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Identification and prevention of shading on rooftop solar systems

Updated: May 4

The issue of shading is painful for a significant percentage of owners of rooftop photovoltaic systems. Often it's a permanent shading from nearby buildings or parts of a building, while sometimes it's a shade created as a result of unbridled growth of vegetation and trees next to the facility. Besides structural shading analysis prior to system installation, there is no comprehensive solution to shading issues, so each case must be handled individually, from identification to finding a solution.

Rooftop solar array shaded by vegitation
Fig 1. Rooftop solar array shaded by vegitation

There are several types of shading from the solar PV persenctive, that can roughly be classified into permanent shading from a building or from building parts, dynamic shading from poles and electrical & communication wiring, shading from temporary parts and additions to the building itself (such as roof equipment, chillers, air conditioners, etc.), and finally shading from trees and nearby vegetation. In the first two cases, we are mostly talking about a "fate" that cannot be changed and must be dealt with in terms of planning and adapting the PV system to the situation in advance. However, while in the later two cases, it is about non-permanent factors that in some cases are not coming to awareness of solar operators at all or with a significant delay. However, after discovery of new shading - it can can be treated and often completely eliminated.

Hence, existing methods to deal with permanent factor shading are involving an appropriate layout planning of the panels, avoiding permanent shading locations and alternatively using panels embedded with optimizers/maximizers, which help to cover a larger part of the roof. The first solution in terms of proper system planning is relevant for fixed shading, while the implementation of optimizers / maximizers is most relevant for dynamic shading such as chimneys, poles and electrical wires. Of course, the solutions are very much localized and adjusted and it should be a combination of both.

Dealing with a temporary shading factor such as trees, vegetation or newly added equipment on the roof is more tricky. In such cases, there is typically a dap of knowledge on behalf of PV operations and hence the early detection is especially important. A shadow signature in the system output profile is unique in terms of time of the day and season of the year, thus "cutting out" generation at fixed hours and over a continuous period of time. A skilled person monitoring such facilities can in theory identify this manually by comparing several consecutive daily power and IV charts during seasonal variations, but there are also several advanced technological solutions to automate this process.

In order to identify newly occurring shading and differentiating it from a permanent seasonal shading, one must utilize either advanced algorithmics involving Artificial Intelligence or / and accurate quantitative performance assessment. Both methods can resolve the shading identification issue help generating an automatic warning upon an abnormal drop in output. With its technology, Soltell's SWMT sensorless technology enables not only the detection of permanent seasonal shadings, but also the segregation of new shadings and the quantification of their effect on system output for the purposes of predictive maintenance.

Commercial and residential solar integrators - interested to know more on Soltell's Sensorless technology to measure PV performance and automatically identify and classify shading, integrated into your solar monitoring/management software? Fill-in the demo request form to get more details.

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