How to Calculate Your Peak Sun-Hours

Reader Contribution by Sarah Hancock
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One important question that many individuals have when deciding whether or not installing a solar energy system is the right move for them is “do I live in an area that receives enough sun to make solar panels worth it?” To answer this question, it’s critical to understand how much sun solar panels need in order to operate effectively, what peak sun-hours are, and how you can calculate the peak sun-hours in your area to get the most out of the solar power that’s up for grabs.

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How much sun do solar panels need to operate effectively?

Although direct sunlight provides optimum conditions for solar energy systems, solar panels produce electricity from the photons present in natural daylight, rather than from the sunlight itself, which means that panels don’t actually need to be installed in direct sunlight to work. Heat isn’t a factor that affects how much electricity PV solar panels can generate either, so a cool spring day could be as productive, if not more, than a sweltering summer day. Even in cloudy weather solar panels can absorb energy to produce power, but it will be at a reduced rate compared to sunny days—typically between 25 and 40 percent.

Panel placement is perhaps a more important factor than natural conditions. If panels are installed in an area on your property that receives a significant amount of shade, they may still be able to produce some electricity (depending on the equipment), but this will usually pose more of an issue than clouds or cold weather. Ideally, solar panels will be installed facing south, but a solar professional can help you determine the best placement for panels on your specific property.

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What are peak sun-hours?

While the amount of sunlight your panels receive is important, a more accurate representation of the amount of power your panels have the potential to produce is peak sun-hours. Note that peak sun-hours is not the same as hours of daylight; a peak-sun hour describes the intensity of sunlight in a specific area and is defined as an hour of sunlight that offers 1,000 watts of photovoltaic power per square meter. Peak sun-hours occur when the sun is highest in the sky and generally increase during summer months and the closer an area is to the equator.

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How do I calculate the peak-sun hours in my area?

Knowing the average number of peak sun-hours where you live can help you decide whether or not solar panels are a worthwhile investment for your home. Most areas in the United States average between 3 and 5 peak sun-hours per day, but this is likely to fluctuate depending on the season.

To calculate your peak-sun hours, use an isolation map to see how much solar energy your location receives throughout the year. You can also take a look at different charts that compile data on solar radiation, including monthly and seasonal averages. To calculate the exact number of peak sun-hours that solar panels will receive on your property, you can purchase an isolation meter or build your own. After placing the meter in direct sunlight, it will give you a reading on current light intensity and solar power supply, which can help you to determine peak sun-hours.

If you find that your peak sun-hours are relatively low, don’t fret — solar energy may still be a viable option. As mentioned above, even with less-than-optimal conditions, solar panels can still produce a decent amount of power and be beneficial for both you and the environment. Consider consulting with a solar expert if you’re unsure whether or not your home is a good candidate for a solar energy system.

A proponent of renewable energy and green living, Sarah Hancock enjoys writing about sustainability and manages the solar blog on You can also find her work on Twitter.