Electricity glossary
From kWh and SAIDI to net billing and COP. Examples use this site's own numbers (U.S. home use 878 kWh a month, 17.30 cents per kWh in 2025) or are marked as illustrations. Type in the box to filter.
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One picture: kW, kWh and cost
The terms
Average price (cents per kWh)
What EIA reports as the price: revenue from a group of customers divided by the kWh they bought. It averages all plans, so it is not the rate on your plan.
Example. U.S. homes paid 17.30 cents per kWh on average in 2025; North Dakota paid 11.81, Hawaii 40.59.
Source: EIA retail sales. Where it appears on this site.
Baseload and peaking plants
Baseload plants run almost all the time; peaking plants run only at the highest demand. The split affects prices and emissions at different hours.
Example. eGRID reports a non-baseload CO2 rate beside the annual one; the non-baseload rate for the U.S. is higher than the annual figure.
Source: EPA eGRID. Where it appears on this site.
CAIDI
Customer Average Interruption Duration Index: SAIDI divided by SAIFI, the average length of one outage.
Example. Median across the same utilities: 96 minutes per interruption, computed as SAIDI over SAIFI for each utility.
Source: Computed from EIA-861. Where it appears on this site.
Capacity factor
Actual output over a period divided by the output if the plant ran at full rating all the time.
Example. PVWatts gives a fixed rooftop panel in Texas a capacity factor of 17.1% in a typical year.
Source: NLR PVWatts v8. Where it appears on this site.
Demand charge
A charge based on your highest power draw in a short window, in kW, rather than on total kWh. Common for businesses, rarer for homes.
Example. Illustration: a 50 kW peak at $12 per kW is $600 a month, however many kWh were used.
Source: EIA Energy Glossary. Where it appears on this site.
Emission rate (CO2 per MWh)
Pounds of carbon dioxide emitted per MWh generated by plants in a place.
Example. U.S. average 767 lb per MWh in eGRID 2023; Vermont 43 lb, West Virginia 1,954 lb.
Source: EPA eGRID. Where it appears on this site.
Energy burden
The share of household income spent on energy. The U.S. Department of Energy treats more than 6% as high.
Example. Typical electricity alone takes 3.6% of median income in Mississippi against 1.3% in Utah.
Source: DOE LEAD; EIA; ACS. Where it appears on this site.
Fixed charge (customer charge)
A flat monthly amount you pay for being connected, whatever you use. It makes the cost per kWh look higher when you use little.
Example. Illustration: a $10 fixed charge on 500 kWh adds 2 cents to every kWh (10 / 500 x 100 = 2).
Source: Utility tariffs (illustration). Where it appears on this site.
Fuel or power cost adjustment
A line on the bill that moves with the utility's fuel or purchased power cost between rate cases.
Example. It is a tariff line, not an EIA field, so you will not find it in the tables on this site.
Source: General reference. Where it appears on this site.
Generation mix
The share of electricity made from each fuel in a place over a year.
Example. U.S. 2025 net generation: gas 40.9%, nuclear 17.7%, coal 16.6%, wind 10.4%, hydro 5.5%, solar 6.8% (EIA-923, plants 1 MW+).
Source: EIA-923. Where it appears on this site.
Heat pump and COP
A heat pump moves heat instead of making it. COP, the coefficient of performance, is units of heat out per unit of electricity in.
Example. A COP of 3 means 1 kWh buys 3 kWh of heat. In Florida a heat pump needs a COP of only 1.73 to match a gas furnace on fuel cost; in Texas 2.30.
Source: EIA prices, our calculation. Where it appears on this site.
Heating and cooling degree-days
A day's mean temperature below 65 F counts as heating degree-days equal to the shortfall; above 65 F, cooling degree-days. Summed over a year, they measure how cold or hot it was.
Example. A normal year (1991 to 2020) in Texas has 2,035 heating and 2,648 cooling degree-days (NOAA).
Source: NOAA NCEI nClimDiv. Where it appears on this site.
Investor-owned, cooperative, municipal
Three kinds of utility owner: shareholders, members of a co-op, or a city. Pricing and regulation differ.
