Sunday, September 25, 2022

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RVelectricity – Just Ask Mike (J.A.M.): How many kWh in a gallon of gasoline?

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM. Today I discuss how many kWh are in a gallon of gasoline and the energy equivalency of different sources.


 


Dear Mike,
I saw your article last week about the kWh of energy in a 20-lb. tank of propane. So how about gasoline? I have a 20-gallon tank of gasoline. Just how does that compare to the energy in an Electric Vehicle? —Robbie

Dear Robbie,
Great question, and once you understand how this works it’s useful for most any energy equivalency calculations.

First of all, you can google the amount of kWh (Kilowatt Hours) of energy in a gallon of gasoline. According to the EPA, one gallon of gasoline is equal to 33.7 kilowatt-hours of energy. Now we have the basic number for our calculations.

ICE (Internal Combustion Engine) calculations

To calculate the energy in a 20-gallon tank of gas all you have to do is multiply 33.7 x 20 = 674 kWh of energy.

Now, let’s assume that if an ICE vehicle gets 30 mpg, that 674 kWh of gasoline can provide 600 miles of range. So 600 miles / 674 kWh = 0.89 miles of range per kWh of gasoline energy.

If we assume $4.00 per gallon of gasoline, that will cost us around 13.3 cents per mile if your vehicle gets 30 mpg.


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EV (Electric Vehicle) calculations

My loaner Volkswagen ID.4 had a 275-mile range with 75 kWh of battery charge. So to calculate the kWh of energy needed per mile of driving we just divide 275 miles / 75 kWh = 3.66 miles of range per kWh of electricity.

If we assume $0.15 per kWh of electricity (that’s what I pay in Maryland), that works out to $11.25 per 75 kWh “tank” of electricity, and it will cost us 4.1 cents per mile for a 275 mile range.

Note that this calculation is based on a 10-hour overnight charge at your house which costs 15 cents per kWh. If you use a fast charger that only takes an hour, then you’ll be paying more like 40 cents per kWh for the convenience.

Why the big difference?

Well, an internal combustion engine isn’t very efficient at converting gasoline energy into miles of driving. There’s a lot of waste in excess heat (notice that big radiator), as well as all that kinetic energy that’s turned into heat every time you step on the brakes.

An electric motor in an EV is much more efficient at turning electric energy into kinetic energy. Plus electric vehicles have been designed to have much lower wind resistance than their ICE counterparts.

I’ve found that an EV can use less than 1/4th of the raw energy of an ICE-powered vehicle. So, if there was an affordable way to convert natural gas into electricity, then transport it where it’s needed without too much efficiency loss, an EV could use a LOT less energy than a gasoline vehicle.

But is this possible? Stand by for more energy science in a few weeks.

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….

Send your questions to me at my new RVelectricity forum here.

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

You don’t want to miss Mike’s webcasts on his YouTube channel.

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Larry Lee
27 days ago

So your numbers show that, if you use the convenient fast charger at Target (or wherever), your cost per mile is the same for a 30 mpg ICE car versus the EV.
So to save $ you must charge at home.
OR you rationalize using EV not for saving $, but because you get less pollution per mile by burning the fuel in a central facility under controlled conditions instead of in an ICE.
Nevertheless, thankfully, the new CARB rule allows hybrid vehicles past 2035 despite their having an ICE.

Mike Sokol
26 days ago
Reply to  Larry Lee

I’ve run the numbers on a plug-in hybrid that has a 33 mile EV range plus another 300 miles on gasoline alone, and they seem to be really practical for local driving with an occasional trip out of town. They have around a 10kWh battery that could be recharged with a reasonable number of solar panels on the roof of your garage. With this sort of setup you might only need to fill up the gas tank a few times a year, depending on how many long trips you make.

Jim
27 days ago

Great Discussion – clearly shows some of the advantages of EV vehicles.
One advantage one has with an ICE vehicle – we can fully ‘charge’ it in a few minutes and head out to a trip of whatever distance our fuel capacity allows.
Many with diesel vehicles add an auxiliary fuel tank to their vehicle greatly expanding the travel distance between ‘recharges’.
Maybe if EV’s standardized their battery pack a ‘filling station’ would be able to quickly swap battery pack for fully charged one and quickly get one back on with their trip.
Unfortunately – a giant maybe.
Certainly interesting discussions.

