What Is the Difference Between Power and Energy?

Power and energy are two main terms used in electrical and electronic systems. Many people think that energy and power are the same concepts. These two terms are related but not the same.

Energy is basically the ability to do work. For example, energy is needed to move a car, heat a house or light a street. The energy produced or consumed does not depend on time. Energy comes in many forms and is expressed in multiple units. The basic unit of energy is the Joule (J). The Kilowatt hour (kWh), which appears on electricity meters and bills, is also a unit of energy. 1 Kilowatt hour is equal to 3,600,000 Joules.

Power is the amount of energy used per unit time. In other words, it is the speed at which work is done. The more power, the faster the energy is used. The unit of power is the Watt. If you use one Kilowatt (kW) of power for one hour, you have used 1 kWh of energy. 1 Watt equals 1 Joule of energy per second and 1 Kilowatt equals 1,000 Joules of energy per second.

Let’s make the subject more understandable with a few examples.

If a car battery can provide 500 Amps of current at 12 Volts, this equals 6 kW of power. This value is the maximum power that can be drawn from the battery instantaneously. To look at the capacity of the battery, i.e. its energy, it is necessary to check the Ampere-hour (Ah) value.

When you leave a light bulb that draws 60 W power from the mains on for 30 days, it will consume 60 W x 24 hours x 30 days = 43,200 Wh, i.e. 43.2 kWh energy. The amount of energy consumed can be multiplied by the unit price of electricity to calculate how much the electricity bill will be.

Energy must change form if something has to happen. For example, to make a table lamp work, you need to convert electrical energy into light. To move an automobile, you need to convert chemical energy into mechanical energy. Even when you ride a bicycle, you are actually converting chemical energy into motion energy. Energy can change form, but power cannot.

Another difference between the two concepts is that energy can be stored, while power cannot. Power is instantaneous and remains constant. Energy, on the other hand, is variable and can be accumulated under favorable conditions.