Hey Reddit! First time poster here, and I wanted some ideas from all of you.

I've got a master's degree in mechanical engineering (hybrid car design) but I work professionally in software. Recently though, I've been jonesing to do a solid engineering (ie, not software) project--mostly because the last one I did was my master's thesis, and even though I love software I'll go crazy if it's all I do with my days.

So I've decided to dedicate myself (after-hours) to an interesting project. I'd love for you guys to give some (realistic) suggestions for something at least tangentially related to sustainable/mechanical engineering (or robotics, or engineering&art).

My two ideas so far are:

1) Energy-neutral modular home, or 2) Self-powered water sanitizer (for Giardia et al in clear drinking water)

But please, leave more suggestions! I will follow through on this project, and will try to complete it in one year (leaving you status updates along the way? and being very transparent about the project? setting up perhaps a schnazzy website for it?). If at all possible, I'd like to do something that might help the world in some way, but that's not a requirement--I'd like to do something challenging and fun (and awesome) and I'll leave it up to you guys to decide what it is!

Thanks all!

TL;DR: Need suggestions for an engineering project that I'll pursue over the next year with great gusto.