how to conceptualize energy units generated, distributed, and eventually used by loads throughout electricity grids (e.g. gigawatt, megawatt, megawatt-hours, kilowatt, kilowatt-hours, etc.)
In: Physics
So, for starters most of what you’re asking for are units of **power**, not energy. Gigawatts, megawatts, and kilowatts are just rates of power production or usage, equivalent to one gigajoule per second, one megajoule per second, and one kilojoule per second.
A few watts will power a night light.
A kilowatt (1,000 watts) will power an electric kettle or microwave oven.
A megawatt (1,000,000 watts) will be the regular output of a standard-sized wind turbine.
A gigawatt (1,000,000,000 watts) will be about half of the peak power outputs of the Hoover or Aswan Dams.
For the others (watt-hours, kilowatt-hours, etc.), those are units of *energy* (no different than joules), but are given in the industry standard units of watt-hours (so, 3600 joules) for various reasons (basically engineering, accounting, emissions, and regulation stuff).
A watt-hour is comparable to the energy of a gram of TNT.
A kilowatt-hour is actually comparable to the caloric value of three snickers bars.
A megawatt-hour is around the value of the energy expended by your heart over 80 years, or the total energy contained within the fuel in the gastank of a normal-sized car.
A gigawatt-hour is the amount of energy contained in the fuel tanks of a large aircraft (think an Airbus A330).
Watts are power and not energy. Watts are a flow rate, and represent a watt-hour after an hour.
Energy flow rate is often limited by hardware. The wattage in a wire or component or generator should never exceed some amount.
Watt-hours, kilowatt-hours, and so on measure total energy. For the consumer, this means money. For the producer, this means coal or uranium or what-have-you. For the environmentalist, at least until we become more renewable, this means carbon.
As for prefixes, a moderately-sized LED will use about a watt. A moderately-sized space heater will use a kilowatt. A house uses maybe 6 kilowatts or so, obviously varying a lot with weather and time of day. A small city may use, by my calculations, very roughly 10 megawatts.
A power plant may produce around 1 gigawatt.
By my very loose math based on googled numbers, America may use about 1 terawatt during the hot hours of a summer day.
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