We Don't Have an Energy Problem, We Have an Exergy Problem

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CC BY 2.0. My "high efficiency" boiler turning high-exergy fuel into CO2, steam and anergy/ Lloyd Alter

Another reason to electrify everything.

After writing a recent post about a UK pilot project which mixes "green" hydrogen with natural gas, a number of readers complained that "criticism of this work is an example of the best being the enemy of the good. We need intermediate solutions."

The problem with intermediate solutions like this is they "lock in" the need for piped gas, which is a high quality fuel being used to create low quality heat. It is a huge waste of exergy.

I am diving into thermodynamics here, and look forward to corrections and comments from experts. We are all being told not to waste energy, yet we were told in school that the first law of thermodynamics is the law of conservation of energy, that "energy cannot be created or destroyed in an isolated system." So you can't "save" energy. What in fact you are saving is exergy, the ability of something to do work, and when exergy is wasted, it's gone. As engineer Robert Bean notes, "When we used energy to heat our homes, we are not destroying any energy; we are merely converting it to a less useful form, a form of less exergy."

Some call that less useful form 'anergy'. Lin-Shu Wang quoted a definition in a study of exergy:

Exergy is the portion of energy that is entirely convertible into all other forms of energy; the remainder is anergy. That is,
energy = exergy + anergy

When you are burning gas of any kind, you are taking the really high grade heat at 1500 degrees to heat water or air to between 50 and 150 degrees. It's inefficient; most is lost to the environment. As Robert Bean puts it, it's like warming your hands with a blowtorch.

Look at what is going into making that "green" hydrogen: We are building wind turbines that generate electricity that electrolyzes water which is run through a vast piping network, and then just...burned? To make hot water or air to keep warm in leaky homes that are just letting it all escape out into the atmosphere again? This is so 19th century, when we had no choice but to use high quality energy to do low quality work. But we do have a choice now.

We know now how to safely and significantly reduce the demand for heat or cooling, with lots of insulation. That's why I am such a big fan of Passivhaus.


Lloyd Alter/ Condenser side of a CO2 heat pump/CC BY 2.0

Then you stop burning high exergy fuels like natural gas or hydrogen and use really low exergy heat sources like the air and the ground with heat pumps. They concentrate the low grade energy that's all around us into exergy, useful if low-grade heat, and are getting better at it all the time. It's silly to burn stuff when you can collect heat from the air around us.

Heat pumps are often filled with greenhouse gases, but that's becoming less of a problem too, with CO2 heat pumps delivering hot water and new, small propane based heat pumps that reduce the worries about the refrigerant.

This is why I don't like the idea of using hydrogen; it's an unnecessary in-between step that is maintaining a 19th century system of burning stuff, using a high- exergy fuel to do a low exergy job. We are still warming our hands with a blowtorch.

NOTE: On the other side, a commenter to my previous post made some very good points, which I repeat here almost in full:

My perspective is that the all or nothing mentality is the idea that you need to go all the way across to heat pumps, rather than using hydrogen for combustion as part of your decarbonisation approach :)....
We should have better insulated houses - but we don't, and it's not a cheap proposition to change. There's wide distrust about cavity wall insulation programmes, and solid insulation would be met with huge resistance. If I were building properties and infrastructure from scratch I would go for an all-electric system, but we aren't in that position generally.
It's a balancing act. What do you do with your system? Use electric heating, with the need to build enough generation, transmission for the electricity to meet peak winter demand? Or use the existing infrastructure to distribute hydrogen rather than natural gas, use salt caverns to store it in large quantities, and generate it over an entire year? If you have a power to gas system working, you then have the ability to install more solar capacity without needing to match supply and demand on such a time-bound basis. Interseasonal storage of electricity via batteries without the conversion losses would be nice, but the technology isn't there. We can't afford to sit around and wait in case it develops on such a scale.
There isn't a silver bullet that resolves everything in one way. Realistically, we need a mixture of heat pumps, biogas, hydrogen, district heating where there is local waste heat available, and more technology as it is invented.