Why Not a Natural Gas Generator?

by jefftkjefftk3 min read9th Oct 202114 comments

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Practical
Personal Blog

In the comments on my posts about backup power, several people suggested looking into natural gas generators. After learning more about them, though, and about our local infrastructure, I don't think they make sense for us.

Unlike propane, which will stay liquid at room temperature with reasonable pressure (~150psi), liquifying natural gas for efficient storage requires extremely low temperatures. This means you want to pipe it in, and our house has a pipe to feed our furnace. This is pretty common here in Boston, the main alternative being oil, delivered by truck.

Gas delivery is extremely reliable: I've never experienced an outage. It has to be this reliable, because appliances have been designed with the assumption that gas won't ever go out. Older furnaces and stoves have pilot lights, which constantly release a small amount of gas and burn it. If the gas went out the pilot would too, and then when the gas came back on the house would slowly fill with gas. This means that if there were to be an outage the utility wouldn't be able to turn the gas back on without technicians going door to door to every affected house.

(This dynamic, where natural gas utilities are trying very hard to always provide sufficient flow, was a contributor to the Lawrence explosions. In switching from an old distribution paper to a new one they missed a sensor. As they turned down the old pipe the sensor started to read low pressure. This triggered the system to increase pressure in the new, unmeasured, pipe, trying to avoid an outage. As it continued to read low pressure the system opened the valve further and further, allowing high-pressure gas to flood the system.)

Because natural gas is so much more reliable than electricity, it is a common choice for permanently installed standby generators. These are typically sized to power an entire home, and do make sense in places with frequent power outages. If you wanted a cheaper option, it is straightforward to convert a portable generator to run on natural gas—many companies sell conversion kits—and you could install an external hookup, the same as you would for a natural gas barbecue.

In thinking about whether a natural gas generator would be useful for us, the main question is what might cause an extended outage. I think there are roughly four causes:

  • Delivery: massive storm, poles are down, huge amount of work required for technicians to get everything working again.

  • Consumption: there is far more demand for power than was expected, and generation cannot keep up.

  • Generation: we aren't able to produce enough power to keep up with demand, likely because some important input is missing.

  • System: something like the 2003 Northeast blackout. Perhaps multiple failures combine in an unexpected way, equipment that is difficult to replace is damaged or untrustworthy, and even though most of the system is still in place and potentially functional it can't be used.

Thinking through these, it seems like the space of "prolonged blackout" that does not include "natural gas outage" isn't that big? We are in a dense area, the kind of place that utilities prioritize for service restoration, so I think local delivery failure is not a major issue for us.

Power in here in MA is 72% natural gas. Something that disrupted gas delivery would likely cause power outages through both (a) generation issues and (b) consumption increases as people switched to resistive heat. A disruption could look like the recent gasoline supply cyberattack, a pipeline accident, or a storm. The latter could also cause issues via consumption; this is what we saw in Texas (while wind turbine failure was heavily blamed at the time, natural gas production issues were a much bigger component).

It seems to me like residential solar, configured in a way that lets you get power when the grid is down, is a better option for us and other people in places where (a) power outages tend to be short and (b) natural gas is a large portion of local utility generation.

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Have you done any research into what the availability of natural gas has been like in your region during past extended power outages for residential users?

Not only can you easily convert gas generators to run on natural gas, you can convert gas generators to be tri-fuel wherein they will run on natural gas, propane, or petrol. To be honest, I'm not sure I remember seeing generators that were natural gas only. I'm sure they exist, but it makes me think they're not widely used...at least for residential.

However, I'm with you in thinking off-grid solar is a good option for you. It's not a great option for me since:

1. I don't plan to stay where I am long enough to recoup the large cost and 

2. like most areas the resale value doesn't even come close to recouping that cost and

3. roof orientation and tree coverage makes it very not-ideal anyway.

Residential solar like that is extremely expensive. Even if you DIY the installation. My source for the costs is a few YouTube channels and the site "signature solar" which seems to be the cheapest source of the parts you will need. A 4kw array even at recent dirt cheap prices of 40 cents a watt is $1600. A single 48v 5kwh battery is $1500, and this is a huge decrease in previous costs. The inverter and charge controller and transfer switch is $1200 minimum. Not to mention rewiring your electrical panel as you need several subpanels to make this work.

You can get dual or tri fuel generators that run on gas and propane for under $1000. You just need a generator receptacle and Interlock kit to connect it to your electrical panel, this is about $150 in parts. An electrician will probably charge $300 or more to install, of course.

You would keep a few bottles of propane in an outdoor but roofed area for your backup fuel source. And have an outdoor natural gas spigot if you want the option.

