What is the Difference Between Watts (W), kilo-watts (kW), and kilo-Watt hours (kWh)?

Understanding the difference between Watts (W), kilo-watts (kW), and kilo-Watt hours (kWh) is a common question and a topic that easily confuses many of us. To keep it simple, they are all fruit, but they are apples and oranges.

A watt is defined as a unit of power, equivalent to one joule per second, corresponding to the rate of energy in an electric circuit. A kilo-watt is simply 1,000 watts. The abbreviation for kilo-watt is kW. So when we say 10 kW, it means 10,000 watts.

A kilo-watt hour is a measure of 1,000 watts for one hour. The abbreviation for kilo-watt hour is kWh. So 1,000 watts during one hour is 1 kWh. The power company measures energy in kWh to calculate your monthly bill.

Here is a practical way to think about how watts, kilo-watts, and kilo-watt hours concerning a solar power system. Let's start with a single solar panel capable of producing 100 watts; this is commonly referred to as a 100-watt solar panel. During the day, when the sunshine is at its peak, the solar panel is capable of generating up to 100 watts of power every second. Think about that; it's a lot of watts.

Next, let's measure that 100 watts of peak power for 60 minutes or 1 hour. Remember that solar panels can produce 100 watts per second under peak conditions. So that's 100 watts X 60 seconds X 60 minutes, which calculates to 360,000 watts per hour, or 360 kW per hour. Therefore, a 100-watt solar panel operating at peak performance could generate 360 kWh of power.

Remember, this is a theoretical example using the definitions and a numerical model. In a real-world setting, a 100-watt solar panel will seldom produce 360 kWh of power. The sunshine is only at the peak for a very limited time. The location, temperature, and other environmental factors like clouds could affect solar panel performance. Plus, solar panels are subject to the laws of physics so that wireline losses, distance, and DC to AC conversion derating must all be factored to estimate actual power production.