So, point being: be very careful when you weigh the pros/cons of getting a job while in college...now, if the job not only pays you, but also gives you REI-related experience, that obviously changes the calculus quite a bit--but, you'll still want to be very mindful of the cost/benefit ratio of how you spend your time, because what you do right now and through your 20s can have a big impact on your life years down the road...Now, how to start in REI: there is no "right" way to start.

Currently, I have been living in the Lisbon area (Cascais) for about 2.5 years.After some investigation into the Portuguese Real Estate market we (my wife and I) decided that with Portugal’s rapidly growing tourist influx that the risk/reward calculus pointed to STR.

Obviously, in markets where tenants will pay a premium for renewable energy the calculus is different and can be included in higher rents. 

I see that this requires a different calculus to get right.

The first step is to acknowledge this and give this fact weight in your calculus going forward. 

But while we're on the topic (which usually isn't even part of the calculus of whether or not solar "makes sense", but I'm humoring you here), your story about your brother losing power... he could have bought a different inverter if he wanted backup power.

Don't forget about Property Management fees too in your calculus: For a STR you are looking at probably around 25%, while LTR is more in the 10% range for PM.  

Part of your calculus for whether to buy, hold and when to sell should be if the property is subject to rent controls and how that will effect future cash flow while you hold the property.If you have any questions about that and where to get that information feel free to let me know.

Are the loan proceeds for personal or business use as that changes the calculus on the cash out? 

If you are investing $25K, the calculus changes.You can do your own review if you know what to look for.