is wrong.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 14th 2015
     
    Posted By: Ed DaviesIf that “be” should be “we”
    Yes it should be we.


    Posted By: Ed Daviesthen, no, we shouldn't worry about the energy from the sun
    I think this highlights the nonsense of this sort of accounting. It seems to be OK to quote one resource i.e. oil, but not another, i.e. solar.
    With this sort of accounting, biomass is fine if you say that the embodied energy of making a flint spark, to start a fire is very low compared to the energy released.

    But as you say, correctly I think, we build on existing technologies and dump the worse ones along the way, so now we use electronic spark generators instead of stones to start the fire.
    Better to not burn things in the first place (melting is not burning).
    • CommentAuthorEd Davies
    • CommentTimeJun 14th 2015
     
    Posted By: SteamyTeaI think this highlights the nonsense of this sort of accounting. It seems to be OK to quote one resource i.e. oil, but not another, i.e. solar.
    It's energy invested, i.e., useful energy we could choose what to do with; it's not total energy going into the system. Otherwise EROEI would always be less than one.

    E.g., we say that a heat pump has a COP of 4 meaning we get out 4 times as much useful energy as the amount of useful energy that goes in. The heat in the air or ground or whatever is useless energy in this accounting. Subtract out the embodied energy of the heat-pump amortized over its life and you get the EROEI.

    (If you want to count the photons hitting your roof you also need to count the photons and decays needed to make the oil. I'm not being serious.)
    • CommentAuthorSeret
    • CommentTimeJun 15th 2015
     
    Posted By: Triassic
    Prieto and Hall conclude that the EROI of solar photovoltaic is only 2.45


    That would still put it well into the "worth doing" category. In the case of rooftop PV it's also displacing energy at the right place (point of use) so avoids pretty much every conversion loss and inefficiency in the system.
  3.  
    REC claim a much quicker EROEI than many panels 1 year I think , so may depend greatly on product / panel purchased.
    •  
      CommentAuthorjoe90
    • CommentTimeJun 16th 2015
     
    Rather than the ethical issues raised above, some (me) may also be concerned with the pay back period for a typical PV installation.
   
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