Assume spherical occupant.

In America that’s been a pretty safe assumption for some time. The problem is that when you take that gift and draw a hard vacuum on it, they tend to burst.

You can't know ahead of time how an occupant will behave, but you can use existing heat load calculations to determine how many kWh will be used on average. Whatever math was done to size the HVAC system can also be used, in conjunction with the normal solar irradiance of the area, to size the solar install. Requirement could be as simple as enough PV to run half the A/C system plus another kW or so.

Would a house builder be allowed to size their solar panels assuming the home owner sets their AC to the 80°F some authorities recommend? Or should they size them for the 70°F I've seen some homes set to?

> depends on occupant behavior

That's easy, occupant must follow recommended behavior.

And be glad that Genetic Control is not issuing a four foot restriction on Humanoid height.

( https://www.google.com/search?q=Get+%27Em+Out+by+Friday )