The reason to do solar is if you live somewhere where it will pay for itself, like San Diego.

Residential solar, especially with incentives, will pay for itself in a large range of places.

Our system here in MA would definitely not have been worth installing just for being prepared for power outages, that's only a side benefit.

A system that uses batteries adds a lot more cost though. One power wall adds 10k plus to the tab and doesn't pay for itself in most areas. To do backup power like you want you basically need batteries, and you need the electrical wiring changes to make this work, which adds several thousand more in electrician costs.

So for the marginal cost increase for "backup" you can get cheaper backup via a generator. This is essentially objective fact in almost all areas, I can link many sources if you want to drill into the details.

That's a much more comprehensive backup than I'm looking at. I'm not worried about a short power outage, and I don't need to have something that will get me through an extended outage at anything close to normal levels of consumption. Instead, if power is out for a long time, I want to have a bit for electronics, refrigeration, fans, sump pump, boiler, etc, depending on the situation. Much of that I can directly run off of the solar, but I have a battery backup system I spent a few hundred dollars on to fill in the gaps. I'm not interested in to wiring it in: in an emergency, I'm okay running an extension cable to whatever it is I've decided to spend the power on.

To use a generator in an extended outage, you either need to store very large amounts of fuel on site, or you need to be able to get more fuel. This post is specifically about whether powering a generator from your utility's natural gas line is worth it.

Ok.  So specifically it's one of those probability things, the natural gas supply is more likely to work than the electric supply, so most widespread long term natural gas outages are going to leave you with service.  But similarly most such outages will leave you with some gasoline somewhere, even if you have to drive 100 miles to get it.  And depending on the climate zone you might still have solar panels.  

Anyways I would like to know what you have in terms of "a bit for electronics, refrigeration, fans, sump pump, boiler, etc, depending on the situation. Much of that I can directly run off of the solar, but I have a battery backup system I spent a few hundred dollars on to fill in the gaps."

Some inverters let you do this.  Do you have an SMA with EPS? What did you spend a few hundred dollars on?

I would like to know what you have in terms of "a bit for..."

https://www.jefftk.com/p/backup-power

Do you have an SMA with EPS?

Yes

What did you spend a few hundred dollars on?

https://www.jefftk.com/news/battery

Awesome, thank you.  Ah I see, at 220 watts just for your furnace your own plot says you should have bought a generator, because a power outage longer than 4 hours is quite possible.  And a shorter power outage you won't miss the lack of heat anyways.

And a proper convenient setup is that you install a generator receptacle, like this one, somewhere outside near the main electrical panel.  This goes to a breaker on your main electrical panel, which is made mutually exclusive with an interlock kit like this one.  

As for generators, which I did the research I found this generator to be a good option.  Cheap, tri fuel, and enough power output to easily run an entire house.  

Another option in your specific case would be to rearrange your electrical panel so that all the important 120v loads are on one side, and then use a 120v generator like a small inverter generator like this one.  This would be more fuel efficient.  
 

Per your original question, if your natural gas plumbing is convenient to the location where the generator receptacle would go, then you might want to pay someone to install a spiggot there where you can fuel the generator on natural gas.  

at 220 watts just for your furnace your own plot says you should have bought a generator, because a power outage longer than 4 hours is quite possible

I think you're overlooking the solar? Which can both run the furnace directly and recharge the battery.

I don't need to have the same level of heat in an emergency as not; only being able to run the furnace for part of the time is still very useful.

This goes to a breaker on your main electrical panel, which is made mutually exclusive with an interlock kit like this one.

I'm not interested in using my normal household wiring in an emergency like this, because I think I'm going to want almost everything to be off. With regular wiring it's too easy to use more power than you intend. Instead, I think I would be just plugging in my furnace, sump pump, basement freezer, etc as needed.

A lot of gas power plants have at least a few hours of onsite storage. Probably more storage than you have battery time.

I believe that the vast majority of power failures, even long ones, are transmission and distribution issues. Not all of them, but it's absolutely the dominant failure mode I've heard about. That makes sense; plants are pretty hardened, and there are a bunch of them. The distribution infrastructure is spread out, exposed, and not nearly as redundant as you'd like to see. Look at https://en.wikipedia.org/wiki/List_of_major_power_outages .

... but how much do you even care about backup power for an outage so short that you could feasibly ride it out on batteries? Power failures are great; all the fans and pumps shut down and things get quiet. Unless of course somebody decides to fire up a damned generator...

