I recently had my job trimmed back due to the state of the economy, so our family naturally went through a cost-cutting initiative. Where can we save money, and how much? When we looked at how much we could save by turning lights off I was shocked.
And that led me to compare various forms of energy use; comparing apples to apples.
Get ready for some math. The first part of the problem is that different energy sources are measured in different units. It would be like driving to Edmonton, but if you drive in a truck the distance is measured in miles, and if you ride a motorcycle it is measured in km. Really it’s the same thing, just different unit.
[I’m using our bills, as provided in Calgary, for this exercise; if you live elsewhere you may have a different system.]
The same applies to energy. Electricity is measured in kW-h. According to a recent electricity bill we tend to average about 450 kW-h per month across the year. The cost for electricity – on the bill I looked at – is 4.3 cents per KW-h.
Natural gas is a different story. We tend to average about 12 GJ per month, though the fluctuation is obviously highly dependent on the season. The cost of natural gas on our latest bill is about 90 cents per GJ.
But GJ and kW-h are just two ways of measuring exactly the same thing. So then the question becomes; what’s the relationship between Kw-h and GJ? It’s the same as asking the relationship between miles and kilometers because, as I said, they are actually measuring the same thing. Well, according to onlineconversion.com to convert GJ to kW-h you multiply by 278. Or, to convert kW-h to GJ you divide by 278.
Personally I’m not a fan of mixed units, so I’m going to favour GJ over kW-h. So to convert my electricity usage to GJ we divide the 450 kW-h per month average by 278 to get a whopping 1.62 GJ of electricity per month.
1.62 GJ of electricity compared to about 12 GJ of natural gas. Clearly we are burning through a whole lot more gas than we are electrons; roughly 7 X as much, as an energy basis.
Cost is another interesting comparison. Electricity costs 4.3 cents per KW-h, so to convert it to GJ you have to multiply the cost by 278 to get 1,195.4 cents per GJ as the comparable cost of electricity. Interestingly, electricity costs about 13 times as much as natural gas. Good thing we only use about 1/7 the amount of electricity energy as we do natural gas energy.
What about fuel? According to the National Energy Board of Canada 1 m3 of “motor gasoline” contains about 35 GJ of energy. Most of us don’t think of fuel in m3 quantities, but in litres. 1 m3 is 1,000 litres, so there is about 0.035 GJ of energy per litre of gasoline.
We don’t keep a close record of our gasoline expenses, but I think a typical year (with a long road trip vacation) runs us about 24,000 km, or about 2,000 km per month. If we assume an average fuel economy of about 13 L / 100 km (our Honda Pilot is a bit thirstier than previous vehicles) then that means we burn in the range of 260 litres per month. On average, including a road trip.
If the energy density of gasoline is 0.035 GJ per litre then that means we go through about 9.1 GJ of energy each month by driving (0.035 * 260). Furthermore, the price of gasoline is hovering under $1/litre, but let’s just use $1 because the math is easier. That means that gasoline costs about $1 / 0.035 GJ, or 2,857 cents / GJ.
So, to put this all in perspective, our monthly energy consumption is as follows:
Electricity – 1.62 GJ
Natural gas – 12 GJ
Gasoline – 9.1 GJ
And the price for these forms of energy are:
Electricity – 1,195 cents /GJ
Natural gas – 90 cents / GJ
Gasoline – 2,857 cents / GJ
So we use more natural gas than either gasoline or electricity (we use just a pittance of electricity), and the price of natural gas is relatively negligible. Gasoline, on the other hand, is far and away the most expensive form of energy, but we use a little less of it than we use of natural gas.
Natural gas powered vehicles are sounding like a really good idea right now!
So let’s think through some practical applications. If you want to reduce your total energy consumption let’s be honest about one thing; fancy light bulbs aren’t going to do much. A “normal” bulb burns energy at a rate 60 W, but a high-efficiency bulb that produces the same amount of light might only burn 6 W instead. That’s a different of 54 W.
Suppose that bulb is on for a total of 8 hours each day, 7 days per week, all month long. That’s a total of about 250 hours per month. The energy savings associated with replacing the old bulb with a high efficiency bulb is therefore 54 W * 250 hours = 13,500 W-H, or 13.5 kW-h. That equals 0.0485 GJ of energy savings each month.
For fun (because engineers find math fun) how far could I drive my car with that amount of gasoline-based energy? There’s about 0.035 GJ of energy per litre of gasoline, so 0.0485 GJ gives me about 1.386 litres in the tank. At 13 L/100 km average fuel efficiency, that will get me about 10.6 km.
If I’m driving at an average of 50 km/h then I would burn through that energy is about 12 minutes. In short, the energy saved from using a high efficiency light bulb instead of a normal efficiency light bulb for 250 hours per month is about the same amount of energy I would burn driving my automobile for 12 minutes.
That’s perspective for you; courtesy of mathematics and your local nerd engineer who spends his Friday nights doing this kind of stuff instead of, you know, hanging out with people … or … stuff. I would have gone out to a movie, but the theatre is 10.6 km away (round trip).
Don’t get me wrong, I support high efficiency bulbs; in fact we have a bunch of them around the house. I’m just not under any delusion that our energy consumption is actually changing in any kind of drastic overnight manner. It’s a long term decision, based on principle, rather than something from which I expect an immediate return.
If you want to reduce your energy consumption then natural gas and gasoline are the ways to go, not electricity. In our house we have a gas stove, a ridiculously inefficient furnace that just… won’t… die…, and very old windows and doors. On the plus side, our water heater is relatively new; it should be somewhat more energy efficient. The reality is that we could make some major reductions to our natural gas energy consumption just by making our home more energy efficient which, believe me, is high on our list of planned upgrades.
Did I mention my work was cut back? Yeah, we can’t exactly afford that right now.
But if you want to save on money, as opposed to energy, then gasoline is definitely the way to go. That was the second highest energy source, and the highest cost / GJ. Cutting your consumption of electricity and natural gas won’t impact your pocket book nearly as much as cutting your driving. You could buy a more fuel efficient vehicle – my personal choice is a 1980 Suzuki GS 1100 – or just don’t drive as often. Like, to the movie theatre.
Yeah, that’s it; I didn’t go to the theatre as a matter of principle. It wasn’t because nobody ever invites me out. No, clearly that isn’t the reason…
Because of how far North Canada is, there are certain pragmatic limits to our energy reduction efforts. I don’t care how energy efficient your home is, when it’s the middle of January you are going to burn a lot more natural gas than the summer. Or you will freeze to death; your call.
And when the total amount of daylight we get in the dead of winter can only be measured with a stopwatch, we kind of need electricity to provide what nature cannot, in terms of lighting. Gasoline really is the only energy source that is – somewhat – optional. And even then, as some car-free folks are finding out, automobiles are not entirely optional.
If there are any other math nerds reading this, I’d love to have somebody double check my numbers. I went over them a few times, but it’s always possible I messed something up.