Energy vs. Power

Dec 23, 2021

Energy and power are two terms heard often in the decarbonization space.  While related, they are not the same.  And when working in this space, it is important to understand the difference between the two.

In What is Energy, it was noted that energy is the capacity to do work. Power is the flow of energy delivered over time.  The two are related by the following formula:

When talking about the power of electric generating plants, the grid, EVs, batteries, etc, power is expressed in Watts (W) as in kilowatts (kW), megawatts (MW), gigawatts (GW), and terawatts (TW).  Here is how these relate to one another:

• 1000W = 1kW
• 1000kW = 1MW
• 1000MW = 1GW
• 1000GW = 1TW

When it comes to capacity ratings of electricity generating plants, we are talking about the amount of electricity the plant can produce when it's running at full blast. To get a sense of the power numbers:

• The Grand Coulee hydro power plant in Washington state has a capacity of 8.6GW of energy.
• The Palo Verde nuclear power plant in Arizona has a capacity of 3.952GW of energy.
• The Solar Star solar farms 1 and 2 in California have capacities of 314MW and 265MW respectively.
• The Los Vientos Wind Farm in Texas has a capacity of 900MW of energy.
• At the household level, a 7.5MW generator handles most needs.

On the energy side, there is no time factor.  One of the basic units for energy is Watt-hr.  Here are examples to provide you a sense of magnitude:

• The US consumed about 4TWh of electricity in 2019.
• A double A (AA) battery stores about 4Wh of energy. 
• An iPhone stores about 5Wh of energy in its battery.
• A Prius holds about 3kWh of energy.
• A Tesla Model S can have an 82kWh battery.
• The new electric Ford F150 truck is estimated to hold about 155kWh of energy.

Here's an analogy that can help understand the distinction between energy and power.  On an EV, think of the energy stored in the batteries as the gas tank and the number of gallons of gas it takes to go one mile (the inverse of the fuel economy) as the power it needs to run.

By knowing the difference between energy and power, you'll have an appreciation on the magnitude of the effort needed to decarbonize our generating of electricity.