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--- electrical:solar:shading [2020/01/07 23:29]
frater_secessus [even shading]
+++ electrical:solar:shading [2020/03/17 15:49]
frater_secessus [Partial shading]
@@ Line 1: / Line 1: @@
+Words of Wisdom:  "The response of a series parallel array to shade will be complicated." -- sensij((https://www.solarpaneltalk.com/forum/solar-panels-for-home/solar-panel-installation/365350-understanding-shade-and-low-light-conditions?p=365396#post365396))
 ====== Partial shading ======
-Partial shading can have surprisingly dramatic effects on panel output. The weirdest part is that //partial// shading can have more devastating effects on output than //full shading// like heavy overcast or evenly shaded forest canopies.
+Partial shading can have surprisingly dramatic effects on [[electrical:solar:output|panel output]]. The weirdest part is that //partial// shading can have more devastating effects on output than //full shading// like heavy overcast or evenly shaded forest canopies.
@@ Line 8: / Line 10: @@
-===== partial shading =====
+It works this way:
-Partial shading is problematic for solar panels because:
+  - partial shade causes //voltage differences// between cells
+  - electricity flows from higher-voltage areas to lower-voltage ones, so voltage differences would cause power to rush into the lower-voltage (shaded) cells
+  - overheating the shaded cell and possibly damaging it
+To prevent damage panel manufacturer's insert diodes between cells or strings of cells.  Partial shading trips the diodes and effectively takes the shaded cells/strings offline for their own protection.
-  - partial shade causes //voltage differences// between cells
-  - voltage differences cause power to rush into the lower-voltage (shaded) cell
-  - overheating the cell and reducing overall voltage
-When a panel is partially shaded the individual cells are running at differing voltages.  If the cells were bare then the unshaded (normal voltage) cells would backfeed power into the shaded (lower voltage) cells, overheating them.  To prevent this, panel manufacturer's insert diodes.  Partial shading trips the diodes and effectively takes the shaded cells/strings offline.
+===== panel configuration for partial shade =====
+The way to avoid the problems associated with partial shade is to avoid partial shade.  :-)  Failing that, there are steps one can take to minimize the losses:
-The takeaway:
-  *  With PWM controllers **parallel panel configurations typically yield more power** in partial shade than serial.
+  * dedicated controllers for each panel is optimal
-  * 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**.
+  * [[electrical:solar:panels|amorphous/thin-film panels]] are less affected by shade
-  * With MPPT controllers and **higher voltage** serial configs (say Vmp is >=3x bank voltage) we see **an increasing serial advantage over parallel in partial shade**. This occurs because the MPPT has a broader range of voltages to sweep and can find power points (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.
+  * 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 **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.
+===== examples =====
+  * [[https://www.youtube.com/watch?v=QzzB1i1w_kM|altE video on partial shading]]
+  * [[https://www.youtube.com/watch?v=ofo1HQyGG8s|wiring shaded panels]]

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