Solar Photovoltaic Planning and Design: Introduction to Light Pollution Simulation Assessment

To achieve the net-zero goal, the International Energy Agency (IEA) has stated that countries will need to triple their renewable energy capacity by 2030 compared to 2022. The development of solar photovoltaics is an important part of this transition. However, the rapid expansion of solar installations has raised public concerns about light pollution and other related issues. ECOVE’s subsidiary, ECOVE Solar Energy, is dedicated to the development of solar photovoltaic investment, construction and operation services. This article specifically discusses how ECOVE effectively reduces light pollution during the planning and design phase of solar photovoltaic systems through simulation evaluation.

Causes of Light Pollution

According to statistics from the Energy Bureau of Taiwan’s Ministry of Economic Affairs, by the end of 2023, Taiwan’s cumulative installed capacity of solar photovoltaic power had reached 12.4 GW, nearly 10 times the growth compared to 2016. In addition, the Legislative Yuan passed a bill in May 2023 requiring new buildings to install a certain capacity of solar energy on their rooftops, aiming to accelerate the development of distributed renewable energy. Because the surface material of solar photovoltaic system modules is made of glass, many people are concerned about whether the reflection of sunlight will cause “light pollution”.

According to the “Guidelines for Light Pollution Management” of the Environmental Protection Administration, Executive Yuan, the so-called “light pollution” refers to the negative impact of artificial light sources on people’s lives. Another common term is “glare,” which refers to the intrusion of dazzling light into our vision. Due to inappropriate brightness distribution, it causes visual discomfort, visual impairment, or emotional disturbance and discomfort. The most common form of light pollution is from street lighting facilities, billboards, or lights on the exterior of buildings.

How does light pollution occur? According to optical theory, the reflectance of sunlight is largely determined by the angle of incidence of the sunlight relative to the surface normal (as shown in the diagram below). A smaller angle of incidence results in a relatively lower reflectance on glass, while a larger angle of incidence results in a relatively higher reflectance. According to tests conducted by domestic research institutes, when the angle of incidence of sunlight and photovoltaic modules is larger than 60°, there will be higher solar reflectance and increased glare intensity, raising concerns about light pollution.

Illustration of Sunlight Incidence and Reflection (Image Edited by ECOVE Solar Energy)

Key Points for Simulating and Assessing Light Pollution

As mentioned earlier, the reflected light from sunlight hitting the solar panel at a large angle of incidence can cause light pollution. Therefore, when considering factors for light pollution simulation assessment, in addition to setting observation points in terms of angle of incidence (which is the location point that determines whether there is light pollution impact or not), the latitude of the location should also be considered, and the relevant parameter conditions for sunlight and photovoltaic module panels should be synchronized. Details are as follows: 

• Sunlight Incidence: After the sun rises in the morning, the azimuth and elevation angles of its rays will change with the time in a day; due to the Earth’s orbit around the sun, the elevation and azimuth angles of the sun’s position also vary with seasons throughout the year (as shown in the diagram below).
• Site Latitude: Taiwan is located between 22° to 25° north latitude, with a difference of nearly 3° between north and south. When the site is located in different counties or cities, it is necessary to take different elevation and azimuth angles of sunlight into consideration.
• Parameter conditions of photovoltaic modules: This includes three basic condition parameters: installation azimuth, tilt angle, and mounting height. As for the glass material on the surface of the photovoltaic module panel, whether it has a surface anti-reflective coating or uses special anti-glare glass, the surface reflectance is not included in the parameters for this light pollution simulation evaluation.

Sun Elevation and Azimuth Chart of Four Seasons in Taiwan (Source: Central Weather Administration)

Simulation and Assessment of Light Pollution

Based on the light pollution simulation assessment parameters defined above, the simulation operation was performed and the light pollution assessment results were obtained. The details are as follows:

• First, we can quickly measure the photovoltaic systems, the azimuth, the tilt angle, and mounting height of solar panels through the extensive use of 3D aerial modeling tools when planning the solar photovoltaic systems. This tool also enables us to obtain accurate data of neighboring lands and buildings and present it in visual format to complete modeling process and obtain data parameters.
• Through the above data parameters, along with the latitude of the site, the elevation and azimuth angle of the sunlight, and other parameters, different angles of light reflection can be drawn using a ray-simulation tool. Finally,
• we can gain results of light pollution evaluation through a virtual prototype of the site created by computer-aided design (CAD) software. (see diagram below).

Light Pollution Simulation Evaluation Diagram (Created by ECOVE Solar Energy)

ECOVE’s Recommendations for Reducing Light Pollution in Solar Photovoltaic Planning and Design

With the rapid growth of solar photovoltaics installation, it is indispensable to address public concerns about light pollution from a professional and scientific perspective. 
With over 10 years of expertise dedicated to the field of solar energy, ECOVE has developed solutions to minimize the impact of light pollution and related issues through implementing potential environmental impact assessment in the early stages of installation based on experience, as well as through the selection of equipment or adjustments to the installation area, type or orientation during the planning and design phase of the system.

In addition to these efforts, we have to face and address public concerns about “light pollution”. When implementing projects, ECOVE always communicates with the public in a prompt manner by providing impact statements using light pollution simulation technology to reduce the worries from the public. In the future, ECOVE will continue improving its photovoltaic installation technology, exploring new solutions, and aligning with the government’s sustainable energy development policy goals to contribute to the sustainable development of the planet.