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Shading on solar panels and how to defeat it without breaking the bank

The picture below is a good example of how shade affects a solar installation.
The shade from the palm tree is just touching part of a single solar panel.


Before the shade hit that one panel, the string of 12 panels was making 2kW of power.

Now it's only making 0.6kW.

So 70% of the entire system output is lost because just one panel is partly shaded.


In this case it's a palm tree, but on most houses there are flues, and A/C units, TV antennas, all of which have a similar effect if they shade solar panels.


When we design a system we do our best to avoid shade by positioning the panels away from it, and the picture above clearly shows that the installer did their best to do exactly that...but trees grow so shade that wasn't there at install time may appear later.


The reason why a single shaded panel brings down the output of the entire string can be likened to a kink in a hose. No kink, the water flows through, but a kink, or shaded panel, brings the flow down to a trickle.


There are some solutions, but before we go through them, remember that time of day, and time of year are very important. If the shade only happens after 5pm or early morning, then it really makes very little difference to power output. You might go from 0.4kW to 0.2kW for an hour. No big deal and not worth spending a lot of money on trying to find a solution.


The solution to shade.

After trying to avoid it with panel placement then....


Fit optimisers on any shaded panels. Optimisers limit the power loss to the shaded panel without dragging down the output of the rest. They do this by matching the current of the other panels by decreasing the voltage of the panel they are connected to.


Optimisers cost about $80-$100 each and are quick and easy to attach if done at the same time as the solar panel installation. If done later, they take a fair bit more work and cost to install.

If you have a Huawei inverter then you can install Huawei optimisers on as few or as many panels as you need to. If you have a SolarEdge inverter you need to install SolarEdge optimisers on every panel (it's just how their system works), and if you have any other string inverter (e.g. SMA, Fronius, Sungrow, Goodwe, Growatt, etc) then you can fit Tigo optimisers to any or all panels.


SolarEdge, Tigo, and Huawei optimisers can also provide reporting on the performance of the panel they are connected to so you can check they are doing their job !! Most times this requires you to purchase an extra bit of hardware or software, or both, over and above the cost of the optimisers


There is another inverter brand called Enphase, that doesn't have optimisers, they have micro inverters instead. As far as handling shade is concerned, micro inverters do the same job, in the same way as optimisers, but micros also convert the panel power from DC to AC right there on the roof instead of sending it down to a central inverter. There are pros and cons for either type of inverter, string or micro, but as far as shade is concerned, it's all the same.


On the subject of optimisers but unrelated to shade, they also offer a nice added bonus.

Using the same technique of raising and lowering voltage to manipulate current flow through a string of panels, they let you have strings of panels split across different roof orientations.


Let's say your North roof has space only for 9 panels, your West 12 panels and your East, 3 panels. You can have 12 panels on the West roof running from one of the two inverter MPPT trackers, and the 9 on North and the 3 on East running from the other MPPT but the 3 on East must be fitted with optimisers. Without optimisers, the panels on the East would drag down the output of the panels on North because they are getting less sun as the afternon progresses.


Pictured below, Huawei optimiser.