Passive solar - the use of the sun to heat space - is a great idea.
Since your house is already built, you can't adjust solar orientation.
The thing to do it work with what you have. It will be hard to get 100% of heating needs from the sun, but you may be able to decrease fossil fuel based heating usage.
* Insulation - An 100% passive solar house is hugely insulated compared to conventional construction. You can get great return on investment with increased attic insulation plus blown in cellulose for the walls. There is a federal tax credit - see my siggy!
* Air sealing - the typical 60's split level has many areas where heated air escapes and cold replacement air comes in. Air sealing can be very effective to reduce heating costs. It is important to have an energy audit done before the air sealing to make sure there are no indoor air quality or safety issues. PM me if you need the name of a good BPI-certified auditor.
* An additional benefit to insulation + air sealing is that when it comes time to replace a furnace or AC, you can save money by putting in a smaller unit.
* We use cordless cellular shades in our south facing windows. In heating season, we open them during the day, close them at night. A friend uses 1" silver faced foam panels. Insulated drapes are a great idea on non-south facing windows.
* If you have an AC needs during the summer, you reduce them with plantings of tall trees in the proper locations.
* In the long term, you may want to augment "passive solar" with solar radiant heating - this could work for you if the basement is no finished and your floors are not carpeted. It is especially easy if you currently have hydronic heating (radiators) not forced air.
very best regards,