The panels will pay for themselves in about 10 years at the current cost of power.

@Chris Herrera hypothetically, if it's joint utilities, would I (the landlord) pay the entire water and gas bill and split the electric bill with the tenant?

@Hanna Park  the wifi is probably the easy part; who is paying for the water and electricity and how much will be harder to determine in most duplexes.

Plumbing, AC/Ducts, Electrical, Kitchen, Bathroom.

I once replaced a smooth top electric stove with a coil top.

Hi Josh, I'm more inland with hotter temps, but I pay about $100 in water, $20 in trash services, and $100-400 in electric a month. 

The first one is trying to negotiate 1 month free rent while the 2nd one wants to sign already with no demands.The second one came in for viewing and the only thing is was curious about was the Electrical Board(Calculating the amps to make sure it was not 60 Amps and that it is 100Amps).

You have to decide if your willing to pay for empty lots (what's the condition of electrical, water, sewer, cement pad etc at these empties) and the Value of the park owned homes.

I was trying out a battery powered one (smaller lot) and left it.

The listing says 4 gas meters, and that is very unusual for a 2 unit.  99% of the time there is 1 gas meter per legal unit (usually 1 electric per floor so that is not a good indicator)   Public records shows 3,647 sq feet, and that is almost always just for legal unit.