How does Solar Panel Glare Affect Aircraft?
Solar panels are a growing source of renewable energy and a revenue generation avenue in the world.
However, while they play a key role in a decarbonized energy economy, there is a frequently overlooked side of these installations the impact of the flat pieces of glass in photovoltaic (PV) modules reflecting light on their surroundings.
Typically, the substantial increase in solar panel installations has raised concerns about the impact of its glare on the smooth running of aviation activities.
When the solar panel is under the flight paths or proximal to an aerodrome, the photovoltaic (PV) glare it produces can impair the ability of pilots to navigate and read the flight instruments.
This article strives to discuss the overview of the potential effects of solar panel glare on aviation operations.
Solar Panel Glare Concerns
Airline passengers wouldn’t want their pilot to be blinded by reflected light when a landing aircraft is approaching a runway.
This concern also applies to air traffic controllers in the tower, directing traffic across the airport and in the sky around it.
A good vision is essential for the safety of everyone working or using the aircraft, and unanticipated glare can take that away.
Typically, solar photovoltaic (PV) arrays can unintentionally cause a more persistent, common, and significant safety threat. The glare from solar panels affects aircraft in two ways:
Sunlight reflection
The PV glare reflected can affect the aircraft staff in the air and on the ground in the following ways:
Pilot distraction: One of the most common sources of safety concerns is the reflection of sunlight off the panels. The glare distractions can be hazardous especially if the effects are felt during the crucial stages of flight such as takeoff and landing.
Air traffic controller distraction: Glare is also known to affect the airport’s air traffic control tower, and hence compromises the safety of the entire aircraft space.
Interference with airport equipment
Solar panels are relatively passive pieces of equipment in terms of electromagnetic perspective. But the glare has the potential to interfere with the radar and other airport equipment.
This can be due to the physical structure of solar panels or radio interference between the electronic equipment.
That means the performance of the radar in detecting aircraft in the airspace can be compromised. These objections can extend up to 18km from the radar site.
What is glare?
Glare is the loss of your ability to see clearly or discomfort produced by the intensity of light in the visual field larger than the intensity of light to which your eyes are adapted.
In other words, glare is when too much light enters your eye the light is usually too much that your eyes are unable to manage.
Glare can occur day or night and maybe a security threat, especially to people operating high-risk machinery.
The “extreme brightness” emanates from a light source or it could be reflected, (e.g. the reflection from solar panels) and can cause distracting glare, disabling glare, discomforting glare, or blinding glare.
What are the Potential Hazards of Solar project glare?
Solar panels are created to absorb sunlight and utilize the photoelectric effect to generate power. Nonetheless, the panel has a front surface that reflects a small percentage of the sunlight.
This reflection is known as glare. Depending on the surface the glare can be:
- Specular: The glare has reflection characteristics like that of a mirror. It is found in smooth surfaces and often produces greater intensity and tighter beams.
- Diffuse: The surface will reflect the light by scattering it in different directions. It’s found in textured glass and anti-reflective coatings and the glare often has lower intensities.
Since comfort is a human feeling, one cannot estimate visual performance easily and requires the use of complex prediction algorithms.
However, prolonged exposure to glare disturbance or distraction can lead to headaches and other physiological effects as well as lower visual performance in terms of:
Permanent eye damage
This is the potential for an after-image and a low potential for an after-image. Typically, if a 7 W/m2 solar insolation enters an observer’s eye, it can cause an after-image lasting between 4 and 12 seconds.
For such scenarios, the glare can cause high irradiance and result in permanent eye damage.
Temporary flash blindness
The yellow glare shows substantial-high retinal irradiance that can cause temporary flash blindness. The blindness is developed due to the bleaching of retina visual pigments.
Factors that Influence the Intensity and Impact of Solar Panel Glare
As more solar panels are installed in urban settings, the overall problem of its glare is gaining more attention. And the more notable concern to date has been the effect of reflected light on airport operations.
However, these effects can be addressed by understanding factors that influence the intensity and impact of solar panel glare.
Here are different aspects that can affect the intensity and impact of the glare, including:
Timing
Since the sun is the collimated point source of light, its moving trajectory can be predicted during the day.
However, the precise timings of solar glare can be modeled via computer simulation, with the typical time when the strongest reflections occur being when the sun is low. That is due to the optical characteristics of solar PV.
That means the solar glare can affect aircraft staff and pilots in the morning and in the evening (shortly after sunrise and before sunset).
Note: The sun’s position during installation is a function of not only the time of the day but also the time of the year.
Direct normal irradiance (DNI)
DNI is the value at which the solar irradiance strikes the solar panel surface perpendicularly to the sun’s rays.
On a typical clear sunny day, the DNI can be 1,000 watts per square meter at solar noon. High DNI increases the strength of the solar source glare.
Type of solar panel
While all types of panels can cause solar glare, the intensity, and duration depend on the design.
However, smooth glass and light-textured cause the most intense glare while the deeply textured one has less intense glare but causes glare for longer periods.
