Trade-offs of natural gas versus electricity with different methods of generating electricity

[engineman]

To change from gas to electric you need wiring work in addition to buying the appliances.

[OyCrumbler]

Originally Posted by Those Who Squirm

In some cities, there has grown a movement to ban appliances that use natural gas, at least in new construction. In a few places, recently enacted city ordinances have gone further, and will require ratepayers to replace their gas appliances at some point in the near future.

Is swapping out gas stoves for electric stoves always a net gain, environmentally speaking?

What if the power used to generate the electricity is dirtier than the natural gas used in a stove?

The major energy draw isn't in the stove or cooking in general, but in heating.

The answer is generally it can be better to use an electrically powered appliance for the vast majority of the US, but that is not currently always so for every single person / household.

For heating, electrical heating can either be a resistance heater or a heat pump. The latter is generally much more efficient and it's also split into air-source and ground-source heat pumps. The latter of these two is generally much more efficient, but is difficult to implement unless you're building the structure with the intent of using ground-source heat pumps from the beginning. In even the air source heat pump case though, even if natural gas were the source of electricity and some of that is converted to waste heat at the generation plant and you have the incumbent transmission and distribution losses, the air source heat pump will for the vast majority of the US be more efficient than a modern natural gas furnace.

There are exceptions to this though such as for places with Fairbanks, Alaska like weather where an air source heat pump would be unable to operate efficiently and therefore it would be electrical resistance heating as a backup which will be less efficient use of natural gas as the source of electricity versus just burning the natural gas directly for heat. For places with extreme weather, even a ground source heat pump can be more efficient, but again that's something you basically needed to have in mind when you built the structure as retrofitting it in can be very costly. Of course, the benefit to the electrical appliance is that there are many different tried and true ways to generate electricity and so it's quite possible that even if the electricity currently running to your house is sourced from an old coal plant, that doesn't necessarily remain the case over the lifetime of your heating system as you can see the pretty massive changes in electricity generation by source in the US: https://www.eia.gov/energyexplained/...-in-the-us.php

For cooking, it has funnily enough, a similar analogous relationship. Electric stoves can either be a resistance heating element or an induction cooker. They are both generally more efficient than the gas stove as the gas stove usually expends a lot of heat radiating out to the sides rather than directly to the cooking vessel, but the induction cooker is substantially faster and somewhat more efficient than the resistance heating element. The problem I found with induction cooking stoves in the US is that the price for good quality induction stoves were comparatively quite high and a bit shocking compared to other parts of the world like in East Asia. That was quite a while ago though and I ended up bringing one from East Asia, so perhaps the price differential isn't quite so high anymore.

[OyCrumbler]

Originally Posted by L00k4ward

The link below discusses industrial natural gas turbines and mentions that the Guinness world record for gas turbine efficiency in 2018 was 63%.

The equivalent efficiency direct fire residential gas furnace wouldn’t even be allowed for installation due to such low efficiency; we perhaps have a few still lingering from the past in people’s homes; not sure how many.
They make residential gas furnaces with efficiency of 98.5%.

To be fair, not sure how much gas is lost in distribution system, it would lower the above.

https://petrotechinc.com/efficiency-of-gas-turbines/

If one adds high voltage transmission, various transformers, residential transmission, other losses in electrical distribution system, etc the losses would mount

It is calculated that industrial natural gas made electricity only delivers 33% of the energy to the residence - losing an astoundingly 67% in the process?

Yet, then everyone claims that electricity is “100% efficient” after the process has wasted 67% of it in production and distribution.

Now finally mini-splits reached the US with the the craziest unjustified prices (they are used for half a century and very inexpensive in India, Asia - and nobody pays tens of thousand of $ there - they can’t afford it otherwise.
The Americans are being fleeced again)

The stats for the best of them are showing the efficiency up to 2-4+ due to the use of the refrigerants, but
in a very narrow temperature range.
So narrow that people perhaps could just live without them? Some portable heater or portable A/C may be enough in some locations?
And how much energy goes into producing the refrigerants? they keep phasing them out?

This we should count too in the calculation of “efficiency”

They are tweaked for cold climates, but to get an average cop of 2 in freezing temperatures - you could never justify the expense of buying, installing and maintaining costs. The capital and maintaining costs in a not very long life span of equipment just don’t add up.

Most of them are not corrosion resistant - and though the best could help maintain humidity levels on the East Coast - one still could be better off with dehumidifier- but thy could be loud

Basically, the mini-splits have their niche, but it isn’t a panacea:the work should continue and the focus should be on improving construction- highly air-sealed and insulated houses with regulated ventilation don’t need any heat or even cooling - or just very little of it.

That should be the goal: not how more energy to produce, but how to save more and to not waste in the whole energy production cycle from the origin to the end user
This is the message that gets lost.

