Gas generator backup power source

Navigating Chile
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As an offshoot of this post on alternative standby power sources, I realized that one option hadn’t been mentioned: propane gas.

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This site provides info on calculating gas consumption, and a decent-sized gas tank is probably needed if operation over days, rather than hours is envisaged.

Gas consumption can be calculated here.
Scaling down the US whopper-size continuous consumption of 4kW used in that example to something more reasonable for Chilito, say 500W continuous, I got the following results:

500W ≈ 1HP
BTU = (HP*10,000) = 10,000 BTU/hr

fuel value lpg btu - Buscar con Google
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According to the above table:

The calorific value of 1 Litre of LPG = 24,000 BTU/hr
So with 500W continuous consumption = 10,000/24000 = 0.42L/hr.

A 15kg balón contains approximately 29 Litres of gas, so could provide 500W continuous power for around 71 hours.

The only drawback I could discover to this setup is the actual price of the gas:

In 15Kg cylinder format it currently runs round CLP $655/Litre. So 72 hours continuous operation would cost CLP $19,000, the price of one balón.

Tank gas (a granel) is much more expensive, at around CLP $1286/Litre. I can only think the difference is due to amortizing the tank costs over its 10-year SEC-mandated lifetime.

Still, as a source of stored energy, with automatic switchover included, from a reliability aspect it makes a lot more sense than some of the gimcrack renewable solutions offered.

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Where you have economical natural gas in the pipelines as in a few cities here in XII region, gas power backup can make sense. For bottled gas, for most residences, not so much. As a result, it is practically unknown in this country, and you would be hard pressed to find a competent and experienced maestro to do a certifiable job and maintenance services, even if you could find the necessary components.

That said, EMARESA/Voltz and some other companies do provide the parts and installation for a gas-powered electrical power backup. You can get these configured for LP or GN, using the American Generac generators that are sold in Chile.

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Looking into this some more, as usual the Devil is in the details.

Fuel consumption Vs power generation isn’t linear. Power is needed to keep that generator spinning, even under low-load conditions. The makers of that Generac device only show fuel consumption at 50% and 100% loading.

With long-term under-running of gasoline or diesel motors, the cylinder walls can “glaze” leading to compression and other problems. Apparently this isn’t an issue with LPG however.

Interestingly enough, there isn’t that much of a price differential between diesel and LPG. Diesel and LPG have similar calorific values

And being Chile, it wouldn’t be unreasonable to suspect that propane could be “watered down” by adding CO2, leading to a lower calorific value.

So yet again a lot of questions need to be answered.

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Among those problems with diesels (ill suited to this type of service) is the business of wet-stacking, where the engine isn’t running hot enough, under enough load, to adequately burn the fuel needed to keep it spinning. It’s unpleasant to clean up and over a period of time it can make for expensive maintenance. For that and other reasons it’s hard to recommend a large and expensive diesel genset for a simple residence if the purpose is to provide full power for all the appliances for just occasional outages. Or any other attempt to run a hydrocarbon genset of any type. And that brings us back to using a moderate capacity battery bank to ride through most of those short-term apagones.

I lived in the back country of Aysén for a time, near the Hudson volcano. Our concept was a bit primitive. For power generation …heck, you really don’t need electricity most of the time. So we ran the genset briefly in the morning and briefly at night. Pretty soon you adjust and live more simply, according to natural light and the wood-stove.