Site assessment or site survey is an important step in the system design and installation process. During the on-site evaluation, the installer should collect all the necessary information required for system design, planning and optimization to improve the timeliness and safety of the installation. The goal of the on-site assessment is to determine the location of the photovoltaic array, roof specifications, shading conditions, and other considerations.
In most urban areas, photovoltaic arrays are installed on the roof of buildings; in the case of large open ground (without shelter from trees or nearby buildings), ground-mounted systems may also be used. There are many options here, usually depending on roof inclination and orientation, or ground conditions.
①Orientation: The ideal orientation is the orientation that enables the module to receive the most sunlight (the northern hemisphere is the true south, and the southern hemisphere is the true north). Unfortunately, when the photovoltaic array is installed on the roof, its orientation is controlled by the roof direction. Through the compass and magnetic declination data, the installer can determine the roof orientation and deviation from the ideal orientation. The orientation of the photovoltaic modules may be the same as the orientation of the roof, and the output power needs to be calculated.
②Inclination: In most systems, the inclination of photovoltaic modules will follow the inclination (or slope) of the roof. The inclination angle can be measured using an inclinometer or angle measuring instrument, and there may also be an inclination angle on the architectural structure drawing of the building. The optimal inclination angle of the system is similar to the local latitude angle. In the case that the roof slope is not equal to the optimal inclination angle of the photovoltaic array, it is necessary to analyze the impact of the output power of the photovoltaic array.
After determining the inclination and azimuth angle of the photovoltaic array, the designer needs to calculate the impact on the output power. This work can generally be done using data tables. In the United States, data tables are available from the National Renewable Energy Laboratory (NREL), and PVGIS online tools are provided, which can be used to calculate the impact of inclination and azimuth on output power at any location in Europe and Africa.
⑵Whether the scene is unobstructed
The shading on the photovoltaic array will significantly reduce the output power. One source of obscuration cannot be avoided, such as dust, dirt, bird droppings, etc., which must be cleaned frequently. During the site survey, all permanent occlusion sources need to be identified. Potential sources of occlusion may include:
① Trees and plants: During the on-site assessment, some arboreal techniques may not cover the photovoltaic array, but after several years of growth, it may quickly block the photovoltaic array. This must be paid attention to and communicate with the owner before installing the system. The owner may agree to pruning the tree frequently to ensure that the photovoltaic array is not blocked. If it is not feasible, for example, the tree is the property of a neighbor, consider changing the location or negotiate with the neighbor.
②Other buildings, including neighboring assets or buildings on site. It needs to be known that newly constructed buildings may obscure areas that currently appear to be suitable for photovoltaic arrays.
③Building components with photovoltaic array installed: If the array location is not suitable, the chimney on the roof, TV antenna, satellite antenna and other components may block the photovoltaic array. Users need to be informed that new facilities to be installed on the roof in the future should not block the photovoltaic array.
④Natural terrain: Mountains or hills may block the photovoltaic array, especially when the position of the sun in the sky is relatively low.
The photovoltaic array should be installed in a place that is not shaded during the day. Shading will reduce the output power and may damage the photovoltaic modules during the life cycle. Shading that occurs early or late in the day may be acceptable, but this should be left to a qualified photovoltaic system designer to make a decision.
It is also important to consider local regulations related to occlusion or “solar path”. Many federal states in the United States have enacted laws that do not allow new trees or expanded houses to cover existing photovoltaic systems on neighbors’ assets. There are no such laws in many places, but good communication between neighbors helps to ensure that other people’s assets will not have a negative impact on the photovoltaic system.
In addition to observing the objects in the scene, it is also important to conduct a thorough occlusion analysis. During the year, the sun does not maintain the exact same position in the sky. Therefore, even if an object does not obscure the recommended site on the site assessment day, it does not mean that the site will not be obscured at other times.