Thursday, April 18, 2019

Yes, Eli has been on sabbatical, but he really has been thinking of the bunnies, especially with Easter coming up.  Well, sometimes it just gets hard to think of something new and interesting and life, or at least Twitter, has become a series of re-runs where all that is needed is a link to some old Rabett Run post (there are some goodies there the Bunny will tell you:).

In any case there has been recent discussion about a chart posted by the Lawrence Livermore Lab folk about US Energy consumption and copied to TwitterSeveral are trying to use this as an argument against fossil fuels pointing to the fact that rejected energy is a large part of electricity generation and more.


This is tied together with a basic confusion first discussed by RayP on Real Climate, that the problem with fossil fuels is not the rejected energy, but the fact that the greenhouse gas emissions remain in the atmosphere and slow the emission of heat to space over centuries.  In a letter to Steve Levitt, Ray dispensed with Nathan Myhrvold's argument that
. . . in effect, that it was pointless to try to solve global warming by building solar cells, because they are black and absorb all the solar energy that hits them, but convert only some 12% to electricity while radiating the rest as heat, warming the planet. Now, maybe you were dazzled by Mr Myhrvold’s brilliance, but don’t we try to teach our students to think for themselves? Let’s go through the arithmetic step by step and see how it comes out. It’s not hard.
Interested or, as in the case of Eli, those with the dread forgetting disease, can follow Ray through the calculation, but the point is that all energy eventually (may take the age of the universe, but eventually) degrades to heat, but some of it can be used in the meantime to do work (move things non-randomly, including electrons).

The reason that fossil fuels are heating the Earth is not that they produce heat as well as work, but that their CO2 emissions continue to increase the amount of thermal energy in the atmosphere, on the surface and in the oceans, over centuries.

Sunlight heats the Earth and is degraded to heat which radiates into space by IR emissions from the surface and the atmosphere.  Increasing the amount of greenhouse gases in the atmosphere slows the rate of radiation so that the Earth has to warm, increasing the rate of radiation to return the system to balance.  Energy added on the surface by fossil fuel combustion or nuclear energy or wind or solar, or whatever is soon degraded to thermal energy and radiated to space.  It's a small one time charge.

The ratio between the work, W that can be done and the energy input U, W/U is the efficiency, and the heat produced is Q. 

Thermodynamics sets the upper limit to efficiency.  Engineering sets the actual limit.  It turns out that renewables like wind and solar are not very efficient, but that the heat that they generate in creating work does not lead to a continual warming of the system over centuries.  The same is true for heat generated in fossil fuel combustion, but, as RayP pointed out a decade ago, that is irrelevant, because the CO2 produced in fossil fuel combustion DOES heat the Earth for centuries.

That being said, it's good to be efficient.  For one thing, it costs less over the long run in the building, operation and maintenance of stuff.  Also, rejected heat is local, which can be both good and bad, depending if you can use the heat for other things like industrial processes, or heating the home.  That gets deep into the weeds and Eli will leave it there

6 comments:

Old_salt said...

The inefficiencies in wind and solar are before the first line in the graph from the boxes on the left. The inefficiencies in the fossil fuels are in the rejected energy on the right. This display makes the renewable fraction for electrification about 70% too small.

This has been my only objection to this graph layout. Incidentally, The US energy usage has been hovering around 100 quads since the turn of the century.

EliRabett said...

strange since both solar and wind have local heating effects.

E. Swanson said...

Nothing like a nice spaghetti graph to add confusion to a debate. These compilations have appeared regularly since the '70's when I first got involved in the energy situation after the Arab/OPEC Embargo against the US. This is a graph of what might be called "economic energy", i.e., the energy which flows thru the economic system. Obviously, if there's no price placed on an energy flow, it's not counted.

For example, where's the accounting for the solar heat gain thru windows in structures? There's not an entry for solar thermal at all. There's no mention of the "services" sector of the economy, which depends heavily on "transportation" (think UPS, railroads and the airlines), so there should be a path from "transportation" directly to "commercial". What about including the "transportation" energy used for commuting, should that flow be ascribed to "commercial" or "industrial" instead of "residential", as neither would function without the fact that people must be able to show up for work before anything happens?

From a climate perspective, there's nothing about the sunlight which is received by the plants in agriculture, where different cover crops influence the flow of sunlight thru the atmosphere and back out. One may argue that such is not important, but replacing natural forest cover with crops and pasture has a direct effect on the micro climate and the return of depleted farm lands to woodlands in the 20th century is another part of the overall question of climate change. The reverse is true for the effects of clearing tropical rain forest, etc. Then too, there's the claim often presented that the "urban heat island" is warming things over time.

One can nit pick a graph like this forever...

E. Swanson said...

Adding to my previous comment about the graph from Lawrence Livermore, consider the column of sources on the LHS. Those are produced quantities, such as oil pumped out of the ground, coal dug up and nat gas pumped into the pipes from the well head. There's no "feedback" in the energy calculation for the the energy required to produce these "sources'. There was lots of discussion about Energy Return on Energy Invested (ERoEI) around a decade ago as the price of oil climbed toward $150 a bbl, pointing out that as ERoEI declines toward 1.0, there's no point in further extraction. Also called "net energy analysis", the energy taken from the "industrial" and "transport" sectors must be shown as a feedback, not as a useful output to other economic activities. Including the fact that there are inefficiencies in both sectors, the break even ERoEI will be greater than 1.0 unless one uses a source like coal to produce oil, etc. Since then, the boom in Fracking has provided a cushion against the threat of immediate decline in oil and gas production, but the frackers are faced with the same dilemma as their wells deplete rapidly and require higher prices to pay for that production compared with conventional production.

The lack of an accounting for "Agriculture" is also misleading, since plants are solar collectors and that energy is much larger than the energy in the form of fuel and chemicals applied to land to enable greater productivity and the energy used to transport and process the food with our industrial scale farming. In reality, our entire economy is powered by solar energy, since our bodies are "run" on that agricultural output, a fact completely missed by those who only see the market prices and technical inefficiencies of the flows shown in the graph. Looking at the graphic, one might conclude that all that's required is to reduce those "inefficiencies" and the energy problems would be greatly diminished. Converting agricultural land to other uses, such as housing, urban high rises and industrial buildings is seen by a "good", even though the effect may be less agricultural output over time. Agriculture is heavily dependent on local climate and changing climate, particularly in the form of more frequent extreme events, represents another area of humanity's situation completely missed in the LLNL graphic.

Don't worry, "we" are going to Mars. Pardon my rant...

EliRabett said...

We are becoming Mars.

Or at least another planet. But you are right if you are only counting energy that can be sold you get a very odd accounting.

E. Swanson said...

There's another problem with that graphic. The data is similar to that from the EIA, shown HERE, but one will notice that there's no break out accounting for imports/exports on the chart, which is shown HERE. One can see the large increase in exports in the past couple of years, as slightly processed natural gas liquids were re-classified as "oil products", instead of "oil production", which was restricted by law after the OPEC/Arab Oil Embargo, as I recall.

From a climate perspective, these data also don't include the energy used to produce the many produces, such as steel and aluminum, which are also imported. The same goes for our exports to other nations. All this makes the accounting for carbon flows, which would be required for defining carbon taxes, much more difficult to determine. One problem I see with the carbon tax proposals I've seen is that exports are compensated for the tax on the way out, therefore, there would be a big incentive to export crude and it's products as the effects within the US would begin to restrict consumption within the US. A fine mess indeed.