Both sides previous revision
Previous revision
Next revision
|
Previous revision
Next revision
Both sides next revision
|
electrical:solar:shading [2020/03/17 15:49] frater_secessus [Partial shading] |
electrical:solar:shading [2020/03/17 16:22] frater_secessus [panel configuration for partial shade] |
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. | 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. |
| |
| ===== reminder: how panels work ===== |
| |
| |
| **Before we begin:** solar panels are "current sour |
| 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: |
| |
| * 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 cells panels have bypass diodes. Basically the shaded panels get cut off, electrically speaking, to protect them. |
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. | |
| |
| |
| |
| |
* 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'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 ===== | ===== examples ===== |