Design Considerations Designing for Efficiency
What does being “energy efficient” really mean to an off-grid home and homeowner?  It means that the power system, house loads, and use patterns waste as little power as possible.  Inefficiency, (created by lack of harmony between these areas) will create higher installation and operating costs.

A well designed off-grid system will generate and distribute power at minimum power loss, but certain losses are unavoidable.  Wiring loss will average 3-5% depending upon the particular wire/cable run. The inverter is 85-90% efficient at converting battery DC to AC power; batteries are 85-95% efficient at absorbing power from the array.  So overall, only 60-65% of array power generated is available as usable AC power (this figure is 90% or greater for a battery-less utility intertie system).  The array has to be sized to compensate for these losses.

Maximum household work must be derived from the power available through the use of energy-lean appliances and lighting, elimination of electricity for any type of heating (space, cooking, hot water), and killing of “phantom loads”.

Phantom loads consume small amounts of power around the clock, even when supposedly turned off.  They can add significantly to the demand on a system, both because of the power they use and inverter power consumed by the AC inverter to power them.  Any component that includes an internal power supply is probably a phantom load.  Here’s a few: stereo, TV, VCR, electric clock, AC adapter, answering machine.  For instance the average stereo consumes 6 watts when not in use, or 6 x 24 hrs = 144 watt-hrs/day.  In New England the stereo’s phantom load requires the usable output of one 60 watt panel, at an installed cost of $350.

What do you do with phantom loads?  The only way to eliminate a phantom load is to physically or electrically unplug the device from its outlet.  They can also be plugged into a switched outlet or power strip, which is turned off when not in use.  And most inverters have a “search watts” feature, which can prevent the inverter from powering phantom loads.