Our solar power dreams are threatened by shadows, we shouldn't ignore them for long

Currently, solar power accounts for 3.3 percent of the total energy produced in the US, and it has become the fastest-growing source of clean energy in the country. The National Renewable Energy Laboratory estimates that by 2050, the share of solar energy in America's total electricity production could reach 45 percent. However, in order to achieve this milestone, solar energy experts will have to make photovoltaic systems more efficient and advanced than ever.

Recently, a team of researchers at the Shanghai Polytechnic University highlighted a point, which is often ignored but affects the performance of single and double photovoltaic cells (cells that convert solar energy into electricity and are found embedded on solar panels) systems connected to parallel and in series. They revealed that shade from different obstacles ranging from big buildings to tree leaves and dust reduces the amount of sunlight falling on solar panels and adversely affects the overall power output.

"In the real world, photovoltaic cells are sometimes shaded by obstacles, which significantly alters the amount of incoming light. The degradation effects make power optimization difficult and result in significant power loss," Huaqing Xie, one of the authors and president of Shanghai Polytechnic University (SSPU), wrote in the paper.

Loss of energy in a small solar system due to shade

When the amount of light received by a solar cell drops because of the shade of an object, the amount of electricity produced by that particular section of the solar panel also reduces, and this power loss is also referred to as a photovoltaic (PV) system shade loss. The researchers suggest that many previous studies have also highlighted output power loss due to shade obstructions.

However, most of them focused only on large PV systems that comprise numerous PV cells and didn't take into account the PV system shade loss in small solar systems consisting of only one or two cells connected in series and parallel. The current study not only analyzes the PV shade loss for small systems but also sheds light on how factors like the size of a shadow impact the output power.

In real-world solar power applications, the amount of power produced by a system can be increased by connecting PV cells in series and parallel arrangements. So the researchers suggest that if you want to create a solar panel, first, it is important to understand the arrangement of cells in the system. Moreover, the area a shadow covers in single or double cell systems also has a critical role in deciding the overall output power.

During their study, the researchers discovered that the amount of electricity produced by single and double cells connected in parallel was almost similar to the "ratio of shade to sunlight." However, power loss was found to be more for a system having cells connected in series, and therefore, the difference between power output and the ratio was also slightly more for such a system. For instance, when 29.6 percent area of a series PV system was covered by a shadow, its output power fell by 57.6 percent.

Professor Xie believes that his team's work represents one of the few works that successfully highlight how cell connection type, shadow area, and shade obstructions affect the performance of small solar systems. Knowledge of all these factors could further allow manufacturers to improve the efficiency of solar panels and reduce power losses. The researchers are now planning to study the impact of different shadows on the power output of PV systems.

The study is published in the Journal of Renewable and Sustainable Energy.

Abstract:

This study explored the adverse impact on photovoltaic (PV) cells (monocrystalline silicon) caused by simulated shadow generated by covering exact size obstacle. Experiments for a single cell and modules with two PV cells in series or parallel connection have been conducted. Under partially shaded conditions, the single cell and parallel module exhibited a decrease in output current, and the decrease ratio was equal to the shading ratio. While series PV modules appeared more deterioration effects including the increase in cell temperature and large decline in output current under different shadow conditions. Shading with 7.4%, 18.5%, or 29.6% area of one of the cells of the series module could result in 15.6%, 37.4%, and 57.6% current decrease, respectively, with excess decrease ratios of 8.2%, 18.9%, and 28.0%. This study allowed us to conclude that the variations in the reduction of the output of PV cells highly depend on the shading conditions of series modules in PV array.