Know the units
Watts and kilowatts describe power. Watt-hours and kilowatt-hours describe energy used over time. One kilowatt equals 1,000 watts. A load drawing one kilowatt continuously for one hour uses one kilowatt-hour.
Record the pattern, not just the total
Daily energy use is important, but it does not show when electricity is required or which loads run together. Record daytime and evening operation, essential circuits and appliances with significant starting demands.
For a preliminary load list, note the appliance, rated power, quantity and estimated daily operating time. Actual use may differ from a nameplate rating, so measurements can improve the assessment.
Turn information into a better brief
Separate essential loads from loads that can be scheduled or switched off during backup. Note planned additions, such as cooling equipment, pumps or new machinery.
Provide bills where available and describe generator operating patterns. This gives an engineer a clearer starting point for system design. It also makes it easier to compare proposals against the same operating requirements.