Energy glossary
Power market and grid terms in plain words. Each one has its formula, the mistakes to avoid and a real example from US plant data.
Output and capacity
Megawatt (MW)
A megawatt measures power: how fast a plant can produce electricity at a given moment. One megawatt is 1,000 kilowatts.
6,809 MWGrand Coulee, the largest US power plant by nameplate capacity
Megawatt-hour (MWh)
A megawatt-hour measures energy: an amount of electricity. It is one megawatt of power delivered for one hour, or 1,000 kilowatt-hours.
37.1 TWhVogtle in 2025, the most energy of any US plant
Capacity factor
Capacity factor is how much electricity a plant actually produced, as a share of what it could have produced running at full power the whole time.
87.8%Nuclear fleet capacity factor in 2025, the highest of any fuel
Heat rate
Heat rate is how much fuel energy a power plant burns to make one kilowatt-hour of electricity. A lower heat rate means a more efficient plant.
7,130 Btu/kWhWest County Energy Center, a gas combined cycle plant, in 2025
Prices and markets
Locational marginal price (LMP)
A locational marginal price is the wholesale price of electricity at one point on the grid. It is the cost of serving one more MWh there, given the plants running and the limits of the lines.
$21.75per MWh between the 10th and 90th percentile ERCOT plant node, 2025 average
Day-ahead and real-time markets
Most US power markets run twice. The day-ahead market sets prices and schedules for each hour of the next day. The real-time market settles the differences as the day actually unfolds.
7.5% vs 3.6%of ERCOT node hours with negative prices in 2025, real-time against day-ahead
Basis
Basis is the gap between the price at a plant's own node and the price at its trading hub. InfraMap reports node minus hub, so a negative basis means the plant's location is worth less than the hub.
75%of large ERCOT wind and solar plants had a negative 2025 basis: their node averaged below their hub
Negative prices
A negative price means sellers pay to deliver electricity in that hour. It happens when output that is hard to turn down meets low demand, or when tax credits make producing worth it even below zero.
18.7%of SPP plant node hours had a negative real-time price in 2025
Renewables and storage
Capture price and capture rate
Capture price is the average price over the hours a plant produced in, weighting each hour by its output. Capture rate divides it by a plain average price, so it shows whether the plant produces in cheap or expensive hours.
60%capture rate of the 10 largest ERCOT solar plants in 2025, against 66% for the 10 largest wind farms
Curtailment
Curtailment is electricity a plant could have produced but did not, because it was told to or chose to cut output. It usually happens when the grid has more supply than it can use or move.
3.66 TWhof wind and solar output curtailed in CAISO in 2025, 4.4% of what was available
Battery energy storage (BESS)
A battery energy storage system charges from the grid or a solar farm and discharges later. Its MW rating says how fast it can discharge, its MWh rating says how much, and together they give its duration.
47%of US battery power can discharge for about four hours
Round-trip efficiency
Round-trip efficiency is the share of electricity put into storage that comes back out. A battery that takes in 100 MWh and returns 85 MWh is 85% efficient.
86.1%of the energy US batteries took in during 2025 came back out
The analyst and the MCP server use these same reviewed definitions. Methods are in the methodology.