For most people it is a financial decision solely to save money, a car is not, its usually a means of transport. So ROI on investment for solar panels and batteries is a very important factor for most, I for one find it very interesting.
I half-convinced a solar skeptic (last year) that prices would rise, and payback would be quicker that anticipated, this was after he saw the setup I had sorted for myself, and though that spending the best part of £10k was madness. He was just ordering a new car at the time, which is standard thing he does every 2-3 years so I was talking to him about the deprecation side of things, as well as the totally fleecing you get for 'extras'.
I suggested if you are only keeping a car for 2-3 years why not buy the next model/spec down or lose some of the toys, and save £5k+ and take that off the solar install cost. Obviously some of the value of the used vehicle would have been in the total spec/extras so a reduced trade-in or sale price but no where near the amount spent. In the end he ignored the suggestion, 'cause gotta have that 360 camera and heated rear seats that are never sat in. however that isn't where it ends.
Due to parts shortages, his new car was delayed and unless he reduced the spec he'd end up waiting possibly up to six months longer. So he decided to get a model that was a cancelled order almost to his spec that would be arriving much sooner, saving him about £3.8k. Obviously after he tells me this I laugh, and he wants to look into solar again, told him good luck getting on the wait list, all the prices have gone up and the ROI will be even longer and now you are paying even more for your bills.
However it got me thinking, I wonder how many people could make a short term sacrifice for a longer term gain? The sort of folk I am on about are the guy above, spends £50k on a car for 2-3 years use losing a huge chunk in the process, but won't spend 10k on something that might last 25 years+ - to me the short sightedness is ridiculous, or maybe it is just lack of knowledge and education in how things work. Perhaps they were put off by the old solar schemes rent-a-roof etc. and they think the prices are high till for what you can get.