there is no incentive for landlords to install them

According to the QLD government, it is acceptable for landlords to raise the rent by, for example, $15 per week after installing a 5kW solar system.

The math for that works out to about $1000 per year in reduced electricity bills for the tenant and $750 per year in extra rental income for the landlord. $750 per year will make the landlord a profit (after upfront costs are paid back) of several thousand dollars by the time the warranty on the solar panel runs out. (*)

I assume it's similar in other states.

So, yes, there is an incentive. If I was a landlord I'd totally install panels. And if I was a renter, anywhere with panels would be at the top of my list. It's an absolute no-brainer and I could simply place the upfront cost on my mortgage.

It's a better deal for the landlord than the tenant, but it's still a good deal for the tenant. And the tenant doesn't have to pay anything upfront and they can feel better about leaving the aircon running all day in summer... with solar your daytime electricity is "cost" is basically the solar feed in tariff, which is just 6c per kWh.

(* Obviously those are rough figures, install costs depend on the house, and electricity savings depends on the angle of the roof, prevailing weather, time of day for electricity use, etc... but those numbers are based on reliable government funded research so it would be in the ballpark)