One example is bread. I was baking bread the other day, and obviously the cost of the ingredients I put in the loaf are less than the cost of buying a loaf at the supermarket, but that doesn’t include the cost of putting the oven on.
Or dry beans vs canned beans; does the cost of boiling the beans actually bring the cost up to be equivalent to canned beans?
I know that everyone’s energy costs are different so it’s not possible for someone to do the calculations for you, but I’ve never bothered to do them for my own case because bills I get from the energy company just tell me how much I owe them for the month, not “you put the oven on for 30 minutes on the 17th of June and that cost you X”. It sounds like a headache to try calculate how much I pay for energy per meal. But if someone else has done that calculation for themselves I’d be interested to read it and see how it works out. My intuition is that, in general, it’s cheaper to make things yourself (e.g. bread or beans like above), but I couldn’t say that for sure without calculating, which as I said seems like it would be a pain in the ass.
Doing the calculation isn’t hard. It’s harder to know how much energy (be it electricity, gas, or whatever) you actually use. It also varies wildly with meals, as some need multiple stove tops (is that the right term?), possibly for varying lengths of time and/or the oven.
Please note that you can not really deduce the energy consumption from a power rating, as those usually are max values and not what it’ll actually need.
I have good enough energy monitoring that I can measure the usage (sort of), and having rather high electricity cost at around 0.40 €/kWh I do pay some attention to it. Running the oven for like an hour will be roughly 1€. Boiling water for pasta or something is probably more like 20 ct (includes cooking the pasta). Just using a lid actually helps a lot here if you make use of a lower power setting after reaching a boil and putting in the pasta.
It’s gonna have to be a very elaborate meal to break 3€. So while it does matter and add up, compared to buying fully prepared food from a restaurant, it isn’t that dramatic even with very high energy prices like these.
Cooking appliances use a lot of power, but they don’t run for whole days at a time, so the energy used also isn’t that dramatic. There’s a relatively recent video by technology connections that goes into detail, and might be of interest (link).