# What is power and energy?

Every single electrical device requires a certain **amount of electrical power to operate**. Technically it is expressed as Joules per second, but that is meaningless to most of us! Let’s just say it is a measure of how much power something needs to do its job. Power is measured in Watts. A thousand Watts equals one kilowatt, abbreviated as kW. The power requirement of devices are usually printed on a label, somewhere on the appliance.

A kettle typically requires 2000 Watts or 2 kW. An old-fashioned bulb might need 100 Watts and a LED light bulb only needs 5 Watts.

**1000 Watts = 1 kiloWatt = 1 kW**

Only when we switch the device on does it start to consume energy. The longer it is on, the more energy it will consume. The time in use becomes a factor.

By multiplying the time in use with the power requirement we get the ENERGY consumed.

**Watts x hours = Watthours **

**kiloWatts ****x hours = kiloWatthours or kWh.**

**kWh ****is what your electricity meter measures **and what you buy from Eskom or your municipality. Should you have a solar system like me, you will get your kWh from the sun! J Most people talk of electrical units, which are the same as kWh.

We can now calculate the **energy consumption **of any device, and we can add together the energy consumption of all the appliances to arrive at a single figure which is the total energy consumption for a given 24 hour day.

**A simple example:**

- Our kettle requires 2 000 Watts and was used for 5 minutes. The energy consumption was 2000 W x 5/60 hrs = 166 Wh
- That old fashioned bulb needs 100 Watts and burns through the night for 10 hours. 100 W x 10 hrs = 1000 Wh
- The TV uses 200 Watts and is on for 4 hours every night. 200 W x 4 hrs =
__800 Wh__ - 1 966 Wh

**Total ****energy consumption**: = 166 + 1000 + 800 = 1 966 Wh or 1.966 kWh.

Interesting to see that the 2000 Watt kettle consumed a lot less energy than the 100 Watt light bulb! All because of the **time in use**.

Now let’s replace the 100 Watt Bulb with a 5 Watt LED light bulb:

- Energy consumption = 5 W x 10 hrs = 50 Wh
- Kettle = 2000 W x 5/60 hrs = 166 Wh
- TV = 200 W x 4 hrs =
__800 Wh__

**Total ****energy consumption**: = 1 016 Wh

Through replacing the bulb, we have lowered consumption by 950 Wh! Everyday! This demonstrates the benefit of energy efficient appliances..

A 2 kWh system will generate 2 kWh (2000 Watt hours) on a daily basis. This system will be more than adequate to satisfy the energy requirement as calculated above.