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Recently, Habré published the topic " Solar energy fell to the level of nuclear ", which resulted in fierce disputes about the legitimacy of the use of price as an indicator of efficiency. After reviewing the comments, I was surprised to find that they did not mention such an indicator as EROEI. And I thought it would be interesting for Habrovites to find out about him.

EROEI (the ratio of Energy Return On Energy Invested) is expressed by a very simple formula:

EROEI = energy gained / energy consumed
In order to extract oil, it is necessary to expend energy on its extraction. In order to get the decay energy of the uranium nucleus, you need to spend energy on the extraction and enrichment of uranium. In order to receive energy from a solar battery, it is necessary to expend energy on its production.

EROEI is a universal indicator of the efficiency of an energy production method. From the point of view of EROEI, there are no renewable and non-renewable energy sources - there are sources whose EROEI decreases with time and sources whose EROEI increases.

EROEI is often criticized, primarily for problems with its calculation. However, unlike the price per kWh, efficiency, occupied space and many other indicators, EROEI is in excellent correlation with reality and perfectly explains the processes occurring in the energy sector.

Let's start with EROEI oil. In the 1930s, EROEI oil reached 100 or more. Not a single source of energy has yet come close to this figure. Ultra-high oil EROEI makes it an ideal energy carrier; therefore, the use of oil is extremely efficient. Although this is a non-renewable resource, non-use of such a rich source of energy just looks silly.

EROEI oil has been steadily declining since; in 1970 it was about 30, and in 2000 it was about 10 to 20 (it is easy to guess that, for example, EROEI of Russian oil is much lower than Saudi oil). Nevertheless, oil is still a very promising source of energy, although the decline in EROEI forces it to gradually replace it.

And here we are confronted with the first, seemingly incomprehensible paradox, which can be perfectly explained with the help of EROEI. As is known, proven reserves of tar sands (oil) sands are several times higher than oil reserves. Quite often there are assertions that their development will become economically viable at a price of n (30, 50, 100 - I have met different options) dollars per barrel of oil. But the development of these deposits is practically not conducted, although only in Canada, deposits of 1.7 trillion barrels have been explored.

The fact is that, in addition to environmental problems, there is also a purely physical problem: EROEI of tar sands is approximately 2/3 . Even according to the most optimistic estimates of EROEI, oil sands will not exceed 5 - this is, of course, more than one, but still not enough. If pessimistic estimates are correct, then no tar sands will be an effective source of energy at any oil price. The same, in general, is true for oil shale.

EROEI of other non-renewable energy sources - coal and gas - is slightly lower than the indicator of oil, and very much depends on the specific process conditions (for example, liquefying gas is a very energy-consuming procedure). EROEI gas can range from 16 to as little as 2, EROEI coal from 14 to 1.5.

An interesting question - EROEI atomic energy. The energy costs of organizing the operation of a nuclear reactor are small in themselves, but the extraction and, especially, the enrichment of uranium ore is a very energy-consuming process. EROEI NPP lies in the range from 5 to 10. It should be noted that if it were not for the low efficiency of the conversion of the energy of fission of uranium into electricity, this figure would be much higher (up to 20). For French nuclear power plants (and France receives most of its electricity through nuclear power plants) EROEI is on average 6.5 . This is not so much, on the one hand, but not so little - on the other. EROEI NPP as a whole is already close to the indicators of oil, and for Russia, probably, it exceeded them.

Very good EROEI hydropower - up to 50 on large rivers, and in extremely good conditions - and up to 200 or more. However, the vast majority of usable rivers are already covered by hydroelectric power plants, so the hydroelectric power EROEI is rather arbitrary. Some sources cite a spread of numbers for currently real projects of 5–15, which is nevertheless quite good. EROEI for tidal and geothermal power plants is in the range of about 1.5-10.

The same applies to EROEI wind turbines. In good conditions, this indicator can reach 50 or more, but in more or less realistic conditions, the spread of EROEI is from 5 to 30 ( here is quite a large study on this topic, including with numbers on other energy sources).

A very difficult situation with solar energy is mainly due to the fact that it is difficult to accurately estimate the service life of the system components. However, even the most optimistic estimates rarely predict an EROEI higher than 10. In adverse conditions, the EROEI of a solar installation may even be less than one. Apparently, solar electrical installations remain the most ineffective of all alternative energy sources. Therefore, despite significant support, there are very few solar power plants, despite the attractiveness of this method of producing energy.

And finally, a special song - the so-called. biofuels. By and large, a significant part of this business is just a scam: EROEI of most types of plant-based fuels (in particular, from corn ) is less or slightly more than one. The costs of fuel and various fertilizers for growing biomass exceed the income in the form of biofuels. Relatively competitive only biofuels from sugar cane (EROEI about 8).

And, finally, a very interesting picture: the dynamics of EROEI of the main sources of energy (and the forecast up to 2020):

Materials for further reading:
art-of-arts.livejournal.com/tag/%D0%BA%D0%BE%D0%BC%D0% BF% D0% B8% D0% BB% D1% 8F% D1% 86% D0% B8% D1 % 8F

PS And yes, as the Minister of Oil of Saudi Arabia, Sheikh Ahmed Zaki Yamani, said, the Stone Age ended not because the stones ran out and the Oil Age ended not because the oil ended.

Source: https://habr.com/ru/post/100525/

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