Can I have one solar system feeding two or more houses?

Q. I have a dual occupancy home. One roof, 2 electricity meters. Can I have one solar system that supplies solar energy to both homes? 

A. Yes you can. Kind of.

Sharing all the solar panels' output

If you want to share the output of all the panels between the 2 residences (which is the most efficient way to ensure you maximise solar self consumption) then your only option is to consolidate the 2 meters in to one. An advantage of this is that you should save on standing charges (only having one official grid connection). A disadvantage is that you only get one electricity bill. Also your retailer may refuse your request to consolidate.

If one person is paying both existing bills then a single meter is not a problem. If the bills are paid by different people then your options are:

Consolidate to one official meter, add your own sub metering to each residence and then use this to divvy up the 'official' bill. For example if the meters showed one residence used 500kWh of grid electricity and the other 1000kWh, then the former would pay a third of the consumption charges and the latter two thirds.  You would have to agree how to divvy up the fixed charges and feed in tariff. I'd suggest 50/50 on those. You could also argue that this is 'unfair' if one residence uses more solar than the other.  I must also mention that this may technically be illegal without an electricity retailers licence! Although if the other party is family and the relationship is not commercial - you should be OK in my unprofessional, non-legal opinion. 

If consolidating to one meter is not possible or practical then you must share the solar array by allocating a fixed number of panels on the roof to each residence and then either having 2 separate inverters, one for each meter, or micro inverters, and sharing the micro inverters between residences. You essentially have 2 separate systems sharing one roof. The benefit of this approach is that each residence is then billed separately by the electricity retailer and the each solar system's ownership is defined.