Comment by kragen | Hacker News Reader

Comment by kragen | Hacker News Reader

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Thermal energy and electrical energy really are the same thing, not two different quantities that happen to be measured in the same units, like grams of lead and grams of gold, or your example of US dollars and Jamaican dollars. When you convert less than half of the chemical energy in the gasoline into mechanical work to move the car, the other 50+% of the energy is converted into heat. Carnot gives us a reversible conversion factor between them, but it depends on the combustion temperature rather than being some kind of constant, as in your Jamaican-dollar example.

Technically you can interconvert grams of lead and grams of gold one to one, too, but interconverting electrical and thermal energy is so easy that it happens all the time unintentionally.

MacKay does in fact cover the Carnot factor you're talking about; his Chapter 21 http://www.withouthotair.com/c21/page_140.shtml begins:

> In the last chapter, we learned that electrification could shrink transport’s energy consumption to one fifth of its current levels; and that public trans- port and cycling can be about 40 times more energy-efficient than car- driving. How about heating? What sort of energy-savings can technology or lifestyle-change offer?

And then he goes into not just household heat pumps, and their achievable coefficients of performance, but also municipal combined heat and power, which take that ≈50% of the chemical energy "lost" from thermal power plants as waste heat and pumps it into your house.

So, far from being ignorant of the issue as you seem to be implying, he presents a more complete picture of the issues than you are presenting.

Specifically for household climate control, I suspect that both heat pumps and CHP are much less relevant now that we have cheap solar. You can think of a heat pump as a way to reduce the amount of solar-panel area that you need to heat your house. The trouble is that solar panels cost €0.13 per peak watt, while heat pumps cost closer to €1 per peak watt, so it may be cheaper to "waste" energy on heating your house resistively with a nichrome wire than to use a carefully engineered heat pump.

For the purposes of energy use, they are not. Heat is fundamentally worth less than the equivilent amount of electrical energy, due to these efficiency losses (which are not just a technology problem). It's misleading to compare them at any point in your analysis unless to highlight the problem with the comparison.

Usually it's fundamentally worth less, but not a specific amount less, the way Jamaican dollars and lead are. And, if you're using resistive heating, they're worth exactly the same amount.

You can convert electricty to heat at 1:1 in the absolute worst case. The opposite is not possible even in the absolute best case, and in practice you are looking at about a 60% exchange rate for 'high-grade' heat.

That "absolute worst case" happens in my house most of the winter, and it's common throughout the rich world. The only place it isn't common is where people don't have electricity yet. Even in Brazil, where nobody needs a space heater, electric water heaters are common.

When that absolute worst case is happening in the house's living space, we can and do "convert" heat to electrical energy savings 1:1, because every joule "wasted" by cooking food with gas, or heating the house with a corn stove, or warming up the floor with sunlight for passive solar gain, is another joule earlier that the space heater's thermostat will turn it off.

Sure, you're using the themodynamically worst heating technology possible (I don't think I have ever lived in a house that used resistive electric heating). That still doesn't make it a useful comparison overall where people often pick better options, nor does it make it so that you're actually converting the other way when you use better options.

As I explained 5 comments up this thread, people are going to stop picking those "better" options because they're no longer economical. I think you just didn't notice that part of my argument, because you never responded to it.

Also, I don't think it's accurate to describe electrical resistance heating as "the thermodynamically worst heating technology possible". Electrical resistance heating is generally close to 100% efficient. It's actually thermodynamically possible to make heaters that are less than 100% efficient; MacKay explains, for example, that he heats his house with a 90%-efficient condensing boiler, and it's common for fireplaces to be around 20% efficient, because most of the heat goes up the chimney instead of heating your house.

Fireplaces are actually thermodynamically possible machines. I understand that you've never seen one, but I assure you that they do exist.

I've actually lived in houses where the fireplace had negative efficiency at times, sucking more heat out of the house (in the form of warm air) than they added back in the form of radiation.

That only makes sense in a situation where renewables have already more than taken over, which kind of makes the point moot. I'll concede your point that traditional fireplaces are even worse than resistive heating, though not that a gas condensing boiler is because you're not getting 90% of the energy in the gas out as electricity.

I'm pretty sure the barrier to the lead-gold mass parity is that due to nuclear stuff they're gonna not trade equal proton/neutron count and while of you flip the ratio you are merely dealing with an energy deficit/excess incurred as you're rearranging the protons and neutrons to transmute between gold and lead which by e=mc² is equivalent to mass... You're gonna run head first into the problem that we with our current proven understanding of atomic nucleus quantum physics, expect the energy excess to need to be turned into an equal split of matter *and antimatter*, which will foul your plans.

We're suspecting there to be some symmetry breakage to explain why we don't really see any globs of antimatter with our telescopes (at least none that show any evidence of being antimatter), but so far no (real) luck.

As for the "0.13€ vs. 1€": you're not gonna get much solar yield in peak winter at least in Central Europe, especially it's gonna be that your PV is going to charge <100hour electricity storage when the sun shows up on those winter days and the heat pump (at least the part that spends a little electricity to lift a lot of heat energy from outside temps to indoor temps) runs approximately continuously.

You might have some kind of e.g. water/water heat pump with salted (not table salt though) water deliberately thawing during daytime (by turning on the circulation between it and outside air) to freeze at much warmer than night air temperatures to buffer those "only mildly freezing" temperatures to improve the efficiency (and at that point, likely also the thermal output power) of the heat pump.

The radiators inside and potential fans for them would also go up in flow to make up for the increased losses through the walls/window-glass.

A big reason why at least in e.g. Germany heat pumps are not at all irrelevant vs. electric resistance "space heaters" is that they're also very efficient at handling spring/autumn (lower thermal delta to lift against; referencing to a resistance heater for scale/reference purposes but clearly not expecting that to be a benchmark) while easily offering summer cooling (with relatively minor incremental complexity).

I don't really know how inherently expensive it is to keep around at least for parts of each city, but existing natural gas central heating boilers are very useful to not just trash before they're broken just because one uogrades to a heat pump, specifically because they are already there (sunk cost/little scrap value) and have basically zero issue delivering extremely spiky power during unannounced winter days (well, takes maybe a day of notice to actually get crew in to the storage&distribution facilities, but weather forecasts easily cope).

Sure, it's not _efficient,_ but we could just divert some synthetic methane during summer to refill the caverns: we kinda want that (at least for hydrogen but methane works too at least for storage) anyways for chemical synthesis factories if we're not just gonna feed them crude oil/natural gas, so other than that chemical factories probably/largely prefer direct hydrogen, continuing to use our existing seasonal storage even if it's not getting refilled from NordStream2 but from local summer-only electrolysis plants and with more hydrogen than methane where the geology allows, seems to me just frugal dealings with nature (reduce, Reuse, recycle).

I think you can, in theory, break apart stable lead nuclei by spallation, transmuting some of them into somewhat lighter elements (first-row platinum-group elements, tungsten, that kind of thing), which you can fairly easily separate by chemical means, then bombard with neutrons and alpha particles until some of them become gold, go through another chemical separation step, and repeat. You need energy input for all of this, but I don't think you need to deal with significant quantities of antimatter, just the occasional positron emission.

I admit I don't know much about nuclear reactions, so please let me know if I'm talking nonsense here.

I agree that Central European capacity factors for solar are pretty bad, and that heat pumps are still economical in more polar countries, and will remain so for a few more years.

I'll answer the rest of your extremely interesting comment later, as I'm being drawn away at the moment, but I want you to know that I appreciate it very much.

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