$ / “Gallon” of Electricity

Earlier I did a broad look at the cost of various camping fuels and how much it took to boil a cup of water. This was based on store costs and actual time to boil for alcohol and an electric stove burner.

There is another way. Looking at the theoretical energy in a unit of fuel or kW-hr for electricity. While this ignores things like the preheat time it takes to get a gasoline stove running, versus the near instant of an alcohol burner, and the heat loss heating up the electric element on the electric stove; it is a more direct comparison of just how much you are paying for that energy, however you use it.

I’m going to be using traditional American units in much of this. Nothing prevents using Metric units, but they have chosen sizes that are not very intuitive to grasp, and generally screwed around names (by naming things for people instead of function) in a way that makes things less than obvious what a unit means at times. For those limited in ability to only doing metric, well, it’s not necessary to follow the details (or you can learn how to do the conversions). It really doesn’t matter as it’s the math relationship that matters, not the units in which it is done.

With that, the first table we need is is a way to convert some fuels and kW-hr of electricity to a standard of heating energy. For that I’m going to use a BTU table. British Thermal Unit. Heat to warm a fixed amount of water a fixed amount. (One pound, one degree F).

http://www.exothink.com/Pages/btu.html also
https://en.wikipedia.org/wiki/Gasoline_gallon_equivalent

Fuel          BTU
kW-hr         3413
Methanol     56800 / gallon
Ethanol      76100 / gallon
Propane      21699 / lb
Propane      91000 / gallon
Butane       21300 / lb
Butane      102600 / gallon
Gasoline    114000 / gallon
Kerosene    128000 / gallon
Diesel #2   129500 / gallon
Coal         12500 / lb

We easily and often see the price of a gallon of gasoline or Diesel oil, so it is convenient here to think in terms of “GGE” or Gallon of Gasoline Equivalent. It gives an instant intuitive grasp.

My baseline electric rate here is 19¢ / kW-hr. Over some small usage you jump to 32¢ /kW-hr. What is that in GGEs? Or how much would it be priced for the same BTUs in gasoline?

114000 / 3413 = 33.4 kW-hr / GGE. Which also matches the value in the Wiki page, so a nice cross check. Now let’s figure out what the GGE costs.

33.4 x $0.19 = $6.35 / gallon as a gasoline equivalent. Gee. So at my very cheapest rate, electricity is priced way higher than gasoline. Now that’s assuming the conversion to useful work is similar. For things like light or running a TV set, it clearly isn’t. But for many things, it is. Heat is a great example. Both an electric heat element and a flame are about 100% efficient in making heat.

I also find it satisfying that when I looked at the actual costs / burn; I got break even at about a $6 rate for a gallon of fuel. This implies I was pretty close and not making some terrible mistake like slipping a decimal point.

But I’m essentially 100% of the time using way over the “baseline” electricity amount. ANY displaced consumption will come out of that higher marginal use. What’s that in GGE terms?

33.4 x $0.32 = $10.69 / GGE. YIKE! I’m paying almost $11 / gallon for my electricity! At that price there’s a lot I can do to cut electricity use by substituting cheaper fuels.

Last time I looked, there was a $0.50 / kW-hr tariff filed with the PUC. They were expected to approve it. I’ve not seen it yet, nor seen a giant jump in my bill, so it is likely still being contemplated. I suspect even the PUC and California Dimocrats have had a lump in their throat over the nice “round” number of $Half A Buck.

33.4 x $0.50 = $16.70 / Gallon (of gasoline equivalent). It’s not hard to see that at this level, you can easily afford to run your own generator, even if 2/3 of the energy goes up in hot exhaust. A general rule of thumb that only works in American units, is that if you take the price of Diesel fuel in $/gallon and shift the decimal point one over, you get the cost of fuel in generating electricity with a Diesel Generator. At the moment, Diesel is running $3.75 / gallon, so it would be about $0.38 / kW-hr. Significantly below $0.50 / kW-hr. Just sayin…

But if your goal is just heat, you can skip all the heat losses in a Diesel Generator. To put an even finer point on it, you could burn that Diesel in a co-generation unit and use the 2/3 that’s “waste” heat for something productive, while making electricity at a profit. (My local school did this. Installed a Capstone Micro-turbine co-generator unit. They use it to heat the swimming pool used for P.E. They use the same gas they ever did, but now get “free” electricity.)

So, for me, using my Coleman Gasoline stove is a very clear “winner”. I’m using $3.25 / gallon fuel to replace $10.69 / GGE electricity. Even using White Gas (Walmart, $7 and change / gallon) is a big win until I’m below the baseline threshold.

