A solar system contains many individual components and elements, each having its calculator.
If you want to figure out the angle that your solar panels must be tilted, you’d use a solar angle calculator. Or maybe you want to figure out the battery size, then you’d use a solar battery calculator.
However, we’re going to be looking at a factor that acts as a variable in almost every calculator. We’re talking about sun hours.
Join us as we break down how to use a sun peak hours calculator to size your system properly.
Peak Sun Hours
To begin with, we have to use metric numbers. This is because electrical capacity is worked out in kilowatts and kilowatt hours (‘kilo’ meaning ‘a thousand’), so we also have to use metric units for other measurements. Don’t worry though, we can easily convert it back to Imperial at the end of the calculation.
Peak sun hours refer to the number of hours in an average day equivalent to 1,000 W per square foot.
This is considered the standard test conditions of sun hours and is also how we determine the wattage of a solar system.
But before we can understand peak sun hours, we need to understand irradiance as it helps us determine the hours.
Solar irradiance is the measure of how much solar power you get based on your location. It’s not to be confused with solar radiation, which is the total amount of energy emitted by the sun.
Irradiance is the amount of energy hitting a specific area, accounting for the loss that isn’t hitting the earth directly.
Peak sun hours use solar irradiance to see the number of hours that a specific area receives peak solar output.
In most off-grid solar calculators, peak sun hours by the state are used as a value to help determine the size of your solar system.
However, it only comes into the equation once you have the battery bank capacity measured in watt-hours.
All of this is calculated automatically so you won’t need to stress yourself out about maths.
The Glass Jar Test
To understand the science behind peak sun hours, scientists visualize the peak by using glass jars filled with water and food coloring. The top of the jar represents 1,000 W per square meter.
Each jar represents an hour of the day and how deep the water is in the jar represents the average irradiance over an hour.
In other words, the first jar will have a small amount of water with it gradually increasing until it reaches the middle jar.
Once in the middle, it will decrease again as it represents noon transitioning into the night.
Scientists take the jars with the least amount of water and start pouring them into the other jars, normally filling 5 jars to the top with the 6th one filling halfway.
Each jar that’s reached 1,000 W per meter squared will represent one hour, so in this case, you’d be in an area with 5 and a half peak sun hours.
Peak Sun Hours Map
Looking at a peak sun-hours map is key to determining the size of our solar panels as well as our solar charge controller.
The map gives you a generalized idea of the world and its different sun hours based on location. It’s usually color coded from peach to dark red, with the darker areas being exposed to more sun.
Peak Sun Hours by State
Most maps have a drop-down menu listing the various states and their average sun hours for that location, making it convenient and easy to use.
If you prefer reading from a map instead of using the drop-down menu, then looking at the color of your area will be better.
Using this value in a solar home calculator that already has the value of your battery component will return the size of your solar panel in watts.
From this, you can determine the number of solar panels needed to match the wattage.
Sun Hours Calculator
Most peak sun hour calculators require your address, city, or zip code as they use a built-in solar map to obtain your solar irradiance.
Once you enter your area, they ask for the angle at which you think your solar panels should be tilted.
If you don’t know this value just yet, the calculator will autogenerate an estimate based on your area’s irradiance. It will also give an accurate estimation of the direction the solar panels must face.
Based on the values that have been entered, the sun hours calculator will return an annual average of peak sun hours per day. The fancier calculators will give you a monthly estimation.
If you want to take it a step further, you can use a PV solar calculator to estimate the size of your whole solar system.
Manual Calculations Using Irradiance Map
If you want to take mathematical matters into your own hands instead of using a solar calculator for your RV or home, you can. This is using an irradiance map instead of the peak sun hour map.
The difference between an irradiance map and a peak sun hour map is that the former gives you a value in kilowatt-hours per meter squared.
Let’s say you are residing in central New Mexico, and when reading the irradiance map gives you a value of 6.5 kilowatt hours per meter squared.
Well, under standard test conditions, you’re trying to figure out how many hours per day you’re receiving 1,000 W per meter squared.
This is where conversions come into play.
Since 1,000 W is equal to 1 kW, everything is equal to 1m squared per kilowatt.
All you need to do is take your 6.5 KwH per meter squared from earlier and multiply it by your 1 m squared per kilowatt. The kilowatts will cancel out and you’re left with the sun hours per day.
This gives you 6.5 hours per day of peak sun hours.
Does Peak Sun Hours Affect Your Decision on Solar?
At the end of the day, if you’re in an area that receives a small number of sun hours, solar might not be the way to go.
Solar panels don’t harness all the sun’s energy hitting its surface. There’s an efficiency loss and other factors that limit the conversion of light to electrical energy.
Areas that don’t receive a lot of sun and tend to have more cloudy and rainy weather won’t receive enough energy to charge their batteries in a day.
For the best return on investment, you should make sure you have at least 4 sun hours per day where you live. If you want to know how much money you’ll save, check out our solar panel ROI calculator.
It’s possible as most solar panels are designed to do their job on not-so-shiny days, but it won’t be the efficient route to take.
Also, rain and snow can damage your solar panels if they’re exposed to them for hours.
The only time when peak sun hours don’t affect your solar system too much is when you’re in an RV.
If you’re using portable solar panels for RVs and you’re moving around the country a lot, the best option would be to look at the solar map to plan your next destination.
The nice part about being a solar user in an RV is that you aren’t faced with the same conditions every day. If an area is too cloudy, drive to the next best.
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