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electrical:solar:shading [2020/02/08 11:24]
frater_secessus [panel configuration for partial shade]
electrical:solar:shading [2022/08/06 15:18] (current)
frater_secessus [Partial shading]
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 +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 ======
  
-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]]Perhaps counterintuivitely, //partial// shading can have more devastating effects on output than //full shading// like heavy overcast or evenly shaded forest canopies.
  
 +===== reminder:  how panels work =====
  
  
 +**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. 
 +Partial shading in this context means:
  
 +  * light is falling on the panel
 +  * but not evenly on the panel -- it is different on some cells
  
- +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 themIn a perfect world each cell would be protect by a lossless, costless diode but that's not possible yet.  :-)
-It works this way: +
- +
-  - 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. +
  
  
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-  * 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    * [[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 **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' 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' 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.((https://diysolarforum.com/threads/mppt-sizing.17947/post-208104))
  
 ===== examples ===== ===== examples =====
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   * [[https://www.youtube.com/watch?v=QzzB1i1w_kM|altE video on partial shading]]   * [[https://www.youtube.com/watch?v=QzzB1i1w_kM|altE video on partial shading]]
   * [[https://www.youtube.com/watch?v=ofo1HQyGG8s|wiring shaded panels]]   * [[https://www.youtube.com/watch?v=ofo1HQyGG8s|wiring shaded panels]]
 +  * [[https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28152689.cfm|Solar Panel Shadows and Bypass Diodes]]
electrical/solar/shading.1581179051.txt.gz · Last modified: 2020/10/11 19:48 (external edit)