In actual measured time to boil, the electric element on my stove took so long to reach red hot, that even alcohol fuel at $10 / gallon was a win. The fuel I’m using is an unknown mix of ethanol and methanol, but some estimates put it at about 1/5 methanol. That would be 11360 BTU. The ethanol contributing 68800. Total 72240 BTU / gallon. That makes it about 72240 / 114000 or 0.63 of a gallon of gasoline. $10 / 0.63 = $15.87 / GGE. If instead I bought racing methanol fuel, it runs about half that, so about $7.80 / GGE. Bulk commercial methanol is about 1/2 that again and clearly a big win.

Yet in actual boil time, alcohol was a net energy cost win. That implies a large percentage of the heat to boil one cup of water goes into the burner and the air on the electric stove. This can be observed in a very long time at full power to start glowing red. This implies very long cook time items would be more efficient by a lot than very short time items like a cup of water. Avoiding burner pre-heat time is a big deal. But this is an interesting benchmark for Real World cost savings. Moving a bunch of short coffee / tea kettle runs to a fuel stove can save $15 / GGE on electricity. MANY fuels meet that hurdle rate!

This also implies that more precise measurements of actual run times / energy costs for different lengths of cook could be a big benefit.

How about Propane? A one pound camp cylinder runs about $3.35 each A pound is 21,699 BTU (lets just call it 21.7 kBTU). 114,000 / 21700 = 5.25 lbs propane / GGE. $3.35 x 5.25 = $17.58 / GGE. Oddly, it too is very fast and efficient at heating a cup of water. So close to a win compared to slow electric elements in actual timed tests. But can we beat it even more?

Locally, propane sells for about $4 / gallon in 5 gallon tanks. I know, in places like Florida it is closer to $2.85 and in Texas down near $2.00, but I don’t live there yet. At 91,000 BTU / gallon that’s 114000 / 91000 = 1.25 price multiplier per gallon to make them comparable, or $5 / GGE for propane in the bigger bottles. Well under the $6.35 / GGE for baseline electricity even before you allow for the poor efficiency of the thick electric elements on short heating tasks.

So that means it’s VERY profitable to use a back yard propane stove to do your cooking. That’s the burners part of it. A lot of gas is used in a gas grill and there isn’t really an equivalent indoor unit in most homes (too much smoke so you need a big fume hood). So I don’t really have a way to compare their relative performances.

One last note: Natural gas, here, is dramatically cheaper than just about anything else. It is measured in Therms and each of those is about a GGE already. IF (and it’s a very big IF..) I’ve picked the right tariff and guessed right, it is running between $0.50 and $2 / GGE summmer vs winter. At that rate it beats everything else.

Clearly THE biggest winner is just putting in a natural gas stove. But close behind it would be a natural gas generator or co-generation unit.

Now those are not small things a guy can just do on the weekend. Setting up a propane stove and cooking on the patio is easy for all of us to do.

In Conclusion

An electric range is not very efficient on fast cook items due to the long warm-up lag. For those things, even alcohol fuel bought in cans is a net small win. Yet even a modest shopping for cheaper bulk fuel makes the alcohol stove a big win.

Many other fuels are also big wins. Gasoline is clearly one, yet even white gas in cans beats the non-lifeline rate.

Propane in the standard BBQ size cans is also a nice win, even for baseline rates.

The biggest win, though, is the natural gas service. Converting appliances is not cheap and not easy, though, so best left for a longer term remodel project.

For now, that back yard propane Man Stove is looking like a sweet deal. Add a trip to the drag strip to pick up a 5 gallon jug of racing fuel for making morning coffee with the camp stove spirit burner, a lot of the household cooking can rapidly be moved off of the (very expensive) electric bill.

This will just get ever more profitable as more wind and solar boondoggles are added to the grid.

Folks in other countries will need to “run the numbers” for themselves based on local prices to decide what is the most economical way to cook some meat, flip some eggs, and make coffee. For me, it’s clearly worth it to use my Coleman gasoline stove, and I’ve been doing that. It has a large warm up time too, so mostly just used for whole meals with a long total burn time. One off coffee and tea I’m still doing on the spirit burner. As summer drags on (and I get the patio cleaned up) I’ll be finding my propane gear and setting up to refill my own 1 lb propane canisters. At that point, making morning coffee on a one burner propane job on the counter will be my regular method.

As I do like the spirit burner for being silent, I’m also going to see where the nearest drag race fuel stop is located. Some 20+ years ago I bought a 5 gallon jug of it. Then it was a little store front about 10 miles from here. I’m hoping something like that is still around. Price was not that much higher than industrial bulk, and far less than in stores in cans. Since there is still drag racing here, I’m pretty sure the State has not driven that fuel into the land of unobtanium… Though I do think they converted from straight methanol to an ethanol base. Anyone with info on that speak up!

With so many fuels “profitable” (natural gas, propane, gasoline, alcohols) I would expect more folks to start shutting off the AEK and breaking out the camp stoves & backyard grills. This isn’t rocket science… even if flame and pressurized gas is involved ;-)

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