Do a load audit
List every electrical device you will run, how much power it draws and how long it runs each day. This one number, daily energy in kWh, drives the size and cost of everything else in the power system.
How
- Make a table with columns: appliance, quantity, watts (from the nameplate or a plug-in meter), hours per day, days per week, AC or DC, and surge or starting watts.
- Multiply watts by hours per day for each item to get watt-hours per day (Wh/day). Divide by 1,000 for kWh/day. Adjust items used only some days by days per week divided by 7.
- Measure real devices with a plug-in energy meter where you can, because nameplate figures are maximums. DOE notes that a fridge runs at full power only about one third of the time it is plugged in.
- Mark anything with a motor (well pump, fridge compressor, washing machine, power tools) and note its starting surge from the manual. These set the inverter surge rating, not the daily energy.
- Include standby loads: routers, chargers, inverter idle draw, alarm panels. They run 24 hours a day and add up.
- Ask the water, thermal, food and animals modules for their pump, fan, heater and refrigeration loads, so nothing is missed.
- Add up the total Wh/day and the largest group of loads that could run at the same time (peak watts).
Safety: Do not open appliances or wire into mains circuits to measure them. Use a plug-in meter or a clamp meter used by a competent person.
Do these first
Sources
- Planning a Home Renewable Energy System. US Department of Energy, Energy Saver, accessed 2026-11
- Balance-of-System Equipment Required for Renewable Energy Systems. US Department of Energy, Energy Saver, accessed 2026-11
- Estimating Appliance and Home Electronic Energy Use. US Department of Energy, Energy Saver, accessed 2026-11