Do Solar Panels Work When Partially Shaded?

As much as a shadow creeping in a corner of your solar system can decrease the energy output of the whole installation. Dusty solar panels on the roof of University in Gandhinagar, India, sparked an idea to investigate the effect of dirt on the efficiency of solar panels.

The study came to the surprising conclusion: air pollutants deposited on solar panels can decrease the amount of produced energy by more than 25 percent simply by obstructing the direct sunlight.

When even something so small like these barely visible particles carried by wind block light accessing the panel, what happens when your panels are shaded by bigger objects? And do solar panels actually work when partially shaded or not at all? To answer these questions we need to start from the beginning.

How do photovoltaic solar panels create electricity?

Commonly used solar panels, also known as photovoltaic solar panels, need direct sunlight to produce electricity.

Each panel consists of solar cells. The energy of the sun knocks the electrons loose from the atoms in these cells, which makes them flow through the semiconductor material inside the panel and produce energy.

This is why a solar panel works the best during the peak sunlight hours when the sunlight hitting the panel is the most concentrated.

Just one solar cell does not supply enough energy. That is why one solar panel consists of a grid of connected cells that together pump the energy through the system. Energy pushed from one cell becomes that initial nudge for the neighboring cell.

And that is how energy flows through the system. Until it hits an obstruction – a shaded cell…

What happens if solar panels are partially shaded?

A typical photovoltaic solar panels consists of a configuration of 32 to 72 solar cells that are connected series. This makes solar panels sensitive to partial shading.

Shaded cells of a solar panel interrupt the energy flow in the grid, which forces other cells work harder to compensate for the loss. It happens because electrons in shaded solar cells are not moving. Therefore, even energy producing potential of neighboring cells is reduced, as they do not receive that initial energy kick to multiply their output.

As a result, the efficiency of the whole grid might decrease by as much as 50 percent [1].

The shading effect on solar panels will reduce the power output of your whole solar system.

For example, if one solar cells is shaded by a leaf, it is not producing any power, while the remaining cells still produce to their full potential. Their energy still passes through the inactive cell and actually transforms into heat energy. Over time this could lead to overheating of the inactive cell and its damage.

Shading has long term effect on solar panels

Partial shading of solar cells does not only decrease the potential of a solar panel to generate power, it also shortens its lifetime because some cells of the grid are constantly overworking and get worn down at a faster rate than expected, and shaded cells are exposed to increasing temperature that could eventually damage the semiconductor material.

Luckily, new technology came up with a solution to allow electricity flow around shaded (inactive) cells. Most modern solar panels are already equipped with these devices. They are called bypass diodes. Bypass diodes protect solar panels by leading the current around inactive cells. And more importantly, they also reduce the effect of partial shading to its actual proportion.

With bypass diodes a shade falling on ten percent of the panel, the amount of generated energy will be also ten percent lower when compared to optimal conditions when solar panels are not in shaded [2].

What usually causes solar panel shading?

Airborne particles casting shade on your solar panels are the least expected option we consider, what are the other sources that block the direct sunlight access?

• Trees and surrounding vegetation: Trees are the most expected reason of shading. Checking for large trees prior installation is necessary. But do not forget to keep an eye on trees every couple of years. Even trees from your neighbor’s property might grow large enough to block the sun for parts of the day.

• Roof: When the sun is low, the angle of your roof, a chimney, or a skylight might cast a shadow on your solar panels.

• Taller buildings: You cannot stop the development in your neighborhood, and it can happen that during those 25 years of having solar panels, someone builds a house that doesn’t allow that afternoon sun reach your panels anymore.

• Clouds: Clouds might seem like an impervious barrier blocking the sunlight, but they still let certain portion of light pass through. This means that your panels will still generate electricity even though at lower amount.

• Snow: A thin layer of snow sitting on your solar panels can have a shading effect on them and reduce their capacity to produce energy, similarly like a layer of airborne dust mentioned in the introduction.

A part of your research prior installation of solar panels includes a careful assessment of potential factors casting shade on the system throughout the year.

Professional providers often use various mapping tools to give you their best estimate when and how much shade would affect your array.

Some solar panel shading solutions

The best solution to deal with shade is to pick a spot on your property (and it doesn’t have to be a roof), where is unobstructed sun access for most of the day.

If you are limited by space and cannot do that try to remove the source of shade if possible. In most cases, trees around our property stand tall enough to cast shade over the panels even if for a couple hours a day. Try to trim tree branches that shade your house the most. In the worst case, you might have to remove the tree completely, but do not forget to plant a new one away from the house to make up for the loss.

When your roof receives a fair amount of sun for most of the day except for a time when a few branches from an old oak throw shade on it, power optimizers or microinverters could also be a solution for you.

This technology collects energy from each panel of the array separately, allowing the harvest of energy from unshaded panels to their fullest potential without being affected by the decreased generation from the shaded area [3].

When your panels get dusty or snowed in, remove the snow and dust gently. Take care to not damage the surface of the panel as that would decrease its efficiency.

For a new technology enthusiasts, amorphous silicon solar cells might offer what you are looking for. Unlike regular silicon panels with crystal structure, amorphous cells have an irregular arrangement.

This structure enables better light absorption and the form of thin film solar cells is suitable even for bended surfaces. The downside is their shorter lifetime and lower ability to generate energy than crystalline panels [4].

Getting deeper into the newest technology, scientists have developed super efficient solar cells capable of capturing 99.7 percent of light. Commonly used solar cells absorb 95 percent. These efficient cells are called “super black, ” and their special feat is the ability to perform almost the same in cloudy conditions as in perfect sunshine [5]. We just have to give it a couple years until this technology will become freely available on the market for a reasonable price.

With the bypass diodes protecting your solar panels, you can be sure that your solar panels will work when partially shaded. Only their power output will decrease according to the level of shading.

In real life situations, finding the absolutely perfect conditions for solar panel placement is nearly impossible, when even the fundamentals of life are based on changing conditions. But since the sun provides inexhaustible source of renewable energy, the future of solar energy is bright and many professionals are focused on achieving the most efficient ways to harvest this energy and minimize the negative effect of shading on the performance of the whole solar system.

We are sure that some amazing solutions will appear in a couple years from now that will minimize even these power output losses.