Pros
It's a small team, so you get higher responsibilities and also you get to make bigger decisions for the company. I think no other solar company does energy audits and performs energy analysis for its customers before proposing a PV system to them and helps achieve them targeted energy savings.
So you get to work on renewable energy as well as energy efficiency. It's a startup, so your ideas are respected.
Cons
Smaller team means more responsibility and longer working hours. The pay could have been better but its a startup so cannot complain.