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Energy and power

The difference between megawatt hours and megawatts

You often hear people talk about megawatts and megawatt hours when they're talking about electricity. Megawatts and megawatt hours are the units for power and energy. But what's the difference?

Power is the rate at which electricity is produced or consumed at any given moment in time.
Electrical power is usually measured in watts (W). One kilowatt (kW) is equivalent to 1,000 watts, and one megawatt (MW) is equivalent to 1,000 kilowatts. The number tells us how much power can potentially be produced, for example by a power plant generating electricity, or consumed, for instance by a light bulb. The power that a power plant, or "generating facility", can produce is also called the "installed generating capacity".

The chart shows Germany's annual installed generating capacity in megawatts (MW) for this year and the last couple of years.

When electricity flows, electrical energy is delivered. Electrical energy is measured in watt hours (Wh). One kilowatt hour (kWh) is equivalent to 1,000 watt hours, and one megawatt hour (MWh) is equivalent to 1,000 kilowatt hours. So, if you left a light bulb with a power of 100 watts on for one hour, exactly 100 watt hours of electrical energy would be delivered. If you left the light bulb on for less than an hour, say a quarter of an hour, the number of watt hours would be lower: in a quarter of an hour, only 25 watt hours of energy would be delivered (100 divided by 4). This means you can measure energy in watt hours even if the period of time is not a full hour. The SMARD chart below shows Electricity generation at fifteen minute intervals.

The chart shows Germany's actual Electricity generation and actual Electricity consumption in megawatt hours (MWh) at fifteen minute intervals today and in the last couple of days.

Electricity consumption is given on the SMARD website in megawatt hours because it is the amount of energy consumed in a certain period of time and not at a certain moment in time. Let's look at our light bulb again: we want to know how much electricity the light bulb has consumed between, say, 4pm and 4:15pm and not its Electricity consumption at exactly 4pm.

So the y-axis in the chart above represents the amount of electrical energy consumed in each quarter of an hour. If you move your mouse over the chart, you can see the exact figures for each quarter of an hour beginning at the time shown. The red line running through the chart represents the amount of energy produced and consumed in each quarter of an hour during the period. If you click on "Market data visuals", you can choose a different interval and period of time and see at a glance how much energy has been consumed in, say, each quarter of an hour, hour or day.