Los edificios no serían muy altos, estarían bien orientados y habría paneles solares en todas las terrazas.
In this sentence, which one is the subject? I thought that los edificios is the subject, doesn´t it?
However, what about habría paneles solares in this phrase? Doesn't habría have to be habrían because the subject is los edificios?
Haber is used when you want to express existence. The English translation is “there is/are”. It is impersonal; it has no subject. That’s why you won’t say “los edificios habrían” - los edificios are a subject! Tener, on the other hand, shows possession or content. It does need a subject, because the subject is the one who possesses or has content. So if you want to say that los edificios possess paneles solares, you should use tener.
https://espanol.lingolia.com/es/gramatica/verbos/haber-tener Everything is explained here + los ejercicios
What are the differences between "tener" and "haber"? A question similar to yours, you can check it out.
https://exerciciosdeespanhol.com/haber-tener/ More ejercicios
It is an impersonal verb equivalent to the English there is/are. An English translation might be
The buildings would not be very tall, they would be well oriented and there would be solar panels on all the terraces.
You might be more familiar with the present form hay than the conditional.
To add to mdewey's answer, the sentence might be objectionable from a stylistic point of view, because there are three coordinate clauses, two with the same subject (los edificios) and an impersonal one.
This might be better:
