Passive solar provides heating, cooling and even lighting with no operating costs.

Passive solar energy can reduce operating costs significantly and should be given high priority with your budget determinations.  For instance, windows can reduce the need for lighting during the daytime hours.  A well-insulated house with will absorb lots of energy if the house has south facing windows.  Low-energy fans will transfer heat away from home spaces that are too warm.  The fans can transfer large amounts of heat energy than they use in electric energy to accomplish that task.

Today you must use care in the amount of money you spend for passive solar gains.

You will want to reduce your total energy operating costs to zero if you can.  One way to do that is to employ as much passive solar energy advantage as possible.  Alternatively, one can also develop a huge active PV solar system to produce enough electrical energy to run heating and cooling systems as well as all other electrical needs necessary for a given lifestyle.

The passive solar option made the most sense until recently.  Solar panel prices have been dropping significantly, so the decision is shifting more in favor of larger active solar systems.  Now you must weigh the cost of conserving against producing equal amounts of energy. I purchased my last solar panels instead of trying to conserve more energy.  An active solar system was definitely less expensive than adding more insulation or other conservation measures.

We will always reach the point of diminishing returns with insulation and additional conservation measures but not so much with active solar.  That is particularly true so long as you do not consistently give surplus energy back to the energy company.