Central air conditioning has proven to be the biggest, least efficient load in any home. It should not be used in off-grid homes. The ideal method of cooling is preventing hot air from getting into your home in the first place. This can be achieved with proper insulation and shading from the sun in summer, to prevent the home from overheating. Open your windows at night for a cool breeze through your home. 

• Light colors for roofs and outside walls Improved wall and roof insulation
• Enhance attic rafters with radiant barrier insulation
• Use windows with low emissions that do not need winter heating
• Window shading 
• Use of fans and natural cross-flow ventilation during the night

Evaporative Coolers

Even if your home experiences low humidity (below 30% in summer), you can use an evaporative cooling unit . These are very commonly used in the Southwest United States and burn very little electricity. The cooler functions similarly to the principle of body perspiration: an electric fan draws atmospheric air to a wet pad, humidifying and cooling it simultaneously. As the conditioned air gets blown into your home, the hot, stale air will be pushed out. The cooling works only with dry atmospheric air when humidity is below 70%. Most evaporative systems are installed on the roof with a bottom discharge blower which directs conditioned air into the home. 

Units mounted on the ground are more expensive than those mounted on the roof. You can add evaporative coolers to the typical refrigeration-type central air conditioning or even on window-mounted units, but these need lots of air-flow to cool the home. Desert climates require units that pump out 3-4 cubic feet of air per minute for each square foot of floor area.

Refrigerant-Based Air Conditioning

Most AC systems are bigger than required to ensure customers get their money's worth: a very quick and impressive cooling of your home without further servicing. But large units do not reduce the inside humidity - a smaller unit operating for a longer period does. All air conditioners that are sold in North America require an EnergyGuide label; use it to check the energy efficiency of various units. Another labeling program, Electrical Efficiency Rating (E.E.R.), computes the energy efficiency by dividing the "cooling power" BTUs by watts of electrical energy consumed. A higher E.E.R. indicates better energy efficiency with a lower operating cost. Do not exchange cost for energy efficiency: this false economy gives you savings that will quickly be overtaken by continually higher operating costs.

This is true for both window air conditioners and central cooling systems. Room air conditioners are cheaper to operate than central units for those who only require air conditioning in a couple of rooms. Your choice of a room air conditioner should depend on the cooling area and the unit's cooling capacity, according to the accompanying table. These units may be heavy loads on an off-grid system but they can reduce humidity and temperature levels drastically. A small unit can be powered by an energy surplus which happens frequently during the hot summer.