What is a megawatt MW, megawatt hour MWh, kilowatt kW and kilowatt hour kWh?
Written by Andrew Sendy
Updated March 12, 2020
4 minutes read
When one first starts looking into electricity, you become bombarded with terms that can become confusing. However, they are relatively easy to understand, and we can go through them all quickly here so you can get back to your solar or electrical research.
Let’s start at the beginning.
What is a watt?
A watt is the basic unit of power.
P (watts)= Voltage (V) x Current (I)
It is a measure of how much electrical energy there is in a circuit and how much electrical work can be done by that circuit.
A kilowatt is simply 1000 watts.
A megawatt, as the name suggests is simply 1,000,000 or 1 million watts of power.
A gigawatt is 1,000,0000,000 or 1 billion watts of power.
Why do we need Mwh and Kwh?
As a society electricity is a commodity. Electricity generators supply the commodity and households and businesses consume commodity.
There was traditionally always a marginal cost of generating electrical energy (long before renewables), and so it became necessary to measure the exact amount of electrical energy that was supplied or used over periods of time.
What is a kilowatt-hour (kWh)
A kilowatt-hour is a measure of the total use of electrical energy over a time period and is equivalent to 1000 watts of power (a kilowatt) being used continuously for 1 hour.
So one-kilowatt hour could be someone using 1000 watts for an hour, or it could be someone using 10,000 watts for 6 minutes (0.1 of an hour). Either way, they have used 1 kilowatt-hour of electrical energy.
What is a megawatt-hour (MWh)?
A megawatt hour is equivalent to 1 million watts of electricity being used for an hour.
1 MWh is equivalent to 1,000 kWhs.
A megawatt hour could be 2 million watts (2 megawatts) of power being used for half an hour or it could be 500 kW (.5 megawatts) of power being used continually for 2 hours.
Why are solar systems sold in kilowatts?
When solar is sold in kilowatts what this really means is that the peak DC capacity of all the solar panels adds up to that amount of kilowatts.
So a system of 20 x 250-watt solar panels will be sold as a 5 kW system.
However, this does not mean that at any one time it will be producing 5 kW of instantaneous power or that it will produce 5 kWh's of power over an hour.
When you look at your inverter or your monitoring on your solar system you will note that the real-world output of solar panels is seldomly around their peak capacity. The actual output depends on solar irradiation, losses in the system design and possibly dirt or shading.
How many kilowatt-hours of power are produced by each kilowatt of solar panels?
The amount of power generated by each peak kW of solar panels varies around the country.
You can find out how much electricity (in kWhs) do solar panels produce in your area each year. This website also shows how much electricity solar panels produce at each time of year in each area and how other factors affect the amount of electricity produced by solar panels.