A load analysis is a systematic accounting of every electrical load in the building: every light fixture, every appliance, every pump, every device. For each load, you determine its wattage and the number of hours per day it operates, which gives you its daily energy consumption in watt-hours. The sum of all daily energy consumption figures gives you the building’s total daily energy demand, which is the primary input to the off-grid system design.

Efficient appliances are critically important in off-grid design. In a grid-connected building, reducing appliance energy consumption saves money but has relatively little effect on the building’s infrastructure. In an off-grid building, every watt of demand must be met by the solar array and stored in the battery bank. An inefficient refrigerator might require twice the solar array and battery capacity needed by an efficient one — a difference in capital cost that far exceeds the price premium of the efficient appliance. Off-grid design disciplines the designer and the occupant to think carefully about energy use in a way that grid connection never does.

Load Analysis Basics

• List every electrical device: lights, refrigerator, pumps, phone chargers, computers, fans

• For each: note rated wattage and estimated hours per day of use

• Daily energy (Wh) = Watts × Hours/day

• Sum all daily energy figures = Total daily load (Wh/day)

• Apply a system efficiency factor of 1.25–1.5 to account for inverter and battery losses

• This is the energy your solar array must produce on an average day