Overshadowing in photovoltaics: How does CAT® handle it?

Many private investors or companies only notice after their solar PV installations are completed that the shadow, which they thought was insignificant, has such a significant impact on the electricity generated from their installations. A bird flying by? Clouds gliding across the sky? Falling leaves? All of these may be the cause of the overshadowing. CAT® addresses this problem with special technology in its top-of-the-line photovoltaic modules.
Any shadow that is cast on the solar installation affects it negatively. The overshadowing limits the access to solar radiation which results in a decrease in the electricity generated.
Fortunately, not all modules are created equal, and CAT® proves that we can minimise the impact of overshadowing on an installation even without using power optimisers – simply by choosing a better and more advanced PV module. Our experts also attach great importance to overshadowing – so we can minimise its impact on the entire installation, resulting in greater savings month after month.

Various types of overshadowing:

1. Spot overshadowing

A conventional photovoltaic module is shown below. Current flows through successive cells connected in series. Any interruption (overshadowing) adversely affects the performance of the panel. Typically, such a module is divided into 3 zones, which allow the flow of electricity to bypass obstacles.

Considering spot shadowing, such as a leaf on the surface of the module, it can be concluded that such a small shadow cannot significantly affect the production of electricity. Unfortunately, nothing could be further from the truth – if the entire cell is covered, it is unable to generate or properly transmit electricity further. One overshadowed cell in a series forces as many as one of the three zones of the photovoltaic module off. This means that until the shadow is removed from the surface of the module, the efficiency of the entire module will drop by as much as 33%.

CAT® photovoltaic modules are designed so that the flow of energy can continue in independent zones connected in parallel. Each row uses flexible paths to transfer electrical charges from cell to cell, thus reducing the impact of obstacles on the panel surface. The architecture of the serial-parallel connections is divided to achieve maximum performance in both horizontal and vertical orientations (six horizontal rows and three vertical columns).

Below, the same spot shadow that disabled as much as 33% of the panel in the conventional module slightly affects one of the 18 zones of the CAT® product. With the special architecture of series-parallel connections, the flow of electricity is possible despite the overshadowing.

2. Linear overshadowing in the horizontal position

For photovoltaic farms and installations on flat roofs, row-to-row overshadowing is a very important factor. In most cases, for the above-mentioned installations, photovoltaic modules are mounted horizontally.

Below is a conventional module and its behaviour under linear overshadowing. As you can see, even a slight overshadowing of the module results in a 33% drop in power. When a shadow is cast on the longer edge of the module, it quickly disables one of the three zones, similarly as in the case of the spot overshadowing.

Analogous overshadowing for CAT® modules induces a proportional decrease in power to the shaded area. If half of the cells in the first row are overshadowed, the other half of the cells continue to operate at 92% of their rated power. Considering the case in which the entire first row of cells is covered, the module’s efficiency will be reduced by only 17%, as opposed to a 33% decrease with conventional PV module architecture.

3. Linear overshadowing in vertical orientation

The manufacturer of CAT® panels and dealers recommend installing the modules in a horizontal orientation, which results in maximising the energy generated and saving money. However, if the module is mounted vertically, it will still have a significant advantage over a conventional panel. When overshadowing occurs at the lower (short) edge of a conventional module, this one will quickly be turned off, since the shadow affects all 3 zones simultaneously.

Let’s get back to the special parallel-serial connections in the CATERPILLAR module. The overshadowing that triggers a complete shutdown of the conventional module in the case of the CAT® panel results in a loss of only 33% of power. 67% of the power generated is better than 0% with a conventional product.

Considering the effect of overshadowing on the module’s power generation potential, the above examples show how the module’s design and special manufacturing can affect the reliability of the power source over its lifetime.

Written by: Rafał Niestępski

Photovoltaic Solutions Expert

email: fotowoltaika@eneria.pl