[NickM]

the first one you will look at is hydrogen, because it's the simplest

Simplest chemically != simplest to use in practice. There are already millions of miles of natural gas pipelines leading directly to peoples' homes, and those pipelines cannot be used with hydrogen (not to mention all the appliances they feed).

Renewable methane is a dead simple drop-in replacement for natural gas. None of the other alternatives you mentioned share that property, and I think you're seriously under-weighting the importance of it.

[hannob]

None of these chemicals will be used in people's homes in any meaningful quantity. That's just not going to happen due to the conersion inefficiencies.

[pfdietz]

Right. The more efficient way to use methane to heat a home (vs. current furnaces) is to burn it in a CC power plant and heat the home with a heat pump.

[slashdev]

I questioned if the gain from the heat pump really exceed the losses from generation and transmission.

It seems CC plants are 45-57% efficient, so let’s go with 50%. A gas furnace is from 80% to 95% depending how old it is.

The heat pump would need to be roughly 2x efficiency to break even. They can be 3x or higher (since they move heat around rather than generating it.) Your statement surprisingly checks out.

So obviously it makes zero sense to use electricity to create methane to then burn for heat. Reality is messy though, sometimes we do things inefficiently because there are other constraints. Being unable to afford to convert to a heat pump system, or being in a climate where it won’t work well.

[pfdietz]

The only way, from an efficiency point of view, that it would make sense to burn gas in a home for heating is with a gas-fired heat pump (or home cogeneration driving an electric heat pump, and also using the waste heat). But these have not been installed much, probably because of cost.

The waste heat from the combined cycle plant could also be used for district heating.

Highest efficiency CC plants are like 62% efficient (but that's on a LHV basis, which ignores latent heat of water of combustion.)

[NickM]

Yes, that would be more efficient, but there are so many edge cases where switching an existing home to use heat pumps is prohibitively difficult or expensive.

Maybe you have radiators that require higher temps than can be efficiently produced by heat pumps. Maybe you live in a place where the air gets too cold for air source heat pumps to be cost effective. Maybe you want to install ground source, but you live in a city and don't have a big enough yard. Maybe you have a big enough yard but local geological conditions aren't conducive to digging deep enough.

Not to mention all the people who just don't want to bother switching, or who don't have the money to switch, or prefer the reliability of the natural gas over the electrical grid, or...etc.

Or just look at the culture wars that are already starting over gas stoves, when nobody has even been required to get rid of their existing gas stove, and people are just talking about changing the rules for new construction.

There are just so many edge cases where it's hard to get people to switch off natural gas. If we can make green methane, all those problems are simultaneously solved with zero disruption to anyone's homes/lifestyles/etc.

[tastyfreeze]

Methane can be produced passively by digesting organic material in an anaerobic environment. Using electricity to synthesize methane is not a good use of electricity when bacteria do it much more efficiently.