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--- electrical:solar:shading [2020/03/17 16:15]
frater_secessus [Partial shading]
+++ electrical:solar:shading [2020/03/17 16:25]
frater_secessus [reminder: how panels work]
@@ Line 8: / Line 8: @@
-**Before we begin:** solar panels are "current sour
+**Before we begin:** solar panels are "current sources";  their voltage pops up into the normal range in any kind of meaningful light(>= 20% [[electrical:solar:output|insolation]]) but current will suffer.
-ces";  their voltage pops up into the normal range in any kind of meaningful light(>= 20% [[electrical:solar:output|insolation]]) but current will suffer.
 Partial shading in this context means:
@@ Line 15: / Line 14: @@
   * but not evenly on the panel -- it is different on some cells
-To prevent power from rushing into the shaded cells panels have bypass diodes.  Basically the shaded panels get cut off, electrically speaking, to protect them.
+To prevent power from rushing into the shaded string and overheating them, panels have bypass diodes between the strings.  Basically the shaded strings get cut off, electrically speaking, to protect them. In a perfect world each cell would be protect by a lossless, costless diode but that's not possible yet.  :-)
@@ Line 23: / Line 22: @@
-  * dedicated controllers for each panel is optimal
+  * **avoiding shade** is best
+  * a **dedicated controller for each panel** is the next best thing
   * [[electrical:solar:panels|amorphous/thin-film panels]] are less affected by shade
   * With **PWM controllers, parallel panel configurations typically yield more power** in partial shade than serial.
-  * With **MPPT controllers** and **low-ish voltage** serial panel configurations (where the total Vmp is <=2x battery bank voltage) it's close but **parallel will probably still yield more**.
+  * With **MPPT controllers** and **low-ish voltage** serial panel configurations (where the total Vmp is <=2x battery bank voltage) **parallel will probably still yield more**.
-  * With **MPPT controllers** and **higher voltage** serial configs (say Vmp is >=3x bank voltage) we see **an increasing advantage of serial panel configs in partial shade**. This occurs because the MPPT has a broader range of voltages to sweep and can find [[https://www.sciencedirect.com/science/article/abs/pii/S0960148113006952|other power peaks]] (panel voltages) that are **low enough to bring the shaded cells back online** but still **high enough to charge the battery bank**.  It's  not reality, but we can think of it as MPPT evenly "shading" the entire panel voltage-wise in order to get max juice from it in partial shade conditions.
+===== exception:  high voltage strings + mppt =====
+There is another approach, which is to **bring the shaded cells/strings back online by bringing the rest of the panel down to their level**.  It sounds counterproductive, but with MPPT controllers and in some higher-voltage series configurations (say Vmp is >=3x bank voltage) it works.
+This occurs because the MPPT has a broader range of voltages to sweep and can find [[https://www.sciencedirect.com/science/article/abs/pii/S0960148113006952|other power peaks]] (panel voltages) that are **low enough to bring the shaded cells back online** but still **high enough to charge the battery bank**.  It's  not reality, but we can think of it as MPPT evenly "shading" the entire panel voltage-wise in order to get max juice from it in partial shade conditions.
 ===== examples =====

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