Effects of Shadow on Solar Panels

Effects of Shadow on Solar Panels

Occasionally customers will call us wondering why they can’t seem to fully charge their batteries despite having plenty of sunshine - more often than not, there’s a shadow being cast on their panels that they either didn’t see or didn’t realise was having an effect.

Occasionally customers will call us wondering why they can’t seem to fully charge their batteries despite having plenty of sunshine – in most cases, there’s a shadow being cast on their panels that they either didn’t see or didn’t realise was having an effect.

Can all shadows on solar panels have an effect?

It may seem surprising, but any form of shadows can affect your solar output. This means it can be very easy to overlook, and you might think it’s a problem with the gear instead. Even small, partial shadows covering just one cell, or the bottom of the panels, can cause the shadowing effect - where the current flowing through the panel drops dramatically, resulting in a significant reduction in solar power generation.

What causes the shadowing effect? 

A reduction in power generation due to shadow can be caused by any form of shadow, both static and dynamic. 

Static shadows are pre-existing obstructions such as trees, buildings, chimneys, and even other solar panels. 

Dynamic shadows are anything temporary, such as clouds, flying objects, tall grass, and even bird droppings and dust build-up. 

Essentially, any form of shadow which prevents sections of the panels from receiving sunlight will cause the shadowing effect.

gif showing different shadows on solar panels

Why do small shadows on solar panels have such a large effect?

It’s easy to understand how a big shadow or a layer of grime covering most of a panel would decrease power generation, but it seems counterintuitive that tiny shadows would have an effect.

Every single cell in a solar panel is wired in a series to create one large flow of current. If one cell is covered by a shadow or object, the current of that cell drops significantly, and the panel current is reduced to the current flowing through the singular obstructed cell. 

If you’ve ever had a string of fairy lights stop working because one bulb is dead, you’ve experienced a similar situation!

You can visualise this like a hose with a kink in it – because it all goes through the one pipe, if doesn’t matter where the kink is or how minor, it will still have an effect on the entire thing.

Whether half of one cell is shaded, or half of a row of cells, the power decrease will be the same and proportional to the percentage shaded. A full cell being shaded might trigger the panel to protect itself and route power around that cell, and will likely result in a 50% drop in output, but if a full row of cells is fully shaded it will drop the output to near zero.

When you understand how one cell’s reduced current reduces the current across the whole panel, it’s easy to see how a small shadow can have such a large effect.

technical gif of how shadows on solar panels prevent power generation

How does a shadow on one panel affect the rest?

When your solar panels are wired in series, they perform the same way that the cells within a single panel perform. 

The current drops across the entire string of panels, so one small shadow will affect all of the panels.

gif showing how shadows on solar panels affects the entire array

How do I stop the shadowing effect?

The best way to deal with it is to prevent the shadows as much as possible, either through careful positioning of the panels or by removing obstructions.

When you’re planning where to put your solar panels, watch how the shadows change across the course of the day, keeping in mind that shadows will also change from summer to winter as the height of the sun changes. This means that trees or buildings might only cast a shadow on your panels during 3 months of the year, so even though you’ve never seen a shadow on your panels before, you might find one when the seasons change. If you can, give yourself plenty of space around the panels to reduce the likelihood of surprise shadows.

gif showing how shadows on solar panels change across the day

The panels themselves can also cast shadows on the other panels if you have them in multiple rows, so you’ll need to account for some extra spacing between rows if you want to avoid shadows. 

Tall grass growing up around the solar panels, or even the solar panels themselves are often overlooked, but can easily cast shadows that will cause a significant drop in power generation. 

How can I mitigate the shadowing effect when there are shadows?

Of course, the best way is to remove the shadow or move your solar panels. Hopefully, this will be as simple as mowing tall grass, cleaning the panels, or trimming back a tree, but if you have work with shadows, the two most simple tools are already included in our solar kit. 

The first is half-cut or half-cell solar panels. Half-cell solar panels help mitigate the shadowing effect by dividing each solar cell into two halves. If one half of a cell is shaded or experiences reduced performance due to shading, the other half can still function optimally, minimising the impact of shading on the overall power output of the panel. This division allows the panel to maintain a higher level of efficiency in partially shaded conditions compared to standard solar panels.

The second is the MPPT charge controller. Maximum Power Point Tracking charge controllers (MPPT) are the most efficient controller to mitigate losses caused by shadowing. Their inbuilt technology allows them to optimise every string's solar output by adjusting voltage to always correspond with the controllers preferred input range. This does mildly mitigate shadowing, although it doesn’t mean you’ll be generating anywhere near the amount of PV input as unobstructed panels.

If you’re unable to remove the shadows or move the panels, the next option would be to add more solar panels in a separate string to make up for the reduced generation of the other panels. This is definitely the least ideal option, as unless you install the panels in a different location to the original set, you’ll likely still be dealing with the same shadows. 


You can learn more about positioning your solar panels here, and if you have any questions feel free to get in touch!