Today on the blog, we're unveiling a new series of ongoing posts called 'Solar Basics'. These posts are intended to answer frequent questions we receive about solar power, ranging from how solar works to some tips for finding the right solar solution for you. If you have any questions you’d like answered, please post them to our Facebook page or leave them in the blog comments for any Solar Basics posting.
At our recent dealer conference, one of our dealers said he gets a lot of customer questions about the terminology associated with the power and electricity output of SunPower solar systems. Specifically, customers are confused about when to use the term 'kilowatt' and when to use ‘kilowatt-hour’ (and what both terms even mean). So here’s a simple explanation you can use when talking with a potential dealer or explaining your system’s output.
Kilowatt (kW) is a measure of power. It’s important to understand that power is a rate statistic that measures the flow of energy conversion within a system (and not the energy itself). When describing a solar installation, kilowatts provide a measure of system capacity. For instance, a 10 kW system acting at full capacity will have 10 kW of energy flowing through at any singular moment.
Kilowatt-hour (kWh) is a measure of electricity. Unlike kilowatts, kilowatt-hour is not a rate statistic and is cumulative. In fact, kilowatt-hours represent the amount of power (in kilowatts) used over a period of time (hours).
One useful example is to think of a stomach, which is a kind of engine that we all have within our bodies. The stomach gets fuel in the form of food, which uses food energy (otherwise known as calories) to power the body. Imagine that you have a completely full stomach beginning the process of digestion. At full capacity, the stomach will digest food and power the body at a specific rate (say 120 calories per hour - a rate statistic similar to kilowatts). Over three hours, your somewhat-less-full stomach will have produced 360 calories of energy (a counting statistic similar to kilowatt-hour). That's enough to power an hour of moderate exercise, so there's a good excuse to burn those calories.
Now back to solar. Let’s say you have a guest over who wants to know how much energy you're producing with your SunPower rooftop installation. You have a 'perfect' 10 kW AC power system that includes all system and module level losses, meaning that at peak production the system is producing exactly 10 kW of power. From 10 am to 4 pm, your system is running at full capacity (a perfect solar day!) with peak sun hours of 5.8 hours. And thanks to SunPower’s market-leading panel efficiency, less roof space is required to capture the 10 kW system output and feed it into your home. To compute the energy output of those six hours, follow this simple calculation:
10 kW AC x 5.8 peak sun hours = 50 kWh from 10am to 4pm
That’s a lot of energy! We hope this helps clear up any confusion around kilowatts and kilowatt-hours. And if you’re a SunPower customer, be sure to check out our in-home monitoring tool to get up-to-date readings of how many kilowatt-hours your system is producing each day.
If you have any further questions or comments, please post them to our Facebook page or leave them below.
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