Kilowatt-Hour (kWh)

A kilowatt-hour (kWh) equals 1,000 watt-hours and is the standard unit for measuring energy consumption and production at the household and system level. Your electric utility measures your usage in kWh, solar system output is projected in kWh per year, and residential batteries are rated in kWh of usable storage.

The average US household consumes roughly 30 kWh per day (about 900 kWh per month), though this varies enormously by region, climate, household size, and efficiency measures. An off-grid cabin might use 3-5 kWh per day, while a large home with electric heating and cooling might exceed 50 kWh daily.

Solar system production is estimated by multiplying the array's kilowatt-peak (kWp) rating by the average peak sun hours at your location. A 6 kWp system in an area receiving 5 peak sun hours per day theoretically produces 30 kWh daily — though real-world output is typically 75-85% of this after accounting for temperature losses, inverter efficiency, wiring losses, and soiling.

For battery sizing, kWh directly answers the capacity question. If you need to store 10 kWh of usable energy and use LiFePO4 at 80% DoD, you need 12.5 kWh of total battery capacity. At 48V, that is roughly 260Ah of battery bank capacity.

Understanding your daily kWh consumption is the single most important number for designing a solar system. Every other sizing decision — array wattage, battery capacity, inverter size, charge controller rating — flows from this baseline energy budget.