Otis Singleton
A megawatt (MW) is a unit of power that equates to one million watts. It is used to measure the rate of electricity consumption and is often used to describe the output capability of power plants. Power plants are assigned two values: megawatts electric (MWe), which refers to the electricity output, and megawatts thermal (MWt), which refers to the input energy required. For example, a coal-fired power plant rated at 1000 MWe and 3000 MWt will require a supply of 3000 MW of heat from burning coal for every 1000 MW of electricity produced. In the context of renewable energy, megawatt-hours (MWh) are used to describe the amount of electricity consumed or produced over a period of time.
| Characteristics | Values |
|---|---|
| Definition | A megawatt (MW) is a unit of power that equates to one million watts |
| Use | Used to measure the rate of electricity consumption and production |
| Use cases | Used by homes and businesses, and to measure the output of power plants |
| Comparison | One megawatt-hour is enough to power an average American home for 1.2 months, or 2 refrigerators for an entire year |
| Comparison | One megawatt-hour is equal to 1,000 kilowatt-hours |
| Comparison | One megawatt is equivalent to 1 million watts |
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What You'll Learn
Megawatt-hour (MWh)
A megawatt-hour (MWh) is a unit of energy referring to the amount of electricity generated or consumed over a period of one hour. One megawatt-hour is equal to 1,000 kilowatts of electricity generated per hour. In other words, it represents the amount of electricity delivered by a system with a power capacity of one megawatt (or one million watts) over a duration of sixty minutes.
Megawatts and megawatt-hours are related but distinct concepts. A megawatt measures the power capacity of an electrical system, indicating its potential to produce energy at a given moment, whereas a megawatt-hour quantifies the actual energy output or consumption over time. To illustrate, a 1 MW solar array operating continuously at full capacity for an hour would generate 1 MWh of electricity.
In practical terms, a megawatt-hour is a substantial amount of energy. It is enough to power two refrigerators or two 60-watt light bulbs for an entire year. In the context of electric vehicles, 1 MWh can propel a car for approximately 3,600 miles, which is the distance between New York City and Los Angeles.
When considering average energy consumption rates, a single megawatt-hour can meet the electricity needs of about 2,000 households in the UK for one hour. In the United States, 1 MW can supply the average home for 1.2 months or run a swimming pool pump continuously for five months.
Megawatt-hours are commonly used to measure the output of power plants and the electricity consumption of cities, states, or entire countries. This metric is valuable for understanding and managing energy production and usage on a large scale, helping to ensure that supply meets demand.
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Megawatts electric (MWe)
A megawatt (MW) is a unit of power that equates to one million watts. When a power source is rated at one megawatt, it means it has the capacity to deliver energy at a rate of one million joules per second. Megawatts are used to measure the rate of energy transfer or production, as well as the amount of electricity needed by a large community or the output of a power plant.
The total possible output or production of a generator or plant is expressed in megawatts, which is known as the generating capacity of the plant. This can be compared to a horsepower rating, or how a generating plant is designed to produce energy at full load. On the other hand, the maximum amount of power a generating plant is capable of producing over the course of an average year is called its generating capability or average annual energy, expressed in average megawatts.
Megawatts are used by homes and businesses to describe the rate of electricity consumption. They are also used to monitor the production of energy and are an important unit for reporting by power stations on how much electricity has been generated. One megawatt of power is enough to power the average American home for 1.2 months, run a swimming pool pump for five continuous months, or even toast almost 90,000 slices of bread. In the UK, approximately 2,000 individual houses could be powered by just one megawatt for a one-hour period.
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Megawatts thermal (MWt)
A megawatt (MW) is a unit of power that equates to one million watts. When a power source is rated as one megawatt, it means the power source has the capacity to deliver energy at a rate of one million joules per second.
Now, coming to the main topic of discussion, Megawatts Thermal (MWt) or MW(th) is one of the two values assigned to a power plant, the other being Megawatts Electric (MWe). MWt refers to the input energy required by the power plant, whereas MWe refers to the electricity output capability of the plant. Power plants are assigned two values as most are heat engines and therefore cannot turn 100% of their input energy into electricity. This is closely related to mechanical power, or how much power an engine can put out. For example, a coal-fired power plant rated at 1000 MWe and 3000 MWt will require a supply of 3000 MW of heat from burning coal for every 1000 MW of electricity it produces. That's approximately 100 kg of coal every second. This means that it puts out 2000 MW of waste heat, usually into a large body of water or the atmosphere. 1000 MWe for every 3000 MWt leads to an efficiency of 33%, which is fairly standard for older plants. The closer a power plant's MWt and MWe ratings are, the more efficient it is.
It is important to note that not all power plants are heat engines. Specifically, hydroelectricity, photovoltaic electricity, and wind power are not heat engines, so they have no megawatt thermal rating. However, these primary energy flows have other types of losses associated with them. Likewise, fuel cells are not heat engines, but they are unable to convert energy without losses.
To provide an example of MWt usage, the design reactor thermal power level was 3250 Megawatts thermal (MWth). The EfW CHP facility is another example, designed to treat 110,000 tonnes of waste per annum at the thermal design point of 39.9 Megawatts thermal (MWth).
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Watt-hours
To understand watt-hours, it is important to know that watts describe the level of power at a specific moment in time. Watt-hours, on the other hand, describe the amount of power consumed over a period of time. For example, if a 60-watt light bulb burns for 3 hours, the total energy expenditure in watt-hours is calculated by multiplying power (in watts) by time (in hours). In this case, the energy usage would be 180 watt-hours.
The use of watt-hours allows for convenient calculations and conversions in electrical engineering. For instance, when discussing solar energy, it is easier to understand the output of a solar array in kilowatt-hours per day than in joules. Similarly, when comparing the energy output of different cities, measurements in gigawatt-hours (GWh) over a year are more practical than using joules.
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Kilowatt-hours (kWh)
To calculate the kWh of an appliance, you need to know the amount of time the appliance is used and its wattage, which is usually found on the label. The formula for calculating kWh is: kilowatts x hours = kWh. For example, if you use a 1,500-watt dishwasher for two hours per day, the calculation would be: 1,500 watts / 1,000 = 1.5 kW; 1.5 kW x 2 hours = 3 kWh per day.
KWh is important for understanding your electricity bill. It is the measure that electric companies use to charge for energy consumption. Knowing the difference between kW and kWh can help you monitor and manage your electricity consumption. For example, a 65-inch LED TV that needs 100 watts (0.1 kW) of power can be used for ten hours before consuming 1 kWh of energy. On the other hand, a 60 kW DC fast EV charger will consume 1 kWh of energy in one minute.
The number of kWh a household uses per day will vary depending on location. In 2021, the average annual electricity consumption for a US residential home was 10,632 kWh, or 886 kWh per month. This equates to 29.5 kWh per day. In Texas, the average annual household electricity consumption is 14,112 kWh, which is 36% higher than the national average.
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Frequently asked questions
A megawatt (MW) is a unit of power that equates to one million watts. It is used to measure the rate of electricity consumption and production.
A megawatt-hour (MWh) is used to describe the amount of electricity consumed or produced by various sources over a period of one hour. For example, if a 1 MW solar array runs for one hour, it will produce 1 MWh.
One megawatt-hour is enough to power an average American household for 1.2 months, or 2 refrigerators for an entire year. In the context of renewable energy, 1 MWh is also equivalent to around 3,600 miles of driving an electric vehicle.
