1) commercial unit of electric energy? …

The kilowatt-hour (symbolized kWh) is a unit of energy equivalent to one kilowatt (1kW) of power expended for one hour (1h) of time. The kilowatt-hour is not a standard unit in any formal system, but it is commonly used in electrical applications. Kilowatt - hour is the commercial unit of electrical energy. We have seen that power is the rate of energy consumed or delivered. If 1 joule of energy is used per second, we say that energy is used at the rate of 1 watt. A kilowatt hour (kWh) is a measure of how much energy you're using.  It is simply a unit of measurement that equals the amount of energy you would use if you kept a 1,000 watt appliance running for an hour: So if you switched on a 100 watt light bulb, it would take 10 hours to rack up 1 kWh of energy.