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.
It depends on your overall energy use but generally that would be negligible when compared to heating and hot water, especially during winter when the furnace runs 24/7.
In particular, during the winter, all excess energy from the oven is heat the furnace doesn’t have to provide so it’s basically free: you’d use that energy anyway.
Generally the economy of scale should technically favor the prebaked bread, at least before the store slaps its value added surcharge for it. The store still needs to pay for the energy (but probably gets it cheaper than you), but also needs to pay to maintain a factory, equipment, employees. So you kinda need to factor in the price of your oven too and its wear and tear.
I just buy the loaf because one thing I know for sure is if I factor in the value of my time, it’s way better and easier to work an hour than spend an hour baking a loaf of bread. The time to bake the bread costs more than if I used that time to work the equivalent time and buy 5 loaves of bread with the money.