Installing solar panels could generate more passive income, but it wouldn't come directly from tenants

Heat and water are the only bills and the land lord electric panel is 35 a month.

By the way, if you to spend a little extra, those interior doors can be replaced with 6 panel doors (like the front door, but hollow) for about $50 each from Home Depot or Lowes. 

About $600 per unitOther miscellaneous expenses: drywall, 2x4s, trim, framed mirrors, caulking, sandpaper, screws, finish nails, various tools, etc.Oh and fence panels & materials $1400 total for all units; we deducted a total of $750 from the first new tenants rent over a period of 3 months to install it.Well that's my story, I would love to hear from others who have similar goals and experiences.  

It's possible you mis-interpreted what your agent meant when they said you could renegotiate after inspection (usually that means for major issues like dangerous electrical panels, structural issues, partially collapsed cast iron sewer line, etc. that weren't obvious at the initial showings, not superficial things like "the AC is rusty" or "we should replace those ugly fans").

Guess we need to figure out what the property is in question.Tons of different type of modularBOCA, panel, singles, double triples, manufactured, everyone calls them something different and they all have different construction and design features.   

My concern would be you pricing yourself out of the market with the solar panels. 

I vote for all electric for the following reasons: -Electric appliances and gas appliances are comparable cost wise, If you're building new, you're already installing a new electric drop, meter, panel and wiring throughout the house so incremental circuits should add much cost vs extending your existing gas line and also getting a gas meter-Electric appliances are more energy efficient (although they can sometimes cost more to operate-Electric is more safe than gas in the case of an earthquake-Electric is the future-CA is planning on phasing out gas

How can there be - 'replace drywall', "replace wood floor panels', etc. etc. 

They might not allow anything but a tradition stick built home.There are some cool homes that are essentially a kit with SIP walls (pre-built, insulated panels) that can be put up in short period of time.