What's the Difference Between a Kilowatt and a Kilowatt-Hour?

During your solar research, you've probably heard the terms kilowatt (kW) and kilowatt-hour (kWh) come up a few times. While these two terms might sound similar on the surface and are sometimes incorrectly used interchangeably, there's actually a big difference in what they measure and how they relate to your solar energy system's output and efficiency.

Since the average person doesn't use these terms in their day-to-day life, it can be confusing to try to understand the difference. In short, kWh is a single unit of energy, whereas kWh is the measurement of units consumed over time. The closest common-language analogy would be miles and miles per hour (mph).

Understanding the distinction between kW and kWh is especially important when you're collecting quotes from prospective solar partners. Knowing the difference will help you interpret and compare different proposals. Let's take a closer look at these two terms and how they each matter when it comes to solar.

What is a kilowatt?

A kilowatt is a measure of power within an electrical system – specifically the rate at which power is being generated at a single point in time. When a solar system is producing power during the day, at any given moment, the inverter will be outputting a certain number of kilowatts. As a result, you may see the kilowatt production of your PV system fluctuating up and down depending on several factors throughout the day and at different times of the year. These factors can include variables such as the angle of the sun, weather patterns, ambient temperature, and more. 

In relation to solar, the kW quoted represents the system's power capacity, but it leaves out information on that system's potential to produce energy over the course of an hour, day, or month. That's where the kWh comes in to represent how much energy the system can produce in a given timeframe.

What is a kilowatt-hour?

A kilowatt-hour is the amount of power generated over a period of time. For example, if a solar system produced 1kW continually for an hour, it has produced 1kWh. Kilowatt-hours are a more accurate representation of overall solar production, as it shows value over time rather than in a single moment. For an easy comparison, kilowatt-hours are also the same unit of energy that the utility company uses to determine energy usage. So, if your utility is charging you 20 cents/kWh, every kWh of solar power produced is offsetting that 20 cents you would have otherwise paid to the utility.

Why the difference matters

If you've received solar proposals from multiple companies, you'll want to ensure you're comparing apples to apples. 5kW is not the same as 5kWh, and your system's size (kW) is less important than your system's production (kWh). If your various quotes are all priced out in the same unit, then you can start comparing right away! If one has quoted you through kW and the other has given you kWh, that complicates things.

For one, the price per kW or kWh quoted could vary greatly on the surface. While one might seem like a better deal cost-wise, it might actually be the opposite when you convert the numbers into the same unit. In the broadest sense, this can be done by multiplying the kW of energy consumption by the total number of hours of operation to get kWh, or dividing the kWh by the total number of hours operation to get the kW.

Not all panels produce the same amount of electricity in a given timeframe and understanding this can help you choose the appropriate panels for your situation. A qualified solar partner will be able to explain different panel options to you so you'll be educated to pick the best one for your house.

If you're interested in going solar but have more questions, we invite you to take a look at our FAQ page or download our complimentary solar and battery guide, "Are Solar & Batteries Right for You?" Also keep in mind that our consultations are free, and since our mission is to educate, you can look forward to a low-pressure experience. Contact us for pricing and information specific to you and your home below.