Did you know?
A standard unit for measuring electricity is the kilowatt (kW), which is equal to 1,000 watts. A watt is a measure of energy named after the Scottish engineer James Watt. One kW of electricity generated or used over the course of one hour is a kilowatthour (kWh). Other units for measuring electricity capacity and electricity generation and consumption:
- Megawatt (MW) = 1,000 kW; megawatthour (MWh) = 1,000 kWh
- Gigawatt (GW) = 1,000 MW; gigawatthour (GWH) = 1,000 MWh
Did you know?
There are three general categories of electricity generating capacity. Nameplate capacity is determined by the generator's manufacturer and indicates the maximum output of electricity a generator can produce at a certain point in time without exceeding specified thermal limits. Net summer capacity and net winter capacity indicate the maximum instantaneous electricity load a generator can support during the respective season. These values may differ because of seasonal changes in the temperature of the cooling water or ambient air used by the generating unit.
Did you know?
Small-scale distributed solar photovoltaic (PV) systems, such as those found on residential and commercial rooftops, have grown significantly in the United States over the past several years. Estimates of small-scale distributed solar PV capacity and generation by state and sector are included in the Electric Power Monthly. As of the end of 2015, almost 40% of total distributed solar PV generating capacity in the United States was in California.
Three terms are important to know when learning about electricity production and consumption:
- Generation is the amount of electricity produced over a period of time.
- Capacity is the maximum level at which electric power (electricity) can be supplied at a point in time under certain conditions.
- Retail sales represent the amount of electricity sold to customers over a period of time and are a proxy for electricity consumption.
The U.S. Energy Information Administration (EIA) publishes data on two general types of electricity generation and electricity generating capacity:
- Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt of total electricity generating capacity.
- Distributed includes, but is not limited to, generators with less than one megawatt of capacity that are usually at or near the location where the electricity is consumed. The most common type of distributed systems are solar photovoltaic systems installed on building rooftops.
In 2015, net generation of electricity from utility-scale generators in the United States was about 4.1 trillion kWh. EIA estimates that an additional 12 billion kWh were generated by distributed solar photovoltaic systems.
About two-thirds of utility-scale electricity generation in the United States came from fossil fuels (coal, natural gas, and petroleum):
- Natural gas—33%
- Renewables other than hydropower—7%
- Petroleum and other—1%
Electricity generating capacity
Sufficient capacity to generate electric power is important. Because electric power can't be stored, enough electricity to meet demand at every moment on the electric power system, or grid, must be continuously produced.
Most of the time, many power plants are not generating electricity at their full capacities. Three major types of generating units vary by intended usage:
- A base load generating unit normally satisfies all or part of the minimum, or base, demand (load) on the system. A base load generating unit runs continuously, producing electricity at, essentially, a constant rate. Base load generating units generally have the largest capacity of the three types of units.
- A peak load generating unit helps to meet requirements during the periods of greatest, or peak, load on the system such as when hot weather increases electricity demand for air conditioning.
- An intermediate load generating unit meets system requirements that are greater than base load but less than peak load. Intermediate load generating units are used during the transition between base load and peak load requirements.
Generators powered by wind and solar energy supply electricity only when these resources are available (i.e., when it's windy or sunny). When these renewable generators are operating, they may reduce the amount of electricity required from other generators to supply the grid.
Distributed generators are connected to the electricity grid, but they are mainly used to supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus is sent to the grid.
At the end of 2015, the United States had about 1.1 billion kW of total utility-scale electricity generating capacity and about 8 million kW of distributed solar photovoltaic capacity.
Generating units fueled by natural gas accounted for the largest share of utility-scale electricity generating capacity in the United States at the end of 2015:
- Natural gas—41%
- Nonhydroelectric renewables—10%
- Other sources—0.4%
Energy sources for U.S. electricity generation
The mix of energy sources used to generate electricity in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of U.S. electricity generating capacity and about 52% of total electricity generation. By the end of 2015, coal's share of electricity generating capacity decreased to 27% and accounted for 33% of total electricity generation. Over the same period, the share of natural gas-fired electricity generating capacity more than doubled from 19% in 1990 to 41% in 2015, and its share of electricity generation nearly tripled from 12% in 1990 to 33% in 2015.
Although both U.S. nuclear and hydropower electricity generating capacity grew slightly between 1990 and 2015, most nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Generation from hydropower, historically the largest source of renewable electricity generation, fluctuates from year to year because of precipitation patterns.
Total monthly U.S. electricity generation from nonhydro renewables now routinely exceeds hydropower generation
Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. In 2013, the total annual electricity generation from nonhydro renewable sources surpassed hydropower generation for the first time.
Wind's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to about 6% in 2015, and its share of total annual electricity generation increased from 0.1% to 5%. While relatively small in terms of its share of total U.S. electricity capacity and generation, solar electric generating capacity has grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 megawatts (MW) in 1990 to 13,406 MW in 2015, with about 8.4 MW of additional distributed generating capacity from solar photovoltaic systems. Solar's share of total U.S. electricity generation in 2015 was about 1.3%, up from about 0.04% in 1990.
Various factors have influenced the mix of energy sources for electricity generation
The major factors that have contributed to changes in the U.S. electricity generation mix in recent years are:
- Declining natural gas prices
- Slowing growth in electricity demand
- Implementing federal air pollution emission regulations
- Meeting state requirements to use more renewable sources
- Using federal and state financial incentives for renewable resources
The declining price of natural gas has been a major contributor to the rise in natural gas-fired electricity generation and the decline in coal-fired generation since 2008. When natural gas prices are relatively low, high-efficiency, natural gas-fired combined-cycle generators can supply electricity at a lower cost than coal-fired generators. Coal-fired power plants then operate less often and earn less revenue, which decreases their profitability and reduces the incentive to invest in new coal-fired generating capacity. In addition, natural gas-fired generators, in contrast to coal-fired generators:
- Can be added in smaller increments to meet grid generating capacity requirements
- Can respond more quickly to changes in hourly electricity demand
- Generally, have lower compliance costs with environmental regulations
Retail electricity sales
U.S. retail electricity sales to end-use customers totaled 3,725 billion kWh in 2015, nearly the same amount as in 2014. The main difference between the amount of electricity generation and the amount of retail sales is the amount of electricity that is lost (as heat) in the transmission and distribution of electricity. The United States also exports and imports some electricity.
Who buys electricity?
Sales of electricity generally went to four types of U.S. retail customers in 2015:
- Residential—1,400 billion kWh (38% of electricity sold)
- Commercial—1,358 billion kWh (36%)
- Industrial—959 billion kWh (26%)
- Transportation—8 billion kWh (0.2%)
Who sells electricity?
Electricity was sold by six major types of providers in 2014 (latest data available at the time of this update):
- Investor-owned utilities—51%
- Power marketers—21%
- Public utilities—14%
- Nonutility and others—1%
- Federal power marketing authorities—1%