Besides, a solar panel that can absorb 90 percent of direct sunlight can reflect over 60% when not facing directly the sun.
Reflective surfaces size and orientation
The orientation and size of the reflective surfaces from the observer can impact the glare size and degree. For instance, a 3-kilowatt PV panel can appear small compared to a 5-megawatt panel at a given distance.
The glare on the larger panel will therefore grow to a much larger size at longer distances than on the smaller panel.
Hence, it will pose a high risk for ocular hazards. The reflective surface orientation will also affect the reflectance and the effective viewable area.
The distance
The distance between the glare source and the observer can affect the subtended source angle and retinal irradiance.
With increasing distance, the atmospheric attenuation caused by air humidity and particulates will lower the retinal irradiance.
Besides, longer distances will yield smaller subtended angles of the fixed glare source.
Human factors
Human aspects including ocular properties as well as light sensitivity can alter the subtended angle, retinal irradiance, and perceived effect of the glare.
The ocular properties are:
- Pupil diameter: The size of the observer’s pupil affects the amount of glare entering the eye and reaching the retina.
- Eye focal length: It’s the value that determines the estimated image size on the retina for a specific subtended angle of the glare. The higher the value, the more the glare impact.
- Ocular transmission: A larger coefficient that accounts for radiation absorbed in the eye will mean more effects of the panel glare.
Remedial Measures for Solar Panel Glare
Solar panel projects located within or in close proximity to an airport property are required to observe some regulations to mitigate the adverse impacts it may cause on pilots and air traffic control towers.
In essence, Solar panels can coexist safely in airports if remedial or preventive measures are taken, including:
Use of special anti-reflective coating
There are modern PV modules that use low iron in high transmission glass and have an anti-reflective coating.
This extra layer of anti-reflective material can further limit sunlight reflection. Reflectivity can be lowered to less than 10% by this anti-reflective coating. This also increases the absorption of sunlight.
Panel glass surface texturing
Another way to limit reflection is by roughening the protective glass surface.
This roughened surface lowers specular reflection which has the potential to produce more concentrated and sharper rays of light. The texture glass layer will lower sunlight reflectivity as it produces diffuse reflections.
PV module re-orientation
Solar PV is flat with known orientation and position. Adjusting the tilt and orientation angle of the panel modules can help lower the effects of solar glare.
Typically, a slight adjustment to the panel’s vertical and alignment angle will alter the direction of the reflection and thus the intensity of glare impact.
However, it’s crucial to note that these changes can affect electricity generation and the decrease in power output has raised some concerns.
Alter the tracking technology
Another option is to alter the choice of tracking technology used. Typical solar panels are built using single-axis tracking that has backtracking.
That means, it can rotate during the day to follow the sun while lowering row-to-row shading at dusk and dawn.
The main drawback with this technology is that the backtracking algorithms position the panel models to reflect more glare.
There are various tracking considerations, but the selection and control of technology can offer the possibility to lower the glare impacts.
Encourage professional installation
Having an integrated engineer-procure-construct partner work on panel installation can help lower the glare effect.
That’s because the partners will coordinate the permitting measures and identify risks including solar panel glare early and hence make any necessary adjustments while installing.
Proper installation will take into account the size of the system, orientation, distance, environmental conditions, and major observation points and hence can help mitigate the negative effects of glare.
Use of solar glare analysis tools
The solar glare analysis tools can help you quantify the assessment of when and where glare will occur and its potential effects on the human eye if a panel is installed.
This is done through the calculation of subtended angle and retinal irradiance of the glare source.
These predictions enable installers to evaluate alternative layouts, designs, and locations, to mitigate the impacts of glare if glare exists in the proposed installation site.
Furthermore, the tool can help increase scattering and the subtended angle (observable size). This can reduce the glare intensity and retinal irradiance, and consequently lower the ocular hazard.
Stipulate solar panel regulations
There are little to no specific regulations addressing the safety impact of solar panels on airport activities.
It’s therefore vital to impose regulations that require installers to perform solar glare analysis to understand the effects of their proposed development on aviation operations.
They should also involve aviation stakeholders to seek feedback on the solar installation and ensure that any possible glare risks are mitigated.
Emergency glare response plan
A response plan that entails procedures to reduce potential glare impact on pilots and air traffic officials can be used to improve safety.
Besides, mitigation measures like screens and barriers, notification to the pilot, and stow procedures can be used if the glare hazard already exists.
Bottom Line
Solar power is redefining the way we think about our homes, our finances, and ultimately our impact on the planet.
Many industries are also adopting solar energy into the products and services that they offer, and technologically advanced companies across the nation are leading the movement.
However, solar panel installation near airspaces has a drawback due to the possible photovoltaic glare effects that can affect the visibility of airport staff and pilots.
The glare reflection has been associated with most of the impairments in the pilot’s ability to fly their planes and to see their instruments.
The more forward the glare and the longer its duration, the more the impairment.
