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?.

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.

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.

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

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?

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.

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

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.

Posted By: atomicbisfthe energy 'invested' must be the same as the energy 'returned'

Wouldn't that mean 100% efficiency in the energy industry?

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!

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.

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.

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).

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.

Rather than the ethical issues raised above, some (me) may also be concerned with the pay back period for a typical PV installation.