It costs less energy to get fossil fuels, but we can't use them as efficiently.

It doesn't take a lot of energy to dig up coal or pump oil from the ground. In contrast, most renewable sources of energy involve obtaining and refining resources, sophisticated manufacturing, and installation. So, at first glance, when it comes to the energy used to get more energy—the energy return on investment—fossil fuels seem like a clear winner. That has led some to argue that transitioning to renewables will create an overall drop in net energy production, which nobody is interested in seeing.

A new study by researchers at the UK's University of Leeds, however, suggests that this isn't a concern at all—in most countries, renewables already produce more net energy than the fossil fuels they're displacing. The key to understanding why is that it's much easier to do useful things with electricity than it is with a hunk of coal or a glob of crude oil. //

Focusing on utility makes a substantial difference. Using the 2020 data, the final, delivered-to-end-user EROI of fossil fuels is quite good, at approximately 8.5, meaning you get about 8.5 units of energy out for every one you invest. (This is averaged across all fuels and uses.) Once you try to do something useful with it, however, it drops dramatically so that the useful-stage EROI is only about 3.5. Which, to be clear, is bad—you want to be getting as much useful energy as possible for every unit of energy you put into things.

Different fuels have very different profiles, however. Natural gas has the highest useful-stage EROI at 9.5, coal is at 7.2, and oil products are only 2, meaning we only get about twice as much energy out of gasoline as we put into producing and using it. Most of these values have been largely unchanged for the past 50 years except for natural gas, which has seen a dramatic drop in the EROI of getting it ready to use (possibly due to the energy costs of fracking—the trend is most notable in the 1980s), and a smaller drop in useful-stage EROI.

A large contributor to these values is how these fuels are put to use. For example, the useful-stage EROI for natural gas in heating buildings is about 12, meaning it can be used reasonably efficiently. The value for heating with oil products is only about 5. Oil products used in road and rail propulsion are also terrible, being just above 2 for rail travel and under 2 for roads.

Renewable energy, in this analysis, is focused on things like wind and solar, which deliver electrons to the grid (things like renewable production of methane are pretty minor at this point). Those can be used for things like heating, rail and road transit, and other uses performed by fossil fuels. Many of these uses are extremely efficient—things like heat pumps and electric motors are much better at turning energy into utility than their fossil fuel equivalents. //

chekk Smack-Fu Master, in training
4y
47
A bit confused by the "Energy efficiency and utility" section:

final-stage EROIs, which tracked the energy used to get a unit of energy to where it's ready for use—so, all the energetic costs of extraction, processing, and delivery
and:
The one thing this doesn't include is the energy cost of the infrastructure needed to extract fossil fuels

What about the energy cost of the infrastructures for processing and delivery? Are those included or not?
To put it a different way, what does "all the energetic costs" actually mean? //

SnoopCatt Wise, Aged Ars Veteran
7m
524
Subscriptor
While the energetic cost of getting energy in the hands of people in a form that's ready for use is a "useful" metric, I think we also need to consider the cost of being able to use energy when we need to. For renewables, this means factoring the cost of batteries or other energy storage mechanisms. //

kevbo Seniorius Lurkius
5y
6
Subscriptor++
I'm looking at the paper: I'm not seeing anything about end-of-life disposal costs. That's one of the "renewable feels like it is more expensive" points: turbine blades and toxic solar panels and batteries need to be disposed of. Of course, it doesn't seem to account for disposing traditional power plants either. I don't know what that end of life cost does to this kind of calculation. I wish it was covered. //

jdbosma Seniorius Lurkius
13y
12
Subscriptor++
It's not clear that this study correctly accounts for the difference between work and heat.
Fossil fuels produce heat. Solar-thermal renewables do too, but photovoltaics and wind produce work (electricity).
Heat is energy that moves from one location to another only under the influence of a termperature difference. Work is energy that can (theoretically) be converted to lifting a weight in a gravitational field, among other useful tasks.
Both work and and heat are energy, i.e. measured in Joules. To convert heat to work is possible, using a heat engine, but under typical conditions no more than about 40% of the heat can be converted to work. The theoretical upper limit on heat engine efficiency is provided by the Carnot relation - achievable implementations always fall short of the maximum.
Direct generation of work energy, as performed by photovoltaics and wind power, is more flexible and in most cases preferable to generation of heat. For one thing, work as electrical power is readily transported over long distances by wire. Work can readily be converted to heat with no loss of energy. When the desired output involves moving heat, a unit of work can sometimes move several times its energy value of heat - this principle is applied in heat pumps for space heating.
It does not make sense to compare the EROI for the heating value of fossil fuels against the electrical value of wind power, since a Joule of work is worth roughly 3x a Joule of heat in some applications, and a Joule of work can always be converted to a Joule of heat when that is desired.
To be most useful, the study should separately compare the EROIs for processes where the output is heat vs. work. //

pete.d Ars Centurion
6y
259
Subscriptor
The article doesn't mention nuclear at all. Did the researchers even consider that energy source, or were they strictly comparing fossil fuels with renewables?

There has been a lot of debate, especially lately, regarding whether nuclear energy is in fact cost-competitive with renewables, even ignoring the lengthy construction times involved. It would've been really interesting to see where nuclear fit into this analysis.