# Section V – A Short Tutorial on the Power Unit of the 21st Century—The Gigawatt

As we move away from fossil fuels, the usefulness of using the BOE as the unit for measuring energy production and consumption diminishes. The reason is that the BOE relates to the thermal release of energy through combustion of some carbon fuel. Do we have any carbon fuels to replace fossil fuels? No, not really. Thus, what will replace fossil fuels will almost certainly be some form of electricity generation—nuclear-electric, geothermal, hydroelectric, solar, wind, etc. Characterizing the future power and energy needs, respectfully, in terms of the electricity generation units of gigawatts (GW) and gigawatt-hours (GWh) is, therefore, useful.

## A. Power and energy are not the same

It is important to recognize that “power” is not the same as “energy”, although they are related. Energy reflects how much power is required over a period of time.

The watt is the international unit measuring the production or consumption of power.[15] Example: When a 100-watt light bulb is turned on, it consumes 100 watts of power continuously. At the end of one second, the bulb has consumed 100 watt-seconds of electrical energy. At the end of one hour—3,600 seconds—the bulb will have consumed 0.36 million watt-seconds. Obviously, such numbers rapidly become quite large. Thus, the number of watt-seconds is divided by 3,600 to yield watt-hours. Then, this is further divided by 1000 to yield kilowatt-hours or kWh. A 100-watt bulb operating for one hour will consume 0.1 kWh of energy. Residential electricity consumption is usually measured in kWh. A typical 2,000 sq. ft. home will consume about 1,000 kWh per month of electrical energy.

## B. Units of power and energy step up and down by increments of 1000

If we divide the number of watts by 1000, this yields the number of kilowatts (kW). A home emergency generator will usually be in the range of 4,000-5,000 watts or 4-5 kW of power.

#### 1 kW = 1,000 watts

Dividing again by 1,000 yields the number of megawatts (MW). Many utility generators are rated in terms of the MW of power produced. These typically natural-gas-fueled generators will be in the range of 100-200 MW of power.

#### 1 MW = 1,000,000 watts

The next step up is to divide the number of MW by 1000 to yield the number of gigawatts (GW). Large baseload utility generators, such as coal and nuclear power plants, are generally in the range of 1000 MW or 1 GW.

#### 1 GW = 1,000,000,000 watts

The final step is to divide the number of GWs by 1000 to yield the number of terawatts (TW). This unit is usually used to describe power consumption at the national or planetary level.

For this paper, U.S. national electrical power needs are described using the unit GW. In 2100, as the United States completes its transition from fossil fuels, the entire energy supply of the United States can be defined in terms of *XX* GW-years, rather than 31.25 billion BOE/yr. The number *XX* GW-years represents a continuous supply of *XX* GW of electrical power 24 hours a day, 365 days a year. The size of this number *XX* will surprise you.