Originally published on Cost of Solar.
A home solar array is only as useful as it is appropriately sized, oriented, and installed. A poorly-matched system installed in a suboptimal location can be a big disappointment, so it’s important to pay attention to a lot of little details when planning to go solar.
Even if you hire a top-notch solar installer, someone who should know way more about solar panel angles and optimal panel orientation and array capacity than you do, if you want to get the best system possible for your home, it can pay to understand the ins and outs of producing solar electricity.
One of the key considerations when installing an array of solar panels, after assessing the structural soundness of the roof, is the direction that the roof is tilted, as well as the angle, or pitch, of the roof. A roof can be repaired or reinforced before installation if it’s damaged, but you can’t do much about the location, orientation, or pitch of the roof, short of moving to a new house, so knowing where and when and for how long the sun hits the potential location of the solar array is important. Because that is variable throughout the year, just as power consumption is variable throughout the day, it can be confusing when trying to pin down the ‘best’ solar panel angle and array orientation.
We’re all pretty aware that the sun appears to move through the sky during the day, from east to west, and that the days are longer (more hours of sunlight) in the summer, with shorter days (fewer hours of sunlight) in the winter. But there’s another variable when it comes to the sun’s energy, and that is the angle of inclination that the sun takes (its ‘height’ in the sky), which also shifts gradually throughout the year, so not only do we have to capture the most energy we can from a sun that’s moving across the sky, but one that’s also moving higher or lower in the sky, depending on the season.
And all of those variables are affected by yet another one, which is the physical location on the planet, because depending on where your house is, the amount of sunlight your solar panels will receive on any given day will vary from another location, such as more to the north or south of you. All of that is to say that there is no ‘one size fits all’ solar array that can be installed the same way every time and yet produce the exact same amount of electricity throughout the year, even not accounting for individual differences in homes or neighborhoods (tree cover, tall buildings casting shade, etc.)
When evaluating your own potential solar site, most likely your roof, it’s helpful to understand the particulars of your situation, such as the pitch, or angle, of the roof, as well as the direction that the intended surface faces, and to then relate that to the path of the sun through the sky during each of the four seasons.
Depending on where and when your house was built, the angle of your roof can be anything from flat (not very common, except in some arid regions) up to 45° or more (such as in snowy locations with steeply pitched roofs), but many homes have an angle somewhere right in the middle, around 30° or so. Because the most cost-effective and efficient way to install solar panels is parallel to the roof, your roof pitch will essentially be your future solar panel angle (unless a fixed-angle racking system is added to it), so it’s an important figure to know.
The other fixed variable is the direction that the home and its roof surfaces are pointed. In the northern hemisphere, the most sun will hit the southern faces of roofs, on average, throughout the year, so a south-facing roof has been the default for most solar installations. However, the sun also lights up the eastern surfaces in the mornings, and western surfaces in the afternoons, so roof planes that aren’t facing true south aren’t necessarily out of the question for solar panels (and western-facing solar arrays may actually be more useful to the grid, as they produce optimally during times of high demand).
Because the location of the sun in the sky each day varies by geographic location, the optimal solar panel angle is usually said to be equal to the latitude of the location, although because the angle of the roof and the latitude aren’t often an exact match, the solar array is usually simply installed parallel to the roof, in a fixed position. And according to a study at EnergySage, that’s probably the best way to do it, because the additional costs of racking to get the best solar panel angle may not achieve enough of a performance gain to make a big difference. In a location with higher electricity prices, it may make the most sense to use additional racking adjust the angle of the array for optimal production, and in other locations, lower electricity costs may not justify any additional expense for racking.
For those who want to boost their solar production in the winter and the summer, and not just have their solar panel angle be fixed year-round, an adjustable racking system may allow for optimal solar electricity generation. By tilting the panels 15° steeper in the winter and 15° down in the summer, it’s possible to increase the amount of energy your system can capture during those seasons, but there are also a number of different ways of determining when and how much to adjust the angle on a solar array if a default 15° isn’t enough for you.
The other major factor in a home solar array is the available roof space for a system that is sized appropriately to both your budget and your electricity needs. For some homes, with multiple-plane roofs, it may not be possible to put the entire array all together at the same angle, and so some solar panels will have to be installed at different angles from the rest, as the photo at the top illustrates.
If cost was no object, the absolute best performing solar electric array would probably be one mounted on poles, using dual axis tracking so that it can effectively track the sun through the sky and remain directly pointed at it all day long, regardless of what season it is. However, for most of us, a fixed angle rooftop solar array, pointed south, is already economically viable in most places, so there’s no need to invest the extra money to get a great return. Basically, the best solar panel angle for you is the one that either matches your roof pitch, because it’s cost-effective to install an array that way, or the one that gets you the most bang for your buck, electricity-wise, in your location, and your local solar installer can help you figure that out.
Image: Tim Fuller
Reprinted with permission.
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