Making an aluminum can window heater is cheap and very effective.
(You make a stack of aluminum cans. You poke holes in the bottom and tops of each can so that the warm air can rise through the stack of cans. You paint the hole thing black. You put it in a sunny window, and it will heat the room. No power.)
That is passive solar.
Now, for the more complex things,... it all depends on where your house is. Too far north and you do not get enough sun, and you get too much cold to have a bunch of windows.
Too far south and any south facing room with lots of windows will be a sauna (at minimum) during the summer.
In the middle, a south facing greenhouse structure can add heat to the house during cold months. South facing windows are also really good. Having those south facing windows shine light onto a heat sink (like a big rock, or a barrel full of water) is really good.
But then you have to balance all of this with shading all of these windows in the summer time. (deciduous trees and awnings that are the right length)
Overall it is a complex problem where you got to figure out the right balance. But when it is in balance, you get a comfortable house with a lower heating bill.
However, it is often hard or impossible to retrofit to an existing house. So, looking at huge mass wood burning stoves or rocket stoves is often easier.
Of course, all of this is after you insulated and sealed your house well.
I've seen houses with big rocks in them before, I hadn't connected that they might have been acting as slow release heat sinks. I also hadn't thought about the role of deciduous trees giving shade in summer and letting light through in winter.
Interesting.
In the British Isles there's just so many old houses with terrible insulation, it's quite a chronic problem. And with the cost of heating skyrocketing I think it's becoming ever more important to get these considerations right. I think I'm going to try my hand at an aluminium passive heater the next time I'm home! Cheers