Fact or Fiction? Liquid propane expands 270 times when released into the atmosphere (ANSWER)

Fact

It’s hard to imagine one gallon of liquid propane (LPG) expanding to 270 gallons of propane vapor when released from the LP tank (motorhomes) or cylinder (towables) of your RV, but it’s true.

“When propane vapor expands as the pressure is reduced, it expands in all directions, and quickly. Its expansion rate is approximately 270 to 1, which means 1 gallon of liquid propane in the tank will expand to 270 gallons of propane vapor when it boils (vaporizes).” Per this comprehensive article by the late Gary Bunzer, the RV Doctor.

Energy-dense propane is an ideal fuel for RV appliances

The fact that one gallon of LPG (liquified petroleum gas) can expand into 270 gallons of vapor makes it an ideal fuel for RV appliances. One of the best examples of the benefits of the energy density of propane is powering an RV absorption refrigerator as this exchange between RV Electricity’s Mike Sokol and JP, an RVtravel.com reader, illustrates.

“Dear Mike,
I’m curious just how much battery power is needed to equal a 20-lb. tank of propane? For example, my 3-way fridge can run for a few weeks on propane mode, but when I try to power it from my batteries and inverter, it won’t even last a day before the battery is dead. Can you explain why this happens? —JP”

“Dear JP,
Ah, yes, it’s the energy density thing. And while modern lithium batteries can store a lot of power, they pale by comparison with a tank of propane. Let’s compare by first calculating how many kWh (Kilowatt Hours) of energy is in a gallon of propane. You can easily look up that the available energy in 1 gallon of propane is equal to 27 kWh of electricity.” *Note: There are approximately 4.6 gallons of propane in a 20-lb. tank.

Mike goes on to do the math providing the answer to JP’s question:

“It would take 200 lead-acid batteries of 100 Ah capacity each to equal the energy in a single 20-lb. tank of propane. Similarly, for lithium batteries, we see that 120,000 Ah / 1,200 Ah = 100 lithium batteries of 100 amp-hrs each to equal one 20-lb. tank of propane energy.” Mike sums it up by stating, “It will be a long time before there’s a battery no bigger than a propane tank that can store 120,000 Wh (watt hours) of energy.”

All-electric RVs

At this point, you might be realizing the impracticality of those promoting all-electric RVs. Why would you want to haul around 100 or 200 batteries, or fewer batteries and a way to keep them charged, to power your refrigerator, water heater, and stovetop/oven, when a compact cylinder of propane can do the same job? As Mike points out in the mentioned article, once fuel cells are perfected and affordable, propane energy will likely be the solution to electrically power your air conditioner, too.

I will close with these words of wisdom from Gary Bunzer’s article mentioned above: “The bottom line is propane can be compressed to a liquid, can be stored easily, and is relatively safe, making it the perfect fuel for use in a motorhome.”

Hopefully, this month’s installment of Fact or Fiction has taught you something new about propane while emphasizing why it is the best choice of energy for RVs.

Click here to learn more about liquified petroleum gas, how it works and why propane vapor is the logical choice for gas stoves, cooktops, ovens, gas heaters, fireplaces, and gas hot water systems.

Dave will be speaking at the 2023 America’s Largest RV Show in Hershey, PA, September 13th – 17th. He would love to meet RVtravel.com readers that will be attending. Feel free to introduce yourself at one of his seminars.

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Previous Fact or Fiction column:

• Fact or Fiction? RV tires tend to lose pressure at high altitudes

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