There are many ways to create shade and conserve energy in your landscape without planting a large tree. You may use large shrubbery or small trees to cast shade onto sidewalks, air conditioning units, lower portions of walls, and west-facing windows to keep them from heating up. Many cultivars (types) of shrubs have a narrow, upright form that is amenable to small spaces.
If you do not have room for even a shrub, you should consider installing a trellis or arbor to support a fast-growing vine in an area where the shade would benefit energy efficiency. A trellis affixed to a west-facing wall that supports a deciduous vine is ideal for shading the wall in summer while permitting passive solar heating of the wall in winter. Likewise, an arbor can be constructed over a patio to create a framework for vines to proliferate and cast shade.