What to do? And how much does it matter…
Here’s some insight into the fact that all shade is not the same and how the mitigation of shading issues are not straight-line computations based on percentages of shading.
When you look at shading as only how it affects solar, you can basically classify in three ways.
- Hard shade with a narrow shadow,
- Hard shade with a short and fat shadow
- Soft shade
Hard shade with a narrow shadow – could be a flagpole or utility pole.
Hard shade with a short and fat shadow – is representative of a building in the foreground and many tree lines.
Soft shade – is of a type quite often temporary whereas a single solar panel here and there are occluded by leaves or bird droppings.
One other term to be familiar with is strings. Let me give you a more simplified explanation.
If you have 36 solar panels on your roof it will be common to have “strings” of 12 panels.
Three strings of 12 panels equals 36 solar panels to make your array.
Why does this matter?
Because shade on any part of a string not only affects the panel it is blocking but also each and every subsequent panel in that string!
Here is where we look to employ our solutions
So here is a key point, shade is shady and will take a certain percentage of the available sunshine away from the full array. The only way to mediate it, short of removing the actual shading object, is to design the solar array so that unshaded panels next to shaded ones aren’t affected by a cascade like affect. This is accomplished by how refined your system employs PowerPoint tracking.
If it is only employed at the inverter to the entire 36 solar panels you will have a maximum impact mismatch between the panels shaded and unshaded. If you “refine it” to each set of the 12 panels in a string you received very favorable results, say an average 65% better than only an inverter level, up or down depending on whether it’s narrow shadow or fat shadow. (Please now see attached chart).
Courtesy of https://www.solarpowerworldonline.com/
Now we can discuss the beautiful solution! Technology today allows us to just about fully mitigate the shade caused mismatch within strings also! Now it is possible to just about wipe out the cascading effects of partial shading of all types. This is done by making each solar panel its own very string.
This is called module level electronics, (module is the proper nomenclature for a solar panel, solar module). Please note in the chart the .3 percentage number, that is representative of a module level electronics system. And lest you forget there is one other type of shade that only module level electronics can mediate. Soft shade. There are small periods of the year under which most of the arrays will be affected by this in varying degrees. This is an amazing advantage.
And not only do we now almost completely mitigate the secondary effects of shading, yet we also get a big bonus! Panel level monitoring! Now the equipment and electronics performance is available to us the installer and you the consumer to see what every panel on your roof is independently doing in real-time throughout the year. This gives assuredness that your system is producing at its optimum while also allowing easy diagnostics when and if there ever appears to be a problem. It is amazingly comforting and useful.
So, are we all done here? Not quite… When those installers come calling with their micro-inverters, now you’ll know why they’re selling them. But companies like Harvest Sun Solar can take all this a big step further. We have gone beyond micro-inverters into something called DC optimizers. They do the same job, they just do it a good bit better with superior durability and even more improved diagnostics. And by having one large efficient inverter down at ground level instead of 36 smaller, less efficient inverters up on the roof system also gains an entire 1% greater or more overall production level. That’s thousands of dollars.
It is our hope that we were able to help you by making solar & shading a little easier to understand… It is engineering after all!
Please check out the accompanying article which inspired me to try and explain what it meant in more general terms…
…And remember that Harvest Sun Solar is here, and what we consider sales is the dissemination of information freely and fairly!
Source: https://www.solarpowerworldonline.com/2018/03/central-string-module-level-mppt-zone-size/