Jim
22 days ago
Reply to  Jim

China has done exactly that. You buy the electric car without a battery and pay a monthly service fee. When you pull into the battery center a robot changes the battery pack from underneath your car. All in about 5 minutes. Unlimited changes with your service fee.

TIM MCRAE
27 days ago

Mike, you get a pass on the math!

BECAUSE you just explained CLEARLY why the only currently efficient way to do EV is Hybrid!

And the best Hybrid is (was) the Chevy Volt!

EV’s can save the planet but not until many problems are solved. In the meantime only Hybrids (and volt like vehicles & Lightnings) should get credits and tax funding.

Joseph Bulger
27 days ago

Mike, good way of presenting the comparison. One thing that I would like to add is that about 90% of all electricity in the U.S. is produced by large rotating mass conventional power plants that have a terrible efficiency or heat rate. Yes some people have solar panels on their roof that helps out but when factored in the cost to install them to charge an EV battery the cost per mile is out the roof.

Mike Sokol
26 days ago
Reply to  Joseph Bulger

Solar panels are getting cheaper all the time, so the ROI numbers are constantly changing. Much more to study on this…

David
27 days ago

Oh my; that means my RV is getting something like .44 cents a mile (downhill with the wind behind it)!

Warren G
27 days ago

I’m not following the math on the cost per mile calculation. Wouldn’t 75kWh x $.15 per kWh be $11.25? $11.25/275 miles range would then be a little over $.04 per mile. We have a Leaf SL Plus and over the 9,000 miles we’ve driven so far we’re getting 3.9 miles per kWh. Our base rate is a little over $.11kWh, so I’ve figured it’s costing about $.03/mile. We added home solar in January, and so far solar has provided about 85% of our year to date consumption, we actually our EV operating cost is even lower.

Mike Sokol
27 days ago
Reply to  Warren G

Oops, you are correct. The medicine I’m on for my bronchitis says not to operate heavy machinery, or apparently not do arithmetic either. Good catch!

Bob p
27 days ago

All your energy calculations are impressive, however in my situation I live in a Park model RV permanently set up in a RV resort with 50A electrical service. I can’t setup a charging station at my house without shutting off power to many of the conveniences we need. Therefore the nearest charging station is 6 miles from home requiring parking an EV at the charging station, taking a ICE cab home and back to pick up the EV (if it hasn’t been stolen while being left alone) and driving home. Plus we live in central FL and all our families(hers and mine) are 600 miles away in northern AL and south central TN requiring multiple recharges to visit. Instead we bought a Toyota Camry Hybrid that gets 47.8 mpg at 75 mph and 13 gal of gas will get us there and 13 gal will return us home, the best of both worlds. At $32,115 for the new car compared to $65,000 for a comparable sized EV I have a lot of 13 gal fill ups. This EV B.S. the current administration’s pushing only works in metropolitan areas

Crowman
27 days ago
Reply to  Bob p

You are right the minute you clear the city limits EV’s are a pain to recharge plus the waiting around time.

George McEwen
27 days ago
Reply to  Crowman

I am thinking an EV is good for a second car that takes you around town which is most driving for people. That would make needing a more reasonable price to purchase.

Warren G
27 days ago
Reply to  George McEwen

That’s what we do. Have a Tundra for pulling our TT and occasional need for a larger vehicle, but almost all of our normal usage is with our Nissan Leaf. Unless we’re traveling with the trailer, almost no trips we do exceed the 200+ mile range. Besides the Leaf, there are several EV’s much less than a Tesla model. EV’s from Chevy, Ford, Hyundai, Kia, Mini, with more coming in the next 1-2 years.

Michael Kidd
27 days ago
Reply to  Bob p

Check out EV4RV [dot] org. It details how to use a current monitoring device that will automatically adjust your EV charger current so you can run your a park model and charge an EV from the same 50 amp service without tripping the breaker. I’ve been doing this for several years now.

TIM MCRAE
27 days ago
Reply to  Michael Kidd

EXACTLY!! COMMON SENSE! 👍👍👍

Take note people!

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