Solar Panel Shading Simulator – See How Shade Really Affects Your Array

About This Tool

We designed this browser-based simulator to answer the common questions of both DIY customers designing their first off-grid installation and electricians troubleshooting commercial arrays. While these concepts are complex, they don’t have to be inaccessible. 

This simulator uses the same equations as those in professional modeling software and simplifies the illustration by demonstrating panels with single bypass diode configurations. Drag the shade, adjust the configuration, and watch the results play out in real time.

Every panel, string, and operating point is calculated — not estimated, not simplified, not hand-waved. Because understanding why your system behaves the way it does is the first step toward making it better.

Grab the shade and drag it around! This simulator is based on perfect irradiance, and is for reference of the concepts of shading only, not for real world production calculations.

Questions about your specific installation? We’re here to help! Contact our team here.

How Shade Affects a Solar Array (It’s Not What You Think)

Some people say, “Even a little shade kills your whole solar system,” but this is a gross oversimplification and can lead to bad design decisions. The real answer depends on the panel technology, how you wire the strings, and what the MPPT (Maximum Power Point Tracker) does about it. 

We’ve built this simulator so you can get the right answer the first time. We understand that shading is one of the most misunderstood topics in solar and that the people asking these questions use the answers to make real purchasing decisions. We want to provide you with the most complete information as you traverse your solar journey. 

The simulator above shows the real effects of shade on a solar array. Drag the shade across the panels to see what happens to voltage, current, and power throughout the system. 

What Happens When You Shade a Solar Panel

Cells inside solar panels connect to each other through a series connection, and all the panels in a single string also connect in series. This leads to two things:

1. The nature of a series connection limits the current flow from all connected parts to the lowest current output. In a solar panel, this means that even unshaded cells output the same current as their shaded neighbors.
2. A shaded cell can also draw power from connected cells, turning that electricity into heat and potentially creating a hazardous electrical environment. 

This is why we have bypass diodes.

Bypass Diodes — What They Actually Do

Every modern solar panel includes a junction box with bypass diodes. Bypass diodes monitor groups of cells in a single panel. When one cell group produces less current, the bypass diode activates and reroutes the current around that cell group–essentially turning off those cells and ignoring them instead of reducing the output of every other cell group.

Here’s what’s counterintuitive: a fully bypassed panel doesn’t produce zero power. Since the panel produces zero volts and the diodes consume some power, the final result is slightly negative volts. This leads to a total of about -0.7V from the shaded panel. 

The unshaded panels typically produce more than enough to make up for this voltage drop, and the MPPT continuously monitors this calculation. Should it restrict the power output from all panels to match the shaded panel, or should it completely bypass the shaded panel and take the voltage drop?

The simulator above shows both options on the IV curve as separate power peaks. 

Split-Cell (Half-Cut) Panels — Why They Handle Shade Better

Modern panels use split-cell (half-cut) technology, where the panel is divided into a top half and a bottom half. The cells in each half are wired in series, but the two halves are wired in parallel. This improves shade tolerance, but it’s often improperly explained.

Here’s what actually happens with a split-cell panel under partial shade:

• If shade covers only one half (top or bottom), the current drops on the shaded half while the other half continues at full output. Since the halves are wired in parallel, the unshaded half still contributes its full current, and the panel operates at roughly 50% capacity instead of being fully bypassed. MPPTs often use this as the optimal choice.
• If shade covers both halves, both bypass diodes may activate, and the panel is fully bypassed — just like a traditional panel.

Toggle the, “Split-Cell Technology,” switch to compare the behavior of split-cell panels to traditional panels. You’ll notice a significant difference in the power curve. 

MPPT and the Multi-Peak Problem

MPPT functions by constantly searching for the voltage where the array produces the most power. 

Under uniform conditions, there’s a single clear peak.

Partial shading creates multiple peaks in the power curve. Each peak represents a different operating strategy:

• The high-voltage peak: Running all panels at lower current so the shaded panels still contribute voltage. This leads to more total panels producing, and each one produces less current.
• The low-voltage peak: Running at higher current and bypassing the shaded panels. This means fewer panels contribute to the total power output, but those contributing run at full power. 

The higher peak depends on how many panels are shaded and how severely they are shaded. A good MPPT tracker, one with global peak scanning, will find the true maximum, but some budget trackers get stuck on the lower peak and continually operate at the wrong voltage. When purchasing an MPPT, always look for the Multiple Peak specification to avoid this issue. 

This simulator shows both peaks and highlights which one the MPPT should choose. 

Shared MPPT vs. Per-String Optimization

Shared MPPT: When multiple parallelled strings share a single MPPT, all strings operate at the same voltage. The MPPT finds the voltage that produces the total maximum power, but this voltage is not optimal for all strings. 

Similarly to shaded cells, the MPPT may choose the unshaded panels and intake zero power from the partially shaded panels. 

Per String Optimization: Microinverters optimize each solar panel individually so each panel can contribute the maximum power possible to the solar system. These optimizers contribute more to the system than recovering a few watts from shaded panels. They prevent a shaded string from reducing the production of the entire array. 

Toggle the, “Per-String MPPT,” switch in the simulator above to see the difference. 

When Partial Shade Is Worse Than Full Shade

Here’s the scenario that surprises most people: a panel with one half partially shaded can cause more power loss than a panel that’s completely shaded.

Why? A fully shaded panel bypasses cleanly — the MPPT adjusts and the rest of the string runs at full power. A partially shaded panel may contribute some current, and the MPPT may adjust to a voltage that does not produce the maximum power for the entire system. 

The simulator shows this plainly. Try shading one half of a single panel and watch the power curve develop two peaks close together. Then fully shade that same panel — you’ll often see the total system power increase because the MPPT can make a clear decision. 

This is also why shade patterns matter more than shade area. A narrow shadow crossing every panel in a string (like a wire or thin branch) can be worse than a large shadow covering two panels completely.

Real-World Takeaways

For System Design

• It’s worth the effort to analyze the shade before installing your solar system as a few panels in the wrong position can affect the entire string.
• If you can’t avoid shade in a concentrated area, consider a string layout that isolates shaded panels to one string rather than spreading the shade across multiple strings.
• Per-string optimization (optimizers or microinverters) provides the biggest benefit in systems with uneven shading across the strings, but these are less beneficial when all strings have equal shading.

For Troubleshooting

• System underperformance in the morning or afternoon usually stems from partial shading of trees, buildings, or a roof–even if the panels look mostly unshaded.
• Some inverters allow you to monitor the current per string which can reveal an underperforming string. This simulator helps explain those numbers.

For Purchasing Decisions

• Installations with partial shade often profit from the real electrical benefit of split-cell panels, and this benefit often justifies any additional cost. 
• Inverters and charge controllers in partially shaded installations should always include global MPPT scanning. Make sure your components actually use this feature.