By the time you get access to basic heat burners, it feels really natural to be using the heat to boil water, however, heat exchangers only become available as a part of much higher tech nuclear research.

Nuclear heat exchangers also deal with much higher temperatures (800 degrees C), whereas low-tier burners produce around 200C which I want to use to produce 180C steam.

why not just use regular boilers and liquid boilers if you want to turn your solid and liquid fuels into steam? the burner and fluid heaters are meant for powering early game refineries, chem plants and oil pumps.

if you're talking about solar power towers, they've been added very recently and balance wise it does seem a bit odd they are available with just basic green science. they're still a good option to power the earlier mentioned lower tech production buildings. (and as a new way to defend your walls)

I'd like to use heater->exchanger chain instead of a burner because heaters have higher fuel efficiency if you utilize their adjacency bonus well.

you're right, that would be more efficient. and that's probably also the reason why you're not allowed to until later :)

But when you do get the opportunity to use heat exchangers, you also no longer need to use heat from burners, as you get access to nuclear tech at the same time. I think it makes sense progression-wise to first play with exchangers using burners and then move on to nuclear reactors.

Having a power production that's not just solid/liquid fuel boiler > steam engines would be great. Making a boiler or similar that needs heat from the early heat exchangers would be refreshing and rewarding for using more steps.

Im already in quantum age, and still use the solar heated oil refinerys. In early game, would be cool, to be able to make some steam and electricity with this method. Using Solar tower->some low budget heat exchanger-->steam engine. Also solar as weapon i dont really use, just build 1 for experimenting, but way way too much resource needed.

I've discovered solar power tower and still using it since I researched it, much later in the game. This tech is accessible very early, as others have said.
1 solar power tower with 6x 500 deg. C heat exchangers = about 50 MW of free electricity from Steam Turbines. It doesn't use any minable resources once built.

This is my model: https://factorioblueprints.tech/blueprint/eb3fd585-43ec-467f-a212-fbf09f5b7da1
Just add tank to store steam overnight and steam turbines to generate electricity.