What Is a Kilowatt Hour (kWh)?

Whether you’ve already committed to installing a solar panel system or are just doing a little window shopping, you’ve probably encountered a lot of unfamiliar terminology. Without a background in solar energy, it can be confusing what all these words mean. Here at Lake Mary Solar, we’re committed to educating our customers on the ins and outs of solar technology so you can feel confident about investing in a solar system. Kilowatt-hour (kWh) is one such term that is commonly used when discussing solar energy, and one that is essential to understand if you want to choose the right photovoltaic (PV) system for your home. In this article, we’ll discuss what a kilowatt-hour is and how it applies to solar energy.

What is a Kilowatt?

To understand what a kilowatt-hour is, let’s start by discussing the watt (W) and kilowatt (kW). Simply put, a watt is a unit of power that is equal to one joule per second. Therefore, a kilowatt is a measure of 1,000 watts of power.

You can easily convert watts to kilowatts by dividing the wattage by 1,000.

For example:

4W / 1,000 = 4kW

With respect to solar systems, a watt or kilowatt refers to how much electricity the system is capable of generating during a single moment in time. When a solar system is generating electricity, the inverter will output a certain number of kilowatts.

It’s common to see this number change throughout the day and during various seasons. This is because a solar system’s ability to generate power is dependent upon many variables, including the temperature, the angle of the sun, and the weather.

When you see a solar system rated at 5kW, its peak power output is usually slightly less than 5kW, at around 4kW to 4.7kW. This is because solar panels are typically tested in perfect conditions inside a laboratory. Moreover, when a solar system ages, it becomes less efficient. But most modern solar panels can maintain approximately 80 percent efficiency over the course of 25 years.

If you’d like to find out how many kilowatts your solar system should be to power your home, check out our solar calculator.


Defining the Kilowatt-Hour

Now that we’ve defined what a kilowatt is, let’s explain how it differs from a kilowatt-hour:

While a kilowatt is a measure of electrical power, a kilowatt-hour is the amount of power generated or consumed during a period of time. More specifically, a kilowatt-hour is equal to 1,000 watts consumed or generated continually for one hour. Therefore, a kilowatt describes the rate at which you use or generate power, while a kilowatt-hour reflects the amount of energy produced or consumed. For example, if your solar system generates 1kW continually for an hour, it has produced one kilowatt-hour.

Because a kWh is a value over time, rather than a single moment, it is a more accurate representation of overall solar energy production than measuring kilowatts alone. Kilowatt-hours also are used by utility companies to measure electricity consumption. So, if your electric company charges you 25 cents/kWh, each kWh your solar system generates is saving you 25 cents. And, if you participate in a net energy metering (NEM) program, you’ll earn credits from your utility company when your solar system generates more kWh than you can use.

Why You Should Understand the Difference

If you’ve received quotes from several solar contractors, you’ll need to understand the difference between kilowatts and kilowatt-hours to get the best price on your solar system. This is because some solar companies will offer quotes based on kilowatts, while others may quote you based on kilowatt-hours. Although one offer might seem like a great deal, it may wind up being more expensive when you convert the values into the same unit.

At Lake Mary Solar, we offer a price-match guarantee for any licensed solar contractor in the state of Florida. So, if you do some shopping around and find a better price, we’ll honor it. But you’ll need to know how to convert between kilowatts and kilowatt-hours if you want to ensure you’re comparing apples to apples.

How To Convert Between kW and kWh

Let’s say you have a 5kW solar system and live in an area with five peak-hours of sunlight per day. If your peak power output is 4.7kW, you can estimate the kWh of your system by multiplying the peak power output by the hours of peak sunlight. Therefore, your system would produce 23.5kWh of power.

4.7kW x 5hrs = 23.5kWh

If you want to convert the kWh back into kW, you simply reverse the process, dividing the kilowatt-hours by the hours of peak sunlight.

23.5kWh/5hrs = 4.7kW


Understanding the difference between kilowatts and kilowatt-hours can be confusing, but it’s an important concept to wrap your head around if you want to get the most value out of your solar panel system. If you’ve reached the end of this article and still don’t quite grasp it, don’t worry! Our experienced Florida solar contractor is happy to educate you on the nuts and bolts of solar technology. Feel free to contact us today with any questions or concerns you may have.

Are you ready to start saving money while reducing your carbon footprint? Get a quote from Lake Mary Solar today and join the solar energy revolution.

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