The ROI on solar is more complicated than a one line answer on a forum post. 

Sounds overly complicated with little-to-no benefit.

Assuming that is close to correct, I think the owner will likely find this complicated and make it a hard sell.  

Complicating the matters are 3 tenants, non of them paying rent. 

It may play out well for you, but the details are tricky, and the adjustment procedure is complicated.

you are not alone nor dumb, i read an American study that 40% of home flippers lose or only break even on their projects. please talk to an attorney with bankruptcy and real estate experience before filing as could have long term complications.

Source: https://es.wikipedia.org/wiki/Demograf%C3%ADa_de_Espa%C3%B1Trust me when I say Spain is in a very complicated situation.

Things get more complicated if you have a legitimate reason to believe the person is lying to you.

The word “tenant” is an extraordinarily generous euphemism in this case.What complicates matters more is that in New York City, someone can claim “squatters rights” after being in a home for just 30 days.

Some of the deal structures on these are overly complicated and involve way too many people, more like a house of cards than an investment strategy.