Conventional Nuclear (AKA Nuclear Fission) a thread for discussion of the pros / cons.

Quote from Zeus46

EROI -- A Tool To Predict The Best Energy Mix Energy Returned on Investment, or EROI, is the ratio of energy returned to energy invested in that energy source, along its entire life-cycle. When the number… http://www.forbes.com

Or, if you prefer more numbers:

Many other studies strongly disagree with the graph in the Forbes article. It shows the EROI for PV at 4, or 2 for buffered energy. Nobody buffers PV. It is generated at peak hours in the middle of the day, when electricity is most needed, so it makes no sense to buffer it. You would only need to buffer it if you wanted all electricity from solar, and for that matter you would have to buffer nuclear power to accomplish that. Either that or throw away most of the nuclear power.

These numbers are also wrong for PV because since they were computed, embodied energy is way down, and efficiency is up, so the EROI is conservatively 10 or more, about the same as oil. Many similar problems with the methodology are described here:

Energy Return on Energy Invested (ERoEI) for photovoltaic solar systems in regions of moderate insolation: A comprehensive response

A recent paper by Ferroni and Hopkirk (2016) asserts that the ERoEI (also referred to as EROI) of photovoltaic (PV) systems is so low that they actual…

www.sciencedirect.com

This is a critique of another paper, but the problems are similar. What I just wrote above is described in much more technical detail, partly as follows:

. . . They also make repeated direct and indirect comparisons between PV and nuclear electricity without adjusting the analysis to ensure consistent boundaries. For example, they add an unreasonably extended storage requirement to PV but not to nuclear, ignoring that PV primarily serves peak loads while nuclear only serves base loads and both of them (not only PV) would require storage in order to satisfy total demand loads. This is problematic because the way in which the analyses are presented to the reader implies that any differences in the reported EROIs are due to data inputs – i.e., something inherent to the technologies or resources under investigation – and not an artefact emerging from methodological inconsistences between the studies being compared. The latter is actually the case here.

Quote from Zeus46

EROI = Quantity of Energy Supplied ÷ Quantity of Energy Used in the Supply Process

What constitute "supply process" is sometimes unclear, or disputed. I think everyone would agree that embodied energy is part of the supply process. For example, the energy it takes to make amorphous silicon for a PV should be included. Until the PV produces more than that amount of energy, it is still an energy sink, not a source. But there are problems estimating this:

1. People do not have a good handle on how much energy it takes to make silicon. It is harder to measure than you might think. As shown in Table 2 of the above report by Raugei et al., the pessimistic estimate of energy investments (mainly embodied energy) was 1,300 units (complicated units -- see Table), but Raugei et al. say it is 290. They say the pessimistic estimate is "Based on old and/or unreliable studies (seven references, of which two are >10 year-old, and two are ‘grey literature’)" while their own is "Based on the latest and most up-to-date peer-reviewed literature."
2. In some cases, waste silicon from semiconductor manufacturing has been used. The energy cost of that is zero. Recycling might also reduce energy cost.
3. Embodied energy has been greatly reduced, and there is every reason to think it will continue to decrease. They are using old numbers where they should be using forward looking projections based on what is likely a year or two from now. See Fig. 1 in the above paper.

Table 2 shows how adjusting assumptions, eliminating double counting, and using more up to date performance data has a large impact on the EROI. Table 2 concludes with four estimates of EROI:

Pessimistic 1.7. Raugei et al. optimistic estimate: 9.1 - 9.7

The pessimistic extended estimate: 0.8. Raugei et al. optimistic extended estimate 6.9 - 8.1

The pessimistic numbers are similar to the ones in the Forbes article (originally from Weissbach et al., https://festkoerper-kernphysik…issbach_EROI_preprint.pdf). The underlying assumptions and analyses made by Weissbach are similar to the study critiqued by Raugei et al.

The supply process for other sources of energy are quite different from PV or wind. They can vary a great deal, making it difficult to estimate or generalize. For example, the energy it takes to extract and refine oil depends on where you get the oil. Middle East oil takes little energy to drill or extract, but to use it in North America you have to send it on tankers a long distance. Oil extraction overhead in the U.S. is much higher, but it is refined close by and sent in pipelines to users. Pipelines are energy efficient. Pimentel estimates oil overhead at 20%, and coal at 8% (p. 17).

