Power and Energy are two important terms widely used in the Engineering sector. However, do you know the key difference between them? Let us explore this ahead 🙂
Power is a quantity measured in Watts (W) i.e. Joules/second (J/s). To understand power, think of a light bulb in your room. You may have noticed that a large bulb is rated for several watts compared to a smaller one and lights up your room more. Why is that? This happens because the large bulb consumes more amount of electricity per unit time. This electricity is a driving force and a form of energy.
Now think of a solar cell. For a solar cell, the power output is dependent on the amount of sunlight. We define this amount of sunlight as irradiance, which is the power falling per unit area on the solar cell (W/m2). Greater the irradiance, higher is the power output of the cell due to the increased electricity produced per unit time.
Is there something missing here? Yes! Power does not give us information about how long a device can actually be useful to us. This is where Energy comes in, which can be defined as the power accumulated over a period of time. We are familiar with Joules (J) which is the classic unit for energy. In principle, Kilowatt hours (KWh) are more useful because 1 KWh = 3.6 * 10^6 J. What is a kWh? If a 1KW device such as a microwave were to be operated for 3 hours/day, the energy consumption is 1 x 3 = 3 KWh/day. Notice the time factor?
We apply a similar principle when comparing a coal and solar plant. Consider that both have a power output of 30 MW (Megawatts), which is also called the capacity. A coal plant usually runs throughout the year which equates to 8760 hours (24 hours/day x 365 days). For simplicity let us take 8000 hours. The annual energy production then becomes 30 MW x 8000 hours/year = 240,000 MWh/year.
A photovoltaic plant on the other hand is different. When we mention a 30 MW plant this is the peak power it would produce under the most favorable conditions (best panel tilt, ideal position of the sun in the sky, favorable temperature, etc.) This peak power is usually produced only for about 1200 hours/year in Austria and the annual energy production is 30 MW x 1200 hours/year = 36,000 MWh/year.
Therefore, when you look at your utility bill, you will see the KWh consumed by your devices. Hence turning off the air conditioner when not required will reduce your bills 🙂 I thank Professor Dr. Höller and my fellow classmates for helping me with this understanding!
References: https://www.youtube.com/watch?v=L8e3FGgJx3Y&ab_channel=SolarQuote
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