Example. Median home price of utilities with 5,000+ accounts: investor-owned 15.54 cents, cooperative 13.73, municipal 12.39 (EIA-861 2024).
Source: EIA-861. Where it appears on this site.
Kilowatt (kW)
A measure of power, the rate at which energy is used or made. Panels, heaters and meters peak in kW; bills are in kWh.
Example. A 1.5 kW space heater running for 2 hours uses 3 kWh.
Source: EIA Energy Glossary. Where it appears on this site.
Kilowatt-hour (kWh)
The unit you are billed in: the energy used by 1 kilowatt of power running for 1 hour.
Example. A 100-watt bulb left on for 10 hours uses 1 kWh. The average U.S. home used 878 kWh a month in 2025 (EIA).
Source: EIA Energy Glossary. Where it appears on this site.
Major event day
A day with outages so large that the usual statistics set it aside, such as a hurricane. SAIDI figures on this site exclude them.
Example. A utility with a hurricane can look reliable in no-major-event numbers. The ranking page says so.
Source: IEEE 1366. Where it appears on this site.
Megawatt and megawatt-hour (MW, MWh)
1 MW is 1,000 kW; 1 MWh is 1,000 kWh. Power plants are rated in MW and counted in MWh of output.
Example. Texas plants of 1 MW or more had 181,852 MW of operating capacity and made 601 TWh in 2025 (EIA-860, EIA-923).
Source: EIA-860, EIA-923. Where it appears on this site.
MMBtu
One million British thermal units, a common unit to compare fuels. 1 kWh equals 3,412 Btu, so 1 MMBtu is about 293 kWh.
Example. It lets you compare 1 Mcf of gas (1.036 MMBtu) with electricity on the same footing.
Source: EIA Energy Explained. Where it appears on this site.
Nameplate capacity
The most a generator can produce, as rated on its plate. Actual output is lower on average.
Example. Texas has 181,852 MW of operating utility-scale capacity (EIA-860 2025); its eGRID nameplate is a different year and definition.
Source: EIA-860. Where it appears on this site.
Net billing
A variant that pays a lower, often time-varying, rate for exported power than the retail rate.
Example. California moved new solar customers to a net billing tariff for applications from 15 April 2023 (CPUC NEM Revisit).
Source: CPUC. Where it appears on this site.
Net metering
A billing arrangement that credits solar power you send to the grid against the power you take.
Example. EIA-861 2024 counts 5,068,500 home net-metered systems in 51 places on this site.
Source: EIA-861 Net_Metering, EIA Energy Glossary. Where it appears on this site.
Retail choice
A market where homes may pick their energy supplier. The wires company stays the same.
Example. 15 places had 5% or more of home accounts served by a supplier other than the wires company in 2024 (EIA-861; includes community choice programs in some states).
Source: EIA-861. Where it appears on this site.
Retail electric provider (supplier)
A company that sells you energy and bills you, while another company delivers it. Called REP in Texas.
Example. 55.7% of Texas home accounts bought from a supplier other than the wires company in 2024 (EIA-861).
Source: EIA-861. Where it appears on this site.
SAIDI
System Average Interruption Duration Index: the minutes a typical customer was without power in a year. Lower is better.
Example. Across utilities with 1,000+ home accounts that report it, the median SAIDI without major events is 98 minutes (EIA-861 2024).
Source: EIA-861 Reliability, IEEE 1366. Where it appears on this site.
SAIFI
System Average Interruption Frequency Index: how many outages a typical customer had in a year.
Example. Median SAIFI among those utilities: 1.01 interruptions a year.
Source: EIA-861 Reliability, IEEE 1366. Where it appears on this site.
Smart meter (AMI)
An advanced metering infrastructure meter that records use by the hour or less and reports it electronically.
Example. 84% of U.S. home meters in the EIA-861 2024 file are advanced meters.
Source: EIA-861 Advanced_Meters. Where it appears on this site.
Solar yield (kWh per kW)
The kWh a panel system makes in a year for each kW of rating.
