Shading analysis: How to pick a sunny spot for solar panels
- 31 Mar 2023
- 7 min
Shadows are the arch-enemies of solar panels. They decrease production greatly, they can cause malfunctions and there is no running away from them. Or is there? When picking a spot for a solar system, contractors perform a shading analysis to ensure that the place is always sunny. In this article, we’ll take a peek at the methods and tools that they use.
One shaded cell can kill a third of your solar production
Why does shading of solar panels have such a drastic impact on energy production? Solar cells in a panel are connected in series. When one cell is shaded, the performance of the next ones in the row also drops. One shaded cell can reduce the production of a whole PV module by 15% to 33%.
It gets worse when you have a string inverter and your panels are also connected in series. When the performance of one panel decreases, a string inverter lowers the production of each panel in a string down to the level of the worst one.
Shading is not just bad for the production, it’s not healthy for panels either. When solar cells get inactive, it puts a strain on others that keep working. You may end up with hot spots: parts of a solar panel that heat up more than the others. Hot spots lead to faster degradation of a module.
Apps and devices will help you find the right spot for PV system
To find a spot where a solar system won’t suffer from shading, contractors use basic geometry, as well as devices and software.
The simplest method you can use is called "1-3". When something is higher than your array, you want the distance in between to be three times bigger than the difference in altitude. Here is an example: when the top of a tree is 10 ft above your panels, you want it to be at least 30 ft away to avoid its shadow.
Remember that in the US you want your panels to face south. The angle of your PV modules can be set equal to your latitude.
If you want a more precise prediction, you can use devices or apps for solar panel shading analysis. For example, Solar Pathfinder is a simple non-electric device that uses a plastic dome to give a panoramic view of the site. All the trees, buildings or other obstacles to the sun are visible as reflections on the surface of the dome and give you an idea of possible shading. There are lots of products similar to Pathfinder that are more or less complicated.
Solar Installation Expert
Devices for shading analysis were popular back in the day but nowadays they are mostly replaced by apps. Below are some of the applications that me and my colleagues use in the field. They take some time to get used to but once you figure out how one of them works, it gets easy.
Shadowmap is a tool for sunlight and shadow visualization, based on worldwide 3D buildings and terrain data. It’s easy to use and it’s available everywhere but it doesn’t factor any obstructions other than buildings — trees, for example.
ShadowCalculator predicts the size of shadows at different times of the day for Google maps location. The app simulates casted shadows and displays day duration, sunrise and sunset times for selected location and date. It also shows the sun's position: sun altitude and sun azimuth.
FindMyShadow takes a while to get used to but allows you to set up your own shading simulations with the objects that you choose to use yourself. It comes with How-to guides that you can refer to when in doubt.
Shading happens: here are solutions
If you can't escape the pesky shadows, try to minimize their damage. Here is a list of measures you can take to lower the effect of shading on solar panels.
Choose solar panels carefully
Some solar panels are better at fighting shade than others. Half-cut cell design essentially splits the panel into two independent halves. When a cell in one half gets shaded, it doesn’t affect the other one.
Manufacturers Sunpower and Solaria use the shingled solar panel design. In this configuration, the panel is built out of shingles and not cells. Shingles are connected in parallel and the performance of one doesn’t affect others. Shingled solar panels lose 40% less energy from shading than standard PV modules.
Consider connecting your panels in parallel
Speaking of parallel connection: connecting your panels in parallel instead of a series connection will help to reduce losses caused by the shading of panels as well. When PV modules are connected in parallel, the performance of one doesn't affect its neighbors. You rarely see it in home systems but it's a popular configuration for a system in a cramped space, such as an RV or a boat installation.
Get creative with array shape
Nobody says that your solar array always has to have a correct rectangular shape. Sometimes installers build trapezoids with panels to avoid shading from a particular object. Experts also recommend mounting modules horizontally and not vertically because it lowers losses from snow heaps blocking the sunlight.
Consider setting up several solar strings
The problem with string inverters is that panels in a string influence each other’s production. Some inverters offer several inputs, for each string its own input. You can set up multiple strings to raise the overall shading tolerance of your system. In the case of shading of one string, other inputs will still operate at their normal capacity.
Get micro inverters or power optimizers for your solar system
Power optimizers can be your salvation if you already use a string inverter and shading causes big problems. Optimizers make each module independent. Some inverters, such as SolarEdge models, are specifically designed to be paired with optimizers.
Micro inverters are a more efficient choice than a string inverter. One micro inverter is designed to be paired with one or two panels so there are no strings and panels don't influence the performance of each other. They also offer better monitoring capabilities and last longer than average string inverters. The downside is the higher price. A system with micro inverters can only support AC batteries.
Maintain your solar panels
Fallen leaves, accumulated dirt, bird droppings — all of it lowers the performance of your array. Follow our tips on cleaning solar panels. Snow heaps can block sunlight for your panels as well. It’s usually better to just wait for them to slide down instead of climbing the roof with a shovel.
Illustrations – Natalya Absalyamova
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