Kilowatt-hours (kWh) represent energy over time, specifically energy multiplied by time. To convert kWh into mass, one must consider the relationship between energy and mass, as described by Einstein's equation E=mc². This equation indicates that energy can be converted into mass, but the conversion requires specific calculations. Understanding the appropriate units for energy and mass is crucial for accurate conversion. Ultimately, while it is theoretically possible to convert kWh into mass, the process involves complex equations and considerations.