Retrofitting existing homes with solar power is often expensive, especially if you are in a state where there are no incentives available. It does tend to pay for itself in 10-15 years. But the real strength of solar power is when it is combined with complementary technologies and green architectural design. Combining solar power generation with ultra-efficient appliances is probably the easiest connection to make. Efficient appliances not only reduce size of the solar installation needed, but also tend to keep the house cooler in the summer, reducing cooling requirements. Lighting needs can be reduced by making use of daylight.
Similarly, designing a home to make sure of passive heating and cooling can also be highly important, because it reduces the energy burden of AC, fans, and heating. Using solar thermal water heaters also helps in this regard. Lastly, making use of intelligent housing designs that optimize housing space and layout, means you can reduce the size of a home while still retaining a feeling of spaciousness. Correctly sizing the home, will help reduce overall energy needs, and hence complement a solar-based energy generation system.