An interesting thing about the 1950 US chart is that in 1950 we wasted about 45% of generated energy (rejected), and 71 years later we wasted 67%. Now that’s progress.

thomas: I believe the argument you’re referring to is patrick ennis’s comment above about the excess heat captured by photovoltaics that would otherwise be reflected back into space. It looks like you didn’t hit the reply button there to have it nested, so I’m just making that clear here.

That’s a great article. Thanks for providing the link. The tl;dr from the article is that Prof. Pierrehumbert, a geophysicist at the University of Chicago, goes through some simple math to show that waste heat is insignificant to global warming. And not only is the rejected energy/waste heat from solar panels negligible, but so is the rejected energy/waste heat from coal-burning power plants. It’s all about the carbon emissions. So, yes, I agree that he did shred that argument.

I have always thought Griffith’s argument was inane. We don’t halve our energy use, because our use is the energy services, not the rejected energy. Use is not the same thing as consumption. The energy that we are actually using on the Sankey chart is 31.8 quads, and the rest is waste along the way. To make Griffith’s electrify everything fantasy work where we don’t have to give anything up because we are “saving” so much energy, we have to find another 16 quads of nukes, hydro, solar, and wind. Good luck with that. https://www.treehugger.com/can-we-fight-climate-change-by-just-electrifying-everything-5185685

Fortunately, LLNL now produces a CO2 flow chart: https://flowcharts.llnl.gov/commodities/carbon . This chart clearly shows that to get the most bang (CO2 reduction) for the buck (cost of solar+wind+storage) for the next several decades, replacing coal and oil should be the focus, not natural gas. In other words, the opportunity cost of electrifying high efficiency gas heating instead of coal-fired generation and oil-transportation is very, very high.

Another issue is that this diagram does not show that heat pumps take energy from the environment. Why is that not important? Should that not be subtracted from Rejected Heat?

I am assuming that this type of analysis assumes that the energy that goes out the flue of a gas furnace is Rejected Heat. If so, then a very high efficiency gas furnace (97% AFUE) has little Rejected Heat. From a thermodynamic point of view, this furnace has a good First Law efficiency but a lousy Second Law efficiency. Natural gas can be use to drive heat pumps with “efficiencies” greater than one and those systems are available today.

My point here is that this diagram is misleading in that it does not properly account for heat pump performance or distinguish between what Rejected Energy is waste heat vs. what is simply required by thermodynamic laws.

I would very much like to see numbers behind the claim of wood pellet power plants. A great deal of wood byproducts are burned within paper mills since the fuel itself is created by paper manufacturing processes and the mills have huge heat and power requirements – these are a great example of onsite combined heat and power. (Though not without other major environmental problems…)

Wood pellets are also a niche fuel for those who like wood or coal stoves in their homes but not the hassle of burning logs or dealing with coal…again, very much a niche product.

But wood pellet power plants on the grid at commercially meaningful outputs? Examples / numbers, please.

A recent book “Electrify” by Saul Griffith, makes the case for electrifying everything and generating that electricity from renewable sources. Doing so would immediately reduce the amount of energy needed by the amount of the rejected energy. Essentially, we could halve our energy use without any reduction in energy use. Its a convincing case.

The essence of getting there is two fold. One is to never buy another fossil fuel anything and replacing those things with electric when their usable life is up. The other is to ramp up renewable generation to match this new demand.

https://www.amazon.com/Electrify-Optimists-Playbook-Energy-Future/dp/0262046237