The energy overhead for ethanol is a can of worms. Pimentel makes a good case that it is negative. It is an energy sink, taking more oil energy to produce than you get out of it. (Chapter 19).

Quote from Wyttenbach

What you produce = 100% - what you invest e.g. 25% for nukes --> 75% is net energy.

e.g. It last more than 5 years to pay back the nukes construction energy only. Expected live time is 40 years avg.

Where on earth did you find the 5 year payback time? A nuclear power plant produces enough energy for 760,000 average houses. That's millions of people. Do you really think that the construction of a nuclear plant takes as much energy as running as city for 5 years?!? Do you suppose millions of people work on the plant for 5 years? It does seem that way in the Vogtle plant in Georgia, but there are not millions of people at work there.

A realistic estimate is that the energy payback time for the plant, the fuel, and future decommissioning is around 3 months:

Energy Return on Investment - World Nuclear Association

Wind turbines take about 6 to 9 months for energy payback, according to various sources. It depends partly on where you put them, and how much wind there is there. PV payback time is disputed, as described above.

Quote from RobertBryant

what is the official energy payback time for Vogtle?

maybe it will be generating electricity in 3months? 5 years time?

The official energy payback time for Vogtle is the same as any other nuclear plant: about 3 months. It is taking much longer to build than planned, but it is not taking much extra energy. Construction is going slowly, so energy expenditure is low. Photos of it show a lot of equipment lying around and not many people at work. Reports describe delay after delay, when they find problems in previous work. In some cases they have to tear up and replace pipes and other components. That takes extra energy, of course.

Other delays do not cost much energy. Such as:

1. For the last few years "COVID-19-related workforce shortages slowed up construction." That does not take extra energy. No one is doing work. Construction equipment and vehicles are sitting around unused.

2. The Atlanta newspapers described a work stoppage caused by paperwork problems, resulting in people waiting around, not doing any work, and not using energy. "[Southern Company power company] partially attributed the latest delay to incomplete and missing inspection records, which are required for the plant to load nuclear fuel. It said it reduced the backlog by more than 30% in recent weeks as it works its way through tens of thousands of records for materials and equipment installed in the first of its two new units."

Whether it starts generating in 3 months or 5 years, the payback time starting from that moment will be 3 months.

Perhaps you are confusing two different numbers? Energy payback time and construction time?

The point I made above is that there are not millions of workers swarming the site, expending as much electricity as 760,000 houses consume, year after year. Yes, it is taking longer than 5 years, but very little is happening during those years.

Quote from RobertBryant

no.

I asked merely for the official energy payback time..

As I said, it is the same as any other nuke.

If you are not confusing the two, why did you add: "maybe it will be generating electricity in 3months? 5 years time?" What difference does the start time make?

Quote from RobertBryant

the commercial $ payback time is probably way different depending on who calculates it how

The commercial payback time depends on politics. It depends on whether the power company can persuade the Georgia Public Service Commission to raise rates high enough to pay for the debacle quickly. Or whether it will take many years. The rate payers (including me) have to fill in a $33 billion hole. We can do it quickly or slowly, but we have to do it. We cannot let the power company go bankrupt. The lights would go out.

If we had cold fusion, we sure could let the power company go bankrupt. I would love to do that! I would also gleefully watch OPEC bite the dust, along with any auto company that does not quickly begin manufacturing cold fusion automobiles. People in Hawaii are driving the power companies into bankruptcy by installing rooftop solar PV. The power companies are doing all they can to impede rooftop solar installations. That's self defeating. They are riling up their customers, and making it more likely people will go for full solar with battery installations, cutting off the power company completely. I am sure none of the people installing rooftop PV weep for the power company execs and stockholders.

Oil companies, power companies, cable TV, cell phone and telephone companies do not have a well of goodwill with the public. When the technology changes and people have the opportunity to dump their services -- for example by "cable cutting" -- they will do it. The cable companies alienate customers by forcing them to pay for channels they don't want. That is foolish.