The top item on the list of many renewable energy experts is to increase the efficiency of the devices you are using. If you are counting on solar power for lighting, you will need far fewer panels if they are powering compact fluorescent bulbs rather than incandescent ones. It doesn’t make sense to pay for renewable power system only to waste three quarters of the energy you are producing by using inefficient lights. This also holds true in many other cases.
Instead of relying on mechanical equipment to keep houses cooled, some of that can be accomplished by the orientation of a house and the arrangement of trees and shrubs that provide shade for cooling and buffering from winds. Passive approaches such as these are less expensive to operate than mechanical systems, and add to the value of the property, as well.
As the last days of summer approach, now can be a good time to look at your home and think about adding plants around the house to help with energy efficiency. According to the USDA, "Late summer or early fall is the optimum time to plant trees in many areas. This gives the tree a chance to establish new roots before winter arrives and the ground freezes. When spring arrives, the tree is ready to grow."
With the memories of summer still fresh in mind, take stock of how the house responded to the summer sun, and which areas might benefit from having additional shade that additional trees could provide. You can also think about the approaching winter, and consider trees that will offer buffering from cold winter winds.
In the summertime, steps you take to keep the outside of the house cooler can help lower (or maybe even eliminate) the amount of air conditioning you need to run. And providing evergreen plants to buffer the north walls, as well as the direction of the prevailing winter winds (often, but not always, to the west), can help stop drafts and help keep the house warmer in the winter.
Regionally appropriate, drought- and pest-tolerant species that are well-suited to your local climate are the best choice. Local experts (in the form of university extensions, commercial arborists, or other sources) can give more specific guidance about selecting appropriate trees for the site you have and the purposes you intend. The USDA Natural Resources Conservation Service web page has good suggestions to help get you started.
You may even consider planting fruit trees, and gain the double benefit of added shade as well as a crop of apples, pears, cherries, or other fruit that you can enjoy in the coming years.