Example. PVWatts: 1,498 kWh per kW a year in Texas against 1,017 in Alaska.
Source: NLR PVWatts v8. Where it appears on this site.
Tariff and rate case
A tariff is the approved price schedule of a utility. A rate case is the process in which the state regulator decides whether to change it.
Example. Co-ops and city utilities usually set their own tariffs; investor-owned utilities need regulator approval in most states.
Source: General reference. Where it appears on this site.
Tiered rate
The price per kWh steps up after you pass set amounts of use in a month.
Example. Illustration: 10 cents for the first 400 kWh and 15 cents above it makes a 600 kWh month cost $40 + $30 = $70.
Source: Utility tariffs (illustration). Where it appears on this site.
Time-of-use rate (TOU)
A price that changes by hour or season: cheaper at night, higher-priced at the evening peak.
Example. EIA-861 2024: 24 of 41 reporting California utilities offered a residential time-of-use rate.
Source: EIA-861 Dynamic_Pricing. Where it appears on this site.
Typical bill
Average monthly kWh per account times the average price for the month. It covers energy only; fixed charges and some taxes are not in it.
Example. At 878 kWh and 17.30 cents the U.S. typical bill is about $152 a month.
Source: EIA monthly sales. Where it appears on this site.
Wires company (delivery utility, TDU)
The company that owns the poles, wires and meters and delivers power. In states with retail choice it may not be the company you pay for energy.
Example. In 2024 Oncor delivered power to 3,477,215 Texas home accounts at 5.19 cents per kWh (EIA-861 Delivery_Companies).
Source: EIA-861. Where it appears on this site.
Sources and what we take from them
| Source | What we take | Joined on |
|---|---|---|
| EIA-861 annual electric power industry report, 2024 final | Utility prices and customer counts, SAIDI and SAIFI, net metering, service territories, retail choice parts A to D, advanced meters, time-of-use programs | Utility ID, state, county FIPS |
| EIA electricity retail sales, annual and monthly (API v2) | State prices by sector, average use, typical bill by month, 2026 to date | State code, sector, year or month |
| EIA-923 generation (2025 final) and EIA-860 generator file (2025) | Generation mix, capacity, planned retirements and additions | State code, fuel group |
| EPA eGRID2023 (rev2, June 2025) | CO2, NOx and SO2 per MWh of generation inside each state | State code |
| NOAA NCEI nClimDiv statewide heating and cooling degree-days | Degree-days: how cold and how hot a state is | State code (Hawaii and DC not covered) |
| NLR (formerly NREL) PVWatts v8 API | Solar output per kW for one point per state | State code (population-weighted centre) |
Definitions follow the EIA Energy Glossary, the 2024 EIA-861 instructions and IEEE 1366 where named; examples marked illustration are our arithmetic, not data.
Periods, retrieval dates and licences: data sources.
Questions
What is the difference between kW and kWh?
kW is how fast energy is used right now; kWh is how much was used over time. A 2 kW heater running for 3 hours uses 6 kWh. You pay for kWh, and some business tariffs also charge for peak kW.
What is a good SAIDI?
Lower is better. The median among utilities with 1,000+ home accounts is 98 minutes a year without major events (EIA-861 2024). The ranking page shows the state averages.
What is the difference between SAIDI and SAIFI?
SAIDI is total minutes without power per customer a year; SAIFI is how many times the power went out. Divide the first by the second and you get CAIDI, the length of an average outage.
Is the average price my rate?
No. It is revenue divided by kWh sold across all customers of a group, so it blends plans, fixed charges and tariffs. Your plan can be higher or lower.
What is net metering in one sentence?
A billing rule that credits the solar power you send to the grid against the power you take, so your bill reflects only the net.
What does COP mean for a heat pump?
It is heat delivered per unit of electricity. A COP of 3 means three kWh of heat for each kWh bought, which is why a heat pump can cost less than gas where electricity is cheap.
Why do states have different terms?
Utilities in different states use different names for the same ideas, such as wires company, TDU or distribution utility. Where we use one name the entry says what it covers.