Older furnaces and stoves have pilot lights, which constantly release a small amount of gas and burn it. If the gas went out the pilot would too, and then when the gas came back on the house would slowly fill with gas.

Appliances with pilot lights have thermopile safety valves to prevent that. If the pilot flame goes out, the thermopile gets cold and the valve closes until somebody manually overrides it (which requires a press-and-hold action). The safety valve normally turns off the main burner as well as the pilot light. I learned to light a pilot in the late 1960s or maybe early 1970s, and I have never in my life seen a pilot light appliance without the safety valve. Here's a patent from 1961 that says it offers an improvement on the "commonly used" thermopile.

I don't know when the thermopile valves became absolutely universal, but I don't think I'd want to use a gas appliance so old that it did not have one. The pilot light would be the least of my worries. Burners rust out, especially old ones. And orifices clog and control valves go bad.

Even if the safety valve sticks open, which is probably its rarest failure mode, a pilot light isn't going to fill a building with a dangerous level of gas. But it might manage to fill your water heater closet with a dangerous level of gas.

Now, the main burner can definitely put out a dangerous amount of gas if it decides to come on with nothing to light it. But that also applies with an electric igniter if nothing checks to make sure the burner actually lights. I had an electrically ignited gas stove that would happily spew gas all day if the igniters failed, which they did. Apparently it was really fun when houses were full of match-lit gas lighting that might be left running unattended all night...

I'm not saying there's no risk from pilot lights, but you make it sound a lot worse than it is.

I suspect the bigger problems are that (a) if, say, a manual stove burner valve were left open, it could spew a lot more gas than a pilot light, and (b) a lot of people simply wouldn't know how to get their pilots going again... although I wonder how many pilot lights are still even out there.

Even now, gas is pretty scary stuff to be piping into your house. At least electricity mostly stays in the wires...

how much do you even care about backup power for an outage so short that you could feasibly ride it out on batteries?

That isn't what I'm worried about, yes. The post is about prolonged blackouts.

Appliances with pilot lights have thermopile safety valves to prevent that.

Maybe some of them? I've worked with a stove with a pilot light for each burner, where if one of them went out you would start to smell gas, and you could relight it with a match even if it had been hours.

If you look on gas company websites, they all say that they will need to send technicians door to door before they're willing to turn the gas back on, and that is what happened here for people who turned their own gas off out of caution around the Lawrence explosions.

Ex: https://www.centerpointenergy.com/en-us/safety/pages/understanding-the-gas-outage-restoration-process-.aspx https://myenergycoop.com/restoring-natural-gas-outages/

My impression is that gas companies use a procedure like this out of an abundance of caution / because there are still very old gas appliances that could be around which could have this issue. But I don't think it would be legal to sell them now, or has been for a long time.

EDIT: Apparently I am wrong about this, heaters require them but stoves (in the United States) do not. :-( This according to some undated forum posts, plus Wikipedia: https://en.wikipedia.org/wiki/Flame_supervision_device - "SD usage in consumer products differs among political units – in the U.S., FSDs are not required by law or regulation for gas range (or gas stove) top burners and consequently are not present on ranges in the U.S. [citation needed]".

But I get the impression that modern gas stoves are always pilotless, in which case only the cooking flame would be an issue, which would hopefully always be supervised.

That isn't what I'm worried about, yes. The post is about prolonged blackouts.

Sorry, I thought you'd said that the solar batteries were your solution.

We have a little dual-fuel generator that can run for quite a while on a barbecue tank (there's usually a full spare around here), and for longer than that on gasoline that could usually be siphoned from the car. It's not hardwired, and it won't heat the house, but it and a couple of long extension cords can keep the freezer from thawing out or the pet snakes from dying of the cold.

I've worked with a stove with a pilot light for each burner, where if one of them went out you would start to smell gas, and you could relight it with a match even if it had been hours.

Hmm. I guess it might not be universal for stoves, since they're small burners that are always supposed to be used under direct supervision? It's true that an N-burner stove would have to have N thermopiles, too. I'm not sure I've ever used a stove with pilot lights, which may explain my not having seen anything without the thermopile. The pilot-light appliances I've used have been house heaters and water heaters; things with big burners that start by themselves.

I absolutely do believe that they send people around, regardless. I mean, even if you have safety devices, things can happen. And I do think that even a stove could probably be dangerous, if say you were heating water for pasta when the gas went out and forgot to shut off the burner...

I thought you'd said that the solar batteries were your solution

Yup: solar, which works for a prolonged blackout (unless the panels are covered by snow or it's fully cloudy).

And then a small amount of batteries (~1kwh) for times when we need some power and there's no sun.