Solar glare: Will your panels be a nuisance or unnoticeable?
If you’re thinking about installing a solar energy system, you might wonder how much solar glare your panels will produce. After all, you don’t want to be a nuisance to your neighbors and people driving through your neighborhood.
Luckily for you, solar glare shouldn’t be a major concern. After all, solar panels are meant to absorb light rather than reflect it, and they’re not any more reflective than water. And we haven’t run into complaints about glare on projects we’ve installed.
In this blog, we’ll learn more about solar panels and their reflections.
But first, let’s nail down some definitions.
First things first
For the purposes of this blog, we’ll be talking about solar photovoltaic panels, rather than concentrated solar power systems that use reflective panels to concentrate sunlight and generate heat. Solar PV systems are the kind we install and are common on homes and businesses.
“Glare” is a continuous source of excessive brightness, according to this Sandia National Laboratories report. “Glint,” meanwhile, is a momentary flash of light. Both of these can cause distractions or other adverse impacts for drivers, pilots, workers and others.
And finally, there’s two kinds of reflection: specular and diffuse. Specular is more direct and can be found on polished surfaces like mirrors and smooth glass. Diffuse reflection can be found on snow and textured glass, as Sandia National Laboratories lays out.
There are a few factors that will determine how much glare you see from a reflective object. Among them are the positions of the light source and the observer relative to the reflective material, in our case the solar panel.
“The amount of light reflected off a solar panel surface depends on the amount of sunlight hitting the surface, its surface reflectivity, geographic location, time of year, cloud cover, and solar panel orientation,” according to this Federal Aviation Administration guide. “The more a surface is polished, the more it shines. Rough or uneven surfaces reflect light in a diffused or scattered manner and, therefore, the light will not be received as bright.”
There’s no question solar panels reflect some sunlight. The question is, how much sunlight?
Remember that solar panels turn sunlight into electricity, so it’s best for them to absorb, not reflect, as much sunlight as they can. To that end, they’re coated with anti-reflective material to ensure better efficiency.
Several studies, helpfully compiled by the National Renewable Energy Laboratory, demonstrate that “PV modules exhibit less glare than windows and water.”
“Solar PV modules are specifically designed to reduce reflection, as any reflected light cannot be converted into electricity,” the NREL adds.
The Sandia National Laboratories report has a handy chart showing a range of “reflectivity” for various materials. Not surprisingly, mirrors top the list. Not far behind is snow, something we see plenty of in the Northland! You’ve probably had to don sunglasses or squint while driving during a bright winter day recently.
PV solar panels, meanwhile, are toward the bottom of the reflectivity scale. It’s on par with water, again, something we see all around us in northern Minnesota and Wisconsin.
So while solar panels do cause some glare and glint, it’s not more than some naturally occurring objects we see all the time.
Like I mentioned above, the position of the light source, reflective object and observer all factor into glare. It also matters whether the material has a smooth or rough surface. That will help determine whether it produces specular or diffuse reflections. Specular reflection will be more concentrated in one direction, while diffuse reflection scatters light in all directions.
Most of the light reflected by solar panels is specular, according to Pager Power, a consulting firm based in the U.K. that has conducted glint and glare assessments.
We can actually predict the angle of specular reflection using physics: The angle of the incoming light, or angle of incidence, equals the angle of reflection. We use an imaginary line perpendicular to the reflective surface, like in the image below, as a reference for the two angles.
In the illustration below, we can show with the sun shining above the house, the reflected light bounces upward. The reflection angle will depend on the position of the sun, which constantly changes throughout the day.
This paper from a Massachusetts consulting firm analyzes the angles at which light strikes and reflects from a solar panel to argue that “glare, if any, from rooftop solar PV panels is not likely to adversely affect surrounding properties in a dense urban neighborhood.”
“In addition, given basic tenets of light reflectivity, the angle of reflected sunlight is likely to be directed sufficiently skyward that it would go over the tops of neighboring buildings at even short distances removed from a building with solar panels on its rooftop,” it added.
The paper was geared toward rooftop systems, however, not ground-mounted systems.
Still, the potential for solar glare has prompted federal regulations concerning solar panels installed at airports. Last year, the Federal Aviation Administration published a final policy that “requires airports to measure the visual impact” of proposed solar energy systems at “federally obligated airports with control towers.”
Like I mentioned above, the angle of the solar panel relative to the sun will help determine how much light it reflects. According to Forge Solar, which produces solar glare analysis tools, “a panel that absorbs 90% of direct sunlight may reflect up to 60% when not directly facing the sun. This situation is common for low-tilt panels during sunset and sunrise.”
But it’s worth noting that 20% of public airports in the U.S. have adopted solar panels in the past decade, according to the University of Colorado Denver. Denver International Airport has more than 42,000 solar panels, according to the researchers. That demonstrates that even in the most sensitive environments, solar panels can be installed safely.
Airports, like many homeowners and businesses, have recognized the potential for solar energy systems to reduce their energy bills and impact on the environment.
While solar panels do reflect some light, they’re about as reflective as things we come across in our daily lives. And most of the light they reflect should be pointed skyward and away from your neighbors.
Of course, you want to be a good neighbor, but installing panels shouldn’t cause any consternation in your community because of solar glare.
Read more from Northland’s solar energy experts:
- Hiring a solar panel installer? Here are some tips
- How long do solar panels last? What consumers should know
- Rapid shutdown: How it makes solar systems safer
- Bifacial solar panels: Are two sides better than one?
- What solar panel is best? Monocrystalline vs. polycrystalline