The average for the US utility-scale fleet is ~44.4% efficiency for natural gas plants. Transmission and distribution loss in the US averaged 5%. 0.444*0.95 = 0.428 or 42.8% efficiency. Certainly a resistive heater that's generally always well above 90% efficiency will compare poorly against a natural gas furnace due to this initial loss.

So probably don't get a resistive heater or at least not solely a resistive heater. Get a heat pump. That average 42.8% efficiency after generation, transmission, and distribution losses means the heat pump needs to average a COP of 2.30 to be competitive with a top of the line 98.5% ultra-efficient natural gas furnace assuming that natural gas has 0% distribution loss. A popular brand of low-temperature air source heat pumps are Mitsubishi's M-Series which at 5 degrees Fahrenheit has a COP of 2.42 and rapidly improve to over 4 as the temperature differential it needs to make it gets lower. So at 5 F, even with the losses, a common cold climate air-source heat pump is more efficient than the top of the line natural gas furnace assuming no natural gas distribution loss. At a COP of 4 which you'd get if you're turning on the heat in the 40s F, that 42.8% efficiency for natural gas generated electricity after generation, transmission, and distribution losses amounts to over 73.8% greater efficiency than the most efficient natural gas furnace that's getting natural gas with zero loss in distribution.

For the vast majority of the US, the vast majority, and for a sizable chunk, for *all* of the time they would turn on their home heating system will be at or above 5F. Of course, there's a lot of variance in this since the majority of people in the US aren't getting their electricity from natural gas, not all natural gas electricity generation plants are built the same (some will be more efficient some will be less), different regions have different temperatures and people have different tolerances of how cold is too cold. That's why saying it's *always* more efficient for electric heating via heat pumps versus natural gas furnaces is too broad of a statement. It's more reasonable to say that electric heating is generally going to be more efficient, but not currently in every single situation for every single household.

Some notes to the comparison, and certainly not exhaustive:

- Natural gas distribution in homes is *not* completely lossless and estimates on this are tricky though are almost universally in single digit range so it's not huge.

- New natural gas furnaces in the US are required to be at least 78% efficient and 98.5% is on the very high range side. Mid-level is more in the 80-90% range whereas I chose the most common cold climate air source heat pump for comparison.

- Heat pump theoretical efficiency is substantially higher than what current heat pumps on the market can do and so there's a lot of room for improvement, but natural gas furnaces are already very close to their theoretical limit.

- Similarly, heat pumps from a different era and ones that are not intended for very cold temperatures have lower efficiencies, so if you find an old heat pump that was not meant for cold weather, then it's probably going to have bad efficiency in very cold temperatures.

- Due to the fairly high variability in efficiency of air-source heat pumps, there may be days where the air source heat pump that derives its electricity from a natural gas generation plant will be less efficient than the natural gas furnace. For example, you may be hit by a string of -20 F or -40F days where the air-source heat pump deriving its electricity from a natural gas generation plant operates something like half as efficient to a third as efficient (basically turned into a resistive heater) in terms of natural gas use versus a natural gas furnace. The way to judge overall efficiency though is to take stock of the heating season as a whole. Since above 0F, the air-source heat pump that derives its electricity from a natural gas generation plant was probably more efficient, so consider how many days in the heating season and at what temperatures you had your heating system on.

- Ground-source heat pumps are generally a lot more efficient and less variable in efficiency than air-source heat pumps especially when it comes to very cold temperatures, but for most people and existing households, it's such a heavy lift to retrofit in that I think it's reasonable to not consider ground source as part of the general case.

- US electricity generation by source for the last decade has continued to swing more towards renewable energy and natural gas power plants have been getting more efficient. These heating systems are meant to last a while so it's possible that even if the electricity generation source for someone now favors a natural gas furnace when it comes to emissions and efficiency (again, generally a minority of people in the US), there's a chance that even those households will swing favorably towards heat pumps within the lifetime of their heating system especially as heat pumps continue to improve.

- How competent of an installation was done whether its heat pumps or natural gas furnace can play a huge part in effective efficiency.

TLDR;
- Ground source heat pump is likely the most efficient but is too difficult for most unless you are building from scratch
- Natural gas furnace will currently and likely remain for a while the likely most efficient / better for emissions if you live in a place with a climate like Fairbanks, Alaska even if electricity is from natural gas or a place where coal is and will remain for the next couple of decades the primary source of electricity
- Air-source heat pump is the most efficiency / better for emissions (outside of much more costly ground source heat pump if trying to fit into an existing building) if your electricity mostly comes from natural gas, and much, much more so if your electricity is primarily from solar, wind, hydroelectricity, nuclear, or geothermal sources.

Absolutely agreed on the importance of well-insulated homes with regulated ventilation regardless of which heating system is used.